During brain development, neural progenitor cells proliferate and differentiate into neural precursors. These neural precursors migrate along the radial glial processes and localize at their final destination in the cortex. Numerous reports have revealed that 14-3-3 proteins are involved in many neuronal activities, although their functions in neurogenesis remain unclear. Here, using 14-3-3/ double knockout mice, we found that 14-3-3 proteins are important for proliferation and differentiation of neural progenitor cells in the cortex, resulting in neuronal migration defects and seizures. 14-3-3 deficiency resulted in the increase of ␦-catenin and the decrease of ␤-catenin and ␣N-catenin. 14-3-3 proteins regulated neuronal differentiation into neurons via direct interactions with phosphorylated ␦-catenin to promote F-actin formation through a catenin/Rho GTPase/Limk1/cofilin signaling pathway. Conversely, neuronal migration defects seen in the double knock-out mice were restored by phosphomimic Ndel1 mutants, but not ␦-catenin. Our findings provide new evidence that 14-3-3 proteins play important roles in neurogenesis and neuronal migration via the regulation of distinct signaling cascades.

17p13.3 microduplication syndrome is a newly identified genetic disorder characterized by duplications in the 17p13.3 chromosome locus, resulting in a variety of disorders including autism spectrum disorder (ASD). Importantly, a minimum duplication region has been defined, and this region exclusively contains the gene encoding 14-3-3ε. Furthermore, duplication of this minimum region is strongly associated with the appearance of ASD in human patients, thus implicating the overexpression of 14-3-3ε in ASD. Using in vitro and in vivo techniques, we have found that 14-3-3ε binds to the microtubule binding protein doublecortin preventing its degradation. We also found that 14-3-3ε overexpression disrupts neurite formation by preventing the invasion of microtubules into primitive neurites, which can be rescued by the knockdown of doublecortin. To analyse the function of 14-3-3ε in neurite formation, we used 14-3-3ε flox mice and found that 14-3-3ε deficiency results in an increase in neurite formation. Our findings provide the first evidence of cellular pathology in 17p13.3 microduplication syndrome.

14-3-3 proteins are ubiquitously-expressed and multifunctional proteins. There are seven isoforms in mammals with a high level of homology, suggesting potential functional redundancy. We previously found that two of seven isoforms, 14-3-3epsilon and 14-3-3zeta, are important for brain development, in particular, radial migration of pyramidal neurons in the developing cerebral cortex. In this work, we analyzed the function of another isoform, the protein 14-3-3gamma, with respect to neuronal migration in the developing cortex. We found that in utero 14-3-3gamma-deficiency resulted in delays in neuronal migration as well as morphological defects. Migrating neurons deficient in 14-3-3gamma displayed a thicker leading process stem, and the basal ends of neurons were not able to reach the boundary between the cortical plate and the marginal zone. Consistent with the results obtained from in utero electroporation, time-lapse live imaging of brain slices revealed that the ablation of the 14-3-3gamma proteins in pyramidal neurons slowed down their migration. In addition, the 14-3-3gamma deficient neurons showed morphological abnormalities, including increased multipolar neurons with a thicker leading processes stem during migration. These results indicate that the 14-3-3gamma proteins play an important role in radial migration by regulating the morphology of migrating neurons in the cerebral cortex. The findings underscore the pathological phenotypes of brain development associated with the disruption of different 14-3-3 proteins and will advance the preclinical data regarding disorders caused by neuronal migration defects.

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Previous studies show that mice with Ywhae deficiency show abnormalities in brain development including defects in neuronal migration of post-mitotic pyramidal neurons as well as neuronal differentiation and proliferation in neuronal progenitor cells. Also, our previous research indicated that the Ywhae knockout mice show moderate defects in working memory and anxiety-like behavior. This previous work was performed using heterozygous mutant mice. Here we performed behavioral analyses using homozygous Ywhae knockout mice and found that the homozygous Ywhae knockout mice have increased locomotor activity, decreased working memory, and increased sociability. Taken together with the results obtained from the previous pathophysiological analyses in the Ywhae knockout mice, the Ywhae knockout mouse is useful for pathophysiological analyses of neuropsychiatric disorders caused by defects during neurodevelopment.