Loci affecting male fertility in hybrids between <Emphasis Type="Italic">Mus macedonicus</Emphasis> and C57BL/6

Male F₁ hybrids between inbred strains and Mus macedonicus have very small testes and are sterile. Cytological analysis of testes shows very few meioses. To determine the genetic basis for this sterility, (C57BL/6J × Mus macedonics) F₁ females were mated to males from C57BL/10J. In about half the male progeny no meiosis I was observed. About half of the animals that progressed through meiosis I showed other indications of low fertility and the balance appeared fertile. QTL analysis of the progeny suggested that loci on proximal Chrs 17 and X were involved in the sterility and a locus on Chr X in variation of body weight. There is also evidence that X//Y dissociation of the pseudo-autosomal region occurs. The QTLs on Chrs X and 17 together account for about 37% of the variance for testis weight. Congenic lines B.MAC-X(1-38), and B.MAC-17(1-23) have been constructed using a modified speed congenic approach. Testis tubules from B.MAC-X(1-38) are narrow and vacuolated. They contain only Sertoli cells and mitotically dividing spermatogonia. Very occasionally a meiotic metaphase can be observed, but no sperm are produced. Homozygous males from B.MAC-17(1-23) are sterile, producing sperm heads but no complete sperm.     

Genetic analysis of X-linked hybrid sterility in the house mouse

Hybrid sterility is a common postzygotic reproductive isolation mechanism that appears in the early stages of speciation of various organisms. Mus musculus musculus and Mus musculus domesticus represent two recently separated mouse subspecies particularly suitable for genetic studies of hybrid sterility. Here we show that the introgression of Chr X of M. m. musculus origin (PWD/Ph inbred strain, henceforth PWD) into the genetic background of the C57BL/6J (henceforth B6) inbred strain (predominantly of M. m. domesticus origin) causes male sterility. The X-linked hybrid sterility is associated with reduced testes weight, lower sperm count, and morphological abnormalities of sperm heads. The analysis of recombinant Chr Xs in sterile and fertile males as well as quantitative trait locus (QTL) analysis of several fertility parameters revealed an oligogenic nature of the X-linked hybrid sterility. The Hstx1 locus responsible for male sterility was mapped near DXMit119 in the central part of Chr X. To ensure full sterility, the PWD allele of Hstx1 has to be supported with the PWD allelic form of loci in at least one proximal and/or one distal region of Chr X. Mapping and cloning of Hstx1 and other genes responsible for sterility of B6–X^PWDY^B6 males could help to elucidate the special role of Chr X in hybrid sterility and consequently in speciation.     

Prdm9 Incompatibility Controls Oligospermia and Delayed Fertility but No Selfish Transmission in Mouse Intersubspecific Hybrids

PR-domain 9 (Prdm9) is the first hybrid sterility gene identified in mammals. The incompatibility between Prdm9 from Mus musculus domesticus (Mmd; the B6 strain) and the Hstx2 region of chromosome (Chr) X from M. m. musculus (Mmm; the PWD strain) participates in the complete meiotic arrest of mouse intersubspecific (PWD×B6)F1 hybrid males. Other studies suggest that also semisterile intersubspecific hybrids are relevant for mouse speciation, but the genes responsible remain unknown. To investigate the causes of this semisterility, we analyzed the role of Prdm9 and Chr X in hybrids resulting from the crosses of PWK, another Mmm-derived inbred strain. We demonstrate that Prdm9 and Chr X control the partial meiotic arrest and reduced sperm count in (PWK×B6)F1 males. Asynapsis of heterosubspecific chromosomes and semisterility were partially suppressed by removal of the B6 allele of Prdm9. Polymorphisms between PWK and PWD on Chr X but not in the Prdm9 region were responsible for the modification of the outcome of Prdm9 - Chr X F1 hybrid incompatibility. Furthermore, (PWK×B6)F1 hybrid males displayed delayed fertility dependent on the Prdm9 incompatibility. While the Drosophila hybrid sterility gene Overdrive causes both delayed fertility and increased transmission of its own chromosome to the offspring, the segregation of Chr X and the Prdm9 region from the mouse (PWK×B6)F1 males was normal. Our results indicate extended functional consequences of Prdm9 - Chr X intersubspecific incompatibility on the fertility of hybrids and should influence the design of fertility analyses in hybrid zones and of laboratory crosses between Mmm and Mmd strains.     

