A Genetic Screen for Mutations That Affect Cranial Nerve Development in the Mouse

Abstract

Cranial motor and sensory nerves arise stereotypically in the embryonic hindbrain, act as sensitive indicators of general and regionspecific neuronal development, and are directly or indirectly affected in many human disorders, particularly craniofacial syndromes. The molecular genetic hierarchies that regulate cranial nerve development are mostly unknown. Here, we describe the first mouse genetic screen that has used direct immunohistochemical visualization methods to systematically identify genetic loci required for cranial nerve development. After screening 40 pedigrees, we recovered seven new neurodevelopmental mutations. Two mutations model human genetic syndromes. Mutation 7-1 causes facial nerve anomalies and a reduced lower jaw, and is located in a region of conserved synteny with an interval associated with the micrognathia and mental retardation of human cri-du-chat syndrome. Mutation 22-1 is in the Pax3 gene and, thus, models human Waardenburg syndrome. Three mutations cause global axon guidance deficits: one interferes with initial motor axon extension from the neural tube, another causes overall axon defasciculation, and the third affects general choice point selection. Another two mutations affect the oculomotor nerve specifically. Oculomotor nerve development, which is disrupted by six mutations, appears particularly sensitive to genetic perturbations. Phenotypic comparisons of these mutants identifies a "transition zone" that oculomotor axons enter after initial outgrowth and in which new factors govern additional progress. The number of interesting neurodevelopmental mutants revealed by this small-scale screen underscores the promise of similar focused genetic screens to contribute significantly to our understanding of cranial nerve development and human craniofacial syndromes.

Olfactomedin-2 mediates development of the anterior central nervous system and head structures in zebrafish

“…A genetic screen for cranial nerve mutations in mouse indicated that Pax3 is required for growth of the facial nerve, as well as formation of the lower jaw (Mar et al, 2005). While these Pax3 phenotypes resemble some of the OM2 phenotypes in our current studies, it is clear that the OM2 phenotypes suggest a more complex regulation of branchiomotor axon growth than has been described for Pax3 in mouse.…”

Focusing Forward Genetics: A Tripartite ENU Screen for Neurodevelopmental Mutations in the Mouse

“…Another reporter screen assaying axon guidance recovered 7 mutants from 57 lines (12%) with 6 affecting the reporter allele expression (Dwyer et al 2011). A immunohistochemical approach to studying cranial nerve development yielded seven mutants from 40 pedigrees [18% (Mar et al 2005)]. …”

A Forward Genetic Screen in Mice Identifies Sema3AK108N, which Binds to Neuropilin-1 but Cannot Signal

“…To identify novel factors essential for the development of the peripheral nervous system (PNS), we have developed a three-generation, forward genetic screen for recessive mutations affecting the patterning and guidance of PNS axonal projections (Mar et al, 2005). First, 8- to 10-week-old, male, C57BL/6 (BL6) mice (F1) were intraperitoneally injected with 300mg of ENU to randomly induce point mutations throughout the mouse genome.…”