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The evolution of sex determination (SD) mechanisms in teleost fishes is amazingly dynamic, as reflected by the variety of different master sex-determining genes identified, even sometimes among closely related species. Pangasiids are a group of economically important catfishes in many South-Asian countries, but little is known about their sex determination system. Here, we generated novel genomic resources for 12 Pangasiid species and provided a first characterization of their SD system. Based on an Oxford Nanopore long-read chromosome-scale high quality genome assembly of the striped catfish Pangasianodon hypophthalmus, we identified a duplication of the anti-Müllerian hormone receptor type II gene (amhr2), which was further characterized as being sex-linked in males and expressed only in testicular samples. These first results point to a male-specific duplication on the Y chromosome (amhr2by) of the autosomal amhr2a. Sequence annotation revealed that the P. hypophthalmus Amhr2by is truncated in its N-terminal domain, lacking the cysteine-rich extracellular part of the receptor that is crucial for ligand binding, suggesting a potential route for its neofunctionalization. Short-read genome sequencing and reference-guided assembly of 11 additional Pangasiid species, along with sex-linkage studies, revealed that this truncated amhr2by duplication is also conserved as a male-specific gene in many Pangasiids. Reconstructions of the amhr2 phylogeny suggested that amhr2by arose from an ancient duplication / insertion event at the root of the Siluroidei radiation that is dated around 100 million years ago. Altogether these results bring multiple lines of evidence supporting that amhr2by is an ancient and conserved master sex-determining gene in Pangasiid catfishes, a finding that highlights the recurrent usage of the transforming growth factor β pathway in teleost sex determination and brings another empirical case towards the understanding of the dynamics or stability of sex determination systems.

Background The patterns of gene expression on highly differentiated sex chromosomes differ drastically from those on autosomes, due to sex-specific patterns of selection and inheritance. As a result, X chromosomes are often enriched in female-biased genes (feminization) and Z chromosomes in male-biased genes (masculinization). However, it is not known how quickly sexualization of gene expression and transcriptional degeneration evolve after sex-chromosome formation. Furthermore, little is known about how sex-biased gene expression varies throughout development. Results We sample a population of common frogs (Rana temporaria) with limited sex-chromosome differentiation (proto-sex chromosome), leaky genetic sex determination evidenced by the occurrence of XX males, and delayed gonadal development, meaning that XY individuals may first develop ovaries before switching to testes. Using high-throughput RNA sequencing, we investigate the dynamics of gene expression throughout development, spanning from early embryo to froglet stages. Our results show that sex-biased expression affects different genes at different developmental stages and increases during development, reaching highest levels in XX female froglets. Additionally, sex-biased gene expression depends on phenotypic, rather than genotypic sex, with similar expression in XX and XY males; correlates with gene evolutionary rates; and is not localized to the proto-sex chromosome nor near the candidate sex-determining gene Dmrt1. Conclusions The proto-sex chromosome of common frogs does not show evidence of sexualization of gene expression, nor evidence for a faster rate of evolution. This challenges the notion that sexually antagonistic genes play a central role in the initial stages of sex-chromosome evolution. Electronic supplementary material The online version of this article (10.1186/s13059-018-1548-4) contains supplementary material, which is available to authorized users.

Reproductive isolation is crucial for the process of speciation to progress. Sex chromosomes have been assigned a key role in driving reproductive isolation but empirical evidence from natural population processes has been restricted to organisms with degenerated sex chromosomes such as mammals and birds. Here we report restricted introgression at sex-linked compared to autosomal markers in a hybrid zone between two incipient species of European tree frog, Hyla arborea and H. orientalis, whose homologous X and Y sex chromosomes are undifferentiated. This large X-effect cannot result from the dominance or faster-X aspects of Haldane’s rule, which are specific to degenerated sex chromosomes, but rather supports a role for faster-heterogametic-sex or faster-male evolutionary processes. Our data suggest a prominent contribution of undifferentiated sex chromosomes to speciation.

