Gene expression in rat leydig cells during development from the progenitor to adult stage: a cluster analysis

Leptin-mediated decrease of cyclin A2 and increase of cyclin D1 expression: relevance for the control of prepubertal rat Leydig cell division and differentiation

The number of adult Leydig cells is one of the factors controlling testosterone secretion by sexually mature testis, and it depends on the proliferative capacity of prepubertal Leydig cells. We investigated here whether this capacity is controlled by leptin because this hormone regulates proliferation in other cell types and has a crucial role in male fertility. Our data show that prebupertal Leydig cells express the Ob/Rb form of leptin receptor and are thus direct targets of this hormone. The analysis of G1/S-phase cyclins by quantitative (real-time) RT-PCR and Western blot points to the leptin-induced decrease in cyclin A2 and subsequent increase in cyclin D1 expression that precedes a leptin-triggered decrease in the number of prepubertal Leydig cells. Quantitative assessments of DNA synthesis by bromodeoxyuridine incorporation and of cycling cell population by Ki67 immunocytochemistry indicate that leptin decreases the cell number by inhibiting cell division and increases mRNA levels of Leydig cell differentiation markers such as relaxin-like factor. Immunohistochemistry of cyclin D1 and relaxin-like factor pointed to the parallel increase of their expression coinciding with the onset of Leydig cell differentiation. Moreover, leptin-treated Leydig cells display increased expression of another differentiation marker (3beta-hydroxysteroid dehydrogenase) that is abolished by knocking down cyclin D1 with small interference RNA. Altogether, our data show that leptin inhibits division of prepubertal Leydig cells via a cyclin D-independent mechanism and suggest that cyclin D1 might be involved in leptin-induced differentiation of Leydig cells.

Microarray technology offers a novel tool for the diagnosis and identification of therapeutic targets for male infertility

Male infertility is now a major reproductive health problem because of an increasing number of environmental pollutants and chemicals, which eventually result in gene mutations. Genetic alterations caused by environmental factors account for a significant percentage of male infertility. Microarray technology is a powerful tool capable of measuring simultaneously the expression of thousands of genes expressed in a single sample. Eventually, advances in genetic technology will allow for the diagnosis of patients with male infertility due to congenital reasons or environmental factors. Since its introduction in 1994, microarray technology has made significant advances in the identification and characterization of novel or known genes possibly correlated with male infertility in mice, as well as in humans. This provides a rational basis for the application of microarray to establishing molecular signatures for the diagnosis and gene therapy targets of male infertility. In this review, the differential gene expression patterns characterized by microarray in germ and somatic cells at different steps of development or in response to stimuli, as well as a number of novel or known genes identified to be associated with male infertility in mice and humans, are addressed. Moreover, issues pertaining to measurement reproducibility are highlighted for the application of microarray data to male infertility.

Role of nuclear receptors in INSL3 gene transcription in Leydig cells

Insulin-like 3 (INSL3) is a hormone produced by testicular Leydig cells throughout life. During embryonic life it regulates an essential step of testicular descent, whereas in adults it acts as a male germ cell survival factor. Despite the importance of INSL3 for male sex differentiation and function, very little is known regarding the molecular mechanisms that regulate its expression. So far, the nuclear receptor SF-1 is the only transcription factor known to regulate the mouse Insl3 promoter in Leydig cells. In order to further our understanding of the transcriptional regulation of INSL3 expression, we have isolated the human INSL3 promoter and tested the effects of the nuclear receptors SF-1, LRH-1, and Nur77 on its activity in Leydig cells. In transfections assays, all three nuclear receptors activated the human INSL3 promoter but especially Nur77, which acted through a novel regulatory element. Thus, the human INSL3 promoter constitutes a novel target for the orphan nuclear receptor Nur77.

Epimorphin(-/-) mice have increased intestinal growth, decreased susceptibility to dextran sodium sulfate colitis, and impaired spermatogenesis

Dynamic and reciprocal epithelial-mesenchymal interactions are critical for the normal morphogenesis and maintenance of epithelia. Epimorphin has been identified as a unique molecule expressed by mesenchymal cells and myofibroblasts and has putative morphogenetic effects in multiple epithelial tissues, including intestine, skin, mammary gland, lung, gallbladder, and liver. To define the in vivo role of epimorphin, we created epimorphin-null mice by targeted inactivation of the epimorphin gene. Male epimorphin-/- mice are sterile due to abnormal testicular development and impaired spermatogenesis. Intestinal growth is increased in epimorphin-/- mice due to augmented crypt cell proliferation and crypt fission during the neonatal (suckling) period, mediated at least in part by changes in bone morphogenetic protein (Bmp) and Wnt/beta-catenin signaling pathways. Colonic mucosal injury and colitis induced by dextran sodium sulfate (DSS) are ameliorated in epimorphin-/- mice, probably due to the increased proliferative capacity of the epimorphin-/- colon. These in vivo findings support the notion that epimorphin is a key stromal regulator of epithelial cell proliferation and growth in the intestine. In addition, our studies demonstrate a novel and critical role for epimorphin in regulating testicular development and growth as well as spermatogenesis.