Female mice of DDK strain are fully fertile in the intersubspecific crosses with Mus musculus molossinus and M. m. castaneus

The female mice of DDK strain are almost infertile when mated with males from other strains. This phenomenon is caused by the early death of F1 embryos owing to the incompatibility system attributed to the ovum mutant (Om) locus on Chromosome (Chr) 11 and known as DDK syndrome. In the present study, DDK females were found to be fully fertile in the intersubspecific matings with the males of two wild mouse-derived strains, MOM (originated from Japanese wild mice, Mus musculus molossinus) and Cas (originated from Philippine wild mice, M. m. castaneus), indicating that no incompatibility exists between DDK oocytes and spermatozoa of MOM and Cas strains. Furthermore, this compatibility has been confirmed by the following two findings: (1) Normal fertility was shown by the two types of backcrosses, DDK females x F(1) (DDK female x MOM male) males and DDK females x F(1) (DDK female x Cas male) males; and (2) the offspring from these backcrosses segregated equally into the homozygotes and heterozygotes as genotyped by the microsatellite markers closely linked to Om locus. MOM and Cas strains would be useful for further investigations on the Om locus. On the other hand, the litter size of F(1) [C57BL/6Cr (B6) female x Cas male] females mated with B6 males was about half that of the mating with DDK males. It would be interesting to investigate whether this reduction in fertility is related to the Om locus or not.     

Developmental study of the different effects on the hybrid sterility of Kit and KitW-v alleles paired with Kit from Mus spretus

The combination of the KitW or KitW-n mutant alleles and KitS from Mus spretus results in male hybrid sterility with small testes. In the present study, reproduction of the combination between KitW-v and KitS alleles was examined. The KitW-v/KitS male was fertile and the histologic structure was normal; the seminiferous tubules showed all of the normal stages of spermatogenesis. The postnatal development of the testis at 8, 12, 16 and 20 days was also studied in the fertile +Kit/+Kit and KitW-v/KitS males and the sterile KitW/KitS. The results showed that at 8 days there was no noticeable difference among the three genotype combinations, while from 12 to 20 days spermatogenesis in the KitW/KitS male nearly stopped before the meiosis stage. The expression of Kit receptor protein from the KitS allele in the sterile testis of the KitW/KitS male was confirmed using western blot analysis. The Kit ligand derived from M. spretus showed two amino acid changes in the extracellular domain compared with that from C57BL and it appears that the ligand-receptor interaction between C57BL and SPR may influence the male hybrid sterility of KitW/KitS.     

Chromosome X modulates incidence of testicular germ cell tumors in <Emphasis Type="Italic">Ter</Emphasis> mice

Germ cell tumor development in humans has been proposed to be part of testicular dysgenesis syndrome (TDS), which manifests as undescended testes, sterility, hypospadias, and, in extreme cases, as germ cell tumors. Males of the Ter mouse strain show interesting parallels to TDS because they either lack germ cells and are sterile or develop testicular germ cell tumors. We found that these defects in Ter mice are due to mutational inactivation of the Dead-end (Dnd1) gene. Here we report that chromosome X modulates germ cell tumor development in Ter mice. We tested whether the X or the Y chromosome influences tumor incidence. We used chromosome substitution strains to generate two new mouse strains: 129-Ter/Ter that carry either a C57BL/6J (B6)-derived chromosome (Chr) X or Y. We found that Ter/Ter males with B6-Chr X, but not B6-Chr Y, showed a significant shift in propensity from testicular tumor development to sterile testes phenotype. Thus, our studies provide unambiguous evidence that genetic factors from Chr X modulate the incidence of germ cell tumors in mice with inactivated Dnd1. Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Radiation effects on Drosophila suzukii (Diptera: Drosophilidae) reproductive behaviour

