Roles Of Myosin-10in Radial Migration Of Cerebral Cortical Neurons

Cortical development is an important process in the establishment of mammal nervoussystem, and it involves the proliferation, differentiation, migration, neurite outgrowth andprojection of cortical nerve cells. During embryonic developmental period, neuralprogenitor cells in the ventricular zone undergo mitosis to generate pyramidal neurons.Postmitotic neurons migrate radially to the appropriate cortical plate area with an inside-out mode, following by accurate neuronal projections to form functional neural circuit andtransmit neural signals. The proper migration relies on the correct orientation of migratingneurons and its unique bipolar morphology. Series of scientific findings suggest that radialmigration is closely related to nervous system disorders such as schizophrenia, autism, etc.The cellular and molecular studies of radial neuronal migration have become a main focusin the related nervous system developmental research area, and researching the cellular andmolecular mechanism of this process has important scientific, medical and socialsignificance.Myosin-10(Myo10), an untraditional member of myosin families, was found interactdirectly both with microfilaments and microtubules to participate in the regulation ofcellular proliferation, adhesion and phagocytosis. Research has previously shown thatMyo10is highly expressed during brain development, however, little is known of the rolethat Myo10is required for neuronal migration in cerebral cortex. Here we report that Myo10is involved in distinct phases of radial migration with its two isoforms, full-length Myo10(fMyo10) and headless Myo10(hMyo10), to regulate orientation and morphogenesis ofradially migrating cortical neurons.Firstly, we analyzed the expression pattern of Myo10in the developing cortex with insitu hybridization and immunohistochemistry methods. Secondly, to determine the functionof Myo10and its isoforms in the expressed area, in utero electroporation was performedwith Myo10shRNA, fMyo10shRNA and hMyo10shRNA at embryonic day15.5, andbrains were analyzed at embryonic day18.5, a period of time when neuronal migration isprevalent. Finally, to further explore the mechanism that Myo10regulates neuronalmigration, we investigated how forced expression of Myo10ΔMoand Netrin-1receptor,Deleted in Colorectal Cancer (DCC) affect the migration defects caused by Myo10shRNAs.This research illustrated that the expression pattern of Myo10is closely involved incortical development during mouse embryonic period, where it mainly existed in the deeperarea of the cerebral cortex. Reducing Myo10expression in the embryonic cortical nervecells by in vivo transgenic method would inhibit the radial migration process, but hadlimited influence in proliferation, differentiation, cell fate decision or radial glialorganization of nerve cells. Further mechanism analysis indicated that fMyo10exists indeeper layers and plays roles in the orientation selection when radial migration starts. Wealso showed that fMyo10orientating radial migration, at least in part, is mediated by DCC. DCC was found expressed overlap with Myo10in the developing cortex. Changing theexpression level of DCC disturbed radial migration as knocking down fMyo10, andimportantly, the overexpression of DCC could partially rescue the migrating defects andaberrant direction in fMyo10-silenced cortical neurons, which suggested that DCC has rolesin orientating migrating neurons with fMyo10. Furtherly, with DCC kanga mice, DCC wasfound regulate the entry of primitive cortical zone with its P3domain. Meanwhile, themotorless hMyo10was detected expressed broadly in the embryonic brain, especially inthe intermediate zone of the developing cortex. Moreover, according to our in vivo and invitro research work, hMyo10was proved to be required for the morphological transitionfrom multipolar to bipolar in the intermediate zone.In conclusion, this study revealed that Myo10has divergent functions with its twoisoforms to control migrating orientation and neuronal morphogenesis with a multistepmechanism. On one hand, full-length Myo10has roles in the orientation of migratingcortical neurons, where the Netrin-1receptor DCC is involved. On the other hand, headlessMyo10has functions in transiting neurons from multipolar to bipolar in shape. In addition,on the basis of the above experimental results, this study analyzed some detailedmechanisms and potential functions of Myo10and DCC, and provided feasible plans andspecific suggestions for the next phase of research work.