Effect of tamoxifen on H-Y antigen expression and gonadal development in chicken embryos

[Mechanism of avian sex determination and differentiation]

Avian sex is determined by genes on the sex chromosomes (ZZ for male and ZW for female). In avian embryo stage, genes on one or two chromosomes control the sex differentiation. Gonad develops to testis in ZZ male and to ovary in ZW female. To date, DMRT1 (Doublesex and mab-3 related transcription factor 1) is considered to be the best candidate gene in controlling the avian gonad differentiation. However, recent study showed that avian sex might be determined by cell autonomous independent of sex hormone signal. Therefore, sex determination gene does not only control the gonadal differentiation, but also control body cells. From this sense, DMRT1 is not the switch gene of avian sex determination. What is the switch factor of avian sex determination, and what is the mechanism of avian sex determination? This review discussed the current progresses on avian sex determination and differentiation from three aspects: W chromosome and ovary development, Z chromosome and testis development, and avian sex determination and cell autonomous.

Tamoxifen induces masculinization of genetic females and regulates P450 aromatase and müllerian inhibiting substance mRNA expression in Japanese flounder (Paralichthys olivaceus)

Japanese flounder, Paralichthys olivaceus, provides an excellent model to elucidate the roles of sex steroid hormones in gonadal sex differentiation because the sex is easily altered by sex steroid treatments or water temperature control during the sex differentiation. We have previously shown that high water temperature, an aromatase inhibitor (fadrozole), or 17alpha-methyltestosterone treatment causes the sex-reversal from genetic females to phenotypic males and suppression of mRNA expression of ovary-type P450 aromatase (P450arom), which is a steroidogenic enzyme responsible for the conversion of androgens to estrogens, in Japanese flounder. In the present study, we demonstrate that treatment of the genetic females with anti-estrogen (tamoxifen) leads to their masculinization, suppresses P450arom mRNA expression, and induces mRNA expression of Müllerian inhibiting substance (MIS), a member of the transforming growth factor-beta (TGF-beta) superfamily, while it has no effect on mRNAs expression of estrogen receptor-alpha (ERalpha) and ERbeta. In contrast, 17beta-estradiol counteracted masculinization of the genetic females by tamoxifen or high water temperature treatment, up-regulated P450arom mRNA expression, and down-regulated MIS mRNA expression. These results strongly suggest that estrogen signaling through ERs dramatically influences the gonadal sex differentiation by regulating P450arom and MIS mRNA expression.

Research note: effect of in ovo 17-beta-estradiol or tamoxifen administration on sexual differentiation of the external genitalia

The effect of in ovo administration of tamoxifen or 17 beta-estradiol on external sexual dimorphism in chickens was investigated. In two trials, fertile eggs were injected with either tamoxifen (200 micrograms per egg) or vehicle (100 microL corn oil) on Day 1 of incubation, or with 17 beta-estradiol (20 micrograms per egg) or vehicle on Day 11 of incubation. Sexes were determined by visual inspection of the external genitalia and by gonadal identification at Day 1 posthatch. Tamoxifen injection resulted in a significantly greater number of phenotypic male identifications, with male:female ratios of 76:24 (Trial 1) and 62:38 (Trial 2) based on external genitalia phenotype. Gonadal sexing corrected these ratios to 46:54 and 44:56, resulting in genital sexing errors of 27% (Trial 1) and 18% (Trial 2). These errors were significantly higher than genital sexing errors of the chicks treated with vehicle (2 and .6% for Trials 1 and 2, respectively). In ovo administration of 17 beta-estradiol resulted in an increased number of female identifications based on genital sex determination, with male:female ratios of 37:63 (Trial 1) and 46:54 (Trial 2). Gonadal sexing corrected these ratios to 54:46 and 51:49, resulting in genital sexing errors of 10 and 6% for Trials 1 and 2, respectively. These errors were significantly higher than genital sexing errors of vehicle-treated chicks (4 and .9% for Trials 1 and 2, respectively). The results of the present study indicate that early embryonic administration of estrogen or an estrogen antagonist alters chicken external sexual dimorphism near the time of hatch.

Early aspects of sex differentiation in the gonads of chick embryos

In chick embryos whose sex had been previously identified by cytokaryologic methods, a light-microscope study of the number and dimensions of the germ cells (GCs) has been made from 2 to 7 days of incubation. Early differences between the sexes have been found. In females the GCs were larger and increased in number earlier than in males. This suggests an earlier differentiation of GCs in females. On the other hand, ultrastructural observations on GCs at 70 h incubation (colonization stage of the genital ridges) have revealed that male and female GCs differ from each other mainly in the amount of rough and smooth endoplasmic reticulum, mitochondria, glycogen particles and lipid droplets. This suggests early morpho-functional differences between male and female GCs.

Sexual differentiation of neuroendocrine systems and behavior

Differentiation of the reproductive system occurs in stages, with early development of the gonads and later differentiation of the brain. The physiological mechanisms that are involved in the sequence of events during sexual differentiation have not been clearly understood. However, recent technological advances have made understanding these mechanisms much more accessible. Many of these techniques have been used to elucidate the nature of steroid-induced effects on target tissues, hormonal and neuroendocrine interactions, and the molecular basis of these processes. This review will focus on the sequence of events and mechanisms associated with sexual differentiation of endocrine, morphological, and behavioral components of reproduction in the chicken and Japanese quail.

On cell contribution to gonadal soma formation in quail-chick chimeras during the indifferent stage of gonadal development

A quail mesonephros was produced in a chicken embryo by orthotopic transplantation of quail left Wolffian duct and intermediate mesoderm between somites 18 and 21 in a 2 day chicken embryo. During the indifferent period of gonadal development in the chicken (day 4-6), no mesonephric (quail) cells take part in forming gonadal somatic cells. At this period all these cells are derived from the surface epithelium. The epithelial cells leave the surface where colonization of primordial germ cells occurs. The mesonephros begins its participation in gonadal soma formation between day 6 and 7, the time of sexual differentiation. These results are discussed in terms of sexual differentiation and the development stage of the mesonephros.

Increased H-Y antigen levels associated with behaviorally induced, female-to-male sex reversal in a coral-reef fish

It has been proposed that H-Y antigen is the synthetic product of sex-determining genes, and that H-Y antigen controls ontogenetic differentiation of the heterogametic sex throughout vertebrates. The coral-reef fish Anthias squamipinnis is a protogynous hermaphrodite in which all individuals mature initially as females. Males result when adult females change sex as a consequence of alterations in behavioral interactions within social groups. Three assay methods were used to measure H-Y antigen levels in the spleens, gonads, and epidermal tissue of 16 adult females and in 16 males that had been induced to change sex from a prior female phase by the removal of a pre-existing male from each of 16 social groups. In 15 male-female pairs, the H-Y antigen levels were higher in male than in female spleen, gonad, and epidermis tissues. The precise temporal relationship between the onset of sex change and the increase in the H-Y antigen level was not examined. If, as we strongly suspect, the temporal relationship proves to be close, the inference will be that the behavioral cues inducing sex change also influence the synthetic activity of genes controlling H-Y antigen production.