Female remating is a widespread behaviour, reported in several insect species. This behaviour can affect the efficiency of sterile insect technique (SIT); however, little is known about the postcopulatory behaviour of some pest species considered as candidates to be controlled by this technique, such as Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae). In this study, we investigated the effects of male and female sterilization on mating and remating behaviour of D. suzukii. First, we tested the occurrence of multiple mating in different combinations between sterile and fertile males and females. Then, we tested the effects of male and female sterility on female propensity to mate and remate. We found an overall low remating rate by D. suzukii females. Male sterility did not influence mating and remating likelihood; however, copula duration of sterile males was shorter compared to fertile males. On the other hand, sterile females were less likely to mate. Our findings encourage further research regarding the use of SIT to control D. suzukii.     

Disruption of genetic interaction between two autosomal regions and the X chromosome causes reproductive isolation between mouse strains derived from different subspecies

Reproductive isolation that initiates speciation is likely caused by incompatibility among multiple loci in organisms belonging to genetically diverging populations. Laboratory C57BL/6J mice, which predominantly originated from Mus musculus domesticus, and a MSM/Ms strain derived from Japanese wild mice (M. m. molossinus, genetically close to M. m. musculus) are reproductively isolated. Their F1 hybrids are fertile, but successive intercrosses result in sterility. A consomic strain, C57BL/6J-ChrX(MSM), which carries the X chromosome of MSM/Ms in the C57BL/6J background, shows male sterility, suggesting a genetic incompatibility of the MSM/Ms X chromosome and other C57BL/6J chromosome(s). In this study, we conducted genomewide linkage analysis and subsequent QTL analysis using the sperm shape anomaly that is the major cause of the sterility of the C57BL/6J-ChrX(MSM) males. These analyses successfully detected significant QTL on chromosomes 1 and 11 that interact with the X chromosome. The introduction of MSM/Ms chromosomes 1 and 11 into the C57BL/6J-ChrX(MSM) background failed to restore the sperm-head shape, but did partially restore fertility. This result suggests that this genetic interaction may play a crucial role in the reproductive isolation between the two strains. A detailed analysis of the male sterility by intracytoplasmic sperm injection and zona-free in vitro fertilization demonstrated that the C57BL/6J-ChrX(MSM) spermatozoa have a defect in penetration through the zona pellucida of eggs.     

A field cage study of the optimal age for release of radio-sterilized Aedes albopictus mosquitoes in a sterile insect technique program

The use of the sterile insect technique (SIT) is being considered as an additional tool for the control of Aedes albopictus (Skuse) (Diptera: Culicidae), the vector of Chikungunya and Dengue viruses in Mauritius. The aim of this study was to assess the competitiveness value of sterile males of different age and under various release conditions. Three release ratios were tested with sterile males of either 1, 3, or 5 days old at release. The competition of sterile males against same age or a mixed age population of fertile males (which is more representative of the field situation) was also investigated. The participation in mating (observed through single female oviposition), the average-induced sterility, and the male competitiveness index indicated that 3-day-old sterile males have the best balance between survival and mating capacity, and should therefore be the favored age of release in the field. Reduction in the cage fertility was obtained at 5-to-1 release ratio; however, it is speculated that at least a 10-fold ratio of sterile-to-fertile males should be chosen to induce substantial sterility in the wild Ae. albopictus population in the SIT pilot release site in Mauritius. Interestingly, this study showed for the first time that the age of the fertile male population against which the sterile males compete is a very important parameter that can significantly affect the sexual performance of sterile males, leading to overestimation of their competitiveness values.     

