Expression And Developmental Studies Of Smad1,Smad2,Smad4 And Smad5 Proteins In The Rat Testis

The testis is a complex organ that serves two crucial functions: synthesis of testosterone and production of spermatozoa. Moreover normal testicular development and maintenance of spermatogenesis during fetal and postnatal life is controlled by intratesticular modulators, such as the gonadotropic releasing hormone (GnRH), the thyrotropin hormone (TRH ), the insulin-like growth factors (IGFs), the endothelin (ET), and the angiotensin- II (AT- II) etc. Anotherimportant local regulator of the testicular functions could be the transforming growth factor - 3 (TGF- 3 ) superfamily members.Transforming growth factor- 3 superfamily members are group of secreted polypeptides that mobilize a complex signaling network to control cell fate by regulating proliferation, differentiation, motility, adhesion, and apoptosis. The superfamily members include TGF- 3 s, activins/inhibins and the bone morphogenetic proteins (BMPs). These factors signal through heteromeric complexes of transmembrane type I and type II Serine/Threonine kinase receptors. Within this complex the type II receptor kinase activates the type I receptor kinase, which subsequently propagates signals to the Smad pathway. Smads are recently identified proteins that mediate intracellular signaling of the TGF- 3 superfamily from the cell-surface to the nucleus. Smads have two conserved domains in their amino- and carboxy-terminal regions termed the MH1 and MH2 domains, respectively, as well as a central proline-rich linker region. Smads are grouped into three classes depending on their structrues and functions. The receptor-regulated Smads (R-Smads) or the pathway-restricted Smads are phosphorylated by specific type I receptors on a carboxy-terminal SS (V/M) S motif. Thus, the TGF- 3 and activin type I receptors activate Smad2 and SmadS, whereas the BMP type I receptors target Smadl, -5, and -8. Then the R-Smads combine with the common-mediator Smads (Co-Smads) forming heteromeric complexes, which translocate into the nucleus to control gene transcription. Smad4 is the only vertebrate Co-Smad identifiedup to now, and it has not SS (V/M) S motif on a carboxy-terminal. The inhibitory Smads (I-Smads), including Smad6 and Smad7, negatively regulate other Smads proteins by preventing their phosphorylation.Despite members of the TGF- P superfamily and their receptors are expressed in the germ cells, Sertoli cells or Leydig cells in the mammalian testes, their roles in spermatogenesis and testicle development are far from clear. In order to shed light on the mechanisms of TGF- P action in spermatogenesis, it is crucial to determine whether and where their downstream signaling molecules are expressed in the testis. We have investigated the expression and function of Smadl, Smad2, Smad4, and SmadS proteins in rat testes during postnatal development. In this study, whole testes were collected from male S.D rats aged 3 days, 7 days, 14 days and 28 days, and adult. We examined, the cellular localization and developmental change by immunohistochemical ABC method with glucose oxidase-DAB-nickel enhancement technique; the quantitative analysis of the the immunostaining by the image anslysis system; the Smads proteins coexistense in the adult rat testis by the double immune staining for CD 14 - Smad4 and Smad2 - Smad4; the stage of the cycling of the seminiferous epithelium in the adult rat testis by PAS reaction; the proteins expression of Smads during rat testicular development by means of western blots.The results were as follows:1. The germ cells of rat testis at the age of 14 days showedSmadl immuoreactivity, positive substance were located in cytoplasm with negative nuclei. No expression was detected in Sertoli cells and Leydig cells. While the western blots showed that Smadl were present throughout testicular development.2. The immunostaining of Smad2 was present in cytoplasm of germ cells in the 7d, 14d, 28d, and adult rat testes. There was positive substance in Sertoli cells and Leydig cells, too. While the western blots sho...