The Molecular Effect Of ADAM17 In The Radial Migration And Differentiation In Mouse Cerebral Cortex

The radial migration of the neuronal progenitor cells is crucial to the formation of layer structure of the cerebral cortex during its development. During the radial migration, neuronal progenitor cells also undergo a morphological change, that they trasit from multipolar cells to bipolar or monopolar cells. A Disintegrin and Metalloprotease 17 (ADAM 17, or TACE) is a transmembrane protease, which is involved in many important physiological functions by processing different substrates, including Notch, several of the EGFR ligands, and a few cell adhesion molecules. However, very little is known about the function of ADAM 17 in cortical development.In order to reveal ADAM17’s function in cerebral cortex development, we used in utero eloctoporation (IUE) to change the expression level of ADAM 17 in the developing mouse telecephalon at embryonic day 14.5 (E14.5). Our results showed that the ADAM 17 knock-down cells can migrate normally to the intermediate zone (IZ) during E14.5-E16.5, but most of them stayed in IZ at E18.5, without further migrating into the cortical plate (CP) like those in the control group. The AD AM17 knockdown cells are also more likely to remain in the multipolar morphology compared to the control cells. Immunohistochemistry results showed that these ADAM17 knockdown cells can differentiate normally from neural stem cells (NSCs) into neuronal intermediate progenitor cells (nIPCs), but did not further differentiate into mature neurons. The defects in radial migration and differentiation could be partially rescued by co-electroporation of the ADAM 17 shRNA plasmid with its resistant AD AM17 expression plasmid. Electropoating the resistant ADAM17 expression plasmid alone did not affect cell outward migration. To investigate which substrate is downstream of ADAM17 during this outward migration of nIPCs, we knocked down several substrates of ADAM 17, including Heparin-binding Epithelial Growth Factor (HB-EGF), L1-CAM and Neuregulinl (NRG1). Knockdown of HB-EGF results in radial migration defects similar to those in the knockdown of ADAM 17, while knocking down of L1-CAM and NRG1 results in different phenotypes such as early cell death. The migration defects in ADAM 17 knockdown group can also be partially rescued by co-electroporating HB-EGF expression plasmid. Our results showed for the first time that ADAM17/HB-EGF plays a crucial role in regulating nIPCs radial migration and morphological transformation.