Postdoctoral Experience, Clayton Foundation Laboratories for Peptide Biology, The Salk Institute, La Jolla, CA, Feb. 1996 - Sept. 1997
PhD, Physiology of Reproduction, University of Missouri, 1996
MS, Physiology of Reproduction, University of Missouri, 1992
BS, Animal Science, University of Idaho, 1989
Omne vivum ex ovo’ or ‘all life from eggs’ was William Harvey’s famous 17th Century dictum! However, it is now well established that not every egg (oocyte) is competent to drive or contribute to normal embryonic development and ultimately successful pregnancy. Indeed, poor oocyte quality may be the single greatest impediment to a successful pregnancy in otherwise healthy women. Poor oocyte competence is exacerbated by a variety of adverse health conditions and maternal age which often necessitate use of costly assisted reproductive technologies (ART). Despite decades of research, the fundamental questions remain of what makes an egg good or bad and how to predict egg quality accurately in a noninvasive fashion or improve oocyte quality in a clinical setting? Our long-term research objective is to elucidate the molecular phenotype of oocytes of poor developmental competence and utilize such information as a platform for development of new treatments/diagnostics to increase efficiency of ART. Foundational studies have identified differences in egg and cumulus cell transcriptome composition associated with oocyte competence. Based on such results, diagnostic and therapeutic strategies to predict or enhance oocyte competence and the functional contribution of differentially expressed transcripts to progression through early embryogenesis are being investigated. The bovine model is foundational to our ongoing studies because ovarian physiology and many aspects of embryo development and ART are similar between cattle and women and because it provides a readily available supply of eggs and a viable platform for functional studies of contribution of genes identified to successful early embryogenesis. Above research focus is also relevant to improvements in reproductive performance in dairy cattle where poor conception rates and high rates of embryonic loss dramatically limit profitability and sustainability.
Novel oocyte-expressed genes critical to fertility
A growing body of evidence supports a key contribution of the oocyte to fertility regulation mediated through an active role in control of follicular development and early embryogenesis. A developmental program intrinsic to the oocyte controls the rate of follicular development and bidirectional communication between the oocyte and nearby somatic (cumulus and granulosa) cells is critical for normal growth of ovarian follicles, cumulus expansion, meiotic maturation and follicle rupture. One of our additional research goals is to enhance understanding of the functional contribution of unique oocyte-expressed genes to reproductive success and the mechanisms involved. During initial analysis of expressed sequence tags (ESTs) from a bovine oocyte cDNA library, we identified an abundant yet novel oocyte-expressed transcript encoding for a gene which we refer to as JY-1. We hypothesized that JY-1 is of potential functional significance to female fertility and subsequently conducted a series of experiments to further characterize JY-1 and its expression and actions relevant to follicular development and early embryogenesis.
Our published results ) established that the JY-1 gene encodes for a species specific secreted protein belonging to a novel protein family. JY-1 mRNA and protein are ovary-specific, present throughout follicular development and restricted exclusively to the oocyte. Recombinant JY-1 protein (rJY-1) is biologically active and treatment with rJY-1 in combination with FSH reduces granulosa cell numbers and impacts granulosa cell estradiol and progesterone production. We have also established that maternal (oocyte derived) JY-1 is required post fertilization for successful progression of embryos to the blastocyst stage. Ongoing studies are investigating the functional contribution of oocyte derived JY-1 to meiotic maturation, cumulus expansion and specific developmental events during the maternal-to-zygotic transition period of early embryogenesis and the mechanisms involved
Regulation of dominant follicle selection
The ovarian cycle is central to the reproductive process, because only mature ovarian follicles release oocytes to be fertilized. However, > 99.9% of follicles die via atresia at various stages of folliculogenesis and never ovulate. Antral follicle development occurs in a characteristic wave like pattern in monotocous species including cattle and humans. A transient increase in serum FSH precedes the onset of a follicular wave and stimulates emergence of a cohort of small antral follicles. Typically, in the face of declining FSH concentrations, a single dominant follicle out of this cohort is selected to continue to grow to ovulatory size, and produces increased amounts of estradiol. The remaining smaller “subordinate” follicles rapidly lose their capacity to produce estradiol and die via atresia.. The process whereby development of a single (dominant) follicle capable of ovulation during each follicular wave and atresia of remaining follicles occurs is referred to as dominant follicle selection. Selection of a single dominant follicle is an evolutionarily conserved mechanism critical to control of number of offspring per pregnancy in monotocous species.
Results of our previously published studies (described below) indicate cocaine and amphetamine regulated transcript (CARTPT), with intraovarian expression only in single-ovulating species, is a novel regulator of ovarian follicular development. Intraovarian expression of CART was first discovered during an bovine ovarian (oocyte) EST sequencing project. The mature CARTPT peptide (CART) is a potent negative regulator of FSH and IGF1 action on granulosa cells in vitro and can inhibit follicular estradiol production in vivo. Follicular fluid CART concentrations in healthy follicles decrease after dominant follicle selection and CARTPT mRNA is lower in healthy versus atretic follicles collected prior to and early after initiation of follicle dominance, suggestive of a regulatory role in the selection process. The inhibitory actions of CART on FSH signaling and estradiol production are dependent on the Go/i-subclass of inhibitory G proteins and linked to multiple components of the FSH signal transduction pathway resulting in reduced CYP19A1 mRNA and estradiol production. Evidence to date supports a potential important functional role for CART in regulation of dominant follicle selection and the species-specific ovulatory quota in monotocous species. Ongoing studies are focused on elucidation of CART mechanism of action in regulation of granulosa cell steroidogenesis and dominant follicle selection, including identification of the specific receptor mediating biological actions of the CART peptide in the bovine ovary and other CART target tissues.
JY-1, an oocyte-specific gene, regulates granulosa cell function and early embryonic development in cattle.pdf
Molecular Determinants of Oocyte Competence: Potential Functional Role for Maternal (Oocyte-Derived) Follistatin in Promoting Bovine Early Embryogenesis.pdf
Cocaine- and Amphetamine-Regulated Transcript Accelerates Termination of Follicle-Stimulating Hormone-Induced Extracellularly Regulated Kinase 1/2 and Akt Activation by Regulating the Expression and Degradation of Specific Mitogen-Activated Protein Kinase Phosphatases in Bovine Granulosa Cells.pdf