Maternal–foetal genomic conflict and speciation: no evidence for hybrid placental dysplasia in crosses between two house mouse subspecies

Interspecific hybridization between closely related mammalian species, including various species of the genus Mus, is commonly associated with abnormal growth of the placenta and hybrid foetuses, a phenomenon known as hybrid placental dysplasia (HPD). The role of HPD in speciation is anticipated but still poorly understood. Here, we studied placental and foetal growth in F₁ crosses between four inbred mouse strains derived from two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. These subspecies are in the early stage of speciation and still hybridize in nature. In accordance with the maternal–foetal genomic conflict hypothesis, we found different parental influences on placental and foetal development, with placental weight most affected by the father's body weight and foetal weight by the mother's body weight. After removing the effects of parents’ body weight, we did not find any significant differences in foetal or placental weights between intra‐subspecific and inter‐subspecific F₁ crosses. Nevertheless, we found that the variability in placental weight in inter‐subspecific crosses is linked to the X chromosome, similarly as for HPD in interspecific mouse crosses. Our results suggest that maternal–foetal genomic conflict occurs in the house mouse system, but has not yet diverged sufficiently to cause abnormalities in placental and foetal growth in inter‐subspecific crosses. HPD is thus unlikely to contribute to speciation in the house mouse system. However, we cannot rule out that it might have contributed to other speciation events in the genus Mus, where differences in the levels of polyandry exist between the species.     

Phylogeography of Chinese house mice (Mus musculus musculus/castaneus): distribution,routes of colonization and geographic regions of hybridization

House mice (Mus musculus) are human commensals and have served as a primary model in biomedical, ecological and evolutionary research. Although there is detailed knowledge of the biogeography of house mice in Europe, little is known of the history of house mice in China, despite the fact that China encompasses an enormous portion of their range. In the present study, 535 house mice caught from 29 localities in China were studied by sequencing the mitochondrial D‐loop and genotyping 10 nuclear microsatellite markers distributed on 10 chromosomes. Phylogenetic analyses revealed two evolutionary lineages corresponding to Mus musculus castaneus and Mus musculus musculus in the south and north, respectively, with the Yangtze River approximately representing the boundary. More detailed analyses combining published sequence data from mice sampled in neighbouring countries revealed the migration routes of the two subspecies into China: M. m. castaneus appeared to have migrated through a southern route (Yunnan and Guangxi), whereas M. m. musculus entered China from Kazakhstan through the north‐west border (Xinjiang). Bayesian analysis of mitochondrial sequences indicated rapid population expansions in both subspecies, approximately 4650–9300 and 7150–14 300 years ago for M. m. castaneus and M. m. musculus, respectively. Interestingly, the migration routes of Chinese house mice coincide with the colonization routes of modern humans into China, and the expansion times of house mice are consistent with the development of agriculture in southern and northern China, respectively. Finally, our study confirmed the existence of a hybrid zone between M. m. castaneus and M. m. musculus in China. Further study of this hybrid zone will provide a useful counterpart to the well‐studied hybrid zone between M. m. musculus and Mus musculus domesticus in central Europe.     

Of mice and the ‘Age of Discovery’: the complex history of colonization of the Azorean archipelago by the house mouse (Mus musculus) as revealed by mitochondrial DNA variation

Humans have introduced many species onto remote oceanic islands. The house mouse (Mus musculus) is a human commensal and has consequently been transported to oceanic islands around the globe as an accidental stowaway. The history of these introductions can tell us not only about the mice themselves but also about the people that transported them. Following a phylogeographic approach, we used mitochondrial D‐loop sequence variation (within an 849‐ to 864‐bp fragment) to study house mouse colonization of the Azores. A total of 239 sequences were obtained from all nine islands, and interpretation was helped by previously published Iberian sequences and 66 newly generated Spanish sequences. A Bayesian analysis revealed presence in the Azores of most of the D‐loop clades previously described in the domesticus subspecies of the house mouse, suggesting a complex colonization history of the archipelago as a whole from multiple geographical origins, but much less heterogeneity (often single colonization?) within islands. The expected historical link with mainland Portugal was reflected in the pattern of D‐loop variation of some of the islands but not all. A more unexpected association with a distant North European source area was also detected in three islands, possibly reflecting human contact with the Azores prior to the 15th century discovery by Portuguese mariners. Widening the scope to colonization of the Macaronesian islands as a whole, human linkages between the Azores, Madeira, the Canaries, Portugal and Spain were revealed through the sharing of mouse sequences between these areas. From these and other data, we suggest mouse studies may help resolve historical uncertainties relating to the ‘Age of Discovery’.     

