Jinsong Zhou

Sex chromosomes evolved from autosomes many times across the eukaryote phylogeny. Several models have been proposed to explain this transition, some involving male and female sterility mutations linked in a region of suppressed recombination between X and Y (or Z/W, U/V) chromosomes. Comparative and experimental analysis of a reference genome assembly for a double haploid YY male garden asparagus (Asparagus officinalis L.) individual implicates separate but linked genes as responsible for sex determination. Dioecy has evolved recently within Asparagus and sex chromosomes are cytogenetically identical with the Y, harboring a megabase segment that is missing from the X. We show that deletion of this entire region results in a male-to-female conversion, whereas loss of a single suppressor of female development drives male-to-hermaphrodite conversion. A single copy anther-specific gene with a male sterile Arabidopsis knockout phenotype is also in the Y-specific region, supporting a two-gene model for sex chromosome evolution.

There are controversies about adverse effects of bisphenol A (BPA), a ubiquitous xenoestrogen, on reproduction and development of male animals. To understand BPA action and assess its risk more completely, we examined the impact of BPA at high doses on the testes of pubertal male Kunming (China) mice. BPA at 0 (control), 160, 480, and 960 mg/kg/day was given by gavage to mice from postnatal days (PND) 31-44, followed by observation of morphology and detection of apoptosis and expressions of Fas/FasL and active caspase-3 on PND 45, 60, and 90 by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling, immunohistochemistry, and Western blotting. There was no effect of BPA at 160 mg/kg/day, however, at 480 and 960 mg/kg/day there was underdevelopment of testes and disruption of spermatogenesis. There were many apoptotic Leydig and germ cells in the testes with apoptotic indices being significantly increased compared with controls. The expression of Fas and active caspase-3 was localized in the same cell types as apoptosis occurred, and expression levels of Fas, FasL, and active caspase-3 were significantly increased compared with controls. The disturbed spermatogenesis, apoptosis and upregulation of Fas, FasL, and active caspase-3 expression persisted to PND 90. The results suggest that high-dose BPA induces apoptosis of Leydig and germ cells in the mouse testis through the Fas-signaling pathway. Therefore, there is concern about reproductive health for humans occupationally exposed to high levels of BPA.