Mutations in C. elegans cuticular collagens can cause a variety of morphological defects, for example Dumpy, Roller and Long animal bodies. We have reported in this meeting two ram genes,
ram-2 and
ram-4, both of which encode cuticular collagens. Mutations of either one of them result in amorphous shape of the male tail sensory rays.
ram-1, as one of the component participating in ray morphogenesis, was mapped by 3- factor cross and deficiencies the right arm of chromosome I. Through a series of cosmid transformation experiments, we have successfully rescued
ram-1 mutant. Subsequently, we confirmed by deletion analysis of the rescuing cosmid that
ram-1 encodes a group 1 cuticular collagen.
bx34 allele generated by EMS mutagenesis is the only
ram-1 allele. The lesion of this allele was mapped to a single nucleotide change from G to A. This mutation led to an amino acid change from glycine (151) to glutamic acid at the beginning of the second Gly-X-Y repeat. As the same amino acid change was found in a number of temperature sensitive (ts) allele of
ram-2 and
ram-4 collagens, we were prompted to examine the temperature sensitivity of
ram-1(
bx34). Preliminary results show that
ram-1(
bx34) is indeed temperature sensitive. At 25oC, animals went into dauer state at an elevated frequency, and the animals appeared sterile with no eggs laid. The defect in oogenesis was found to the cause for this sterility. Moreover, temperature-dependent increase in the severity of swollen sensory rays was noticed. In contrast to the phenotype at 20oC, the rays appeared more swollen at 25oC but less swollen at 16oC. Additional phenotypes associated with
ram-1 are being characterized. For example, gonad migration defect has been noted. In male tail, sensory rays are simply composed of three types of cell, including the structure cells, neuronal cells and the hypodermis. Cell-specific markers have been used to reveal defects of the hypodermis and structural cells in
ram-1 mutant. Both of these cell types displayed a swollen morphology while neuronal cells remained normal. In addition, transgenic animals with the
ram-1 promoter tagged with gfp marker revealed
ram-1 expression to be in the posterior hypodermal syncytium. The detailed spatial and temporal expression pattern of this gene will be reported.