Mutants of Dictyostelium discoideum with defects in the regulation of discoidin I expression.

Discoidins are proteins, coded by a multigene family, which are regulated by extracellular factors during growth and development of Dictyostelium discoideum. In this paper we describe the isolation and characterization of mutants which misregulate the expression of the discoidin I subgroup. One mutant (III29) induces discoidin I during late growth phase but does not express it during development. Another mutant (VI41) has significantly reduced discoidin levels under all conditions tested, while two mutants (VI88 and X27) express discoidin early during exponential growth and accumulate more discoidin protein than the wild type. The defects are due to abnormal regulation of transcription in all mutants except VI41. Experiments in which mutants and wild type are mixed suggest that the mutant phenotypes are not caused by changes in extracellular signals. Since multiple members of the multigene family are affected, it can be concluded that the intracellular signals regulating discoidin expression are changed rather than the genes themselves. The mutants are thus likely to have defects in the reception or intracellular processing of environmental signals.