To identify the molecular mechanisms that regulate cell specification in the CNS, we have selected the mouse retina and hypothalamus, both of which arise from the ventral embryonic forebrain, as model systems to ask this question. Each structure offers unique advantages for our studies.
The retina is perhaps the best-characterized region of the central nervous system, and provides an excellent system to identify the novel molecular mechanisms that regulate neuronal cell fate. The retina is comprised of seven major cell types, each identified by unambiguous morphology and molecular markers, and changes in their differentiation are easily measured. Defects in the differentiation of retinal photoreceptors often result in blindness. We are interested in developing a detailed understanding of the molecular mechanisms that guide photoreceptor and retinal glial development and function, which may in turn provide insight into the development of therapies for photoreceptor dystrophies.
In contrast to the relative simplicity of the retina, the hypothalamus is comprised of many different cell types that are organized into discrete nuclei. Each major hypothalamic nucleus been shown to be critical essential homeostatic and instinctive behaviors, which range from the sleep-wake cycle, to feeding and body weight, and to the care of offspring, although the identity and connectivity of the cell types that mediate these behaviors is largely unknown. Identification of genes that selectively control the differentiation of individual hypothalamic neuronal subtypes thus provides an excellent opportunity to directly determine their contribution to experimentally tractable and medically important behaviors.
We use functional genomics and proteomics to rapidly identify molecular mechanisms that regulate cell specification and survival in both retina and hypothalamus. We have profiled gene expression in both these tissues, from the start to the end of neurogenesis, characterizing the cellular expression patterns of over 1800 differentially expressed transcripts in both tissues. Working together with the lab of Heng Zhu in the Department of Pharmacology, we have also generated a protein microarray comprised of nearly 20,000 unique full-length human proteins, which we use to identify biochemical targets of developmentally important genes of interest.
Using these unique resources, we have identified the E3 SUMO ligase Pias3 and the zinc finger transcription factors Sall3 as essential regulators of mouse retinal photoreceptor subtype specification, and identified ERRb as essential for rod photoreceptor survival. We have identified long noncoding RNAs that modulate the activity of key transcription factors in developing retina to control cell identity. We have also found that the homeodomain factor Lhx2 is a central regulator of retinal glial development and function, and acts in mature glia to repress initiation of hypertrophic gliosis while simultaneously promoting expression of glial-derived neuroprotective factors.
In the hypothalamus, we have identified transcription factors that are essential for development of the central circadian oscillator; we discovered that tanycytes of the hypothalamic median eminence are a diet-responsive neural progenitor cell population; and also identified novel secreted proteins that regulate food intake. Future work will investigate the function of novel candidate regulators of retinal and hypothalamic cell identity, the role of previously uncharacterized hypothalamic cell subtypes in regulating motivated behaviors, and the contribution of tanycyte-derived neurogenesis to the regulation of feeding and body weight.