Role of FET-1 as a possible ovarian sex determining gene in avians

Abstract

The mass culling of male chicks of egg-laying breeds is ethically and financially questionable, estimated to cost South African commercial breeders $10 million annually, and close to $1 billion worldwide. Understanding sex determination in birds is essential to the development of an all-female chicken breed, which would eliminate the need for mass culling. In birds, where females are ZW and males are ZZ, sex determination is hypothesised to be the result of either a W determinant or Z dosage. One of the few candidate W determinants is the Female Expressed Transcript -1 (FET-1), previously localized to the W chromosome with female specific expression. The aim of this research was to further investigate the function of FET-1 and its potential role in avian sex determination. RT-PCR on extracted RNA from E4.5 gonads confirmed FET-1 expression. Unexpectedly, expression was significantly higher in females than in males. A local alignment search of FET-1 against the chicken genome suggested multiple FET-1 integrations in the Z chromosomes and autosomes, consistent with retroviral elements such as FET-1. Using RACE (Rapid Amplification of cDNA Ends) two long intergenic non-coding RNA (lincRNA) populations were identified that overlapped d along the FET-1 transcript. RNA expression was observed for both of the lincRNA populations as well as the FET-1 protein-coding sequence at E4.5 and E6.5 embryos; stronger gonadal and epidermal staining observed in females compared to males, suggesting a sex-specific role. Whole mount IHC using a rabbit polyclonal anti-FET-1 antibody showed the presence of FET-1 protein in the epidermis but not the gonads. Collectively the data suggests that FET-1 is not likely to be a W determinant; however predominant expression in female suggests a role in the development of sex-specific characteristics.