For decades, only few tissues and cell types were defined as steroidogenic, capable of de novo steroid synthesis from cholesterol. However, with the refinement of detection methods, several tissues have now been added to the list of steroidogenic tissues. Besides their critical role as long-range acting hormones, steroids are also playing more discreet roles as local mediators and signaling molecules within the tissues they are produced. In testis, steroidogenesis is carried out by the Leydig cells through a broad network of proteins, mediating cholesterol delivery to CYP11A1, the first cytochrome of the steroidogenic cascade, and the sequential action of enzymes insuring the production of active steroids, the main one being testosterone. The knowledge that male germ cells can be directly regulated by steroids and that they express several steroidogenesis-related proteins led us to hypothesize that germ cells could produce steroids, acting as autocrine, intracrine and juxtacrine modulators, as a way to insure synchronized progression within spermatogenic cycles, and preventing inappropriate cell behaviors between neighboring cells. Gene expression and protein analyses of mouse and rat germ cells from neonatal gonocytes to spermatozoa showed that most steroidogenesis-associated genes are expressed in germ cells, showing cell type-, spermatogenic cycle-, and age-specific expression profiles. Highly expressed genes included genes involved in steroidogenesis and other cell functions, such as Acbd1 and 3, Tspo and Vdac1-3, and genes involved in fatty acids metabolism or synthesis, including Hsb17b4 10 and 12, implying broader roles than steroid synthesis in germ cells. These results support the possibility of an additional level of regulation of spermatogenesis exerted between adjacent germ cells.
Keywords: Germ cells; Spermatogenesis; Steroidogenesis; Testis.
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