No abstract

Spermatogenesis is a complex developmental process whereby diploid spermatogenic stem cells become haploid and undergo a series of morphological changes to produce physically mature spermatozoa. Crucial to this process are a number of RNA-binding proteins, responsible for the posttranscriptional control of essential mRNAs and particularly pertinent to the two periods of inactive transcription that occur in spermatogenesis. One such group of RNA-binding proteins is the Musashi family, specifically Musashi-1 (MSI1) and Musashi-2 (MSI2), which act as key translational regulators in various stem cell populations and have been linked with the induction of tumorigenesis. In the present study, we examined the differential expression of mammalian MSI1 and MSI2 during germ cell development in the mouse testis. MSI1 was found to be predominately localized in mitotic gonocytes and spermatogonia, whereas MSI2 was detected in meiotic spermatocytes and differentiating spermatids. Extensive examination of the function of Musashi in spermatogenesis was achieved through the use of two transgenic mouse models with germ cell-specific overexpression of full-length isoforms of Msi1 or Msi2. These models demonstrated that aberrant expression of either Msi1 or Msi2 has deleterious effects on normal spermatogenesis, with Msi2 overexpression resulting in male sterility. Studies undertaken on human testicular seminoma tumors provide further insights into the relevance of MSI1 and MSI2 overexpression as diagnostic markers to human stem cell cancers. Overall this study provides further evidence for the unique functions that RNA-binding protein isoforms occupy within spermatogenesis, and introduces the potential manipulation of the Musashi family proteins to elucidate the mechanisms of posttranscriptional gene expression during germ cell development.

Mammalian females are born with a finite number of nonrenewing primordial follicles, the majority of which remain in a quiescent state for many years. Because of their nonrenewing nature, these "resting" oocytes are particularly vulnerable to xenobiotic insult, resulting in premature ovarian senescence and the formation of dysfunctional oocytes. In this study, we characterized the mechanisms of ovotoxicity for three ovotoxic agents, 4-vinylcyclohexene diepoxide (VCD), methoxychlor (MXC), and menadione (MEN), all of which target immature follicles. Microarray analysis of neonatal mouse ovaries exposed to these xenobiotics in vitro revealed a more than twofold significant difference in transcript expression (p < 0.05) for a number of genes associated with apoptotic cell death and primordial follicle activation. Histomorphological and immunohistological analysis supported the microarray data, showing signs of primordial follicle activation and preantral follicle atresia both in vitro and in vivo. Sperm-oocyte fusion assays on oocytes obtained from adult Swiss mice treated neonatally revealed severely reduced sperm-egg binding and fusion in a dose-dependent manner for all the xenobiotic treatments. Additionally, lipid peroxidation analysis on xenobiotic-cultured oocytes indicated a dose-dependent increase in oocyte lipid peroxidation for all three xenobiotics in vitro. Our results reveal a novel mechanism of preantral ovotoxicity involving the homeostatic recruitment of primordial follicles to maintain the pool of developing follicles destroyed by xenobiotic exposure and to our knowledge provide the first documented evidence of short-term, low- and high-dose (VCD 40-80 mg/kg/day, MXC 50-100 mg/kg/day, MEN 7.5-15 mg/kg/day) neonatal exposure to xenobiotics causing long-term reactive oxygen species-induced oocyte dysfunction.

No abstract