UC San Diego

Reproductive endocrinology is focused on the hypothalamic- pituitary-gonadal (HPG) axis. The gonadotropin-releasing hormone (GnRH) neurons of the hypothalamus are the primary regulators of the HPG axis and thus, reproductive function in mammals. Therefore, the molecular and developmental properties of GnRH neurons are important for our knowledge of reproductive function and our understanding of infertility. GnRH gene expression is restricted to a dispersed population of neurons within the hypothalamus. These studies elucidate some of the molecular processes that contribute to this strict specification. The research presented in this dissertation utilizes both immortalized cell culture and genetically modified animal models to study the regulation of the GnRH gene and neuron. Herein are described the identification of novel distal cis- regulatory elements and trans regulatory proteins that contribute to GnRH gene expression and neuronal specification during development. While previous research identified and characterized some cis-regulatory elements, recent evidence suggested that additional upstream sequences might provide further specification for proper targeting to the GnRH neurons. Studies characterizing the upstream enhancer within the rat GnRH regulatory sequence revealed Nuclear Factor 1 as a new regulator of the GnRH gene. Using DNA sequence from the recently completed rat genome and an in silico approach termed phylogenetic footprinting, two novel, evolutionarily conserved elements were identified and shown to regulate neuron-specific gene expression of GnRH. Prader-Willi syndrome (PWS) is a human contiguous multigene disorder characterized by obesity, hypothalamic hypogonadism, and developmental delay. The genetic cause of PWS is the loss of expression from the 15q11-13 chromosomal region. This region contains several genes, including one that encodes the MAGE family member, necdin. The research presented herein demonstrates the necessity of necdin for proper GnRH gene expression and neuronal development. The findings provide a mechanism by which the loss of necdin could contribute to the infertility observed in PWS. This dissertation utilizes both in vitro and in vivo approaches to elucidate important regulators of GnRH gene transcription and neuronal migration in development and significantly contributes to our understanding of reproductive control by the hypothalamic GnRH neurons