Abstract
Studies of the Y chromosome in primates, rodents and carnivores provide compelling evidence that the male specific region of Y (MSY) contains functional genes, many of which have specialized roles in spermatogenesis and male-fertility. Little similarity, however, has been found between the gene content and sequence of MSY in different species. This hinders the discovery of species-specific male fertility genes and limits our understanding about MSY evolution in mammals. Here, a detailed MSY gene catalogue was developed for the horse – an odd-toed ungulate. Using direct cDNA selection from horse testis, and sequence analysis of Y-specific BAC clones, 37 horse MSY genes/transcripts were identified. The genes were mapped to the MSY BAC contig map, characterized for copy number, analyzed for transcriptional profiles by RT-PCR, examined for the presence of ORFs, and compared to other mammalian orthologs. We demonstrate that the horse MSY harbors 20 X-degenerate genes with known orthologs in other eutherian species. The remaining 17 genes are acquired or novel and have so far been identified only in the horse or donkey Y chromosomes. Notably, 3 transcripts were found in the heterochromatic part of the Y. We show that despite substantial differences between the sequence, gene content and organization of horse and other mammalian Y chromosomes, the functions of MSY genes are predominantly related to testis and spermatogenesis. Altogether, 10 multicopy genes with testis-specific expression were identified in the horse MSY, and considered likely candidate genes for stallion fertility. The findings establish an important foundation for the study of Y-linked genetic factors governing fertility in stallions, and improve our knowledge about the evolutionary processes that have shaped Y chromosomes in different mammalian lineages.
Highlights
Mammalian Y chromosome stands out from the rest of the genome because it is male specific, constitutively haploid and exhibits unique structural and functional features [1,2,3]
Y chromosome genes have been mapped and/ or functionally analyzed in carnivores [11,12] and cattle [13,14,15,16], and to a limited extent in river buffalo [17], pig [18,19], sheep [20,21] and rabbit [22]. These studies clearly show that mammalian Y chromosomes carry a rich repertoire of functional genes, several of which might play a role in spermatogenesis and male fertility
A plasmid library enriched with ECAY cDNA sequences was constructed
Summary
Mammalian Y chromosome stands out from the rest of the genome because it is male specific, constitutively haploid and exhibits unique structural and functional features [1,2,3]. Y chromosome genes have been mapped and/ or functionally analyzed in carnivores [11,12] and cattle [13,14,15,16], and to a limited extent in river buffalo [17], pig [18,19], sheep [20,21] and rabbit [22]. These studies clearly show that mammalian Y chromosomes carry a rich repertoire of functional genes, several of which might play a role in spermatogenesis and male fertility
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