Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Genetic variation in South Indian castes: evidence from Y-chromosome, mitochondrial, and autosomal polymorphisms

Background

Major population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations.

Results

We report new data on 155 individuals from four Tamil caste populations of South India and perform comparative analyses with caste populations from the neighboring state of Andhra Pradesh. Genetic differentiation among Tamil castes is low (R_ST = 0.96% for 45 autosomal short tandem repeat (STR) markers), reflecting a largely common origin. Nonetheless, caste- and continent-specific patterns are evident. For 32 lineage-defining Y-chromosome SNPs, Tamil castes show higher affinity to Europeans than to eastern Asians, and genetic distance estimates to the Europeans are ordered by caste rank. For 32 lineage-defining mitochondrial SNPs and hypervariable sequence (HVS) 1, Tamil castes have higher affinity to eastern Asians than to Europeans. For 45 autosomal STRs, upper and middle rank castes show higher affinity to Europeans than do lower rank castes from either Tamil Nadu or Andhra Pradesh. Local between-caste variation (Tamil Nadu R_ST = 0.96%, Andhra Pradesh R_ST = 0.77%) exceeds the estimate of variation between these geographically separated groups (R_ST = 0.12%). Low, but statistically significant, correlations between caste rank distance and genetic distance are demonstrated for Tamil castes using Y-chromosome, mtDNA, and autosomal data.

Conclusion

Genetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected and replicated in South Indian caste populations from two different geographic regions.     

Shape differences rather than size differences between castes in the Neotropical swarm-founding wasp <Emphasis Type="Italic">Metapolybia docilis</Emphasis> (Hymenoptera: Vespidae,Epiponini)

Background  

Swarm-founding epiponine wasps are an intriguing group of social insects in which colonies are polygynic (several queens share reproduction) and differentiation between castes is often not obvious. However, caste differences in some may be more pronounced in later phases of the colony cycle.     

Gene expression patterns associated with caste and reproductive status in ants: worker‐specific genes are more derived than queen‐specific ones

Variation in gene expression leads to phenotypic diversity and plays a central role in caste differentiation of eusocial insect species. In social Hymenoptera, females with the same genetic background can develop into queens or workers, which are characterized by divergent morphologies, behaviours and lifespan. Moreover, many social insects exhibit behaviourally distinct worker castes, such as brood‐tenders and foragers. Researchers have just started to explore which genes are differentially expressed to achieve this remarkable phenotypic plasticity. Although the queen is normally the only reproductive individual in the nest, following her removal, young brood‐tending workers often develop ovaries and start to reproduce. Here, we make use of this ability in the ant Temnothorax longispinosus and compare gene expression patterns in the queens and three worker castes along a reproductive gradient. We found the largest expression differences between the queen and the worker castes (~2500 genes) and the smallest differences between infertile brood‐tenders and foragers (~300 genes). The expression profile of fertile workers is more worker‐like, but to a certain extent intermediate between the queen and the infertile worker castes. In contrast to the queen, a high number of differentially expressed genes in the worker castes are of unknown function, pointing to the derived status of hymenopteran workers within insects.     

Cell cycle arrest by a gradient of Dpp signaling during Drosophila eye development

Background  

The secreted morphogen Dpp plays important roles in spatial regulation of gene expression and cell cycle progression in the developing Drosophila eye. Dpp signaling is required for timely cell cycle arrest ahead of the morphogenetic furrow as a prelude to differentiation, and is also important for eye disc growth. The dpp gene is expressed at multiple locations in the eye imaginal disc, including the morphogenetic furrow that sweeps across the eye disc as differentiation initiates.     

Prediction of a key role of motifs binding E2F and NR2F in down-regulation of numerous genes during the development of the mouse hippocampus

Background  

We previously demonstrated that gene expression profiles during neuronal differentiation in vitro and hippocampal development in vivo were very similar, due to a conservation of the important second singular value decomposition (SVD) mode (Mode 2) of expression. The conservation of Mode 2 suggests that it reflects a regulatory mechanism conserved between the two systems. In either dataset, the expression vectors of all the genes form two large clusters that differ in the sign of the contribution of Mode 2, which for the majority of them reflects the difference between down- or up-regulation.     

