Roles for the stem cell factor LIN41 in ependymal cell function and hydrocephalus

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Hydrocephalus can be defined as excessive accumulation of cerebrospinal fluid (CSF) in the brain ventricles. The condition can be either congenital or acquired and is caused by excess CSF production, reduced absorption or impaired fluid flow. With an incidence of about 2 per 1000 children at birth, it is well established that pediatric hydrocephalus has a significant heritable component. Mutations in currently known risk genes most likely account for only a portion of nonsyndromic developmental hydrocephalus. Syndromic forms of hydrocephalus are frequently associated with neural tube defects (NTDs) or ciliopathies such as Bardet-Biedl Syndrome. Studies in the mouse have revealed significant overlap in the genetic pathways required for morphogenesis of the neural tube and the ventricular system. Moreover, disruption of several pathways associated with NTDs, including planar cell polarity, can lead to developmental hydrocephalus in the absence of closure defects. Ciliopathies can affect either primary or motile cilia. Whereas the primary cilium is thought to coordinate growth and morphogenic signals, motile cilia contribute to CSF flow. Defects in either primary or motile cilia can lead to hydrocephalus. We have been studying the molecular functions and developmental roles of the Lin41 gene product. Null mutations of Lin41 in the mouse are embryonic lethal and cause failure of neural tube closure. The NTD phenotype has been attributed to premature neuronal differentiation, however the results of targeted deletion in neural progenitors have not yet been reported. To better understand Lin41 function in embryonic and postnatal cortical development, we have generated a conditional mouse mutant and used Emx1-Cre to specifically delete Lin41 in radial glia of the dorsal telencephalon. Using this model, we have not observed any deleterious effect on cortical neurogenesis per se. However, more than 25% of the affected mutants develop postnatal hydrocephalus. This result is consistent with our previous finding that Lin41 is specifically expressed in ependymal cells of the postnatal brain. In our preliminary data, we present experimental evidence that LIN41 is required for functional maturation of ependymal cells. We also show that deletion of Lin41 in cultured ependymal cells leads to a reduction in cilia length and beating frequency. This research proposal is designed to more fully characterize the hydrocephalus phenotype and the defects in ependymal ciliogenesis and function. Our experiments will make use of our conditional mutant for in vivo studies coupled to studies at the molecular level using a primary ependymal cell culture model. Mechanistically, we will test the relevance of several proposed functions for LIN41 as RNA binding protein and as E3 ubiquitin ligase for ependymal cell differentiation. Together, these model systems and our experimental program will allow us to explore new pathways and pathomechanisms for developmental hydrocephalus.