Two genes, dig-1 and mig-10, involved in nervous system development in C. elegans

Burket, Christopher T

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Two genes, dig-1 and mig-10, involved in nervous system development in C. elegans

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We are using genetic and molecular techniques to study a simple model organism, C. elegans, to determine the cues involved in the formation of the nervous system. Two molecules currently being studied in the laboratory play roles in the formation of the IL2 neurons, a class of sensory neurons in C. elegans. The first gene, dig-1, influences the sensory process or dendrite and is involved in adhesion as well as potentially providing directional information during development. The second gene, mig-10, influences the axon and may be involved in a cell signal cascade. Genetic screens of C. elegans using Ethyl methyl sulfonate (EMS) as a mutagen resulted in the isolation of mutants with defects in the IL2 sensory map; sensory processes followed aberrant paths, appearing to be defasciculated. Complementation tests showed that the mutations failed to complement n1321, a known allele of dig-1; thus, these new mutations were alleles of dig-1 (Ryder unpub. results). Several of these new alleles of dig-1, including nu336 and n1480, have been further studied to elucidate the role of this gene in sensory map formation. A dig-1 candidate gene was identified that encodes a protein that is a member of the immunoglobulin super-family (IgSF). The candidate gene is predicted to be a large gene, with a transcript of approximately 45Kb. The encoded protein contains three distinct regions and is similar to the hyalectan family of proteoglycans. N terminal region 1 contains immunoglobulin and fibronectin-like domains. Central region 2 is an area that is highly repeated with a potential to have GAGs attached. C-terminal region 3 contains domains associated with adhesion. Polymerase chain reaction (PCR) products from alleles nu336 and n1480 were amplified and sequenced from the candidate gene. The DNA lesion present in the candidate gene from both alleles fit the method for how that mutation was generated. The point mutation in allele nu336 removes a potential glycosylation site. The large re-arrangement in allele n1480 truncates the transcript, suggesting that the protein is also truncated. The sequencing results along with rescuing data (R. Proenca, personal communication) showed that the candidate gene for dig-1 was the gene of interest. Each of the alleles was further studied to determine how severe that allele was by looking at the neuronal process aspect and the brood size as well as displacement of the gonad. In general, alleles with severe defects in the nervous system also had severe gonad displacement, suggesting the gene functions similarly in the two tissues. To determine if the gene was expressed at the RNA level, reverse transcriptase polymerase chain reaction (RT-PCR) was used. Most of the RT-PCRs amplified a cDNA of the appropriate size that showed dig-1 was expressed at the RNA level. RT-PCR further suggested that all three regions were in one transcript as well as confirming part of the predicted exon structure to be correct. In addition, northern analysis showed the presence of a large transcript in wildtype worms as well as a smaller truncated transcript from allele n1480. To investigate developmental differences mixed stage of RNA and embryonic RNA from wildtype animals were compared using gene specific primers. The initial RT-PCR showed potential alternative splicing occurring at the 5? end of the gene during development. To examine expression at the protein level, two recombinant proteins from dig-1 were successfully made by cloning cDNA products from the 5?and 3? end of dig-1. The constructs were sequenced and shown to be in frame. The recombinant proteins (Ant1Con1 and Ant3Con3) were mass produced and sent to a commercial source for injection into pre-screened rabbits. Western analysis showed the presence of an antibody in the serum from two of the rabbits. These antibodies should prove useful in future determination of correctness of our models of DIG-1 function. IgSF members have been shown to have many roles in nervous system development. DIG-1 could act in either an attractive or a repellent role to position sensory processes during development. DIG-1 might also change its function over time; early in development DIG-1 could be adhesive and later become repellant as more sugars are added. The gene mig-10 is involved in sensory map formation. To localize MIG-10 expression, several transgenic animals were generated by injection of two constructs that should recombine in the worm to create a MIG-10::GFP fusion protein. Ten transgenic lines were generated and screened by PCR for the presence of the correct recombinant construct. If this construct makes functional, rescuing protein, the GFP expression should reflect the expression pattern of the MIG-10 protein.

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