Gastrointestinal microbiota of wild and inbred individuals of two house mouse subspecies assessed using high‐throughput parallel pyrosequencing

The effects of gastrointestinal tract microbiota (GTM) on host physiology and health have been the subject of considerable interest in recent years. While a variety of captive bred species have been used in experiments, the extent to which GTM of captive and/or inbred individuals resembles natural composition and variation in wild populations is poorly understood. Using 454 pyrosequencing, we performed 16S rDNA GTM barcoding for 30 wild house mice (Mus musculus) and wild‐derived inbred strain mice belonging to two subspecies (M. m. musculus and M. m. domesticus). Sequenced individuals were selected according to a 2 × 2 experimental design: wild (14) vs. inbred origin (16) and M. m. musculus (15) vs. M. m. domesticus (15). We compared alpha diversity (i.e. number of operational taxonomic units – OTUs), beta diversity (i.e. interindividual variability) and microbiota composition across the four groups. We found no difference between M. m. musculus and M. m. domesticus subspecies, suggesting low effect of genetic differentiation between these two subspecies on GTM structure. Both inbred and wild populations showed the same level of microbial alpha and beta diversity; however, we found strong differentiation in microbiota composition between wild and inbred populations. Relative abundance of ~ 16% of OTUs differed significantly between wild and inbred individuals. As laboratory mice represent the most abundant model for studying the effects of gut microbiota on host metabolism, immunity and neurology, we suggest that the distinctness of laboratory‐kept mouse microbiota, which differs from wild mouse microbiota, needs to be considered in future biomedical research.     

Use of a natural hybrid zone for genomewide association mapping of craniofacial traits in the house mouse

The identification of the genes involved in morphological variation in nature is still a major challenge. Here, we explore a new approach: we combine 178 samples from a natural hybrid zone between two subspecies of the house mouse (Mus musculus domesticus and Mus musculus musculus), and high coverage of the genome (~ 145K SNPs) to identify loci underlying craniofacial shape variation. Due to the long history of recombination in the hybrid zone, high mapping resolution is anticipated. The combination of genomes from subspecies allows the mapping of both, variation within subspecies and inter‐subspecific differences, thereby increasing the overall amount of causal genetic variation that can be detected. Skull and mandible shape were measured using 3D landmarks and geometric morphometrics. Using principal component axes as phenotypes, and a linear mixed model accounting for genetic relatedness in the mapping populations, we identified nine genomic regions associated with skull shape and 10 with mandible shape. High mapping resolution (median size of significant regions = 148 kb) enabled identification of single or few candidate genes in most cases. Some of the genes act as regulators or modifiers of signalling pathways relevant for morphological development and bone formation, including several with known craniofacial phenotypes in mice and humans. The significant associations combined explain 13% and 7% of the skull and mandible shape variation, respectively. In addition, a positive correlation was found between chromosomal length and proportion of variation explained. Our results suggest a complex genetic architecture for shape traits and support a polygenic model.     

The role of biogeography in shaping diversity of the intestinal microbiota in house mice

The microbial communities inhabiting the mammalian intestinal tract play an important role in diverse aspects of host biology. However, little is known regarding the forces shaping variation in these communities and their influence on host fitness. To shed light on the contributions of host genetics, transmission and geography to diversity in microbial communities between individuals, we performed a survey of intestinal microbial communities in a panel of 121 house mice derived from eight locations across Western Europe using pyrosequencing of the bacterial 16S rRNA gene. The host factors studied included population structure estimated by microsatellite loci and mitochondrial DNA, genetic distance and geography. To determine whether host tissue (mucosa)‐associated communities display properties distinct from those of the lumen, both the caecal mucosa and contents were examined. We identified Bacteroides, Robinsoniella and Helicobacter as the most abundant genera in both the caecal content and mucosa‐associated communities of wild house mice. Overall, we found geography to be the most significant factor explaining patterns of diversity in the intestinal microbiota, with a comparatively weaker influence of host population structure and genetic distance. Furthermore, the influence of host genetic distance was limited to the mucosa communities, consistent with this environment being more intimately coupled to the host.     