The homolog of Ciboulot in the termite (<Emphasis Type="Italic">Hodotermopsis sjostedti</Emphasis>): a multimeric β-thymosin involved in soldier-specific morphogenesis

Background  

Caste differentiation in social insects is a type of polyphenism that enables division of labor among members of a colony. This elaborate social integration has attracted broad interest, although little is known about its regulatory mechanisms, especially in Isoptera (termites). In this study, we analyzed soldier differentiation in the damp-wood termite Hodotermopsis sjostedti, focusing on a possible effector gene for caste development. The gene for an actin-binding protein, HsjCib, which shows a high level of expression in developing mandibles during soldier differentiation, is characterized in detail.     

Topographical cues of direct metal laser sintering titanium surfaces facilitate osteogenic differentiation of bone marrow mesenchymal stem cells through epigenetic regulation

Objectives

To investigate the role of hierarchical micro/nanoscale topography of direct metal laser sintering (DMLS) titanium surfaces in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), as well as the possible underlying epigenetic mechanism.

Materials and methods

Three groups of titanium specimens were prepared, including DMLS group, sandblasted, large‐grit, acid‐etched (SLA) group and smooth titanium (Ti) group. BMSCs were cultured on discs followed by surface characterization. Cell adhesion and proliferation were examined by SEM and CCK‐8 assay, while osteogenic‐related gene expression was detected by real‐time RT‐PCR. Immunofluorescence, western blotting and in vivo study were also performed to evaluate the potential for osteogenic induction of materials. In addition, to investigate the underlying epigenetic mechanisms, immunofluorescence and western blotting were performed to evaluate the global level of H3K4me3 during osteogenesis. The H3K4me3 and H3K27me3 levels at the promoter area of the osteogenic gene Runx2 were detected by ChIP assay.

Results

The DMLS surface exhibits greater protein adsorption ability and shows better cell adhesion performance than SLA and Ti surfaces. Moreover, both in vitro and in vivo studies demonstrated that the DMLS surface is more favourable for the osteogenic differentiation of BMSCs than SLA and Ti surfaces. Accordingly, osteogenesis‐associated gene expression in BMSCs is efficiently induced by a rapid H3K27 demethylation and increase in H3K4me3 levels at gene promoters upon osteogenic differentiation on DMLS titanium surface.

Conclusions

Topographical cues of DMLS surfaces have greater potential for the induction of osteogenic differentiation of BMSCs than SLA and Ti surfaces both in vitro and in vivo. A potential epigenetic mechanism is that the appropriate topography allows rapid H3K27 demethylation and an increased H3K4me3 level at the promoter region of osteogenesis‐associated genes during the osteogenic differentiation of BMSCs.

     

Syncytins expression in cultured trophoblast cells according to differentiation status

Background  

Data of syncytin 1 and 2 env gene expression in human placenta and participation in the syncytialisation phenomena has been reported. However, there are not many studies on simultaneous changes in expression of both syncytins in culture. We sought evidence on the relative expression of syncytins and syncytin 1 receptors in trophoblast cell culture treated with a differentiation inducing factor (forskolin).     

Caste‐biases in gene expression are specific to developmental stage in the ant Formica exsecta

Understanding how a single genome creates and maintains distinct phenotypes is a central goal in evolutionary biology. Social insects are a striking example of co‐opted genetic backgrounds giving rise to dramatically different phenotypes, such as queen and worker castes. A conserved set of molecular pathways, previously envisioned as a set of ‘toolkit’ genes, has been hypothesized to underlie queen and worker phenotypes in independently evolved social insect lineages. Here, we investigated the toolkit from a developmental point of view, using RNA‐Seq to compare caste‐biased gene expression patterns across three life stages (pupae, emerging adult and old adult) and two female castes (queens and workers) in the ant Formica exsecta. We found that the number of genes with caste‐biased expression increases dramatically from pupal to old adult stages. This result suggests that phenotypic differences between queens and workers at the pupal stage may derive from a relatively low number of caste‐biased genes, compared to higher number of genes required to maintain caste differences at the adult stage. Gene expression patterns were more similar among castes within developmental stages than within castes despite the extensive phenotypic differences between queens and workers. Caste‐biased expression was highly variable among life stages at the level of single genes, but more consistent when gene functions (gene ontology terms) were investigated. Finally, we found that a large part of putative toolkit genes were caste‐biased at least in some life stages in F. exsecta, and the caste‐biases, but not their direction, were more often shared between F. exsecta and other ant species than between F. exsecta and bees. Our results indicate that gene expression should be examined across several developmental stages to fully reveal the genetic basis of polyphenisms.     

