The RNA-binding protein MARF1 promotes cortical neurogenesis through its RNase activity domain.

Cortical neurogenesis is a fundamental process of brain development that is spatiotemporally regulated by both intrinsic and extrinsic cues. Although recent evidence has highlighted the significance of transcription factors in cortical neurogenesis, little is known regarding the role of RNA-binding proteins (RBPs) in the post-transcriptional regulation of cortical neurogenesis. Here, we report that meiosis arrest female 1 (MARF1) is an RBP that is expressed during neuronal differentiation. Cortical neurons expressed the somatic form of MARF1 (sMARF1) but not the oocyte form (oMARF1). sMARF1 was enriched in embryonic brains, and its expression level decreased as brain development progressed. Overexpression of sMARF1 in E12.5 neuronal progenitor cells promoted neuronal differentiation, whereas sMARF1 knockdown decreased neuronal progenitor differentiation in vitro. We also examined the function of sMARF1 in vivo using an in utero electroporation technique. Overexpression of sMARF1 increased neuronal differentiation, whereas knockdown of sMARF1 inhibited differentiation in vivo. Moreover, using an RNase domain deletion mutant of sMARF1, we showed that the RNase domain is required for the effects of sMARF1 on cortical neurogenesis in vitro. Our results further elucidate the mechanisms of post-transcriptional regulation of cortical neurogenesis by RBPs.

The newly identified migration inhibitory protein regulates the radial migration in the developing neocortex.

Neuronal migration is a crucial process in the organization of the developing cerebral cortex. Although a number of positive regulatory mechanisms of radial migration have been identified, negative cell-autonomous mechanisms have yet to be fully described. Here we report a newly identified Migration Inhibitory Protein (MINP, formerly known as 2900011O08Rik) that negatively regulates radial migration. MINP mRNA was specifically detected in the central and peripheral nervous system, and especially enriched in the cerebral cortex. MINP immunoreactivity co-localized with the neuronal marker Tuj1 and was detected in the cytoplasm of post-mitotic neurons. To elucidate the function of MINP in the developing brain, we performed in utero electroporation of MINP siRNA, MINP shRNA, or MINP-overexpressing vectors into mouse cortices and carried out in vivo migration assays. Whereas knockdown of MINP did not alter neuronal morphology, the radial migration was found accelerated by MINP knockdown, and reduced by MINP overexpression. This migration phenotype was also confirmed in vitro, indicating that MINP regulates neuronal migration in a cell-autonomous fashion. Furthermore, downregulation of MINP affected microtubule stability by interacting with tubulin that is a potential mechanism involved in the regulation of neuronal migration.