Inference of selection and stochastic effects in the house mouse hybrid zone

We explored the transition of 13 X-linked markers across two separate portions of the house mouse hybrid zone, asking whether such a comparison can distinguish the effects of selection from random factors. A heuristic search in the likelihood landscape revealed more complex likelihood profiles for data sampled in two-dimensional (2D) space relative to data sampled along a linear transect. Randomized resampling of localities analyzed for individual loci showed that deletion of sites away from the zone center can decrease cline width estimates whereas deletion of sites close to the center can significantly increase the width estimates. Deleting localities for all loci resulted in wider clines if the number of samples from the center was limited. The results suggest that, given the great variation in width estimates resulting from inclusion/exclusion of sampling sites, the geographic sampling design is important in hybrid zone studies and that our inferences should take into account measures of uncertainty such as support intervals. The comparison of the two transects indicates cline widths are narrower for loci in the central part of the X chromosome, suggesting selection is stronger in this region and genetic incompatibilities may have at least partly common architecture in the house mouse hybrid zone.     

Adaptative evolution of the Vkorc1 gene in Mus musculus domesticus is influenced by the selective pressure of anticoagulant rodenticides

Anticoagulant rodenticides are commonly used to control rodent pests worldwide. They specifically inhibit the vitamin K epoxide reductase (VKORC1), which is an enzyme encoded by the Vkorc1 gene, involved in the recycling of vitamin K. Therefore, they prevent blood clotting. Numerous mutations of Vkorc1 gene were reported in rodents, and some are involved in the resistant to rodenticides phenotype. Two hundred and sixty‐six mice tails were received from 65 different locations in France. Coding sequences of Vkorc1 gene were sequenced in order to detect mutations. Consequences of the observed mutations were evaluated by the use of recombinant VKORC1. More than 70% of mice presented Vkorc1 mutations. Among these mice, 80% were homozygous. Contrary to brown rats for which only one predominant Vkorc1 genotype was found in France, nine missense single mutations and four double mutations were observed in house mice. The single mutations lead to resistance to first‐generation antivitamin K (AVKs) only and are certainly associated with the use of these first‐generation molecules by nonprofessionals for the control of mice populations. The double mutations, probably obtained by genetic recombination, lead to in vitro resistance to all AVKs. They must be regarded as an adaptive evolution to the current use of second‐generation AVKs. The intensive use of first‐generation anticoagulants probably allowed the selection of a high diversity of mutations, which makes possible the genetic recombination and consequently provokes the emergence of the more resistant mutated Vkorc1 described to date.     

Problem‐solving skills are linked to parental care and offspring survival in wild house sparrows

Individuals within a population often exhibit consistent differences in important behavioral traits such as parental care. One interesting, yet largely unexplored explanation for the existence of these consistent differences among parents is the idea that cognitive differences between individuals could lead to between‐individual variation in parenting behavior. I used a wild population of house sparrows (Passer domesticus) to test the nature of the relationship between aspects of cognitive ability (problem‐solving performance and learning) and parental care behavior, both measured in the wild. Furthermore, because parental care is tightly linked to fitness, I also investigated the relationship between problem‐solving performance and offspring survival. Parent sparrows were presented with a novel problem‐solving task that required them to remove an obstacle to obtain food. While there was no relationship between the ability to complete the task and measures of parental care (nestling provisioning rate or likelihood of provisioning with large food items), parents that solved the task quickly had higher provisioning rates than slow solvers. Additionally, the ability of fathers to complete the problem‐solving task was positively related to offspring survival. These results provide evidence that aspects of problem‐solving performance are positively correlated with parenting behavior and fitness in the wild.     

