• Danielle Rayêe, IackPamela MenesesPMInstitute of Biomedical Sciences, Federal University of Rio de Janeiro, Brazil., Raissa R Christoff, Michele R Lourenço, Christiane Bonifácio, Jürgen Boltz, Roberto Lent, and Patricia P Garcez.
• Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Brazil; Institute of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, NY, United States.
• Neuroscience. 2021 Nov 21; 477: 14-24.

AbstractThe corpus callosum (CC) is a major interhemispheric commissure of placental mammals. Early steps of CC formation rely on guidance strategies, such as axonal branching and collateralization. Here we analyze the time-course dynamics of axonal bifurcation during typical cortical development or in a CC dysgenesis mouse model. We use Swiss mice as a typical CC mouse model and find that axonal bifurcation rates rise in the cerebral cortex from embryonic day (E)17 and are reduced by postnatal day (P)9. Since callosal neurons populate deep and superficial cortical layers, we compare the axon bifurcation ratio between those neurons by electroporating ex vivo brains at E13 and E15, using eGFP reporter to label the newborn neurons on organotypic slices. Our results suggest that deep layer neurons bifurcate 32% more than superficial ones. To investigate axonal bifurcation in CC dysgenesis, we use BALB/c mice as a spontaneous CC dysgenesis model. BALB/c mice present a typical layer distribution of SATB2 callosal cells, despite the occurrence of callosal anomalies. However, using anterograde DiI tracing, we find that BALB/c mice display increased rates of axonal bifurcations during early and late cortical development in the medial frontal cortex. Midline guidepost cells adjacent to the medial frontal cortex are significant reduced in the CC dysgenesis mouse model. Altogether these data suggest that callosal collateral axonal exuberance is maintained in the absence of midline guidepost signaling and might facilitate aberrant connections in the CC dysgenesis mouse model.Copyright © 2021 IBRO. Published by Elsevier Ltd. All rights reserved.

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