Modeling microcephaly with cerebral organoids reveals a WDR62-CEP170-KIF2A pathway promoting cilium disassembly in neural progenitors.

Primary microcephaly is caused by mutations in genes encoding centrosomal proteins including WDR62 and KIF2A. However, mechanisms underlying human microcephaly remain elusive. By creating mutant mice and human cerebral organoids, here we found that WDR62 deletion resulted in a reduction in the size of mouse brains and organoids due to the disruption of neural progenitor cells (NPCs), including outer radial glia (oRG). WDR62 ablation led to retarded cilium disassembly, long cilium, and delayed cell cycle progression leading to decreased proliferation and premature differentiation of NPCs. Mechanistically, WDR62 interacts with and promotes CEP170's localization to the basal body of primary cilium, where CEP170 recruits microtubule-depolymerizing factor KIF2A to disassemble cilium. WDR62 depletion reduced KIF2A's basal body localization, and enhanced KIF2A expression partially rescued deficits in cilium length and NPC proliferation. Thus, modeling microcephaly with cerebral organoids and mice reveals a WDR62-CEP170-KIF2A pathway promoting cilium disassembly, disruption of which contributes to microcephaly.

Zika virus infection disrupts neurovascular development and results in postnatal microcephaly with brain damage.

Zika virus (ZIKV) infection of pregnant women can result in fetal brain abnormalities. It has been established that ZIKV disrupts neural progenitor cells (NPCs) and leads to embryonic microcephaly. However, the fate of other cell types in the developing brain and their contributions to ZIKV-associated brain abnormalities remain largely unknown. Using intracerebral inoculation of embryonic mouse brains, we found that ZIKV infection leads to postnatal growth restriction including microcephaly. In addition to cell cycle arrest and apoptosis of NPCs, ZIKV infection causes massive neuronal death and axonal rarefaction, which phenocopy fetal brain abnormalities in humans. Importantly, ZIKV infection leads to abnormal vascular density and diameter in the developing brain, resulting in a leaky blood-brain barrier (BBB). Massive neuronal death and BBB leakage indicate brain damage, which is further supported by extensive microglial activation and astrogliosis in virally infected brains. Global gene analyses reveal dysregulation of genes associated with immune responses in virus-infected brains. Thus, our data suggest that ZIKV triggers a strong immune response and disrupts neurovascular development, resulting in postnatal microcephaly with extensive brain damage.

MiR-302/367 regulate neural progenitor proliferation, differentiation timing, and survival in neurulation.

How neural progenitor cell (NPC) behaviors are temporally controlled in early developing embryos remains undefined. The in vivo functions of microRNAs (miRNAs) in early mammalian development remain largely unknown. Mir-302/367 is a miRNA cluster that encodes miR-367 and four miR-302 members (miR302a-d). We show that miR-302b is highly expressed in early neuroepithelium and its expression decline as development progresses. We generated a mir-302/367 knockout mouse model and found that deletion of mir-302/367 results in an early embryonic lethality and open neural tube defect (NTD). NPCs exhibit enhanced proliferation, precocious differentiation, and decreased cell survival in mutant embryos. Furthermore, we identified Fgf15, Cyclin D1, and D2 as direct targets of miR-302 in NPCs in vivo, and their expression is enhanced in mutant NPCs. Ectopic expression of Cyclin D1 and D2 increases NPC proliferation, while FGF19 (human ortholog of Fgf15) overexpression leads to an increase of NPC differentiation. Thus, these findings reveal essential roles of miR-302/367 in orchestrating gene expression and NPC behaviors in neurulation; they also point to miRNAs as critical genetic components associated with neural tube formation.

Lin28 promotes the proliferative capacity of neural progenitor cells in brain development.

Neural progenitor cells (NPCs) have distinct proliferation capacities at different stages of brain development. Lin28 is an RNA-binding protein with two homologs in mice: Lin28a and Lin28b. Here we show that Lin28a/b are enriched in early NPCs and their expression declines during neural differentiation. Lin28a single-knockout mice show reduced NPC proliferation, enhanced cell cycle exit and a smaller brain, whereas mice lacking both Lin28a alleles and one Lin28b allele display similar but more severe phenotypes. Ectopic expression of Lin28a in mice results in increased NPC proliferation, NPC numbers and brain size. Mechanistically, Lin28a physically and functionally interacts with Imp1 (Igf2bp1) and regulates Igf2-mTOR signaling. The function of Lin28a/b in NPCs could be attributed, at least in part, to the regulation of their mRNA targets that encode Igf1r and Hmga2. Thus, Lin28a and Lin28b have overlapping functions in temporally regulating NPC proliferation during early brain development.