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Fetal germ cell development is regulated by an elaborate combination of cell-extrinsic and cell-intrinsic signals. Here we identify a novel role for the Krüppel-like transcription factor Gli-Similar 3 (Glis3) in male germ cell development in the mouse embryos. Glis3 is expressed in male germ cells during the brief window of time prior to initiation of piRNA-dependent retrotransposon surveillance. Disruption of Glis3 function led to a widespread reduction in retrotransposon silencing factors, aberrant retrotransposon expression and pronounced germ cell loss. Experimental induction of precocious Glis3 expression in vivo before its normal expression resulted in premature expression of several piRNA pathway members, suggesting that GLIS3 is necessary for the activation of the retrotransposon silencing programs. Our findings reveal an unexpected role for GLIS3 in the development of male germ cells and point to a central role for GLIS3 in the control of retrotransposon silencing in the fetal germline.

Sex determination of the gonad is an extraordinary process by which a single organ anlage is directed to form one of two different structures, a testis or an ovary. Morphogenesis of these two organs utilizes many common cellular events; differences in the timing and execution of these events must combine to generate sexually dimorphic structures. In this chapter, we review recent research on the cellular processes of gonad morphogenesis, focusing on data from mouse models. We highlight the shared cellular mechanisms in testis and ovary morphogenesis and examine the differences that enable formation of the two organs responsible for the perpetuation of all sexually reproducing species., (Copyright © 2012 S. Karger AG, Basel.)