The focus of my research program is to understand the molecular mechanisms governing reproductive tract and gonadal development with particular emphasis on the role played by Müllerian Inhibiting Substance (MIS). MIS, a member of the TGF-b superfamily of growth and differentiation factors, is produced by Sertoli cells during embryonal development and is required for normal reproductive development in male embryos. The signal activity of MIS is the regression of the Müllerian duct, the precursor of the uterus, fallopian tubes and upper vagina. MIS is also produced both in the adult testis by Sertoli cells and in the ovary by granulosa cells, where its exact role remains to be fully explored. Based on in vitro and in vivo evidence, it is our hypothesis that signal transduction by MIS, via its heteromeric serine/threonine kinase receptor, is required to maintain reproductive competence of the gonad and to prevent hyperplastic growth. The goals of my research are to (I) understand the developmental, cell-specific and sexually dimorphic mechanisms regulating the expression of the MIS type II receptor (MISRII) in Leydig cells, Sertoli cells, and granulosa cells during different stages of development (II) to understand the role played by MIS in the adult gonad and its regulation of steroidogenesis (III) the postnatal differentiation of Müllerian duct structures and the consequences of perturbed development.
We are currently investigating the cis- and trans-acting factors necessary and sufficient for MISRII expression in Leydig cells, the testosterone-producing cells of the testes. We have found that an orphan nuclear receptor, SF-1 is required to bind to one of two sites in the MISRII proximal promoter for full expression. We have also determined that another DNA site is also required for full promoter activity and we are attempting to uncover the protein binding to the site. The physiological relevance of these findings is being studied with homologous “knock-in” strategies.
We have found that MIS inhibits the expression of Cyp17 mRNA in Leydig cells both in vivo and in vitro, which results in drastically reduced testosterone production. In addition to having shown the inhibition of Cyp17 expression by MIS in vivo , Alex Trbovich has recently shown that MIS also regulates Cyp17 kinetics by increasing the Km of its hydroxylase activity. We are also studying the expression of StAR, the protein that performs the rate-limiting step in steroid hormone synthesis from cholesterol. We have shown that MIS increases the expression of StAR mRNA in Leydig cells and that it does so by relieving feedback inhibition by testosterone. We have also shown that MIS regulates the expression of gonadotropin genes in pituitary cells and are currently investigating the molecular details of this phenomenon further.
Additional studies we are pursuing involve the role of b-catenin in postnatal Müllerian duct development. Although the uterus is indispensable for propagation, and thus survival, of mammalian species, its differentiation from the primordial Müllerian ducts is not well understood. Disruption of the genes for some members of the Wnt family of secreted signaling factors in mice has produced uterine phenotypes that either block formation of the Müllerian ducts and subsequent uterine development or alter postnatal differentiation or function. Conventional Wnt-mediated signal transduction occurs by the stabilization of b-catenin and its translocation to the nucleus and interaction with the transcription factors TCF/LEF to modulate target gene expression. Additionally, b-catenin plays an essential role in linking adherens junctions with the actin cytoskeleton. We are investigating the function of b-catenin in uterine development and have found that targeted deletion of b-catenin in mouse uterus leads to progressive replacement of smooth muscle with fat in the myometrium that results in a phenotype that resembles lipoleiomyoma. This phenotype is more complex than that observed when Wnt7a is deleted indicating a more global role for b-catenin. We propose to continue these studies to provide a better understanding of postnatal uterine development.
Representative Publications:
1. Houk CM, Pearson E, Martinelle N, Donahoe PK, and Teixeira J. (2004), Androgen Mediated Feedback Inhibition of Steroidogenic Acute Regulator Protein. Endocrinology 145:1269-1275.
2. Trbovich AM, Martinelle N, Pearson EJ, O’Neill FO, Donahoe PK, Sluss PM, and Teixeira J. (2004) The cytochrome P450 C17 hydroxylase and C17-20 lyase activities in Leydig cells are differentially altered by Müllerian inhibiting substance and cAMP. J Steroid Biochem Mol Biol 92:199-208.
3. Arango NA, Pearson EJ, Donahoe PK, and Teixeira J. (2004) Genomic structure and expression analysis of the mouse testis-specific ribbon protein (Trib) gene. Gene 343:221-227.
4. Arango NA, Szotek PP, Manganaro TF, Oliva E, Donahoe PK, Teixeira J. Conditional deletion of beta-catenin in the mesenchyme of the developing mouse uterus results in a switch to adipogenesis in the myometrium. Dev Biol. 2005 Dec 1;288(1):276-83.
Contact Information
Phone: 617-724-1616
Fax: 617-724-5057
E-mail: teixeira@helix.mgh.harvard.edu
