Zebrafish Minichromosome Maintenance Protein 5 Gene Regulates the Development and Migration of Facial Motor Neurons via Fibroblast Growth Factor Signaling

Abstract

Minichromosome maintenance protein 5 (MCM5), a member of the microchromosomal maintenance protein family, plays an important role in the initiation and extension of DNA replication. However, its role in neural development in zebrafish remains unclear. Here, we used morpholino (MO) and CRISPR/Cas9 to knock down <i>mcm5</i> and investigated the developmental features of facial motor neurons (FMNs) in the hindbrain of zebrafish. We found that knockdown of <i>mcm5</i> using <i>mcm5</i> MO resulted in a small head, small eyes, and a blurred midbrain-hindbrain boundary, while MO injection of <i>mcm5</i> led to decrease in FMNs and their migration disorder. However, the mutant of <i>mcm5</i> only resulted in the migration defect of FMNs rather than quantity change. We further investigated the underlying mechanism of <i>mcm5</i> in the development of hindbrain using in situ hybridization (ISH) and <i>fgfr1a</i> mRNA co-injected with <i>mcm5</i> MO. Results from ISH showed that the fibroblast growth factor (FGF) signaling pathway was changed when the MCM5 function was lost, with the decrease in <i>fgfr1a</i> and the increase in <i>fgf8</i>, while that of <i>pea3</i> had opposite trend. FMN development defects were rescued by <i>fgfr1a</i> mRNA co-injected with <i>mcm5</i> MO. Our results demonstrated that FGF signaling pathway is required for FMN development in zebrafish. Specifically, <i>mcm5</i> regulates FMN development during zebrafish growing.