Somatotropic and gonadotropic axes linkages in infancy, childhood, and the puberty-adult transition

Integrative neuroendocrine control of the gonadotropic and somatotropic axes in childhood, puberty, and young adulthood proceeds via multiple convergent and divergent pathways in the human and experimental animal. Emerging ensemble concepts are required to embody independent, parallel, and interacting mechanisms that subserve physiological adaptations and pathological disruption of reproduction and growth. Significant advances in systems biology will be needed to address these challenges.

In search of rat stem Leydig cells: identification, isolation, and lineage-specific development

Leydig cells (LCs) are thought to differentiate from spindle-shaped precursor cells that exhibit some aspects of differentiated function, including 3beta-hydroxysteroid dehydrogenase (3betaHSD) activity. The precursor cells ultimately derive from undifferentiated stem LCs (SLCs), which are postulated to be present in testes before the onset of precursor cell differentiation. We searched for cells in the neonatal rat testis with the abilities to: (i) proliferate and expand indefinitely in vitro (self renew); (ii) differentiate (i.e., 3betaHSD and ultimately synthesize testosterone); and (iii) when transplanted into host rat testes, colonize the interstitium and subsequently differentiate in vivo. At 1 week postpartum, spindle-shaped cells were seen in the testicular interstitium that differed from the precursor cells in that they were 3betaHSD-negative, luteinizing hormone (LH) receptor (LHR)-negative, and platelet-derived growth factor receptor alpha (PDGFR alpha)-positive. These cells were purified from the testes of 1-week-old rats. The cells contained proteins known to be involved in LC development, including GATA4, c-kit receptor, and leukemia inhibitory factor receptor. The putative SLCs expanded over the course of 6 months while remaining undifferentiated. When treated in media that contained thyroid hormone, insulin-like growth factor I, and LH, 40% of the putative SLCs came to express 3betaHSD and to synthesize testosterone. When transplanted into host rat testes from which LCs had been eliminated, the putative SLCs colonized the interstitium and subsequently expressed 3betaHSD, demonstrating their ability to differentiate in vivo. We conclude that these cells are likely to be the sought-after SLCs.

Hormonal regulation of Leydig cell proliferation and differentiation in rodent testis: a dynamic interplay between gonadotrophins and testicular factors

Studies over the last few decades have documented that LH is the principal regulator of Leydig cell function. Recent studies indicate that locally produced intratesticular factors are equally important in modulating Leydig cell development and function. In the present review, results of studies on Leydig development and function with rodent models, in conjunction with recent advances in our understanding, are discussed. Studies on Leydig cell development revealed that there are two different waves of proliferation: the first one is independent of LH and the other is dependent on LH. In addition to LH, FSH plays a major role in Leydig cell development and function by modulating the production of Sertoli cell-derived factors. Studies directed towards understanding the oestrogen-mediated inhibition of Leydig cell proliferation revealed that collagen IV-mediated signalling is involved in Leydig cell proliferation and 17beta-oestradiol inhibits this event. Leydig cell proliferation and differentiation is associated with changes in gene expression. Research in this area has identified several genes that are involved in Leydig cell proliferation and differentiation; the possible role of these genes in the context of Leydig cell development are discussed in this review.

Insights into GABA receptor signalling in TM3 Leydig cells

Gamma-aminobutyric acid (GABA) is an emerging signalling molecule in endocrine organs, since it is produced by endocrine cells and acts via GABA(A) receptors in a paracrine/autocrine fashion. Testicular Leydig cells are producers and targets for GABA. These cells express GABA(A) receptor subunits and in the murine Leydig cell line TM3 pharmacological activation leads to increased proliferation. The signalling pathway of GABA in these cells is not known in this study. We therefore attempted to elucidate details of GABA(A) signalling in TM3 and adult mouse Leydig cells using several experimental approaches. TM3 cells not only express GABA(A )receptor subunits, but also bind the GABA agonist [(3)H]muscimol with a binding affinity in the range reported for other endocrine cells (K(d) = 2.740 +/- 0.721 nM). However, they exhibit a low B(max) value of 28.08 fmol/mg protein. Typical GABA(A) receptor-associated events, including Cl(-) currents, changes in resting membrane potential, intracellular Ca(2+) or cAMP, were not measurable with the methods employed in TM3 cells, or, as studied in part, in primary mouse Leydig cells. GABA or GABA(A) agonist isoguvacine treatment resulted in increased or decreased levels of several mRNAs, including transcription factors (c-fos, hsf-1, egr-1) and cell cycle-associated genes (Cdk2, cyclin D1). In an attempt to verify the cDNA array results and because egr-1 was recently implied in Leydig cell development, we further studied this factor. RT-PCR and Western blotting confirmed a time-dependent regulation of egr-1 in TM3. In the postnatal testis egr-1 was seen in cytoplasmic and nuclear locations of developing Leydig cells, which bear GABA(A) receptors and correspond well to TM3 cells. Thus, GABA acts via an atypical novel signalling pathway in TM3 cells. Further details of this pathway remain to be elucidated.