BIOCHEMICAL-CHARACTERIZATION AND LOCALIZATION OF TRANSGLUTAMINASE IN WILD-TYPE AND CELL-DEATH MUTANTS OF THE NEMATODE CAENORHABDITIS-ELEGANS

Transglutaminase activity was characterized in extracts of the nematod e Caenorhabditis elegans using a microtiter plate method, and found to be Ca2+-dependent, optimal at pH 8.0, and to be inhibited by EGTA, am monia, iodoacetamide and GTP. Monoclonal and polyclonal antibodies rai sed against human tissue transglutaminase also inhibited the activity and detected a 61-kDa protein from the worm lysate. Constitutive expre ssion of the enzyme in the wild-type intestinal cells was revealed by immunohistochemistry. Potential protein substrates for the enzyme were found in worm lysates using a biotin-labelled amine substrate. There is a basal level of protein-bound epsilon(gamma-glutamyl)lysine cross- links, characteristic of transglutaminase activity, formed in situ in adult wild-type animals. Developmental studies have revealed that the enzyme activity is highest in adult animals, and relatively higher in L1 larvae than in other larval stages. As compared to wild types, lowe r transglutaminase activity has been measured in lysates of ced-3, ced -4 and ced-9 mutants. Cross-link levels were also low in ced-4 and ced -9 mutants. By contrast, the crosslink content was high in several pha gocytosis mutants. The highest concentration was found in the ced-5; c ed-7 double phagocytosis mutants which carry an extra number of dead c ells during their lifespan. In accordance with this finding, several t ransglutaminase-immunopositive cells were found in both the embryos an d in the head of these double phagocytosis mutants. The results sugges t that a transglutaminase is involved in, or related to, the death pro gram of cells in C. elegans and the expression and crosslinking activi ty of the enzyme may be perturbed in some ced mutants.