Mutants forDrosophilaIsocitrate Dehydrogenase 3b Are Defective in Mitochondrial Function and Larval Cell Death

Abstract

The death of larval salivary gland cells during metamorphosis in Drosophila melanogaster has been a key system for studying steroid controlled programmed cell death. This death is induced by a pulse of the steroid hormone ecdysone that takes place at the end of the prepupal period. For many years, it has been thought that the ecdysone direct response gene Eip93F (E93) plays a critical role in initiating salivary gland cell death. This conclusion was based largely on the finding that the three “type” alleles of E93 cause a near-complete block in salivary gland cell death. Here, we show that these three mutations are in fact allelic to Idh3b, a nearby gene that encodes the β subunit of isocitrate dehydrogenase 3, a mitochondrial enzyme of the tricarboxylic acid (TCA) cycle. The strongest of the Idh3b alleles appears to cause a near-complete block in oxidative phosphorylation, as mitochondria are depolarized in mutant larvae, and development arrests early during cleavage in embryos from homozygous-mutant germline mothers. Idh3b-mutant larval salivary gland cells fail to undergo mitochondrial fragmentation, which normally precedes the death of these cells, and do not initiate autophagy, an early step in the cell death program. These observations suggest a close relationship between the TCA cycle and the initiation of larval cell death. In normal development, tagged Idh3b is released from salivary gland mitochondria during their fragmentation, suggesting that Idh3b may be an apoptogenic factor that functions much like released cytochrome c in mammalian cells.

Mitochondrial fission, integrity and completion of mitophagy require separable functions of Vps13D inDrosophilaneurons

“…The endogenous matrix enzyme pyruvate dehydrogenase E1ɑ (PDH) was also strongly reduced in the PolyUb+ objects (Figure 1, Supplement 2A&B). In addition, exogenous expression of an epitope tagged version of the fulllength matrix enzyme isocitrate dehydrogenase 3β (UAS-Idh3b-HA) (Duncan, Kiefel, and Duncan 2017) labels mitochondria but failed to label the PolyUb+ objects (Figure 1, Supplement 2C). From these observations we therefore infer that the PolyUb+/Ref 2p+/ATP5A+/mitoGFP-objects are derived from mitochondria that have somehow lost soluble matrix components.…”

Ecdysone controlled cell and tissue deletion

“…The E93 gene was previously identified as a primary response gene, encoding a large DNA binding protein that influence the transcription of secondary response genes in both salivary glands and midgut [69]. However, a more recent study demonstrated that mutant alleles of E93 used in earlier studies were in fact alleles of a nearby gene Isocitrate dehydrogenase 3b (Idh3b), which encodes a key enzyme of the citric acid cycle in the mitochondria [70]. Further work will be necessary to fully resolve the controversy as to whether E93 has any role in cell death.…”

Lactate dehydrogenase and glycerol-3-phosphate dehydrogenase cooperatively regulate growth and carbohydrate metabolism during Drosophila melanogaster larval development

“…In contrast, larvae that harbor mutations in either the mitochondrial pyruvate carrier or malate dehydrogenase 2 are able to complete larval development with relatively mild phenotypes (Bricker et al, 2012;Wang et al, 2010). Similarly, larvae that lack zygotic isocitrate dehydrogenase 3b exhibit developmental delays but are able to survive until metamorphosis (Duncan et al, 2017). These observations suggest that, although glycolysis and oxidative phosphorylation are necessary for development, larvae do not require a fully functional TCA cycle.…”