Sex-restricted non-Mendelian inheritance of mouse Chromosome 11 in the offspring of crosses between C57BL/6J and (C57BL/6J × DBA/2J)F1 mice

We report on the observation of sex-restricted, non-Mendelian inheritance over a region of mouse Chromosome (Chr) 11, occurring in the offspring of crosses between two commonly used Mus musculus-derived inbred strains, C57BL/6J and DBA/2J. In the surviving backcross progeny of reciprocal matings between (C57BL/6J × DBA/2J)F₁ hybrids and the C57BL/6J parental strain, we observed the preferential appearance of C57BL/6J alleles along a region of Chr 11. The deviation from Mendelian predictions was observed only in female offspring from both reciprocal backcrosses, and not in males from either cross. The sex-specificity of the observed non-Mendelian inheritance points to an explanation based on embryonic or neonatal lethality. Our data add to previously obtained evidence for a Chr 11 locus or loci with sex-specific and allele-specific effects on viability. Received: 19 December 1997 / Accepted: 10 June 1998     

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.     

A study of morphology,cytology and sterility in interspecific hybrids and amphidiploids of Nicotiana knightiana X N. umbratica

Summary Interspecific hybrids and amphidiploids of Nicotiana knightiana Goodspeed (n= 12)x N. umbratica Burbidge (n = 23) resembled either parent in some characters and were intermediate in other characters. The F₁ hybrids (2n = 35) showed mostly univalents during meiosis, while the amphidiploids (2n = 70) formed bivalents almost regularly. The former were completely sterile and the latter fully male fertile but predominantly female sterile. This female sterility was due to disintegration of the embryo sacs leading to collapsed ovules. The few fertile ovules, however, showed normal development of embryo sac and embryo. The occurrence of fertile and sterile ovules was believed to be due to segregation of the genes governing sterility.     

Genetic analysis of neonatal death with growth retardation in F1 male Dh/+ mice

Nearly all F₁ male mice with Dh/+ genotype between DDD female and DH–Dh/+ male die within a few days after birth; however, this is not observed in the reciprocal cross. The F₁ Dh/+ males usually exhibit growth retardation prior to death. To identify the putative genetic locus or loci in DDD genome that cause the abnormalities in the presence of the Dh, a linkage analysis was carried out in backcross progeny of a cross of (DDD female × DH–+/+ male) F₁ female × DH–Dh/+ male. Appearance of growth retardation was examined from the day of birth, and both growth-retarded and normally weaned Dh/+ males were genotyped for microsatellite marker loci spanning autosomes and the X Chromosome (Chr). Significant evidence for linkage was identified on the distal edge of the X Chr, near the microsatellite marker of DXMit135. Furthermore, among mice from DDD female × reciprocal F₁ Dh/+ male produced between DH–Dh/+ and progenitor strains (C57BL/6J, C3H/HeJ and BALB/cA), only the progeny from ♀DDD ×♂(♀DH–Dh/+×♂C3H/HeJ) F₁ Dh/+ male did not show any lethality and/or growth retardation. Thus, the lethality in F₁ Dh/+ males accompanied by growth retardation is caused by the interactions between the Dh gene, X Chr, and Y Chr. Based on the CAG repeat sequence length polymorphism among Mus musculus musculus Sry gene, C3H/HeJ was different from C57BL/6J, BALB/cA, and DH. These data suggest that there are at least two functional types of Y Chr in Mus musculus musculus. Received: 22 January 1999 / Accepted: 5 April 1999     

Mouse hybrid sterility and testicular function

Crosses of BALB/c female mice and inbred wild male mice (PWD, PWK) produce fertile female progeny, but the male offspring are sterile. The hybrid male sterility is a direct action of the hybrid sterility genes Hst-1s and Hstws. Previous reports concluded that spermatogenic arrest effected the sterility. However, the testicular steroidogenesis of hybrid sterile male mice has not been elucidated. In the present report, the steroidogenic capacity of hybrid sterile and parental strain males was directly assessed by quantifying testosterone secretion by maximally stimulated testes perfused in vitro. Additionally, Leydig cell mass and germ cell volumes were morphometrically determined. The experimental results confirm the deleterious impact of the Hst-1s/Hstws genotype on spermatogenesis and demonstrate for the first time that the steroidogenic capacity of hybrid sterile testes is reduced. The biochemical defects that cause the impairment of testicular function are unknown.     

