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The present study reports the modulation of basement membrane (BM) components, laminin, entactin, and type IV collagen, expression in prepubertal rat Sertoli cell by the thyroid hormone T3. Immunocytochemical studies of permeabilized Sertoli cells in culture showed that T3 treatment (10[-7] M for 24 h) increased the number of cells staining positive for laminin and/or entactin (from 58 +/- 5.3% to 86.4 +/- 6.5%, P < 0.01). In contrast, a strong inhibition of type IV collagen immunopositivity was observed. Western blot analysis of Sertoli cell-conditioned media indicated that T3 treatment significantly (P < 0.01) increased the level of secreted entactin by 60-65% without affecting the levels of laminin A and B1/B2 chains. Moreover, thyroid hormone treatment of Sertoli cells significantly reduced type IV collagen secretion by 62% (P < 0.05). Slot blot analysis of poly-A RNA demonstrated a significant (P < 0.01) increase in the level of entactin messenger RNA (mRNA) by 140% (P < 0.01) and a 50% reduction of type IV collagen alpha1 chain mRNA after thyroid hormone treatment. No effect of the hormone was observed on the accumulation of the laminin B1 and B2 chain mRNAs in Sertoli cell cultures. These effects cannot be ascribed to changes in the degradation of BM components, because no effect of thyroid hormone was observed on plasminogen activators or metalloproteinase secretion by Sertoli cells. These observations indicate the Sertoli cell as a source of entactin within the testis, demonstrate the ability of T3 to differentially regulate the expression of BM components, and can be regarded as a part of the integrated mechanism by which thyroid hormone affects testicular development and differentiation.

The aim of this study was to investigate the ontogenesis of the nuclear T3 receptor among the different cell types in the rat testis from fetuses at the 19th day of gestation and animals 1, 5, 15, 20, and 60 days after birth. Whole testis, tubular fraction, nontubular fractions, and Sertoli cells cultured in vitro or enriched in vivo by irradiation were used. The results demonstrate that high affinity, low capacity T3-binding sites are localized only in Sertoli cells; the binding specificity and affinity (Kd ranges from 0.8 +/- 0.2 to 2.6 +/- 0.4 nM) do not change significantly with the age of the animals and are comparable to those observed for T3 receptors in other mammalian tissues. In the whole testis, the concentration of receptors changes during gonadal development, being maximally expressed in the fetus (154.3 +/- 8.1 fg T3 bound/10(6) nuclei) and from 1 (203.4 +/- 10.9 fg T3 bound/10(6) nuclei) to 5 (185.3 +/- 15.1 fg T3 bound/10(6) nuclei) days of postnatal life, decreasing significantly at 15 and 20 days (65.4 +/- 2.0 and 57.9 +/- 1.9 fg T3 bound/10(6) nuclei, respectively) and being virtually absent in the adult. The same change in receptor concentration was found in Sertoli cells obtained by different techniques. This ontogenetic profile coincides with the pattern of Sertoli cell proliferation and differentiation, thus suggesting a role of thyroid hormones in the regulation of growth and maturation of the somatic cells of the seminiferous epithelium.