Role of laminin in the morphogenetic cascade during coculture of Sertoli cells with peritubular cells

A laminin-based local regulatory network in the testis that supports spermatogenesis

In adult rat testes, the basement membrane is structurally constituted by laminin and collagen chains that lay adjacent to the blood-testis barrier (BTB). It plays a crucial scaffolding role to support spermatogenesis. On the other hand, laminin-333 comprised of laminin-α3/ß3/γ3 at the apical ES (ectoplasmic specialization, a testis-specific cell-cell adherens junction at the Sertoli cell-step 8-19 spermatid interface) expressed by spermatids serves as a unique cell adhesion protein that forms an adhesion complex with α6ß1-integrin expressed by Sertoli cells to support spermiogenesis. Emerging evidence has shown that biologically active fragments are derived from basement membrane and apical ES laminin chains through proteolytic cleavage mediated by matrix metalloproteinase 9 (MMP9) and MMP2, respectively. Two of these laminin bioactive fragments: one from the basement membrane laminin-α2 chain called LG3/4/5-peptide, and one from the apical ES laminin-γ3 chain known as F5-peptide, are potent regulators that modify cell adhesion function at the Sertoli-spermatid interface (i.e., apical ES) but also at the Sertoli cell-cell interface designated basal ES at the blood-testis barrier (BTB) with contrasting effects. These findings not only highlight the physiological significance of these bioactive peptides that create a local regulatory network to support spermatogenesis, they also open a unique area of research. For instance, it is likely that several other bioactive peptides remain to be identified. These bioactive peptides including their downstream signaling proteins and cascades should be studied collectively in future investigations to elucidate the underlying mechanism(s) by which they coordinate with each other to maintain spermatogenesis. This is the goal of this review.

Reconstruction of a seminiferous tubule-like structure in a 3 dimensional culture system of re-aggregated mouse neonatal testicular cells within a collagen matrix

Male gonad development is initiated by the aggregation of pre-Sertoli cells (SCs), which surround germ cells to form cords. Several attempts to reconstruct testes from dissociated testicular cells have been made; however, only very limited morphogenesis beyond seminiferous cord formation has been achieved. Therefore, we aimed to reconstruct seminiferous tubules using a 3-dimensional (D) re-aggregate culture of testicular cells, which were dissociated from 6-dpp neonatal mice, inside a collagen matrix. We performed a short-term culture (for 3 days) and a long-term culture (up to 3 wks). The addition of KnockOut Serum Replacement (KSR) promoted (1) the enlargement of SC re-aggregates; (2) the attachment of peritubular myoid (PTM) cells around the SC re-aggregates; (3) the sorting of germ cells inside, and Leydig cells outside, seminiferous cord-like structures; (4) the alignment of SC polarity inside a seminiferous cord-like structure relative to the basement membrane; (5) the differentiation of SCs (the expression of the androgen receptor); (6) the formation of a blood-testis-barrier between the SCs; (7) SC elongation and lumen formation; and (8) the proliferation of SCs and spermatogonia, as well as the differentiation of spermatogonia into primary spermatocytes. Eventually, KSR promoted the formation of seminiferous tubule-like structures, which accompanied germ cell differentiation. However, these morphogenetic events did not occur in the absence of KSR. This in vitro system presents an excellent model with which to identify the possible factors that induce these events and to analyze the mechanisms that underlie cellular interactions during testicular morphogenesis and germ cell differentiation.

Transforming growth factor-beta2 mediates mesenchymal-epithelial interactions of testicular somatic cells

Transforming growth factor-beta2 (TGFbeta2) is an important mediator of growth and differentiation. We here describe for the first time the complete sequence of the TGFbeta2 complementary DNA derived from peritubular myoid cells of the rat testis. The size of the rat TGFbeta2 complementary DNA was 1245 bp, and the deduced protein sequence contained 414 amino acids. Sequence comparison with the human and mouse amino acid sequences demonstrated 96.4% and 97.9% sequence identities, respectively. To elucidate the functional role of TGFbeta2 in testicular somatic cells, we studied its secretion in vitro in monocultures and cocultures of mesenchymal peritubular and epithelial Sertoli cells. The highest amounts of TGFbeta2 protein were secreted in the cocultures and by peritubular cells, whereas Sertoli cells secreted only minor amounts. Stimulation experiments with FSH revealed a reduced secretion of TGFbeta2 in cocultures, probably mediated by a paracrine interaction of the FSH-responsive Sertoli cells. In contrast, TGFbeta2 secretion by peritubular cells was increased after stimulation with glucocorticoids and after addition of recombinant TGFbeta2, indicating an autoregulation of TGFbeta2. Furthermore, application of recombinant TGFbeta2 to cocultures resulted in an enhanced aggregation and cell clustering of Sertoli cells, pointing to an important role of TGFbeta2 in the paracrine interaction of peritubular and Sertoli cells of the developing rat testis.

