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Comments on KL Chow (1999) International C. elegans Meeting "Dosage of ram-5 gene is critical for sensory ray morphogenesis in C. elegans" (0)
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KL Chow (1999). Dosage of ram-5 gene is critical for sensory ray morphogenesis in C. elegans presented in International C. elegans Meeting. Unpublished information; cite only with author permission.
During normal tissue morphogenesis, cell adhesion and repellent molecules have to be expressed in the right level at the right place and right time. Deviation from the normal expression level may not be tolerated for tissue function nor animal vitality. In our study of ram-5 mutation, it was noticed that ram-5 mutant animals rescued by transformation constantly threw progeny with missing ray phenotype. A strong correlation of missing ray phenotype and the rescue activity was established. We speculate that there was a causative relationship between the ram-5 gene dosage and missing ray phenotype and thus employed both genetic and molecular approaches to test this notion. In the genetic analysis, two stable transgenic lines, KC61 and KC62 were used. These stable lines carried truncated and wild type ram-5 genes in a him-5 background. They showed 18% and 100% ray loss respectively. When heterozygous mutant transgenic worms were generated from them to lower the transgene dosage, the percentage of ray loss dropped to 0% and 53% respectively. A positive correlation between ray loss and transgene copy number was established in these lines by Southern analysis. This result argues that high level of ram-5 product might interfere the regular ray assembly process. When truncated ram-5 gene product was expressed in him-5 worms, both swollen ray tip and lumpy ray phenotype were observed. However, when the WT ram-5 gene was injected into the him-5 worm, it did not give these phenotypes. The results suggest that truncated RAM-5 protein can compete with the WT RAM-5 protein for its interacting components to form inactive complexes. By lowering of functional complex level, swollen ray tip or lumpy ray phenotype was resulted. Further over-expression of the truncated protein would lead to severe ray loss. We propose that ram gene products function as a multi-protein complex in a specific stoichiometry. Alteration of the ratio of these proteins will adversely affect the formation of functional complexes. As a result, ray cell assembly cannot take place and rays fail to attach to the cuticle to establish proper morphology.
