Abstract
In the neonatal mouse ovary, clusters of oocytes called nests break into smaller cysts and subsequently form individual follicles. During this period, we found numerous mast cells in the ovary of MRL/MpJ mice and investigated their appearance and morphology with follicular development. The ovarian mast cells, which were already present at postnatal day 0, tended to localize adjacent to the surface epithelium. Among 11 different mouse strains, MRL/MpJ mice possessed the greatest number of ovarian mast cells. Ovarian mast cells were also found in DBA/1, BALB/c, NZW, and DBA/2 mice but rarely in C57BL/6, NZB, AKR, C3H/He, CBA, and ICR mice. The ovarian mast cells expressed connective tissue mast cell markers, although mast cells around the surface epithelium also expressed a mucosal mast cell marker in MRL/MpJ mice. Some ovarian mast cells migrated into the oocyte nests and directly contacted the compressed and degenerated oocytes. In MRL/MpJ mice, the number of oocytes in the nest was significantly lower than in the other strains, and the number of oocytes showed a positive correlation with the number of ovarian mast cells. The gene expression of a mast cell marker also correlated with the expression of an oocyte nest marker, suggesting a link between the appearance of ovarian ? 4mast cells and early follicular development. Furthermore, the expression of follicle developmental markers was significantly higher in MRL/MpJ mice than in C57BL/6 mice. These results indicate that the appearance of ovarian mast cells is a unique phenotype of neonatal MRL/MpJ mice, and that ovarian mast cells participate in early follicular development, especially nest breakdown.
Highlights
Mast cells (MCs) reside in most tissues and act as sentinel cells in both innate and adaptive immunity [1,2]
The appearance of ovarian MCs in neonatal MRL mice At P0, toluidine blue (TB) staining revealed that the MRL mouse ovaries contained numerous metachromatic cells (Figure 1A); these cells had tryptase alpha/beta 1 (Tpsab1)-positive granules in their cytoplasm (Figure 1B)
In MRL mice, the ovarian MCs were observed from E15.5; and the MC density in the whole ovary area significantly increased at E17.5, peaked at P0, and gradually decreased from P0 to postnatal day 14 (P14) (Figure 1G)
Summary
Mast cells (MCs) reside in most tissues and act as sentinel cells in both innate and adaptive immunity [1,2]. MCs are classified into 2 distinct subpopulations, namely, connective tissue MCs (CTMCs) and mucosal MCs (MMCs) These cell types are distinguished by their staining characteristics, cytoplasmic granule size, T cell dependency, and expression of MC proteases and inflammatory mediators [7]. In several species, including human, the adult ovaries have different immune cells, such as macrophages, neutrophils, eosinophils, and MCs [8,9,10,11] The appearance of these immune cells in the ovary is altered by the estrus cycle during the periovulatory period. It has been suggested that MCs accumulate in mammary glands and uteri to mediate the structural reconstructions associated with altered sex hormones during the estrus cycle or pregnancy [12,13,14] These reports indicate that MCs play some roles in reproductive functions. It has been reported that a few MCs are present in the neonatal ovaries of C57BL/6 (B6) mice, the functional relationship between MCs and the perinatal ovary is unclear [16]
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