Mesenchymal entactin-1 (nidogen-1) is required for adhesion of peritubular cells of the rat testis in vitro

Epithelial-like Sertoli cells isolated from immature rat testis aggregate to form tubule-like structures when cultured on a monolayer of mesenchyme-derived peritubular cells. At the end of this morphogenetic process both cell types are separated by a basement membrane. In this study the gene expression of monocultures and direct cocultures of peritubular cells and Sertoli cells was examined using DD-RT-PCR. One of the isolated cDNA clones showed high homology to the cDNA encoding the basement membrane component entactin-1 (nidogen-1). Even though the entactin-1 (nidogen-1) gene is transcribed in peritubular cells, Sertoli cells, and in direct cocultures, the mRNA is translated only by the peritubular cells. No entactin-1 (nidogen-1) was detected in the Sertoli cells by Western blotting. Moreover, peritubular cell monocultures and cocultures showed the presence of one single band at 152 kDa in the supernatant, whereas in cell lysates two bands were detectable at 152 kDa and 150 kDa. Perturbation experiments using monoclonal antibodies directed against entactin-1 (nidogen-1) were performed with peritubular cells and Sertoli cells, respectively, and demonstrated loss of cell adhesion of the peritubular cells, while the Sertoli cells remained adherent. From these data we conclude that entactin-1 is exclusively produced and secreted by mesenchymal peritubular cells, and affects adhesion of peritubular cells in an autocrine manner.

Sequences 5' of the basement membrane laminin beta 1 chain gene (LAMB1) direct the expression of beta-galactosidase during development of the mouse testis and ovary

The murine LAMB1 gene encoding laminin beta 1 is expressed in the developing male and female gonads and mesonephros. To identify the cis-acting elements regulating the expression of LAMB1, murine transgenic lines were generated by fusing regions of the LAMB1 gene to the Eschericia coli lacZ gene. The p3.9LAM beta gal construct contained approximately 4 kb of 5' flanking sequence and directed beta-galactosidase expression in many different organs including the kidney, mammary gland, and the male and female genital systems, the focus of this report. In male embryos, between gestational ages E 14.5 and birth beta-galactosidase was transiently expressed in the prospermatogonia cells of the testis and in the differentiating epithelial cells in the ductus deferens, ductus epididymis, and seminal vesicles. In female embryos, beta-galactosidase was not detected in the ovary until about 1 week after birth; at this time, beta-galactosidase was expressed by oocytes of primary and secondary follicles. In contrast, transgenic mice carrying the first 0.7 kb of LAMB1 fused to the lacZ gene expressed beta-galactosidase only in the prospermatogonia cells of the testis. Thus, the cis-acting element(s) necessary for the expression of the LAMB1 gene in prospermatogonia cells are located in the first 0.7 kb of LAMB1 5' flanking sequence; element(s) required for expression of the LAMB1 gene in oocytes and epithelial cells of the mesonephric ducts, mesonephric tubules, the ductus deferens, ductus epididymis, and seminal vesicles are located with 4 kb 5' of the transcription initiation site.

Testicular development involves the spatiotemporal control of PDGFs and PDGF receptors gene expression and action

Platelet-derived growth factors (PDGFs) are growth-regulatory molecules that stimulate chemotaxis, proliferation and metabolism primarily of cells of mesenchymal origin. In this study, we found high levels of PDGFs and PDGFs receptors (PDGFRs) mRNAs, and specific immunostaining for the corresponding proteins in the rat testis. PDGFs and PDGFRs expression was shown to be developmentally regulated and tissue specific. Expression of PDGFs and PDGFRs genes was observed in whole testis RNA 2 d before birth, increased through postnatal day 5 and fell to low levels in adult. The predominant cell population expressing transcripts of the PDGFs and PDGFRs genes during prenatal and early postnatal periods were Sertoli cells and peritubular myoid cells (PMC) or their precursors, respectively, while in adult animals PDGFs and PDGFRs were confined in Leydig cells. We also found that early postnatal Sertoli cells produce PDGF-like substances and that this production is inhibited dose dependently by follicle-stimulating hormone (FSH). The expression of PDGFRs by PMC and of PDGFs by Sertoli cells corresponds in temporal sequence to the developmental period of PMC proliferation and migration from the interstitium to the peritubulum. Moreover, we observed that all the PDGF isoforms and the medium conditioned by early postnatal Sertoli cells show a strong chemotactic activity for PMC which is inhibited by anti-PDGF antibodies. These data indicate that, through the spatiotemporal pattern of PDGF ligands and receptors expression, PDGF may play a role in testicular development and homeostasis.