Spermatogonial morphology and kinetics during testis development in mice: a high-resolution light microscopy approach

Abstract

Despite the knowledge of spermatogonial biology in adult mice, spermatogonial development in immature animals has not been fully characterized. Thus, the aim of this study was to evaluate the ontogeny of the morphological development of the spermatogonial lineage inC57BL/6mouse testis, using high-resolution light microscopy. Spermatogonial morphology, chronology, and absolute number were determined for different agespostpartum(pp). The morphology of spermatogonia in immature mice was similar to that of adult spermatogonia, although their nuclear diameter was slightly smaller. The A1spermatogonia were first observed on day 2pp, and only 24 h later, differentiating type A3and A4spermatogonia were observed in the seminiferous cords. This result indicated a shortening of the spermatogonial phase for immature mice of about ∼2.5 days when compared with adult mice and suggests that gonocytes and/or A1spermatogonia could directly become A4spermatogonia, skipping the developmental sequence of type A spermatogonia. These A4spermatogonia are functional as they develop into type B spermatogonia by day 5pp. At day 8pp, while differentiation to spermatocytes begins, the Aundspermatogonia reach their maximal numbers, which are maintained through adulthood. The various details of the spermatogonial behavior in immature normal mice described in this study can be used as a baseline for further studies under experimental or pathological conditions.