Clinal patterns of autosomal genetic diversity within Europe have been interpreted in previous studies in terms of a Neolithic demic diffusion model for the spread of agriculture; in contrast, studies using mtDNA have traced many founding lineages to the Paleolithic and have not shown strongly clinal variation. We have used 11 human Y-chromosomal biallelic polymorphisms, defining 10 haplogroups, to analyze a sample of 3,616 Y chromosomes belonging to 47 European and circum-European populations. Patterns of geographic differentiation are highly nonrandom, and, when they are assessed using spatial autocorrelation analysis, they show significant clines for five of six haplogroups analyzed. Clines for two haplogroups, representing 45% of the chromosomes, are continentwide and consistent with the demic diffusion hypothesis. Clines for three other haplogroups each have different foci and are more regionally restricted and are likely to reflect distinct population movements, including one from north of the Black Sea. Principal-components analysis suggests that populations are related primarily on the basis of geography, rather than on the basis of linguistic affinity. This is confirmed in Mantel tests, which show a strong and highly significant partial correlation between genetics and geography but a low, nonsignificant partial correlation between genetics and language. Genetic-barrier analysis also indicates the primacy of geography in the shaping of patterns of variation. These patterns retain a strong signal of expansion from the Near East but also suggest that the demographic history of Europe has been complex and influenced by other major population movements, as well as by linguistic and geographic heterogeneities and the effects of drift. Z.H.R. was supported by a BBSRC Studentship, T.Z. by a Wellcome Trust Bioarchaeology Studentship, M.E.H. by an MRC Studentship, F.R.S. by the Leverhulme Trust, and L.P. by Ph.D. grant PRAXIS XXI/BD/13632/97 from Fundacao para a Ciencia e a Tecnologia. D.C.R. is a Glaxo Wellcome Research Fellow. C.T.-S. is supported by the CRC, and M.A.J. is a Wellcome Trust Senior Fellow in Basic Biomedical Science, supported by grant 057559. Iberian sample collection was partially funded by multidisciplinary project grant PR182/96 6745 from Complutense University.

Six Y-linked tetranucleotide microsatellites were typed in a sample of continental Italians and Sardinians. Significant differences in allele distributions were found between peninsular Italy and the island. Patterns of distinct allelic associations were evident in Sardinia and in the mainland. STR haplotypes in a subset of Sardinian chromosomes were monophyletically related and indicated that additions/deletions of a single tetranucleotide unit had to sequentially occur within a historical time-scale (about 9,000 years). Assumptions on both the time elapsed since the peopling of the island and the number of mutational events led us to estimate (by three different methods) a rate of 2.7-11 x 10(-4) mutations per generation per locus--at the upper end of the range of values reported in the literature.

Many models of sex-biased dispersal predict that the direction of sex-bias depends upon a species' mating system. In agreement with this, almost all polygynous mammals show male-biased dispersal whereas largely monogamous birds show female-biased dispersal (FBD). The hamadryas baboon (Papio hamadryas hamadryas) is polygynous and so dispersal is predicted to be male biased, as is found in all other baboon subspecies, but there are conflicting field data showing both female and male dispersal. Using 19 autosomal genetic markers genotyped in baboons from four Saudi Arabian populations, we found strong evidence for FBD in post-dispersal adults but not, as expected, in pre-dispersal infants and young juveniles, when we compared male and female: population structure (Fst), inbreeding (Fis), relatedness (r), and the mean assignment index (mAIc). Furthermore, we found evidence for female-biased gene flow as population genetic structure (Fst), was about four times higher for the paternally inherited Y, than for either autosomal markers or for maternally inherited mtDNA. These results contradict the direction of sex-bias predicted by the mating system and show that FBD has evolved recently from an ancestral state of male-biased dispersal. We suggest that the cost–benefit balance of dispersal to males and females is tightly linked to the unique hierarchical social structure of hamadryas baboons and that dispersal and social organization have coevolved.

Azoospermia factor (AZF) region microdeletions, which account for about 10-15% of patients with oligoazoospermia, seem to lack a close genotype-testicular phenotype correlation. Although many genetic and non-genetic factors may contribute to this outcome, it was thought that a spontaneous regression of testicular germ cells might also play a relevant role. The opportunity for carrying out two different testicular biopsies one year apart in an AZFc-microdeleted patient enabled corroboration of this possibility. Indeed, the first biopsy showed a spermatocyte maturation arrest with mean Johnsen scores of 4 and 3.9 in the right and left testes respectively. One year later, the right testicular biopsy showed a picture of Sertoli cell-only syndrome in 90% of the tubules examined, and of spermatogonial maturation arrest in the remaining tubules, with a mean Johnsen score of 2.1. The almost complete absence of germinal cells was confirmed by four left testicular sperm aspirations (TESA), conducted at the same time as the biopsy during an intracytoplasmic sperm injection cycle, which showed the almost exclusive presence of Sertoli cells (85% of the whole cell population). No spermatozoa could be retrieved by TESA or testicular biopsy. To our knowledge, this is the first case of a spontaneous regression of the germinal cell epithelium over time in a patient with a Yq microdeletion without the apparent intervention of any cause known to affect the germinal epithelium.

Two hypervariable Y-specific markers, the YCAII and DYS19 STRs, and the more stable Y Alu Polymorphism (YAP) have been analysed in about 1400 individuals of 21 different populations, mainly from Europe but also from the Middle East, Africa and Asia. On the basis of the frequency distributions of these three Y-markers we compare, using different statistical analyses, their power in detecting population genetic structure and in distinguishing closely related groups. The pattern of populations' genetic affinities inferred from the three markers considered altogether suggests a strong genetic structure that, with a few exceptions, broadly corresponds to the linguistic relatedness and/or geographic location of the sampled populations.

