Zfp42, also known as Rex1 (reduced expression gene 1), is a well-known stem-cell marker duplicated from YY1 in the eutherian lineage. It has been associated with various biological processes. In embryonic stem cells, it may be involved in the regulation of differentiation, cell cycle, and pluripotency. It also plays a role in spermatogenesis, early embryogenesis, and placental development. In addition, it has implications in epigenetic regulation, especially in genomic imprinting [1].

In Rex1 knockout (KO) mouse models, male mice showed an age-associated decrease in sperm counts, abnormal sperm morphology, and mild testicular atrophy. Microarray analysis in these KO mice identified GRTP1 as a transcript with a 4.5-fold higher level in wild-type compared to Rex1(-/-) mice. Also, Rex1 disruption enhanced the expression of ectoderm, mesoderm, and endoderm markers in murine embryonic stem cells, suggesting its role in reducing retinoic-acid-induced differentiation [2,3].

In conclusion, Zfp42 is a significant gene involved in multiple biological processes including stem-cell-related functions, spermatogenesis, and epigenetic regulation. Studies using KO mouse models have revealed its role in testicular function and embryonic stem-cell differentiation, providing insights into related disease mechanisms and potential therapeutic targets.