THE CONGESTED-LIKE TRACHEAS GENE OF DROSOPHILA-MELANOGASTER ENCODES AMEMBER OF THE MITOCHONDRIAL CARRIER FAMILY REQUIRED FOR GAS-FILLING OF THE TRACHEAL SYSTEM AND EXPANSION OF THE WINGS AFTER ECLOSION

A recessive semi-lethal mutation resulting from the insertion of a P-l acW transposon at the cytological position 23A. on the polytene chromo somes of Drosophila melanogaster was found to affect the unfolding and expansion of the wings resulting in a loss of venation and a marked d ecrease in their size. Lethality was polyphasic with numerous animals dying during early larval development and displaying apparently collap sed tracheal trees. The gene was therefore designated as congested-lik e tracheae, or colt. The colt mutation resulted from the insertion of a P-lacW transposon within the coding region of a 1.4-kb transcript. W ild-type function was restored by inducing a precise excision of the P -lacW transposon, while a deletion of the colt locus, produced by impr ecise excision of the P element, showed a phenotype similar to that of the original P insert. The colt gene consists of a single exon and en codes a protein of 306 amino acids made of three tandem repeats, each characterized by two predicted transmembrane segments and a loop domai n. The COLT protein shares extensive homology with proteins in the mit ochondrial carrier family and particularly with the DIF-1 protein of C aenorhabditis elegans, which has been shown to be maternally required for embryonic tissue differentiation. Our analysis revealed that zygot ic colt function is dispensable for normal embryonic morphogenesis but is required for gas-filling of the tracheal system at hatching time o f the embryo and for normal epithelial morphogenesis of the wings.