IMP-L3, A 20-HYDROXYECDYSONE-RESPONSIVE GENE ENCODES DROSOPHILA LACTATE-DEHYDROGENASE - STRUCTURAL CHARACTERIZATION AND DEVELOPMENTAL STUDIES

IMP-L3, a gene isolated as a potential mediator of imaginal disc morph ogenesis in Drosophila melanogaster, encodes lactate dehydrogenase (LD H). The predicted amino acid sequence of IMP-L3 is 58-61% identical to those of human IDHs. In cultured imaginal discs, IMP-L3 transcript le vels and LDH enzyme activity increase in response to the steroid hormo ne, 20-hydroxyecdysone. In embryos, IMP-L3 transcript and LDH activity appear in developing somatic muscles by late stage 13, well before th e onset of muscular contraction. High levels of transcript and LDH act ivity persist throughout embryogenesis and throughout larval developme nt. The gene has been localized by in situ hybridization and deficienc y mapping to 65A7-65B2 on the third chromosome. LDH activity is reduce d to similar to 50% of wild type in animals heterozygous for a deficie ncy that removes the 65A-B region. Embryos deficient for the 65A-B reg ion lock LDH activity. We conclude that IMP-L3 is the only gene that e ncodes LDH in Drosophila. (C) 1997 Wiley-Liss, Inc.