DEVELOPMENTAL GENETIC-ANALYSIS OF TROPONIN-T MUTATIONS IN STRIATED AND NONSTRIATED MUSCLE-CELLS OF CAENORHABDITIS-ELEGANS

We have been investigating a set of genes, collectively called mups, t hat are essential to striated body wall muscle cell positioning in Cae norhabditis elegans. Here we report our detailed characterization of t he mup-2 locus, which encodes troponin T (TnT), Mutants for a heat-sen sitive allele, called mup-2(e2346ts), and for a putative null, called mup-2(up1), are defective for embryonic body wall muscle cell contract ion, sarcomere organization, and cell positioning, Characterizations o f the beat-sensitive allele demonstrate that mutants are also defectiv e for regulated muscle contraction in larval and adult body wall muscl e, defective for function of the nonstriated oviduct myoepithelial she ath, and defective for epidermal morphogenesis, We cloned the mup-2 lo cus and its corresponding cDNA. The cDNA encodes a predicted 405-amino acid protein homologous to vertebrate and invertebrate TnT and includ es an invertebrate-specific COOH-terminal tail. The mup-2 mutations li e within these cDNA sequences: mup-2(up1) is a termination codon near NH2 terminus (Glu94) and mup-2(e2346ts) is a termination codon in the COOH-terminal invertebrate-specific tail (Trp34). TnT is a muscle cont ractile protein that, in association with the thin filament proteins t ropomyosin, troponin I and troponin C, regulates myosin-actin interact ion in response to a rise in intracellular Ca2+, Our findings demonstr ate multiple essential functions for TnT and provide a basis to invest igate the in vivo functions and protein interactions of TnT in striate d and nonstriated muscles.