Analysis of meiosis regulators in human gonads: a sexually dimorphic spatio-temporal expression pattern suggests involvement of DMRT1 in meiotic entry.

The mitosis-meiosis switch is a key event in the differentiation of germ cells. In humans, meiosis is initiated in fetal ovaries, whereas in testes meiotic entry is inhibited until puberty. The purpose of this study was to examine the expression pattern of meiosis regulators in human gonads and to investigate a possible role of DMRT1 in the regulation of meiotic entry. The expression pattern of DMRT1, STRA8, SCP3, DMC1, NANOS3, CYP26B1 and NANOS2 was investigated by RT-PCR and immunohistochemistry in a series of human testis samples from fetal life to adulthood, and in fetal ovaries. DMRT1 was expressed in testes throughout development but with marked spatio-temporal changes. At the early fetal period of 8-20 gestational weeks (GW) and at infantile mini-puberty, DMRT1 was predominantly expressed in Sertoli cells, whereas at later stages of gestation (22-40 GW), during childhood and in post-pubertal testes, DMRT1 was most abundant in spermatogonia, except in the A-dark type. In fetal ovaries, DMRT1 was detected in oogonia and oocytes until 20 GW, but was completely down-regulated following meiotic entry. STRA8, SCP3 and DMC1 were expressed mainly in oocytes and spermatogonia in accordance with their role in initiation and progression of meiosis. The putative meiosis inhibitors, CYP26B1 and NANOS2, were primarily expressed in Leydig cells and spermatocytes, respectively. In conclusion, the expression pattern of the investigated meiotic regulators is largely conserved in the human gonads compared with rodents, but with some minor differences, such as a stable expression of CYP26B1 in human fetal ovaries. The sexually dimorphic expression pattern of DMRT1 indicates a similar role in the mitosis-meiosis switch in human gonads as previously demonstrated in mice. The biological importance of the changes in expression of DMRT1 in Sertoli cells remains to be established, but it is consistent with DMRT1 reinforcing the inhibition of meiosis in the testis.