An ankyrin-related gene (unc-44) is necessary for proper axonal guidance in Caenorhabditis elegans.

Abstract

Abstract. Caenorhabditis elegans unc-44 mutations result in aberrant axon guidance and fasciculation with inappropriate partners. The unc-44 gene was cloned by transposon tagging, and verified by genetic and molecular analyses of six transposon-induced alleles and their revertants. Nucleotide sequence analyses demonstrated that unc-44 encodes a series of putative ankyrin-related proteins, including AO49 ankyrin (1815 aa, 198.8 kD), AO66 ankyrin (1867 aa, 204 kD), and AOI3 ankyrin (x<4700 aa, ~<517 kD). In addition to the major set of •6 kb alternatively spliced transcripts, minor transcripts were observed at -,3, 5, 7, and 14 kb. Evidence is provided that mutations in the *14-kb AO13 ankyrin transcript are responsible for the neuronal defects. These molecular studies provide the first evidence that ankyrin-related molecules are required for axonal guidance.TrIOUGH the molecular basis of neural development has been the object of intense study in recent years, the detailed mechanisms of axon guidance remain unknown (for general reviews see Dodd and Jessell, 1988;Jessell, 1988;Takeichi, 1988;Sanes, 1989;Takeichi, 1991;Rathjen et al., 1992;Gumbiner, 1993; for C. elegans reviews see Hedgecock et al., 1987;Wadsworth and Hedgecock, 1992).Mutations in the unc-44 gene affect the direction of axonal outgrowth for many axons (Hedgecock et al., 1985;Siddiqui, 1990;Siddiqui and Culotti, 1991;Mclntire et al., 1992), including the postdeirid (PDE) ~ axon, which normally extends from the postdeirid sensillum on the lateral surface of the nematode to the ventral nerve cord (White et al., 1986). In unc-44 mutants, the initial direction of PDE axon outgrowth along the basement membrane is apparently random, and the misdirected PDE axon fasciculates with inappropriate partners (Hedgecock et al., 1985 The discovery that the C. elegans unc-6 gene encodes a laminin B chain-related product provided evidence that directed axonal outgrowth and cell migration require interactions with the extracellular matrix (Hedgecock et al., 1990), and that these interactions use laminin or related proteins in both invertebrates and vertebrates (Jessell, 1988;Sanes, 1989;Hedgecock et al., 1990;Serafini et al., 1994). The product of the unc-5 gene, which affects dorsalward cell migrations and axon outgrowth, has been proposed to be a cell surface protein which may interact with the extracellular matrix (Leung-Hagesteijn et al., 1992). Thus, it was likely that other mutations affecting axonal outgrowth and guidance were defects in cytoskeletal or extracellular matrix structures. The actin/a-actinin framework of growth cone filopodia or the spectrin/ankyrin network underlying the cytoplasmic surface of the plasma membrane could be the targets for mutations affecting axon outgrowth and growth cone adhesion. In this study, we have discovered that the wild-type unc-44 gene, which is required for proper axonal guidance, encodes a series of putative ankyrin-related proteins.Ankyrin (or bands 2.1 and 2.2) has been most thoroughly studied in erythrocyte "ghost...

unc-44 Ankyrin and stn-2 γ-Syntrophin Regulate sax-7 L1CAM Function in Maintaining Neuronal Positioning in Caenorhabditis elegans

“…The FB site is far apart from the AB and PB motifs, making it possible that FERM proteins can bind SAX-7 simultaneously with UNC-44 or STN-2. In contrast, the closeness of the AB and PB motifs (17 amino acids apart) and the large size of the conventional ankyrin isoform (220-240 kDa) (Otsuka et al 1995) makes it more unlikely that both proteins bind SAX-7 simultaneously. If this hypothesis holds, then phosphorylation of the AB motif may be important for STN-2 to interact with SAX-7.…”

“…Animals homozygous for different unc-44 alleles exhibit pleiotropic phenotypes, which is not surprising as unc-44 is broadly expressed in multiple tissues (Chen et al 2001). These phenotypes include a Dpy (Dumpy, short and fat) body that is uncoordinated and barely moves as well as multiple neuronal defects such as neuron and axon migration defects (Hedgecock et al 1985;Otsuka et al 1995), thus making it a challenge to ascertain if unc-44 phenotypes include defects in maintaining neuronal positioning. To circumvent this difficulty, we performed genetic experiments using sensitized sax-7 and unc-44 mutant backgrounds.…”

“…To test this hypothesis, we examined UNC-44 accumulation in sax-7(eq1) animals using an anti-UNC-44 antibody (Otsuka et al 1995). No detectable difference from wild-type animals was seen ( Figure 4), thus suggesting that SAX-7 is not likely to regulate UNC-44 localization.…”

“…unc-44 genetically interacts with sax-7 to maintain neuronal positioning: C. elegans contains a single ankyrin gene, unc-44 (Otsuka et al 1995). To test the hypothesis that ankyrin interaction is important for SAX-7 function, we examined unc-44 mutant animals for displaced neurons.…”

The death domain motif found in Fas (Apo‐1) and TNF receptor is present in proteins involved in apoptosis and axonal guidance

“…Unc-5 [2 I] and Unc-44 [22]. an ankyrin-related gene product, It is noteworthy that cytoskeletal rearrangement is an early event of apoptosis.…”