Growth factors as mediators of testicular cell-cell interactions.

The development of testicular function may require local cell-cell interactions to regulate tissue growth and differentiation. Locally produced growth factors may mediate the differential growth of mesenchymal, epithelial and germinal cells that occurs during fetal, prepubertal and postpubertal testis development. The complex co-ordination of differential and temporal cellular growth suggests that a variety of locally produced factors may be involved. Presently, a number of growth factors have been identified in the testis, including IGF-I, TGF-alpha, TGF-beta, NGF, IL-1, FGF, SGF and SCSGF. These factors may mediate interactions involving growth stimulation, growth inhibition and differentiation in this tissue (Table 2 and Figure 1). Endocrine agents are also necessary for testis development and function. In many organs, endocrine hormones appear to alter local cell-cell interactions. Similarly, gonadotrophins may modulate growth factor interactions within the testis. Understanding testicular cell-cell interactions involving growth factors requires evaluation of the cellular site of factor expression, production, secretion, target cell action and in vivo significance. Presently, none of the proposed cell-cell interactions involving growth factors have evaluated all these criteria. Further cellular and molecular analysis of these intercellular interactions are necessary to clarify the role of growth factors in the development and maintenance of testicular function.