Differential expression of genes for aromatase and estrogen receptor during the gonadal development in chicken embryos

Abstract

In birds, differentiation of embryonic gonads is not as strictly determined by the genetic sex as it is in mammals, and can be influenced by early manipulation with a sex steroid hormone. Thus administration of an aromatase inhibitor induces testis development in the genetic female, and administration of estrogen induces a left ovotestis in the genetic male embryo. Another feature of avian gonadogenesis is that only the left ovary develops in most species. Molecular mechanisms underlying these features at the level of gene expression have not been elucidated. In this paper, we present evidence that a gene for aromatase cytochrome P-450, an enzyme required for the last step in the synthesis of estradiol-17 , is expressed in medullae of the left and right gonads of a female chicken embryo, but not in those of a male chicken embryo, and that an estrogen receptor gene is expressed only in epithelium (and cortex later, in the female) of the left, not the right, gonad of both sexes, but the expression in the male left gonad is temporary and restricted to an early stage of development. Differential expression of these two genes serves well to explain the above features of gonadal development in birds. Furthermore, in ovo administration of estradiol-17 from the 5th to the 14th day of incubation does not cause expression of the estrogen receptor gene in the right gonad of chicken embryos of either sex, suggesting that the absence of expression of the estrogen receptor gene in the right gonad is not the result of down-regulation, but may be regarded as an important cause of the unilateral ovarian development.

Isolation of chicken homolog of the FOXL2 gene and comparison of its expression patterns with those of aromatase during ovarian development

“…These investigations revealed that cFoxL2 protein distribution was restricted to the medullar part of the ovary during early development. The same region of expression has been reported for aromatase transcripts Nakabayashi et al, 1998;Nishikimi et al, 2000;Oreal et al, 2002) and for the aromatase protein (Smith et al, 2003). The double immunolocalization of cFoxL2 and aromatase proteins to the sections of the left female gonad at E14 in our study demonstrated that cFoxL2 and aromatase proteins are expressed in the same cells.…”

“…Estrogens seem to play a crucial role in cortex formation and germ cell and supporting cell proliferation. The right chicken ovary lacking expression of estrogen receptors has a very thin cortex and regresses (Nakabayashi et al, 1998). In contrast, the left gonad develops into a functional ovary.…”

Sex determination: insights from the chicken

“…) females, expression is also turned off in the right gonad. (32,35) Taken together, these data indicate that estradiol synthesised in the medulla of female gonads mediates female sex determination by stimulating development of the cortex through ERa. Transient expression of ERa in ZZ embryos explains the susceptibility of males to feminisation by exogenous estradiol.…”

“…(30,31) Conversely, ZZ males treated with estradiol become feminised, although this is not permanent. The two terminal enzymes necessary for estrogen synthesis, P-450aromatase and 17bHSD, are expressed only in ZW female gonads at the onset of morphological differentiation (day 6-6.5; stage 29-30) (32)(33)(34) (Fig. 4).…”

Immunohistochemical Localization of Estrogen Receptor in the Embryonic Gonad of Male Quail Embryo During Gonadal Differentiation

“…Estrogen was reported to play a role in sex determination and gonadal differentiation in birds (Smith & Sinclair, 2004). Strikingly, estrogen and its receptor are asymmetrically expressed in avian embryonic gonads during sexual differentiation Nakabayashi et al, 1998). Asymmetric expression of estrogen and its receptor in chicken embryonic gonads is related to left-right gonadal asymmetry in birds (Intarapat & Stern, 2014).…”