Induction of spermatogenic synchrony by retinoic acid in neonatal mice

Abstract

Retinoic acid (RA) is required for the successful differentiation and meiotic entry of germ cells in the murine testis. The availability of RA to undifferentiated germ cells begins in a variable, uneven pattern during the first few days after birth and establishes the asynchronous pattern of germ cell differentiation in adulthood. It has been shown that synchronous spermatogenesis can be induced in 2 d postpartum mice, but not in adult mice, by treating vitamin A sufficient males with RA. In this study, neonatal males were treated at different ages with a single dose of RA and spermatogenesis was examined after recovery to adulthood. The failure of exogenous RA to alter asynchrony correlates with the appearance of meiotic preleptotene spermatocytes within the seminiferous epithelium.

Keywords: asynchronous spermatogenesis; differentiation; preleptotene spermatocytes; retinoic acid; spermatogenic wave; spermatogonia; synchronous spermatogenesis.

Figure 1. Degrees of synchrony resulting from RA treatment of mice at different neonatal ages. (A–D) Representative cross sections of an adult male testis after vehicle treatment (A), RA treatment at 4 dpp (B), 6 dpp (C) and 8 dpp (D) followed by recovery into adulthood. (E–H) Graphical representation of all 12 stages in cross sections of the seminiferous epithelium after vehicle treatment (E), RA treatment at 4 (F), 6 (G), and 8 (H) dpp and recovery to 65 dpp. (I–K) Resulting synchrony factors with treatment of vehicle or RA at 4 (I), 6 (J), and 8 (K) dpp. * p < 0.05. ** p < 0.005. All error bars represent standard error of the mean. Scale bars represent 100 µm.

Figure 2. Quantification of STRA8-immunopositive cells per tubule 24, 48 and 72 h post-RA injection at 4, 6 and 8 dpp, respectively. Filled bars represent data from vehicle treated animals and open bars represent data from RA treated animals. All error bars represent the standard error of the mean. * p < 0.05 ** p < 0.005

Figure 3. RA induces cell apoptosis in the neonatal male testis. The average number of TUNEL-positive cells per tubule after vehicle or RA treatment at each treatment age is shown. Filled bars represent data from vehicle treated animals and open bars represent data from RA treated animals. All error bars represent the standard error of the mean. *p < 0.05.