A Genome-Wide Association Study Points out the Causal Implication of SOX9 in the Sex-Reversal Phenotype in XX Pigs

Abstract

Among farm animals, pigs are known to show XX sex-reversal. In such cases the individuals are genetically female but exhibit a hermaphroditism, or a male phenotype. While the frequency of this congenital disease is quite low (less than 1%), the economic losses are significant for pig breeders. These losses result from sterility, urogenital infections and the carcasses being downgraded because of the risk of boar taint. It has been clearly demonstrated that the SRY gene is not involved in most cases of sex-reversal in pigs, and that autosomal recessive mutations remain to be discovered. A whole-genome scan analysis was performed in the French Large-White population to identify candidate genes: 38 families comprising the two non-affected parents and 1 to 11 sex-reversed full-sib piglets were genotyped with the PorcineSNP60 BeadChip. A Transmission Disequilibrium Test revealed a highly significant candidate region on SSC12 (most significant p-value<4.65.10-10) containing the SOX9 gene. SOX9, one of the master genes involved in testis differentiation, was sequenced together with one of its main regulatory region Tesco. However, no causal mutations could be identified in either of the two sequenced regions. Further haplotype analyses did not identify a shared homozygous segment between the affected pigs, suggesting either a lack of power due to the SNP properties of the chip, or a second causative locus. Together with information from humans and mice, this study in pigs adds to the field of knowledge, which will lead to characterization of novel molecular mechanisms regulating sexual differentiation and dysregulation in cases of sex reversal.

Sex Reversal in Non-Human Placental Mammals

“…In other words, the association between sex reversal in pigs and the SOX9 gene was only highlighted with more than 80 affected cases, which is very surprising when compared with some 'real monogenic' recessive traits mapped by using very few affected animals (from 3 to 12, depending on the disease) [Charlier et al, 2008]. Agreeing with this supposed complexity of the mode of inheritance, no single homozygous chromosome segment could be identified among the affected piglets of the design, and numerous haplotypes seem to be linked with the XX sex reversal trait even if 3 of them were found associated at a frequency of ∼ 64% [Rousseau et al, 2013]. Two hypotheses could explain this situation: (i) the mutation is very ancient and has invaded different haplotypes, or (ii) there are different mutations of the same SOX9 locus leading to a sex reversal phenotype.…”

“…Thus, if XX sex reversal in pigs has a monogenic recessive mode of inheritance, the penetrance of the trait is incomplete (i.e., some cases remain as normal females even with a homozygous mutated genotype). Interestingly, more than 10 years later and thanks to the development of a commercial porcine high throughput SNP60 BeadChip, XX sex reversal in pigs was mapped on porcine chromosome 12 to the SOX9 locus [Rousseau et al, 2013]. In this recent study, familial cases from the INRA's study have been genotyped with other 26 half/full-sib families collected between 2006 and 2010 from the Large-White population of some French breeding companies.…”

Deep sequencing of a candidate region harboring the SOX9 gene for the canine XX disorder of sex development

“…Moreover, an extensive genome‐wide association study (GWAS) of XX DSD pigs revealed that the candidate region harbors the SOX9 gene (Rousseau et al . ). These findings clearly indicate that searching for the causative mutation in the SOX9 region, especially in its upstream sequence, is justified.…”

“…; Rousseau et al . ), but in some human cases of this disorder, an autosomal dominant sex‐limited model, associated with duplication of the regulatory sequence upstream from SOX9 gene, was described (Cox et al . ).…”

Testicular XX (<b><i>SRY</i></b>-Negative) Disorder of Sex Development in Cat

“…However, the inactivation of SOX9 is responsible for XY ( SRY -positive) DSD [Foster et al, 1994]. Finally, despite the fact the causal mutation is still unknown, alterations at the SOX9 locus have been linked to XX ( SRY -negative) DSD in pigs [Rousseau et al, 2013].…”