Abstract
During mammalian development, establishing functional neural networks in stratified tissues of the mammalian central nervous system depends upon the proper migration and positioning of neurons, a process known as lamination. In particular, the pseudostratified neuroepithelia of the retina and cerebrocortical ventricular zones provide a platform for progenitor cell proliferation and migration. Lamination defects in these tissues lead to mispositioned neurons, disrupted neuronal connections, and abnormal function. The molecular mechanisms necessary for proper lamination in these tissues are incompletely understood. Here, we identified a nonsense mutation in the Eml1 gene in a novel murine model, tvrm360, displaying subcortical heterotopia, hydrocephalus and disorganization of retinal architecture. In the retina, Eml1 disruption caused abnormal positioning of photoreceptor cell nuclei early in development. Upon maturation, these ectopic photoreceptors possessed cilia and formed synapses but failed to produce robust outer segments, implying a late defect in photoreceptor differentiation secondary to mislocalization. In addition, abnormal positioning of Müller cell bodies and bipolar cells was evident throughout the inner neuroblastic layer. Basal displacement of mitotic nuclei in the retinal neuroepithelium was observed in tvrm360 mice at postnatal day 0. The abnormal positioning of retinal progenitor cells at birth and ectopic presence of photoreceptors and secondary neurons upon maturation suggest that EML1 functions early in eye development and is crucial for proper retinal lamination during cellular proliferation and development.
Highlights
During mammalian development, establishing functional neural networks in stratified tissues of the mammalian central nervous system depends upon the proper migration and positioning of neurons, a process known as lamination
We describe a novel allele of murine Eml[1], tvrm[360], bearing a nonsense mutation generated by chemical mutagenesis in the Translational Vision Research Models (TVRM) program at The Jackson Laboratory[18,19]
The TVRM program at The Jackson Laboratory identified an ENU-derived mouse model, tvrm[64], which presented with a grainy appearing fundus that harbored a mutation in the retinitis pigmentosa 1 gene (Rp1)[18], designated, C57BL/6J-Rp1tvrm64/PjnMmjax (MMRRC 043579)
Summary
During mammalian development, establishing functional neural networks in stratified tissues of the mammalian central nervous system depends upon the proper migration and positioning of neurons, a process known as lamination. Disruptions in retinal architecture are observed early in development and likely due to the improper positioning of mitotic apical progenitor nuclei during the cell cycle. Comparison of quantitative RT–PCR levels of Eml1tvrm[360] and WT control mRNA revealed a significant 2.5-fold reduction of Eml[1] mRNA in tvrm[360] whole eyes compared to WT mice (relative normalized expression; two tailed t-test; p < 0.0001) (Fig. 1b).
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