14-3-3 Proteins in Neuronal Migration and Neuromorphogenesis during Cortical Development and Neurodevelopmental Disorders

Abstract

The development of the human brain is a vastly complex process resulting in an elaborate network of over one hundred billion neurons, with each neuron having thousands of synaptic connections. The proper organization of these cells and the formation of their processes is essential for the construction of a functional brain. Disruptions in this process result in a number of developmental disorders; including, epilepsy and autism spectrum disorder (ASD). 17p13.3 microduplication syndrome is a newly identified genetic disorder resulting in a variety of defects including ASD. Importantly, a minimum duplication region strongly associated with ASD has been classified and exclusively contains the gene encoding the protein 14-3-3[epsilon], strongly implicating the overexpression of 14-3-3[epsilon] in ASD. Using in vitro and in vivo techniques, we have found that 14-3-3[epsilon] binds to the microtubule binding protein doublecortin, preventing its degradation resulting in increased doublecortin protein levels. We also found that 14-3-3[epsilon] overexpression disrupts neurite formation by preventing the invasion of microtubules into primitive neurites, which can be rescued by the knockdown of doublecortin. Our findings provide the first evidence of cellular pathology in 17p13.3 microduplication syndrome. In addition the functions of 14-3-3[epsilon] in cortical development, in this work we have also analyzed the role of 14-3-3[gamma], another 14-3-3 isoform. Williams Syndrome (WS) is a neurodevelopmental disorder caused by deletions in the 7q11.23 chromosome locus resulting in intellectual disabilities. Typical WS patients present a 1.5-1.8Mb deletion whereas atypical patients have a larger than 1.8 Mb deletion, which includes the gene encoding 14-3-3[gamma]. Interestingly, atypical WS patients commonly exhibit epilepsy. Furthermore, there is a reciprocal duplication syndrome to WS, which also results in epilepsy and intellectual disabilities. Taken together with the fact that defects in neuronal migration typically result in epilepsy, we analyzed if the overexpression and knockdown of 14-3-3[gamma] causes neuronal migration defects. We found that the overexpression and the knockdown of 14-3-3[gamma] in utero results in delays in neuronal migration due to decreased neuronal migration velocity. Furthermore, we found no defects in neurogenesis when 14-3-3[gamma] levels are altered. These results indicate that balanced expression of 14-3-3[gamma] is required for proper neuronal migration.%%%%Ph.D., Neuroscience – Drexel University, 2017