Testicular factors involved in testis descent

Testis descent is the male-specific developmental process by which the gonads descend from their original position in the abdomen to the final position in the scrotum. Scrotal positioning of the testes, as it occurs in many mammals, is essential for spermatogenesis. Since the time of John Hunter in 1762, many scientists have studies testis descent, which turned out to be a complex process, involving an interplay of different structures and factors. Due to this complexity, the understanding of the structural and molecular mechanisms underlying the process of testis descent is still far from complete

Hormonal control of gubernaculum development during testis descent: gubernaculum outgrowth in vitro requires both insulin-like factor and androgen

The gubernaculum connects the gonad to the inguinoscrotal region and is involved in testis descent. It rapidly develops in the male fetus, whereas development in the female fetus is lacking. Possible factors involved in gubernaculum development are androgens, anti-Mullerian hormone (AMH), and insulin-like factor (Insl3). Sexual dimorphism in gubernaculum development correlated with the mitotic activity of cells in the gubernacular bulbs from male and female fetuses. Androgen receptor expression was restricted to the mesenchymal core of the gubernacular bulb, whereas skeletal muscle was detected in its outer layer. In an organ culture system devised to further study gubernaculum development in vitro, morphology of gubernacular explants grown in the presence of testes was comparable with that of gubernacula developed in vivo. Testicular tissue or medium containing R1881, a synthetic androgen, had a growth stimulatory effect on gubernacular explants compared with ovarian tissue or basal medium only. Moreover, Amh-/-, Amh+/-, and Insl3+/- testes stimulated the growth of gubernacular explants to the same extent as control testes. Insl3-/- testes, however, did not produce such an activity. This study reveals an essential role for both androgen and Insl3 in the gubernaculum outgrowth during transabdominal testis descent

Construction of 3D models of the CYP11B family as a tool to predict ligand binding characteristics

Aldosterone is synthesised by aldosterone synthase (CYP11B2). CYP11B2 has a highly homologous isoform, steroid 11β-hydroxylase (CYP11B1), which is responsible for the biosynthesis of aldosterone precursors and glucocorticoids. To investigate aldosterone biosynthesis and facilitate the search for selective CYP11B2 inhibitors, we constructed three-dimensional models for CYP11B1 and CYP11B2 for both human and rat. The models were constructed based on the crystal structure of Pseudomonas Putida CYP101 and Oryctolagus Cuniculus CYP2C5. Small steric active site differences between the isoforms were found to be the most important determinants for the regioselective steroid synthesis. A possible explanation for these steric differences for the selective synthesis of aldosterone by CYP11B2 is presented. The activities of the known CYP11B inhibitors metyrapone, R-etomidate, R-fadrazole and S-fadrazole were determined using assays of V79MZ cells that express human CYP11B1 and CYP11B2, respectively. By investigating the inhibitors in the human CYP11B models using molecular docking and molecular dynamics simulations we were able to predict a similar trend in potency for the inhibitors as found in the in vitro assays. Importantly, based on the docking and dynamics simulations it is possible to understand the enantioselectivity of the human enzymes for the inhibitor fadrazole, the R-enantiomer being selective for CYP11B2 and the S-enantiomer being selective for CYP11B1

Androgen action during male sex differentiation includes suppression of cranial suspensory ligament development

The cranial suspensory ligament is located on the border of the cranial (mesonephric) mesentery in adult female mammals, which runs between the cranial pole of the internal genitalia and the dorsal abdominal wall. Absence of the cranial suspensory ligament in male mammals depends upon exposure of its primordium to fetal testicular androgens and is a prerequisite for testis descent. Female rats were exposed to 5alpha-dihydrotestosterone propionate at different stages of genital development, and cranial suspensory ligament development was studied in neonatal and in adult animals. Androgens suppressed cranial suspensory ligament development when exposure started during the early stages of genital development, until day 19 postconception (pc). Androgen receptor expression was immunohistochemically detected in the cranial mesentery of both sexes from day 16 pc onwards. A decrease of androgen receptor expression in female fetuses from day 18 pc onwards coincided with the appearance of a differentiated cranial suspensory ligament, as evidenced by the expression of two cell differentiation markers: alpha-smooth muscle (alpha-SM) actin and desmin. alpha-SM actin was located on the outer border of the cranial mesentery of both sexes at day 17 pc, and expression increased only in female fetuses. On day 19 pc, desmin expression was also detectable in the a-SM actin-positive cells. Proliferation and apoptosis indices of cells in the cranial mesentery, as analysed by 5'-bromodeoxyuridine incorporation and by detection of DNA strand breaks (TUNEL method) respectively, did not show any difference between the sexes, neither on day 17 nor on day 18 pc. Since primordial cells of the cranial suspensory ligament highly express the androgen receptor during the period of gestation when androgens can suppress cranial suspensory development, altered morphogenesis of these cells may be a direct consequence of androgen action