Sexually dimorphic expression of Dmrt1 and γH2 AX in germ stem cells during gonadal development in Xenopus laevis

摘要

In many animals, primordial germ cells ( PGC s) migrate into developing gonads. There, they proliferate and differentiate into female and male germ stem cells ( GSC s), oogonia and spermatogonia, respectively. Few studies have focused on the molecular mechanisms underlying the development of GSC sex determination. Here, we investigated the expression of the transcription factor Dmrt1 and a phosphorylated form of the histone variant H2 AX (γH2 AX ) during gonadal development in Xenopus laevis . During early sexual differentiation, Dmrt1 was expressed in the GSC s of the ZW (female) and ZZ (male) gonads as well as somatic cells of the ZZ gonads. Notably, the PGC s and primary GSC s contained large, unstructured nuclei, whereas condensed, rounder nuclei appeared only in primary oogonia during tadpole development. After metamorphosis, Dmrt1 showed its expression in secondary spermatogonia, but not in secondary oogonia. Like Dmrt1, γH2 AX was expressed in the nuclei of primary GSC s in early developing gonads. However, after metamorphosis, γH2 AX expression continued in primary and secondary spermatogonia, but was barely detected in the condensed nuclei of primary oogonia. Taken together, these observations indicate that spermatogonia tend to retain PGC characteristics, compared to oogonia, which undergo substantial changes during gonadal differentiation in X. laevis . Our findings suggest that Dmrt1 and γH2 AX may contribute to the maintenance of stem cell identity by controlling gene expression and epigenetic changes, respectively. Primordial germ cells (PGCs) migrate into developing gonads in many animals. There, they proliferate and differentiate into oogonia and spermatogonia. What is the difference between them? From their differential morphology and expression patterns of a transcription factor Dmrt1 and γH2AX in an amphibian, Xenopus laevis , we show that spermatogonia tend to retain more PGC characteristics, compared to oogonia.