Synaptic specialization requires interactions between presynaptic postsynaptic, and glial partners. The development of mouse neuromuscular junctions is pre- patterned within a narrow central band of muscle, where motor axons undergo two aspects of presynaptic differentiation: regulated branching and specialization of nerve terminals. Evidence suggests that acetylcholine (ACh) inhibits nerve branching and presynaptic specialization, yet it is unclear whether the inhibition is mediated through postsynaptic or non-postsynaptic AChRs. Postsynaptic AChRs may play a role in pre- patterning the synapses and in eliciting a retrograde signal to induce presynaptic specialization. Here we have used genetic methods to address these issues. We report that clustering of postsynaptic AChRs is absent in muscle AChRa1 mutant mice. Like mice deficient in ACh biosynthesis, presynaptic axons are highly branched with synaptic sites distributed in a broader muscle territory, suggesting that postsynaptic AChRs are involved in pre- patterning synapses and mediates ACh inhibition of nerve branching. Surprisingly, presynaptic specialization is present in the absence of postsynaptic AChR clusters. Additional evidence supports that ACh inhibits specialization of nerve terminals through non-postsynaptic AChRs. These results suggest that ACh negatively regulates these two aspects of presynaptic differentiation via distinct mechanisms. Also presented here, through data obtained from mice that lack Schwann cells due to a loss of erbB2, are preliminary evidence for a possible role of Schwann cells in the timing of presynaptic development, in part of an ongoing project to determine the role of Schwann cells in NMJ development

We utilized induced pluripotent stem cells (iPSCs) derived from Huntington's disease (HD) patients as a human model of HD and determined that the disease phenotypes only manifest in the differentiated neural stem cell (NSC) stage, not in iPSCs. To understand the molecular basis for the CAG repeat expansion-dependent disease phenotypes in NSCs, we performed transcriptomic analysis of HD iPSCs and HD NSCs compared to isogenic controls. Differential gene expression and pathway analysis pointed to transforming growth factor β (TGF-β) and netrin-1 as the top dysregulated pathways. Using data-driven gene coexpression network analysis, we identified seven distinct coexpression modules and focused on two that were correlated with changes in gene expression due to the CAG expansion. Our HD NSC model revealed the dysregulation of genes involved in neuronal development and the formation of the dorsal striatum. The striatal and neuronal networks disrupted could be modulated to correct HD phenotypes and provide therapeutic targets.