Human spermatogenesis as a model to examine gene potentiation

The first tier of control over the expression of genic domains utilizes chr omatin structure. Before the onset of transcription, the chromatin domain t hat encompasses the gene(s) must assume an open conformation. This renders large segments of the genome available to the tissue-specific and ubiquitou s trans-factors necessary for proper expression of the genes present. This process has been termed potentiation. It is a necessary obligate, but alone it is not sufficient for gene expression. Spermatogenesis, the development of a viable fertile male gamete, provides a : unique model to begin to add ress the underlying mechanism(s) governing differentiation and tissue-speci fic gene expression. Male gametogenesis is typified by the activation of nu merous genes whose products have novel functions, as well as testis-specifi c forms of constitutively expressed somatic genes. We have shown that mouse : spermatogenesis represents a selective potentiative process (Kramer et al ., 1998. Development 125:4749-4655) but little is known about its human cou nterpart. To fill this void we have examined the potentiative state of seve ral spermatid-expressed genes,during the latter Stages of human spermatogen esis. We have shown that spermatid-expressed genes are potentiated by the p achytene stage of differentiation. Furthermore, we establish that a chromat in domain functions as a discrete structural unit during differentiation. I nterestingly, some of these open structures are maintained in the mature sp ermatozoon. (C) 2000 Wiley-Liss, Inc.