Elongated cilia on neural stem cells of the vertebrate hindbrain are required to prevent congenital hydrocephalus

Motile cilia are responsible for the movement of extracellular fluids. Loss of cilia motility in the ventricles of the central nervous system during embryogenesis results in congenital hydrocephalus (CH), a pathological accumulation of liquor.

Mutations in genes that regulate the fate of neural stem cells (NSC) have recently been associated with CH as well.

In the chicken hindbrain, NSC are found within the rhombomere boundaries (RhBs). Interestingly, in the frog Xenopus laevis, cells of the RhB bear elongated, probably motile cilia.

Based on these studies, the rhombencephalon of X. laevis was examined for the presence of stem cells. Sox2-positive NSC in RhBs were conserved in Xenopus, substantiating that RhBs function as NSC niches. To detect elongated cilia, the expression of foxj1, a master regulatory transcription factor for cilia elongation, was analyzed. foxj1 expression coincided with Sox2-positive RhB cells and the elongated cilia of these cells were significantly longer than those of the cells in the rhombomere proper.

To investigate the role of elongated cilia on the RhB stem cell niche, foxj1 loss of function (LOF) was performed using a foxj1 morpholino oligomer (MO) and the CRISPR/Cas9 system. In both cases, foxj1 LOF reduced cilia length and induced ventricle dilation, a CH-specific phenotype. foxj1 LOF also altered the typical stem cell niche morphology.

Together, these data strongly suggest that elongated cilia on NSC are required for stem cell physiology and that cilia length-regulated maintenance of neural stem cell niches in the hindbrain of vertebrates is crucial to prevent congenital hydrocephalus.