Do sterile females affect the sexual performance of sterile males of Anastrepha ludens (Diptera: Tephritidae)?

The release of sterile males to suppress the Mexican fruit fly Anastrepha ludens (Loew) population was simulated in field cages to compare the sexual performance of sterile males with wild females in the presence and absence of sterile females. Using different release ratios of sterile and wild individuals, this study showed that the presence of sterile females negatively affected the sexual performance of sterile males in mating with wild females. We found that the sterility induced was proportional to the magnitude of the sterile/fertile ratio. These results indicate that the release of sterile males without sterile females can significantly improve the efficiency of the sterile insect technique for the control of A. ludens.     

Male hybrid sterility of mice with the genomic region of the KitW mutation and the KitS allele from Mus spretus

Two congenic strains, C57BL-Kit^W and C57BL-Kit^S, were generated. The Kit^W allele originated from strain WB-Kit^W and the Kit^S allele from Mus spretus. The Kit^W/Kit^S males showed hybrid sterility with small testes, but the females were fertile. The development of the seminiferous tubules of Kit^W/Kit^S males stopped before the spermatocyte stage and they were almost free of sperm. The Kit gene is located at position 42 on chromosome 5. We investigated in the C57BL-Kit^S congenic strain which part of the chromosomal region adjacent to the Kit^S allele is introduced from SPR into a C57BL background. The region between positions 42 and 44 was derived from SPR. Eleven amino acid substitutions of the Kit^S cDNA were detected by comparison with the sequence data of the +^Kit cDNA from C57BL; seven were in the extracellular domain, one in the transmembrane domain, two in the kinase I domain, and one in the carboxy-terminal tail. The Kit mRNA derived from both Kit^W and Kit^S alleles was expressed in the sterile testes of Kit^W/Kit^S males.     

Coevolution of Cryptosporidium tyzzeri and the house mouse (Mus musculus)

Two house mouse subspecies occur in Europe, eastern and northern Mus musculus musculus (Mmm) and western and southern Mus musculus domesticus (Mmd). A secondary hybrid zone occurs where their ranges meet, running from Scandinavia to the Black Sea. In this paper, we tested a hypothesis that the apicomplexan protozoan species Cryptosporidium tyzzeri has coevolved with the house mouse. More specifically, we assessed to what extent the evolution of this parasite mirrors divergence of the two subspecies. In order to test this hypothesis, we analysed sequence variation at five genes (ssrRNA, Cryptosporidium oocyst wall protein (COWP), thrombospondin-related adhesive protein of Cryptosporidium 1 (TRAP-C1), actin and gp60) in C. tyzzeri isolates from Mmd and Mmm sampled along a transect across the hybrid zone from the Czech Republic to Germany. Mmd samples were supplemented with mice from New Zealand. We found two distinct isolates of C. tyzzeri, each occurring exclusively in one of the mouse subspecies (C. tyzzeri-Mmm and C. tyzzeri-Mmd). In addition to genetic differentiation, oocysts of the C. tyzzeri-Mmd subtype (mean: 4.24 × 3.69 μm) were significantly smaller than oocysts of C. tyzzeri-Mmm (mean: 4.49 × 3.90 μm). Mmm and Mmd were susceptible to experimental infection with both C. tyzzeri subtypes; however, the subtypes were not infective for the rodent species Meriones unguiculatus, Mastomys coucha, Apodemus flavicollis or Cavia porcellus. Overall, our results support the hypothesis that C. tyzzeri is coevolving with Mmm and Mmd.