To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.07.019 Byline: Christopher T. Burket (a), Christina E. Higgins (a), Lynn C. Hull (a), Patricia M. Berninsone (b), Elizabeth F. Ryder (a) Keywords: Adhesion; Fasciculation; Neuron; Development; Immunoglobulin superfamily; Migration; Proteoglycan; Caenorhabditis elegans Abstract: The adhesion of growing neurites into appropriate bundles or fascicles is important for the development of correct synaptic connectivity in the nervous system. We describe fasciculation defects of animals with mutations in the C. elegans gene dig-1 and show that dig-1 encodes a giant molecule (13,100 amino acids) of the immunoglobulin superfamily. Five new alleles of dig-1 were isolated in a screen for mutations affecting the morphology or function of several classes of head sensory neurons. Mutants showed process defasciculation of several classes of neurons. Analysis of a temperature-sensitive allele revealed that dig-1 is required during embryogenesis for normal process fasciculation of one class of head sensory neuron. Partial sequencing of two alleles, RNA interference (RNAi) and rescuing experiments showed that dig-1 encodes a giant molecule of the immunoglobulin superfamily. DIG-1 protein contains many domains associated with adhesion, is likely secreted, and has some features of proteoglycans. dig-1 mutants were originally isolated due to their displaced gonads [Thomas, J.H., Stern, M.J., Horvitz, H.R., 1990. Cell interactions coordinate the development of the C. elegans egg-laying system. Cell 62, 1041-52]; thus, dig-1 alleles were also characterized for their effects on gonad placement. Mutant phenotypes suggest that DIG-1 may mediate cell movement as well as process fasciculation and that different regions of the protein may mediate these functions. Author Affiliation: (a) Worcester Polytechnic Institute, Department of Biology and Biotechnology, 100 Institute Road, Worcester, MA 01609, USA (b) Boston University Goldman School of Dental Medicine, Department of Molecular and Cell Biology, Boston Medical Center, 715 Albany Street Evans-437, Boston, MA 02118, USA Article History: Received 13 March 2006; Revised 17 July 2006; Accepted 18 July 2006