DEVELOPMENTAL-CHANGES IN HETEROPLASMY LEVEL AND MITOCHONDRIAL GENE-EXPRESSION IN A DROSOPHILA-SUBOBSCURA MITOCHONDRIAL DELETION MUTANT

Eighty percent of DNA molecules are deleted in the mitochondrial popul ation of an adult mutant strain of D. subobscura. Both intact and dele ted genomes are autonomous monomers. The heteroplasmy level, which is lower in germ tissue, increases from the oocytes (60%) to the third la rval instar (83%), and is then maintained throughout the life of the f ly. The mtDNA/nuclear DNA ratio is on average two-times greater in the heteroplasmic strain than in the wild-type strain, irrespective of th e stage, but the cellular content of mitochondria is elevated only in the embryos and pupae of the mutant strain. The steady state concentra tions (SSCs) of the transcripts affected by the deletion are greatly r educed at the larval and adult stages, and less so at the pupal stage of the mutant strain compared with the wild-type. The SSCs of these tr anscripts are identical in the two strains at the embryonic stage. The Fusion transcript, indicating that the deleted genome is expressed, w as detected at all stages. The mechanisms involved in the changes in t he heteroplasmy level during the course of development and in its main tenance from the third larval instar onwards are discussed.