Both Nuclear and Cytoplasmic Components Are Defective in Oocytes of the B6.YTIR Sex-Reversed Female Mouse

Abstract

In the mammalian gonadal primordium, activation of the Sry gene on the Y chromosome initiates a cascade of genetic events leading to testicular organization whereas its absence results in ovarian differentiation. An exception occurs when the Y chromosome of Mus musculus domesticus from Tirano, Italy (Y(TIR)), is placed on the C57BL/6J (B6) genetic background. The B6.Y(TIR) progeny develop only ovaries or ovotestes despite Sry transcription in fetal life. Consequently, the XY offspring with bilateral ovaries develop into apparently normal females, but their eggs fail to develop after fertilization. Our previous studies have shown that the primary cause of infertility can be attributed to oocytes rather than their surrounding somatic cells in the XY ovary. This study attempted to identify the defects in oocytes from the B6.Y(TIR) female mouse. We examined the developmental potential of embryos from XY and XX females after exchanging their nuclear components by microsurgery following in vitro maturation and fertilization. The results suggest that both nuclear and cytoplasmic components are defective in oocytes from XY females. In the XY fetal ovary, most germ cells entered meiosis and their autosomes appeared to synapse normally while the X and Y chromosomes remained unpaired during meiotic prophase. This lack of X-Y pairing probably caused aneuploidy in some secondary oocytes following in vitro maturation. However, normal numbers of chromosomes in the rest of the secondary oocytes indicate that aneuploidy alone can not explain the nuclear defect in oocytes.

The behavior of the X- and Y-chromosomes in the oocyte during meiotic prophase in the B6.YTIR sex-reversed mouse ovary

“…We have previously reported similar findings (Amleh et al 2000). However, in the present study, we examined a larger number of oocytes over a wider range of developmental stages (17.5-20.5 dpc).…”

“…For genotyping of the fetuses/offspring from the cross between B6 females and B6.Y TIR males or B6 females and B6 males, liver sample was digested overnight in a lysis buffer and the lysate was used for PCR amplification of the Y-encoded Zfy gene as described previously (Amleh et al 2000). For genotyping of the fetuses/offspring from the cross between B6 females and Paf carrier males, liver sample was used to extract total RNA using TRIzol (Invitrogen), and the precipitate was dissolved in DEPCtreated water.…”

Switch from BAX-dependent to BAX-independent germ cell loss during the development of fetal mouse ovaries

“…Although it is inevitable to lose a considerable number of cells during processing, this method is suitable for comparing the germ cell populations at different stages and of different genotypes. In addition, dissociated cells give us the advantage to be able to identify precisely meiotic sub-stages by immunolabeling of synaptonemal complex (SC) components (Amleh et al, 2000;McClellan et al, 2003). The results suggest a switch from BAX-dependent to BAX-independent mechanism involved in germ cell elimination during ovarian development.…”

Retinoic acid, meiosis and germ cell fate in mammals

“…Therefore, the initial sex differentiation of a germ cell is determined not by its chromosomal constitution, but by its environment (McLaren, 1995;McLaren, 2003). However, the completion of meiosis and the formation of functional gametes are influenced by the sexchromosome composition of the germ cell (Amleh et al, 2000;Bradbury, 1983;Burgoyne, 1987;McLaren, 1981;Park and Taketo, 2003;Taketo-Hosotani et al, 1989).A well-accepted hypothesis to explain the effect of tissue environment on germ cell fate has been that the developing testicular tissue produces a meiosis-inhibiting factor (Buehr et al, 1993;Francavilla and Zamboni, 1985;McLaren, 1984). This factor was supposedly produced at around 12.0 dpc by immature Sertoli cells, the supporting somatic cells in the developing testis, and considered likely to be a short-range diffusible factor (McLaren and Buehr, 1990;McLaren and Southee, 1997).…”

“…Therefore, the initial sex differentiation of a germ cell is determined not by its chromosomal constitution, but by its environment (McLaren, 1995;McLaren, 2003). However, the completion of meiosis and the formation of functional gametes are influenced by the sexchromosome composition of the germ cell (Amleh et al, 2000;Bradbury, 1983;Burgoyne, 1987;McLaren, 1981;Park and Taketo, 2003;Taketo-Hosotani et al, 1989).…”