Transforming growth factor-β (β1, β2, and β3) gene expression and action during pubertal development of the seminiferous tubule: Potential role at the onset of spermatogenesis

Abstract

The potential role of transforming growth factor-β (TGFβ) as a mediator of cell-cell interactions during the pubertal development of the seminiferous tubule was examined. Mesenchymal-derived peritubular cells and epithelial-like Sertoli cells were isolated from prepubertal, midpubertal, and late pubertal rat testes. The developmental expression of the multiple forms of TGFβ (TGFβ1, -β2, and -β3) in whole testis and isolated somatic cell types was determined using a nuclease protection analysis. TGFβ1 and TGFβ2 mRNA expression was predominant in the immature testis and decreased at the onset of puberty. TGFβ3 mRNA expression, the most abundant form of TGFβ present, peaked at an early pubertal stage, coincident with the initiation of spermatogenesis. Peritubular and Sertoli cells expressed each isoform of TGFβ during development. Peritubular cell mRNA expression of TGFβ1, -β2, and -β3 decreased during pubertal development upon differentiation of this cell type. Sertoli cell expression of TGFβ1 increased slightly and plateaued during pubertal development. TGFβZ mRNA expression was evident only in immature prepubertal Sertoli cells. Sertoli cell mRNA expression of TGFβ3 increased transiently at the onset of puberty, corresponding with the peak of expression observed during the analysis of whole testicular development, Immunoblot analysis indicated that both cultured peritubular and Sertoli cells can produce the proteins for TGFβ1, -β2, and -β3. Analysis of the hormonal regulation of TGFβ expression revealed that FSH caused a dramatic decrease in Sertoli cell TGFβ2 expression while having no effect on TGFβ1 or TGFβ3 expression. Potential actions of TGFβ in the seminiferous tubule were also examined. TGFβ1 inhibited TGFα-induced [3H]thymidine incorporation into peritubular cell DNA with cells from each developmental stage examined. TGFβ1 had no effect on Sertoli cell proliferation. Previously, germinal cells have been shown to be responsive to TGFβ. This study demonstrates the potential of having a unique hormone-dependent pattern of TGFβ isoform expression during postnatal organ development. Observations demonstrate that the suppression of TGFβ2 expression, in part in response to FSH, and the transient increase in TGFβ3 expression correlate with the onset of puberty and the induction of spermatogenesis.