Defining the impact of estrogen on spermatogonial fate

Di-n-butyl phthalate causes estrogenic effects in adult male Murray rainbowfish (Melanotaenia fluviatilis)

Phthalic acid esters (PAEs) are a class of synthetic industrial chemicals commonly found in the aquatic environment worldwide. PAEs have been recognised as anti-androgens in male mammals but little is known about their endocrine disrupting effects in fish. This study investigated the effects of 7-day exposures to nominal (measured) concentrations of 125 (62), 250 (140), 500 (230) and 1,000 (383) μg/L of di-n-butyl phthalate (DnBP) on the biomarkers of reproduction in adult male Murray River rainbowfish (Melanotaenia fluviatilis) using molecular, biochemical and histological endpoints. None of the tested concentrations of DnBP had any effect on survival or the vital body indices of the fish. The sizes of spermatogonia, Type A and B spermatocytes and spermatids were significantly smaller relative to the controls after treatment with DnBP. This was accompanied by a significant increase in the proportion of spermatogonia in fish treated with 250-1,000 μg/L of DnBP in comparison to the unexposed fish. At the end of the exposure period, the expressions of the transcripts for the androgen receptors α and β were significantly elevated in the livers of the fish treated with 500 and 1,000 μg/L of DnBP. In addition, there was also an increase in the circulating concentrations of vitellogenin in the plasma in the higher treatment groups. An induction in the activity of aromatase was noted in the brains of 1,000 μg/L DnBP-treated fish. This was accompanied by an increase in the hepatic expression of the genes (here and later, whenever the phrase gene expression is used as a synonym for gene transcription although it is acknowledged that it is also regulated, e.g., by translation, mRNA stability and protein stability) encoding for the oestrogen receptors α and β and choriogenin L. Collectively, an increase in the proportion of spermatogonia in the testes, the upregulation of the genes for the oestrogen receptors and choriogenin in the liver, an induction in the brain aromatase activity and the increase in the circulating levels of plasma vitellogenin suggest that continuous exposures for 7 days to sub-acute concentrations of DnBP can adversely affect the reproductive health of the male Murray rainbowfish by an estrogenic mode of action.

TEX11 modulates germ cell proliferation by competing with estrogen receptor β for the binding to HPIP

Klinefelter syndrome (KS), characterized by the presence of more than one X-chromosome in men, is a major genetic cause of male infertility. Germ cell degeneration in KS patients is thought to be the consequences of overexpression of some genes on the X-chromosome. However, the identity of these genes and the underlying mechanisms remain unclear. Testis-expressed 11 (TEX11) is an X-chromosome-encoded germ-cell-specific protein that is expressed most abundantly in spermatogonia and early spermatocytes in the testes. In our search for TEX11-interacting partners using the yeast two-hybrid system, we identified hematopoietic pre-B cell leukemia transcription factor-interacting protein (HPIP), which anchors estrogen receptors (ER) to the cytoskeleton and modulates their functions. We found that mouse spermatogonial stem cells expressed Tex11, Hpip, and Esr2 but not Esr1. In cultured cells, TEX11 competed with ERβ for binding to HPIP. Upon treatment with 17β-estradiol or an ERβ agonist diarylpropionitrile, TEX11 promoted the nuclear translocation of ERβ and enhanced its transcriptional activities. On the other hand, TEX11 suppressed the nongenomic activities of ERβ in the cytoplasm, as indicated by reduced phosphorylation of AKT and ERK signaling molecules. Overexpression of TEX11 in mouse germ-cell-derived GC-1 and GC-2 cells suppressed the cell proliferation and the expression of cFos, Ccnd1, and Ccnb1 that were stimulated by 17β-estradiol or diarylpropionitrile and elevated the expression level of the proapoptotic Bax gene. The negative effect of TEX11 on cell proliferation suggests that increased expression of TEX11 in the germ cells may partially contribute to the spermatogenic defect observed in KS patients.