Chicken hemogen homolog is involved in the chicken-specific sex-determining mechanism

In chicken, the left and right female gonads undergo a completely different program during development. To learn more about the molecular factors underlying side-specific development and to identify potential sex- and side-specific genes in developing gonads, we separately performed next-generation sequencing-based deepSuperSAGE transcription profiling from left and right, female and male gonads of 19-day-old chicken embryos. A total of 836 transcript variants were significantly differentially expressed (p < 10^-5) between combined male and female gonads. Left-right comparison revealed 1,056 and 822 differentially (p < 10^-5) expressed transcript variants for male and female gonads, respectively, of which 72 are side-specific in both sexes. At least some of these may represent key players for lateral development in birds. Additionally, several genes with laterally differential expression in the ovaries seem to determine female gonads for growth or regression, whereas right-left differences in testes are mostly limited to the differentially expressed genes present in both sexes. With a few exceptions, side-specific genes are not located on the sex chromosomes. The large differences in lateral gene expression in the ovaries in almost all metabolic pathways suggest that the regressing right gonad might have undergone a change of function during evolution.

Section: High Usual Suspects Ratiosupporting

confidence: 83%

Gene Expression of Chicken Gonads Is Sex- and Side-Specific

Scheider

Afonso-Grunz²,

Hoffmeier³

et al. 2014

“…DMRT1 is located on what is probably the most ancient evolutionary strata shared amongst all major lineages, supporting the notion that it is a universal testis determinant in birds [Chue and Smith, 2011;Zhou et al, 2014]. Recently, another Z-linked gene, HEMGN , has been implicated in testicular morphogenesis in the chicken [Nakata et al, 2013] ( fig. 1 A).…”

Section: Avian Sex Determination and Gonadal Sex Differentiationmentioning

confidence: 61%

“…This gene encodes a nuclear protein, Hemogen, which is involved in haematopoiesis in mammals (but not gonadal sex differentiation). It is expressed in male but not female embryonic chicken gonads, and forced overexpression in ZW females can induce upregulation of male marker genes, including DMRT1 [Nakata et al, 2013]. It is possible that HEMGN lies upstream of DMRT1 in chicken gonadal sex differentiation.…”

Section: Avian Sex Determination and Gonadal Sex Differentiationmentioning

confidence: 99%

Sex Reversal in Birds

Major

Smith²

2016

Sexual differentiation in birds is controlled genetically as in mammals, although the sex chromosomes are different. Males have a ZZ sex chromosome constitution, while females are ZW. Gene(s) on the sex chromosomes must initiate gonadal sex differentiation during embryonic life, inducing paired testes in ZZ individuals and unilateral ovaries in ZW individuals. The traditional view of avian sexual differentiation aligns with that expounded for other vertebrates; upon sexual differentiation, the gonads secrete sex steroid hormones that masculinise or feminise the rest of the body. However, recent studies on naturally occurring or experimentally induced avian sex reversal suggest a significant role for direct genetic factors, in addition to sex hormones, in regulating sexual differentiation of the soma in birds. This review will provide an overview of sex determination in birds and both naturally and experimentally induced sex reversal, with emphasis on the key role of oestrogen. We then consider how recent studies on sex reversal and gynandromorphic birds (half male:half female) are shaping our understanding of sexual differentiation in avians and in vertebrates more broadly. Current evidence shows that sexual differentiation in birds is a mix of direct genetic and hormonal mechanisms. Perturbation of either of these components may lead to sex reversal.

“…In this context, it has recently been reported that the Z-chromosome gene hemogen is expressed at higher levels in the left and right medulla of male gonads than of female gonads between HH28 and HH35. Overexpression of this transcription factor in female embryos caused decreased FOXL2/ P450arom expression and increased SOX9 expression compared to controls and a degree of female to male gonad sex reversal, suggesting that this gene could also play a role in testis determination [Nakata et al, 2013].…”

Section: L:r Asymmetry and Sex (Gonadal) Determinationmentioning

confidence: 99%

Gonadal Asymmetry and Sex Determination in Birds

Guioli¹,

Nandi

Zhao

et al. 2014

Although vertebrates display a superficial bilateral symmetry, most internal organs develop and locate with a consistent left:right asymmetry. There is still considerable debate as to when this process actually begins, but it seems that, at least for some species, the initial steps occur at a very early stage of development. In recent years, a number of model systems, including the chick embryo, have been utilised to increase our understanding of the molecular basis of this complex developmental process. While the basic elements of asymmetry are clearly conserved in chick development, the chick embryo also exhibits an additional unusual asymmetry in terms of the development of the gonads. In the female chick embryo, only 1 gonad and accessory structures fully develop, with the result that the adult hen has only 1 ovary and a single oviduct - both on the left side. With a small number of exceptions, this is a consistent feature of avian development. Here, we describe the morphological development and molecular basis of this unusual asymmetry, consider the implications for avian sex determination, and discuss the possible biological reasons why many birds have adopted a single-ovary system.