Contrasting patterns of polymorphism and selection in bacterial‐sensing toll‐like receptor 4 in two house mouse subspecies

Detailed investigation of variation in genes involved in pathogen recognition is crucial for understanding co‐evolutionary processes between parasites and their hosts. Triggering immediate innate response to invading microbes, Toll‐like receptors (TLRs) belong presently among the best‐studied receptors of vertebrate immunity. TLRs exhibit remarkable interspecific variation and also intraspecific polymorphism is well documented. In humans and laboratory mice, several studies have recently shown that single amino acid substitution may significantly alter receptor function. Unfortunately, data concerning polymorphism in free‐living species are still surprisingly scarce. In this study, we analyzed the polymorphism of Toll‐like receptor 4 (Tlr4) over the Palearctic range of house mouse (Mus musculus). Our results reveal contrasting evolutionary patterns between the two recently (0.5 million years ago) diverged house mouse subspecies: M. m. domesticus (Mmd) and M. m. musculus (Mmm). Comparison with cytochrome b indicates strong directional selection in Mmd Tlr4. Throughout the whole Mmd western Palaearctic region, a single variant of the ligand‐binding region is spread, encoded mainly by one dominant haplotype (71% of Mmd). In contrast, Tlr4 in Mmm is much more polymorphic with several haplotypes at intermediate frequencies. Moreover, we also found clear signals of recombination between two principal haplogroups in Mmm, and we identified eight sites under positive selection in our dataset. Our results suggest that observed differences in Tlr4 diversity may be attributed to contrasting parasite‐mediated selection acting in the two subspecies.     

Validating standardised personality tests under semi‐natural conditions in wild house mice (Mus musculus domesticus)

Personality traits in animals are often measured using standardised behavioural tests for activity, boldness/shyness, sociability, aggression and exploration. These tests are quick and convenient, as well as easy to repeat. As the interest in studying the impact of animal personality on ecological and evolutionary consequences has been growing rapidly, there is increasing focus on cross‐validating measurements taken during these tests with behaviours shown under natural situations. In our experiment, we aimed to study the relationship between standardised measurements for activity, exploration and anxiety‐like behaviour measured in Open Field, Novel Object and Elevated Plus Maze tests with exploration and colonisation in semi‐natural conditions. We carried out a semi‐natural enclosure experiment in parallel with standardised behavioural tests, creating a scenario similar to an invasion or dispersal event. We compared behaviours in standardised tests and in enclosures for animals of two populations of wild house mice (Mus musculus domesticus). Several behavioural variables taken during the standardised tests, such as distance moved and time spent with novel object, were negatively correlated with space‐use in the enclosure while being highly positively correlated among each other. Based on their relationship with space use, we refer to behavioural measurements from standardised tests as activity/exploration. The time spent near the walls in an open field, probably reflecting anxiety, was not correlated to any other variable or the behaviour in the enclosure. In addition, we found differences in activity/exploration behaviour between the two populations in the standardised tests, but not during the colonisation of the novel environment. These results emphasise that researchers have to be careful when trying to extrapolate behaviour shown in standardised laboratory test setups to more natural, ecologically relevant situations. This has to be taken into account in distantly related species but even when studying the wild relative of laboratory rodents, for which these standardised tests have originally been developed.     

Morphology, growth and reproduction in the Australian house mouse: differential effects of moderate temperatures

The house mouse ( Mus musculus domesticus ) was introduced into Australia two centuries ago and is now succeeding in a wide range of habitats and climatic regions. To explore how mice exploit such extreme environments, we compared growth rate, morphology and reproductive success of animals reared under differing thermal regimes (13 °C 'cool', 22 °C 'moderate' and 30 °C 'warm') in laboratory mice derived from wild stock. 'Warm' group young were smaller and grew more slowly than those from other groups. At 6 weeks of age, body mass was less in 'warm' than in 'cool' treatment individuals; and liver mass/body mass also was less in 'warm' than in 'cool' treatment individuals. Paired kidney mass/body mass and paired adrenal mass/body mass were less in 'warm' than in 'cool' and 'moderate' treatment mice. Low heritability values indicate that these effects were from the temperature treatments rather than genetic influences. Irrespective of temperature treatment, females were more likely to produce a litter from post-partum matings if they were experienced, rather than young or reproductively naïve, and also bore more young from post-partum matings. These observations contribute to understanding of the sudden plague activities of mice in some parts of Australia and also their sparse distribution in the interior of the continent.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 21–30.     

