Disruptions in cell-cell interactions and signaling during fetal development can result in obvious birth defects, but more subtle deficiencies are increasingly being recognized as manifesting in diseases that are not recognized until much later in life. My laboratory’s investigations into female and male gonad development are inspired by the quest to understand the fetal basis of sex-specific adult diseases in reproductive endocrinology. Our interest in female gonad development is focused on formation of the unique cellular niche, the follicle, which ensures survival and maturation of the female gamete. We discovered a cluster of homeobox transcription factors that are expressed during ovary development whose disruption results in follicle failure and oocyte death, classic components of premature ovarian failure, a devastating disease that leads to premature menopause in adult females. Our interest in male gonad development is centered on local regulation of androgen synthesis. A fundamental difference in male versus female sex differentiation in mammalian species is that only the male fetus produces hormones: androgens. Studies show that optimal development of the mammalian male reproductive tract requires exquisite timing and critical thresholds of androgen production, but little is known about how this is controlled. Indeed, defective androgen synthesis or activity during fetal development is emerging as a component of adult male infertility and decreased virility. Thus, the major goals of my research are to discover local cell-cell interactions and molecular mechanisms that are used to establish the nascent ovarian follicle niche within the developing ovary, and that control the onset and maintenance of fetal testosterone synthesis in the developing testis.
Female Development and Reproduction:
Two existential threats to female fertility include the premature loss of the ovarian reserve and early implantation/placentation failure. The Jorgensen lab has focused on members of the Iroquois homeobox transcription factor family, IRX3 and IRX5 (Irx3/5), and discovered that they play critical roles in establishing oocyte-pregranulosa cell interactions within newly formed primordial follicles. Recently, we recognized uncanny parallels in molecular signaling pathways related to IRX3 expression within the developing ovary and in the uterine stroma upon implantation. Indeed, knockout models of Irx3 uncovered profound detrimental phenotypes in both the integrity of the ovarian reserve and outcomes reliant on early implantation. We’ve determined that both situations are linked to critical implementation of cell differentiation, movement, and new cell-cell contact and interaction. We are currently working, along with the Indrani Bagchi lab at UIUC, to further our understanding of IRX3 in these two events critical to female fertility. We plan to:
· Distinguish roles for IRX3/5 in mediating germline nest breakdown and primordial follicle formation to establish responsive follicles with healthy oocytes
· Establish IRX3 as a critical step in decidualization that promotes a successful implantation and placentation program
· Uncover cell-specific downstream targets and protein partners for IRX3/5 in mediating ovary and uterine events
· Discover a unique relationship between b-catenin and IRX3, both of which are multifunctional proteins with dedicated roles for promoting cell-cell interactions.
Our ultimate goals are to increase our understanding of the biology that results in a healthy ovarian reserve and optimal uterine conditions for early embryo survival.
Male Gonad Development:
Fetal Testis Androgen Synthesis
A fundamental difference in male versus female sex differentiation in mammalian species is that only the male fetus produces hormones: androgens. Studies show that optimal development of the mammalian male reproductive tract requires exquisite timing and critical thresholds of androgen production, but little is known about how this is controlled. Fetal Leydig cells within the developing testes function as the primary source of androgens by expressing several genes that facilitate stepwise transformation of cholesterol to androgens. Previous studies established that Sertoli cell signals stimulate fetal Leydig cell differentiation. We used small molecule fluorescent in situ hybridization (smFISH) and copy number qPCR to uncover detailed expression profiles of steroidogenic pathway genes. Our preliminary data uncovered three phases of steroidogenic pathway gene expression over the lifetime of fetal Leydig cells: 1) differentiation, characterized by a gradual increase in expression, likely corresponding to accumulation of differentiating fetal Leydig cells; 2) stimulation of a profound increase in expression, suggesting new responsiveness of fetal Leydig cells to outside stimuli; and 3) dedifferentiation with an equally dramatic decrease in expression to pre-differentiation levels by the time of birth, suggesting an external source that forces a transition to dedifferentiation. Perhaps not surprising is that androgens levels parallel steroid pathway gene expression. These observations inspire the Jorgensen lab to pursue two fundamental questions: What stimulates rapid increases in androgen production? And then, what induces active repression of androgen production? Our specific goals are to discover:
· The transcript level differences between distinct progenitor subpopulations of fetal Leydig cells.
· Whether the journey of these subpopulations differ with respect to the rise and fall of fetal Leydig cell activity.
· The identity of cell types that influence fetal Leydig cell activity or the transition to a dedifferentiated state.
· A new understanding of the microenvironment for fetal Leydig cell function.
· The timing and extent to which DHH/GLI3, SF1, and cAMP/PKA regulate steroidogenic genes and androgen synthesis during differentiation, stimulation, and dedifferentiation phases.
· The binding sites for GLI3, SF1, CREB, CRTC2, coactivators/corepressors, and locations for on each steroidogenic pathway gene.
· The identity of binding motifs within enhancer/repressor sequences that may not be associated with the known transcription factors.
Ultimately, we aim to piece together the cellular source and identity of signals that impinge on fetal Leydig cells to control gene transcription and androgen output. We believe that our results will help us to uncover potential targets for endocrine disruption or resolve yet unidentified causes for variations in sex differentiation.