UCLA

Neural circuit development is dependent on the precise patterning of the spinal cord and the specific wiring of axons. Netrin1 has been historically studied for its axon guidance properties. However, studies have found netrin1 to be involved in other physiological functions, including suppressing Bone Morphogenic Protein (BMP) signaling. During development, BMP signaling patterns the dorsal spinal cord, setting the framework for the formation of neural circuits. This finding postulates netrin1 as a molecule that regulates multiple processes in the spinal cord: 1. As a potential modulator of spinal cord patterning and 2. As a mediator of neural circuit formation. In this thesis, I summarize findings from studies focused on investigating these distinct roles of netrin1 in spinal cord development. First, we assessed the role of nertin1 in the patterning of the spinal cord. We found that ectopic expression of netrin1 reduces the number of dorsal interneurons (dI) in the spinal cord and inhibits the differentiation of mouse ESCs into dorsal dIs. In contrast, the loss of netrin1 in vivo increases BMP-dependent dorsal progenitors (dP). Furthermore, we find that netrin1 modulates BMP signaling by affecting levels of pSmad1/5/8, the effectors of BMP signaling, as well as the Ids, BMP downstream target genes. Together, these findings suggest a new role for netrin1 in the developing spinal cord, modulating BMP signaling. Then, I assessed netrin1 in the context of axon guidance. I aimed to assess if cleavage of ventricular zone (VZ)-derived netrin1 could facilitate the transfer of netrin1 to the pial surface where it acts as an axon guidance cue. I used epitope-specific immunohistochemistry to characterize the distribution of netrin1 protein and observed that the antibodies decorate different spinal cord regions. I tracked myc-tagged-netrin1 and observed multiple myc-tagged fragments in the lysates. Additionally, I observed that the electroporation of c-terminally tagged netrin1-myc results in efficient localization of netrin1 and myc to the pial surface. This preliminary data supports the hypothesis that netrin1 cleavage products have the capacity to differentially localize within the spinal cord. Together, these studies advanced our understanding of nerin1-mediated activities in the developing spinal cord.