Frequency and distribution of t-haplotypes in the Southeast Asian house mouse (Mus musculus castaneus) in Taiwan

t-haplotypes are a meiotic drive system found on the 17th chromosome of the house mouse (Mus musculus). They can be found in wild populations of all four genetically differentiated subspecies. The drive phenomenon is male-specific, such that heterozygous males (+/t) show non-Mendelian transmission and transmit the t-chromosome to > 90% of their offspring. So far the most comprehensive studies on the frequencies of t-haplotypes in natural populations have been on just one of the subspecies (M. musculus domesticus). We applied molecular methods to accurately screen t-haplotypes in a large number of populations of a second subspecies (M. musculus castaneus) distributed in Taiwan. We found that the overall t-haplotype frequency is low in M. m. castaneus (0.108), and the chromosomes are patchily distributed among its populations, closely resembling the situation found in M. m. domesticus. Further, we found the frequencies of t-haplotypes in our sample did not differ in relation to the sex or age of mice. This resemblance in the frequency and distribution among populations of the two distinct subspecies suggests that similar general mechanisms might be responsible for the low frequencies in both subspecies.     

Semi‐supervised determination of pseudocryptic morphotypes using observer‐free characterizations of anatomical alignment and shape

Accurate, quantitative characterization of complex shapes is recognized as a key methodological challenge in biology. Recent development of automated three‐dimensional geometric morphometric protocols (auto3dgm) provides a promising set of tools to help address this challenge. While auto3dgm has been shown to be useful in characterizing variation across clades of morphologically very distinct mammals, it has not been adequately tested in more problematic cases where pseudolandmark placement error potentially confounds interpretation of true shape variation. Here, we tested the sensitivity of auto3dgm to the degree of variation and various parameterization settings using a simulation and three microCT datasets that characterize mammal tooth crown morphology as biological examples. The microCT datasets vary in degree of apparent morphological differentiation, with two that include grossly similar morphospecies and one that includes two laboratory strains of a single species. Resulting alignments are highly sensitive to the number of pseudolandmarks used to quantify shapes. The degree to which the surfaces were downsampled and the apparent degree of morphological differentiation across the dataset also influenced alignment repeatability. We show that previous critiques of auto3dgm were based on poorly parameterized alignments and suggest that sample‐specific sensitivity analyses should be added to any research protocol including auto3dgm. Auto3dgm is a useful tool for studying samples when pseudolandmark placement error is small relative to the true differences between specimens. This method therefore represents a promising avenue forward in morphometric studies at a wide range of scales, from samples that differ by a single genetic locus to samples that represent multiple phylogenetically diverse clades.     

Synthesis of oleyl oleate wax esters in Arabidopsis thaliana and Camelina sativa seed oil

Seed oil composed of wax esters with long‐chain monoenoic acyl moieties represents a high‐value commodity for industry. Such plant‐derived sperm oil‐like liquid wax esters are biodegradable and can have excellent properties for lubrication. In addition, wax ester oil may represent a superior substrate for biodiesel production. In this study, we demonstrate that the low‐input oil seed crop Camelina sativa can serve as a biotechnological platform for environmentally benign wax ester production. Two biosynthetic steps catalysed by a fatty alcohol‐forming acyl‐CoA reductase (FAR) and a wax ester synthase (WS) are sufficient to achieve wax ester accumulation from acyl‐CoA substrates. To produce plant‐derived sperm oil‐like liquid wax esters, the WS from Mus musculus (MmWS) or Simmondsia chinensis (ScWS) were expressed in combination with the FAR from Mus musculus (MmFAR1) or Marinobacter aquaeolei (MaFAR) in seeds of Arabidopsis thaliana and Camelina sativa. The three analysed enzyme combinations Oleo3:mCherry:MmFAR1?c/Oleo3:EYFP:MmWS, Oleo3:mCherry:MmFAR1?c/ScWS and MaFAR/ScWS showed differences in the wax ester molecular species profiles and overall biosynthetic performance. By expressing MaFAR/ScWS in Arabidopsis or Camelina up to 59% or 21% of the seed oil TAGs were replaced by wax esters, respectively. This combination also yielded wax ester molecular species with highest content of monounsaturated acyl moieties. Expression of the enzyme combinations in the Arabidopsis fae1 fad2 mutant background high in oleic acid resulted in wax ester accumulation enriched in oleyl oleate (18:1/18:1 > 60%), suggesting that similar values may be obtained with a Camelina high oleic acid line.     

