Characterization of CPG 15 During Cortical Development and Activity Dependent Plasticity

Regulation of gene transcription by neuronal activity is thought to be key to the translation of sensory experience into long-term changes in synaptic structure and function. Here we show that cpgl5, a gene encoding an extracellular signaling molecule that promotes dendritic and axonal growth and synaptic maturation, is regulated in the somatosensory cortex by sensory experience capable of inducing cortical plasticity. Using in situ hybridization, we monitored cpgl5 expression in 4-week-old mouse barrel cortex after trimming all whiskers except D1. We found that cpgl5 expression is depressed in the deprived barrels and enhanced in the barrel column corresponding to the spared D1 whisker. Induction of cpgl5 expression is significantly diminished in adolescent as well as adult CREB knockout mice. cpgl5's spatio-temporal expression pattern and its regulation by CREB are consistent with a role in experience-dependent plasticity of cortical circuits. Our results suggest that local structural and/or synaptic changes may be a mechanism by which the adult cortex can adapt to peripheral manipulations. The balance between proliferation and apoptosis is critical for proper development of the nervous system. Yet, little is known about molecules that regulate apoptosis of proliferative neurons. Here we identify a soluble, secreted form of CPGl5 expressed in embryonic rat brain regions undergoing rapid proliferation and apoptosis, and show that it protects cultured cortical neurons from apoptosis by preventing activation of caspase 3. Using a lentivirus-delivered small hairpin RNA, we demonstrate that endogenous CPG15 is essential for the survival of undifferentiated cortical progenitors in vitro and in vivo. We further show that CPGl5 overexpression in vivo expands the progenitor pool by preventing apoptosis, resulting in an enlarged, indented cortical plate and cellular heterotopias within the ventricular zone, similar to the phenotypes of mutant mice with supernumerary forebrain progenitors. CPGl5 expressed during mammalian forebrain morphogenesis may help balance neuronal number by countering apoptosis in specific neuroblasts subpopulations, thus influencing final brain size and shape. Thesis Supervisor: Elly Nedivi Title: Fred and Carol Middleton AssistanProfes~r of Neurobiology Acknowledgements First I would like to thank my advisor Elly Nedivi for taking time to be a mentor to me and for teaching me how to be a scientist. Without her faith in me I would not be where I am today, and I cannot put into words my gratitude. I would also like to thank the past and present members of the Nedivi Lab, everyone has taught me so such in my time here. Just as important as the scientific lessons I learned are the friendships forged with lab members that will last a lifetime. I would next like to thank my committee Martha Constantine-Paton, Rosalind Segal and especially Carlos Lois for being a second mentor, and his helpful technical advice. I would like to thank my entire family especially my mother Regina Harwell, my father Willie Green and my brother Reggie Harwell for raising me and teaching me how to be a man. I certainly would not have made it this far without your guidance and love. Finally, this would not have been possible without the love and unwavering support of my wife Lynn. She is by far the best thing that has happened to me since moving to Boston, and I am grateful everyday for having her love and support.