[show abstract][hide abstract] ABSTRACT: Cadherins are one of the major families of adhesion molecules with diverse functions during embryonic development. Fat-like cadherins form an evolutionarily conserved subgroup characterized by an unusually large number of cadherin repeats in the extracellular domain. Here we describe the role of the Fat-like cadherin CDH-4 in Caenorhabditis elegans development. Cdh-4 mutants are characterized by hypodermal defects leading to incompletely penetrant embryonic or larval lethality with variable morphogenetic defects. Independently of the morphogenetic defects cdh-4 mutant animals also exhibit fasciculation defects in the ventral and dorsal cord, the major longitudinal axon tracts, as well as migration defects of the Q neuroblasts. In addition CDH-4 is essential for establishing and maintaining the attachment between the buccal cavity and the pharynx. Cdh-4 is expressed widely in most affected cells and tissues during embryogenesis suggesting that CDH-4 functions to ensure that proper cell contacts are made and maintained during development.
[show abstract][hide abstract] ABSTRACT: The microtubule-associated tau proteins become functionally and structurally altered in Alzheimer's disease (AD). To analyze tau modification and its role in a non-vertebrate animal model, we produced transgenic Caenorhabditis elegans strains with a panneuronal expression of human tau and a pseudohyperphosphorylated (PHP) tau construct that mimics AD-relevant tau modification. We show that human tau in C. elegans becomes highly phosphorylated and exhibits conformational changes similar to PHP tau and human PHF tau. Both, wt tau and PHP tau induced a progressive age-dependent development of a phenotype of uncoordinated locomotion (unc) in the absence of neuronal degeneration. However, only PHP tau induced a defective pattern of motor neuron development as indicated by the presence of gaps in the dorsal cord, commissures on the wrong side and local broadening of axons. The data indicate that C. elegans is capable of highly phosphorylating human tau to an AD-like state whereas only stable disease-like tau modification induce developmental defects suggesting a specific interference of pathologic tau with intracellular mechanisms of axonal outgrowth and pathfinding.
Neurobiology of aging 07/2007; 30(1):22-33. · 5.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ventral cord in C. elegans is the major longitudinal axon tract containing essential components of the motor circuit. In genetic screens using transgenic animals expressing neuron specific GFP reporters, we identified twelve genes required for the correct outgrowth of interneuron axons of the motor circuit. In mutant animals, axons fail to navigate correctly towards the ventral cord or fail to fasciculate correctly within the ventral cord. Several of those mutants define previously uncharacterized genes. Two of the genes, ast-4 and ast-7, are involved in the generation of left-right asymmetry of the two ventral cord axon tracts. Three other genes specifically affect pioneer-follower relationships between early and late outgrowing axons, controlling either differentiation of a pioneer neuron (lin-11) or the ability of axons to follow a pioneer (ast-2, unc-130). Navigation of the ventral cord pioneer neuron AVG itself is defective in ast-4, ast-6 and unc-130 mutants. Correlation of these defects with navigation defects in different classes of follower axons revealed a true pioneer role for AVG in the guidance of interneurons in the ventral cord. Taken together, these genes provide a basis to address different aspects of axon navigation within the ventral cord of C. elegans.
[show abstract][hide abstract] ABSTRACT: The nervous system consists of diverse subtypes of neurons, whose identities must be specified during development. One important aspect of the differentiation program of neurons is the expression of the appropriate set of genes controlling axon pathway selection. We have identified a novel Znfinger/homeodomain containing transcription factor, zag-1, required for particular aspects of axonal pathfinding. In zag-1 mutants, motorneuron commissures either branch prematurely or fail to branch at the correct point. Ventral cord interneurons show defects in the guidance towards the ventral cord and also in the ventral cord. Several neurons misexpress differentiation markers, including glutamate receptor subunits and chemosensory receptors. zag-1 is expressed transiently in embryonic and postembryonic neurons during differentiation as well as in some mesodermal tissues. Null mutants of zag-1 are unable to swallow food and die as L1 larvae with a starved appearance, indicating that zag-1 has an additional role in pharynx development. The vertebrate homolog, deltaEF1, is highly conserved and known to act as transcriptional repressor in various tissues. Our data indicate that zag-1 also acts as transcriptional repressor controlling important aspects of terminal differentiation of neurons.
Development 09/2003; 130(16):3795-805. · 6.21 Impact Factor