Putative chemical signals about sex, individuality, and genetic background in the preputial gland and urine of the house mouse (Mus musculus)

To explore whether preputial gland secretions and/or urine from the house mouse (Mus musculus) can be used for coding information about sex, individuality, and/or the genetic background of strain [ICR/albino, Kunming (KM), and C57BL/6], we compared the volatile compositions of mouse preputial glands and urine using a combination of dichloromethane extraction and gas chromatography coupled with mass spectrometry (GC-MS). Of the 40 identified compounds in preputial gland secretions, 31 were esters, 2 sesquiterpens, and 7 alcohols. We failed to find any compound unique to a specific sex, individual, or strain. However, many low molecular weight compounds between the sexes, most compounds among individuals, and several compounds among the 3 strains varied significantly in relative ratios. These quantitative differences in preputial gland volatiles (analog coding) are likely to convey information about sex, individual, and the genetic background of mouse strain. We identified 2 new main and male-elevated compounds, 1-hexadecanol (Z=3.676, P=0.000, N=19 in ICR; Z=3.576, P=0.000, N=18) and 1-hexadecanol acetate (Z=3.429, P=0.000, N=19 in ICR; Z=3.225, P=0.001, N=18), which were eluted in GC chromatogram after the 2 sesquiterpens. They might also be potential male pheromones, in addition to the well-known E-beta-farnesene and E,E-alpha-farnesene. Additionally, a few compounds including 1-hexadecanol also varied with strains and might also code for genetic information. Of the 9 identified volatile compounds in male urine, (s)-2-sec-butyl-4,5-dihydrothiazole and R,R-3,4-dehydro-exo-brevicomin are known urine-originated male pheromones from previous studies. We also detected 6-hydroxy-6-methyl-3-heptanone, a male urinary pheromonal compound, which had not been directly detected by GC-MS previously. Chemical analysis shows that the genetically more closely related ICR and KM strains had a higher similarity in the volatile compositions of preputial glands and urine than that between ICR or KM and C57BL/6. R,R-3,4-dehydro-exo-brevicomin, in particular, was sensitive to genetic shifts and differed in relative abundance among the 3 strains, whereas (s)-2-sec-butyl-4,5-dihydrothiazole differed between ICR or Km and C57BL/6. Hence, these 2 compounds might code for information about their genetic background.     

The easy road to genome‐wide medium density SNP screening in a non‐model species: development and application of a 10 K SNP‐chip for the house sparrow (Passer domesticus)

With the advent of next generation sequencing, new avenues have opened to study genomics in wild populations of non‐model species. Here, we describe a successful approach to a genome‐wide medium density Single Nucleotide Polymorphism (SNP) panel in a non‐model species, the house sparrow (Passer domesticus), through the development of a 10 K Illumina iSelect HD BeadChip. Genomic DNA and cDNA derived from six individuals were sequenced on a 454 GS FLX system and generated a total of 1.2 million sequences, in which SNPs were detected. As no reference genome exists for the house sparrow, we used the zebra finch (Taeniopygia guttata) reference genome to determine the most likely position of each SNP. The 10 000 SNPs on the SNP‐chip were selected to be distributed evenly across 31 chromosomes, giving on average one SNP per 100 000 bp. The SNP‐chip was screened across 1968 individual house sparrows from four island populations. Of the original 10 000 SNPs, 7413 were found to be variable, and 99% of these SNPs were successfully called in at least 93% of all individuals. We used the SNP‐chip to demonstrate the ability of such genome‐wide marker data to detect population sub‐division, and compared these results to similar analyses using microsatellites. The SNP‐chip will be used to map Quantitative Trait Loci (QTL) for fitness‐related phenotypic traits in natural populations.     

