This is the Home of the Section on Molecular Endocrinology, headed by Maria L Dufau, MD, PhD
The Section on Molecular Endocrinology investigates the molecular basis of peptide hormone and their receptors in the control of gonadal function. Studies encompass the structure and transcriptional regulation of luteinizing hormone and prolactin receptors. This Section studies the regulatory mechanism (s) involved in the progress of spermatogenesis and control of Leydig cell function. Investigates novel gonadotropin-regulated genes of relevance to the progression of testicular gametogenesis, Leydig cell function and other endocrine processes.
Current studies concentrate on the function and regulation of Gonadotropin Regulated Testicular RNA Helicase (GRTH/DDX25), a member of the DEAD-box family of RNA helicases discovered in this laboratory, which is expressed in male germ cells of mice, rat and human, predominantly in meiotic spermatocytes and round spermatids, and is also present in Leydig cells. The characterization of GRTH null mice developed in this laboratory demonstrated that this gene is essential for the progress of spermatogenesis and participates in the process of elongation. GRTH null mice are sterile due to lack of sperm with spermatogenic arrest at the round spermatid stage 8 that fail to elongate. GRTH is a multifunctional protein which participates in the transport of relevant mRNAs from nucleous to cytoplasmic sites of germ cells for storage in Chromatoid Bodies of round spermatids awaiting translation at later stages of spermatogenesis. This is followed by their transit in association with phospho-GRTH and binding to actively translating polyribosomes, where it may participate in translation. It is also a regulator of miRNA biogenesis and an inhibitor of germ cell apoptosis. Testosterone and its derivatives are essential for transcription of GRTH in germ cells through its paracrine effects via androgen receptors in Sertoli cells. Other studies have identified a functional cis-binding element on the GRTH gene for Germ Cell Nuclear Factor (GCNF) which is required for GRTH transcription in post-meiotic germ cells. This work provided evidence for cell specific actions of androgen on GCNF in GRTH transcription. Studies of this group have linked testosterone produced in Leydig of the interstitial compartment under Luteinizing Hormone stimulus to the induction of GRTH in germ cells through paracrine actions via androgen receptors present in Sertoli cells. Future studies are directed toward learning how the Androgen signal(s) through Sertoli cells is passed to the germ cells (round spermatids). This is to include involvement of classical and non-classical pathways of androgen action. Also, other work will encompass identification of paracrine factor(s) and transcription factor(s) activated by androgen induced by gonadotropin that may affect GCNF which in turn stimulates GRTH transcription and consequently expression, essential for the progress of spermatogenesis. Other studies will investigate GRTH’s role in translation of mRNAs essential in spermatogenesis.
Early studies of this Section in the human demonstrated the presence of a missense mutation (R242H) in GRTH gene in 5.8% of an infertile azoospermic Japanese population which abolish the phospho-form of GRTH and presumably its function at cytoplasmic sites. This mutation was predicted to impact structurally an adjacent region of Thr239 residue and presumably the binding pocket for PKA kinase. The recently developed GRTH knock-in mice (KI) carrying the human mutated GRTH gene, are sterile, lack sperm with arrest at the same level as the KO mice. These mice lack phospho-GRTH with preservation of non-phospho GRTH. This finding highlights the importance of the presence of phospho-GRTH in the progress of spermatogenesis. Studies are concentrated in understanding mechanistically the role of both phospho- and non-phospho-GRTH on the development of germ cells during spermatogenesis and its participation in the process of elongation.
Recent studies, using site directed mutagenesis, have identified Threonine 239, structurally adjacent to the patient’s mutant site as the GRTH phospho-site. Molecular Modeling provided structural basis for the role of R242 and other critical solvent exposed residues at the GRTH/PKA interface on the control of GRTH phosphorylation at T239. The surface topography of GRTH/PKA interface is relatively shallow and extended. Also, has unique distribution of basic and acidic surface residues. These provided the basis for development of effective pharmacophore inhibitors that corresponds to the GRTH/PKA interface which can effectively and specifically associate and block the phosphorylation of GRTH in in vitro systems. Our intent is to proceed with the development of a human male contraceptive by applying initially the in vitro findings to studies of mice in vivo.