Molecular insight into the genesis of ranked caste populations of western India based upon polymorphisms across non-recombinant and recombinant regions in genome

Background

Large-scale trade and cultural contacts between coastal populations of western India and Western-Eurasians paved for extensive immigration and genesis of wide spectrum of admixed gene pool. To trace admixture and genesis of caste populations of western India, we have examined polymorphisms across non-recombining 20 Y-SNPs, 20 Y-STRs, 18 mtDNA diagnostic sites, HVS-1 plus HVS-2 regions; and recombining 15 highly polymorphic autosomal STRs in four predominant caste populations- upper-ranking Desasth-brahmin and Chitpavan-brahmin; a middle-ranking Kshtriya Maratha; and a lower-rank peasant Dhangar.

Results

The generated genomic data was compared with putative parental populations- Central Asians, West Asians and Europeans using AMOVA, PC plot, and admixture estimates. Overall, disparate uniparental ancestries, and l.1% GST value for biparental markers among four studied caste populations linked well with their exchequer demographic histories. Marathi-speaking ancient Desasth-brahmin shows substantial admixture from Central Asian males but Paleolithic maternal component support their Scytho-Dravidian origin. Chitpavanbrahmin demonstrates younger maternal component and substantial paternal gene flow from West Asia, thus giving credence to their recent Irano-Scythian ancestry from Mediterranean or Turkey, which correlated well with European-looking features of this caste. This also explains their untraceable ethno-history before 1000 years, brahminization event and later amalgamation by Maratha. The widespread Palaeolithic mtDNA haplogroups in Maratha and Dhangar highlight their shared Proto-Asian ancestries. Maratha males harboured Anatolianderived J2 lineage corroborating the blending of farming communities. Dhangar heterogeneity is ascribable to predominantly South-Asian males and West-Eurasian females.

Conclusions

The genomic data-sets of this study provide ample genomic evidences of diverse origins of four ranked castes and synchronization of caste stratification with asymmetrical gene flows from Indo-European migration during Upper Paleolithic, Neolithic, and later dates. However, subsequent gene flows among these castes living in geographical proximity, have diminished significant genetic differentiation as indicated by AMOVA and structure.     

CFTR and Wnt/beta-catenin signaling in lung development

Background  

Cystic fibrosis transmembrane conductance regulator (CFTR) was shown previously to modify stretch induced differentiation in the lung. The mechanism for CFTR modulation of lung development was examined by in utero gene transfer of either a sense or antisense construct to alter CFTR expression levels.     

Comparative phylogeography of two co‐distributed but ecologically distinct rainbowfishes of far‐northern Australia

Aim

To test the influence of historical and contemporary environment in shaping the genetic diversity of freshwater fauna we contrast genetic structure in two co‐distributed, but ecologically distinct, rainbowfish; a habitat generalist (Melanotaenia splendida) and a habitat specialist (M. trifasciata).

Location

Fishes were sampled from far northern Australia (Queensland and Northern Territory).

Methods

We used sequence data from one mitochondrial gene and one nuclear gene to investigate patterns of genetic diversity in M. splendida and M. trifasciata to determine how differences in habitat preference and historical changes in drainage boundaries affected patterns of connectivity.

Results

Melanotaenia splendida showed high levels of genetic diversity and little population structure across its range. In contrast, M. trifasciata showed high levels of population structure. Whereas phylogeographic patterns differed, both species showed a strong relationship between geographical distance and genetic differentiation between populations. Melanotaenia splendida showed a shallower relationship with geographical distance, and genetic differentiation was best explained by stream length and a lower scaled ocean distance (11.98 times coast length). For M. trifasciata, genetic differentiation was best explained by overwater distance between catchments and ocean distance scaled at 1.16 × 10⁶ times coast length.

Main conclusions

Connectivity of freshwater populations inhabiting regions periodically interconnected during glacial periods appears to have been affected by ecological differences between species. Species‐specific differences are epitomized here by the contrast between co‐distributed congeners with different habitat requirements: for the habitat generalist, M. splendida, there was evidence for greater historical genetic connectivity with oceans as a weaker barrier to gene exchange in contrast with the habitat specialist, M. trifasciata.