Abstract
Partitioning-defective proteins (PAR) are detected to express mainly in the cytoplast, and play an important role in cell polarity. However, we showed here that PAR6, one kind of PAR protein, was localized in the nuclei of mouse oocytes that formed primordial follicles during the perinatal period, suggesting a new role of PAR protein. It is the first time we found that, in mouse fetal ovaries, PAR6 appeared in somatic cell cytoplasm and fell weak when somatic cells invaded germ cell cysts at 17.5 days post coitus (dpc). Meanwhile, the expression of PAR6 was observed in cysts, and became strong in the nuclei of some germ cells at 19.5 dpc and all primordial follicular oocytes at 3 day post parturition (dpp), and then obviously declined when the primordial follicles entered the folliculogenic growth phase. During the primordial follicle pool foundation, the number of PAR6 positive germ cells remained steady and was consistent with that of formed follicles at 3 dpp. There were no TUNEL (apoptosis examination) positive germ cells stained with PAR6 at any time studied. The number of follicles significantly declined when 15.5 dpc ovaries were treated with the anti-PAR6 antibody and PAR6 RNA interference. Carbenoxolone (CBX, a known blocker of gap junctions) inhibited the expression of PAR6 in germ cells and the formation of follicles. Our results suggest that PAR6 could be used as a potential marker of germ cells for the primordial follicle formation, and the expression of PAR6 by a gap junction-dependent process may contribute to the formation of primordial follicles and the maintenance of oocytes at the diplotene stage.
Highlights
The establishment of the primordial follicle pool is a complex process that includes the formation of cysts through oogonia mitosis, the startup of initial meiosis, the breakdown of cysts, and the formation of primordial follicles when germ cells are arrested at the diplotene stage [1]
Germ cells in fetal ovaries can develop to form primordial follicles or undergo apoptosis, which depends on molecular regulatory mechanism that remains elusive, for example, why can only a few oocytes cooperate with somatic cells to form primordial follicles, which kind of germ cells are selected to form the primordial follicles with ovarian somatic cells, why can not the oocytes finish their first meiosis and arrest at the diplotene stage, which factors control these?
The results demonstrated for the first time that PAR6 was expressed in the mouse fetal ovary with a spatio-temporal character (Fig. 1)
Summary
The establishment of the primordial follicle pool is a complex process that includes the formation of cysts through oogonia mitosis, the startup of initial meiosis, the breakdown of cysts, and the formation of primordial follicles when germ cells are arrested at the diplotene stage [1]. Two others are protein kinases called Par-1, and Par-5, which belong to the 14-3-3 family of phosphoserine-binding proteins [2] Their localizations are mutually exclusive which may provide a general mechanism to establish cortical domains in polar cells
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