Z and W chromosomes of chickens: studies on their gene functions in sex determination and sex differentiation

Abstract

Since the discovery of SRY/Sry as a testis-determining gene on the mammalian Y chromosome in 1990, extensive studies have been carried out on the immediate target of SRY/Sry and genes functioning in the course of testis development. Comparative studies in non-mammalian vertebrates including birds have failed to find a gene equivalent to SRY/Sry, whereas they have suggested that most of the downstream factors found in mammals including SOX9 are also involved in the process of gonadal differentiation. Although a gene whose function is to trigger the cascade of gene expression toward gonadal differentiation has not been identified yet on either W or Z chromosomes of birds, a few interesting genes have been found recently on the sex chromosomes of chickens and their possible roles in sex determination or sex differentiation are being investigated. It is the purpose of this review to summarize the present knowledge of these sex chromosome-linked genes in chickens and to give perspectives and point out questions concerning the mechanisms of avian sex determination.

Disruption of FEM1C-W gene in zebra finch: evolutionary insights on avian ZW genes

“…Avian ZW chromosome genes reported so far appear to be conserved widely across species: SMAD2 (Mizuno et al 2002), ATP5A1 , UBE2R2 (Scholz et al 2006), UBAP2 (Handley et al 2004), NIPBL (Berlin and Ellegren 2006), SPIN (Itoh et al 2001), HINT1 (Hori et al 2000;O'Neill et al 2000), CHD1 (Ellegren 1996). ZW genes are clustered on the chicken Z chromosome at the terminal end of short arm and the centromeric region of long arm (Fig.…”

Avian sex determination: what, when and where?

“…As in other gallinaceous birds, the chicken has heteromorphic sex chromosomes. The large chicken Z sex chromosome has over 350 genes, while the smaller, heterochromatic W chromosome has very few, probably less than twenty (Mizuno et al, 2002;Stiglec et al, 2007). Recent studies indicate that the Z sex chromosome is strongly conserved across all birds, while the W is far less conserved and has undergone varying degrees of degradation (Shetty et al, 1999;Nanda and Schmid, 2002;Raudsepp et al, 2002;Berlin and Ellegren, 2006).…”

Rowley Review

“…Gonadal development has been most extensively studied in the Chicken embryo (Clinton 1998;Mizuno et al 2002;Smith and Sinclair 2004). Those few other birds that have been examined at the embryonic stages show a broadly similar pattern of gonadal morphogenesis (Gasc 1978).…”

“…In XY embryos, SRY initiates formation of testes during embryonic life, whereas formation of ovaries occurs in the absence of SRY (reviewed in Capel 1998). However, birds lack SRY and have a non-homologous set of sex chromosomes, designated ZZ male and ZW female (Takagi and Sasaki 1974;Griffiths 1991;Coriat et al 1993;McBride et al 1997;Mizuno et al 2002;Stiglec et al 2007). Despite some important advances in the past few years, our understanding of avian sex determination is still incomplete.…”