Numerous population samples from around the world have been tested for Y chromosome-specific p49a,f/TaqI restriction polymorphisms. Here we review the literature as well as unpublished data on Y-chromosome p49a,f/TaqI haplotypes and provide a new nomenclature unifying the notations used by different laboratories. We use this large data set to study worldwide genetic variability of human populations for this paternally transmitted chromosome segment. We observe, for the Y chromosome, an important level of population genetics structure among human populations (FST = .230, P < .001), mainly due to genetic differences among distinct linguistic groups of populations (FCT = .246, P < .001). A multivariate analysis based on genetic distances between populations shows that human population structure inferred from the Y chromosome corresponds broadly to language families (r = .567, P < .001), in agreement with autosomal and mitochondrial data. Times of divergence of linguistic families, estimated from their internal level of genetic differentiation, are fairly concordant with current archaeological and linguistic hypotheses. Variability of the p49a,f/TaqI polymorphic marker is also significantly correlated with the geographic location of the populations (r = .613, P < .001), reflecting the fact that distinct linguistic groups generally also occupy distinct geographic areas. Comparison of Y-chromosome and mtDNA RFLPs in a restricted set of populations shows a globally high level of congruence, but it also allows identification of unequal maternal and paternal contributions to the gene pool of several populations.

This is an open-access article distributed under the terms of the Creative Commons Attribution License.-- et al., Non-recombining sex chromosomes are expected to undergo evolutionary decay, ending up genetically degenerated, as has happened in birds and mammals. Why are then sex chromosomes so often homomorphic in cold-blooded vertebrates? One possible explanation is a high rate of turnover events, replacing master sex-determining genes by new ones on other chromosomes. An alternative is that X-Y similarity is maintained by occasional recombination events, occurring in sex-reversed XY females. Based on mitochondrial and nuclear gene sequences, we estimated the divergence times between European tree frogs (Hyla arborea, H. intermedia, and H. molleri) to the upper Miocene, about 5.4–7.1 million years ago. Sibship analyses of microsatellite polymorphisms revealed that all three species have the same pair of sex chromosomes, with complete absence of X-Y recombination in males. Despite this, sequences of sex-linked loci show no divergence between the X and Y chromosomes. In the phylogeny, the X and Y alleles cluster according to species, not in groups of gametologs. We conclude that sex-chromosome homomorphy in these tree frogs does not result from a recent turnover but is maintained over evolutionary timescales by occasional X-Y recombination. Seemingly young sex chromosomes may thus carry old-established sex-determining genes, a result at odds with the view that sex chromosomes necessarily decay until they are replaced. This raises intriguing perspectives regarding the evolutionary dynamics of sexually antagonistic genes and the mechanisms that control X-Y recombination., Financial support was provided by the Swiss National Science Foundation (http://www.snf.ch/E/Pages/default.aspx; grants 3100A0-108100 and 31003A-129894 to NP) and the Ministerio de Ciencia e Innovación (http://www.micinn.es/portal/site/MICINN/; grant CGL2008-04271-C02/01/BOS to IMS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Objective: To present a case of Marfan syndrome and concurrent congenital obstructive azoospermia. Design: Case report. Setting: Tertiary-care academic hospital. Patient(s): A man with Marfan syndrome and obstructive azoospermia. Intervention(s): The patient was evaluated for azoospermia that was proved to be due to congenital absence of large segments of vas deferens and epididymis bilaterally. Main Outcome Measure(s): Evaluation for testicular sperm extraction and ICSI procedure. Result(s): The patient is a candidate for testicular sperm extraction and ICSI. Conclusion(s): The Marfan syndrome and azoospermia may be associated in sporadic cases.

Background As children with velocardiofacial syndrome (VCFS) develop, they are at increased risk for psychopathology; one third will eventually develop schizophrenia. Because VCFS and the concomitant symptomatology result from a known genetic origin, the biological and behavioral characteristics of the syndrome provide an optimal framework for conceptualizing the associations among genes, brain development, and behavior. The purpose of this study was to investigate the effect of the parental origin of the 22q11.2 microdeletion on the brain development of children and adolescents with VCFS. Methods Eighteen persons with VCFS and 18 normal control subjects were matched individually for age and sex. Results of DNA polymorphism analyses determined the parental origin of the deletion. Nine persons with VCFS had a deletion on the maternally derived chromosome 22; 9 persons, on the paternally derived chromosome 22. High-resolution magnetic resonance imaging scans were analyzed to provide quantitative measures of gray and white matter brain tissue. Results Total brain volume was approximately 11% smaller in the VCFS group than in controls. Comparisons between VCFS subgroups (maternal vs paternal microdeletion 22q11.2) indicated a significant 9% volumetric difference in total volume of cerebral gray matter (volume was greater in patients with paternal microdeletion) but not cerebral white matter. Significant age-related changes in gray matter were detected for subjects whose 22q11.2 deletion was on the maternal chromosome. Conclusions Children and adolescents with VCFS experience major alterations in brain volumes. Significant reduction in gray matter development is attributable to presence of 22q11.2 microdeletion on the maternal chromosome.