True hermaphrodites: an experimental model in the mouse

Distinct roles of androgen receptor, estrogen receptor alpha, and BCL6 in the establishment of sex-biased DNA methylation in mouse liver

Sexual dimorphism in gene regulation, including DNA methylation, is the main driver of sexual dimorphism in phenotypes. However, the questions of how and when sex shapes DNA methylation remain unresolved. Recently, using mice with different combinations of genetic and phenotypic sex, we identified sex-associated differentially methylated regions (sDMRs) that depended on the sex phenotype. Focusing on a panel of validated sex-phenotype dependent male- and female-biased sDMRs, we tested the developmental dynamics of sex bias in liver methylation and the impacts of mutations in the androgen receptor, estrogen receptor alpha, or the transcriptional repressor Bcl6 gene. True hermaphrodites that carry both unilateral ovaries and contralateral testes were also tested. Our data show that sex bias in methylation either coincides with or follows sex bias in the expression of sDMR-proximal genes, suggesting that sex bias in gene expression may be required for demethylation at certain sDMRs. Global ablation of AR, ESR1, or a liver-specific loss of BCL6, all alter sDMR methylation, whereas presence of both an ovary and a testis delays the establishment of male-type methylation levels in hermaphrodites. Moreover, the Bcl6-LKO shows dissociation between expression and methylation, suggesting a distinct role of BCL6 in demethylation of intragenic sDMRs.

Different levels of testicular organization during gonadal differentiation in B6.Y(Tir) mice manifesting sex reversal

B6.Y(Tir) (mice with Y chromosome from a strain in Tirano, Italy, and autosomes and X-chromosomes from the B6 strain) mice provide an excellent model for analysing sex development that occurs during gonadal differentiation; however, the molecular mechanisms that contribute to sex reversal are unclear. Our aim has been to establish which molecular events participate in this sex reversal. The pattern of gene expression related to testicular [Sry (sex-determining region of the Y chromosome), Sox9 (Sry-related high-mobility group box gene 9) and Mis (Müllerian-inhibiting substance)] and ovarian [Wnt4 (Wingless-type MMTV (murine-mammary-tumour virus) integration site family, member 4), Rspo1 (cysteine-rich secretory protein containing a thrombospondin type 1 repeat) and Stra8 (stimulated by retinoic acid gene 8)] differentiation was analysed by applying immunofluorescence and real-time RT-PCR (reverse transcription-PCR), focusing on XY gonads from the B6.Y(Tir) mouse, but also analysing the normal strains CD-1 and C57BL/6J (B6). The expression of genes related to the process of sexual differentiation was altered in the case of the B6.Y(Tir) strain, both at the transcript and protein level, inducing differentiation of ovaries and ovotestes, but not the formation of the testes, which were normal. Our results indicate that the expression of testicular genes is inhibited at various levels, permitting the expression of ovarian genes such as Wnt4, Stra8 and Rspo1. However, their activity was not clear when the data were averaged. Correlation analysis indicated that an ovary differentiation pathway is activated when the testicular differentiation pathway is inhibited.

Effect of simulated microgravity on testosterone and sperm motility in mice

We examined changes in the serum testosterone level and in sperm in the testis and epididymis by using tail-suspended mice, which are a simulation model of the body fluid shift in space, to evaluate the possibility of spermatogenesis failure in space environment. We also studied pathological disorders of the testis in the tail-suspended mice. Tail suspension was imposed with a tail harness to a degree at which the hindlegs of mice did not touch the floor of the housing unit. In control mice, the tail was similarly fixed with a tail harness to impose the same stress, except that a hindleg remained on the floor. Body weight was not significantly different between the 2 groups during 7 days, and testicular weight was significantly different. The testosterone level was significantly lower in the tail-suspended group (0.71 +/- 1.24 ng/mL) than in the control group (2.38 +/- 3.50 ng/mL; P <.05). Microscopy with hematoxylin and eosin (HE) and periodic acid-Schiff (PAS) staining showed a small proportion of seminiferous tubules with impairment of spermatogenic function in the tail-suspended group, and multinucleated giant cells were occasionally noted. Terminal deoxynucleotidyl tranferase-mediated nick end-labeling staining revealed positive cells even in animals in which impairment was considered to be mild based on HE and PAS staining. Many cells showed intense p53 immunostaining compared to the control group, with more intense staining of the nucleus in the tail-suspended group. The proportion of motile sperm was slightly but not significantly reduced in the tail-suspended group. However, the mean movement velocity of the motile spermatozoa was significantly decreased.