Copy number variations of CBF genes at the Fr‐A2 locus are essential components of winter hardiness in wheat

Winter hardiness is important for the adaptation of wheat to the harsh winter conditions in temperate regions and is thus also an important breeding goal. Here, we employed a panel of 407 European winter wheat cultivars to dissect the genetic architecture of winter hardiness. We show that copy number variation (CNV) of CBF (C‐repeat Binding Factor) genes at the Fr‐A2 locus is the essential component for winter survival, with CBF‐A14 CNV being the most likely causal polymorphism, accounting for 24.3% of the genotypic variance. Genome‐wide association mapping identified several markers in the Fr‐A2 chromosomal region, which even after accounting for the effects of CBF‐A14 copy number explained approximately 15% of the genotypic variance. This suggests that additional, as yet undiscovered, polymorphisms are present at the Fr‐A2 locus. Furthermore, CNV of Vrn‐A1 explained an additional 3.0% of the genotypic variance. The allele frequencies of all loci associated with winter hardiness were found to show geographic patterns consistent with their role in adaptation. Collectively, our results from the candidate gene analysis, association mapping and genome‐wide prediction show that winter hardiness in wheat is a quantitative trait, but with a major contribution of the Fr‐A2 locus.     

A test for Y‐linked additive and epistatic effects on surviving bacterial infections in Drosophila melanogaster

Y‐ and W‐chromosomes offer a theoretically powerful way for sexual dimorphism to evolve. Consistent with this possibility, Drosophila melanogaster Y‐chromosomes can influence gene regulation throughout the genome; particularly immune‐related genes. In order for Y‐linked regulatory variation (YRV) to contribute to adaptive evolution it must be comprised of additive genetic variance, such that variable Ys induce consistent phenotypic effects within the local gene pool. We assessed the potential for Y‐chromosomes to adaptively shape gram‐negative and gram‐positive bacterial defence by introgressing Ys across multiple genetic haplotypes from the same population. We found no Y‐linked additive effects on immune phenotypes, suggesting a restricted role for the Y to facilitate dimorphic evolution. We did find, however, a large magnitude Y by background interaction that induced rank order reversals of Y‐effects across the backgrounds (i.e. sign epistasis). Thus, Y‐chromosome effects appeared consistent within backgrounds, but highly variable among backgrounds. This large sign epistatic effect could constrain monomorphic selection in both sexes, considering that autosomal alleles under selection must spend half of their time in a male background where relative fitness values are altered. If the pattern described here is consistent for other traits or within other XY (or ZW) systems, then YRV may represent a universal constraint to autosomal trait evolution.     

Selective blockade of B7‐H3 enhances antitumour immune activity by reducing immature myeloid cells in head and neck squamous cell carcinoma

Immature myeloid cells including myeloid‐derived suppressor cells (MDSCs) and tumour‐associated macrophages (TAMs) promote tumour growth and metastasis by facilitating tumour transformation and angiogenesis, as well as by suppressing antitumour effector immune responses. Therefore, strategies designed to reduce MDSCs and TAMs accumulation and their activities are potentially valuable therapeutic goals. In this study, we show that negative immune checkpoint molecule B7‐H3 is significantly overexpressed in human head and neck squamous cell carcinoma (HNSCC) specimen as compared with normal oral mucosa. Using immunocompetent transgenic HNSCC models, we observed that targeting inhibition of B7‐H3 reduced tumour size. Flow cytometry analysis revealed that targeting inhibition of B7‐H3 increases antitumour immune response by decreasing immunosuppressive cells and promoting cytotoxic T cell activation in both tumour microenvironment and macroenvironment. Our study provides direct in vivo evidence for a rationale for B7‐H3 blockade as a future therapeutic strategy to treat patients with HNSCC.