The EDTP gene was first found in the flesh fly as a substrate of cathepsin L with tyrosine phosphatase activity. Later it turned out that its human homolog MTMR14 (also known as hJumpy or MIP) dephosphorylates the lipids PI(3)P and PI(3,5)P2 rather than proteins, and is linked to myotubular myopathies. In Drosophila, EDTP is expressed in the ovaries, embryos, and fat body, and its null alleles are lethal. However, the role of EDTP in adult muscles and its impact on lifespan and reproduction remained unknown.
The researchers used the DJ694 line, generated by a GAL4 enhancer trap inserted into the first intron of the EDTP gene. Semi-quantitative RT-PCR confirmed reduced EDTP mRNA levels in DJ694 homozygotes. To check the phenotypes, they measured fertility (egg count and the proportion of adults that hatched), lifespan, locomotor activity, and muscle and ovary morphology. To prove causality, they used genetic rescue: they introduced UAS-EDTP constructs activated by the same DJ694 GAL4 driver. Temporal rescue was performed with a temperature-sensitive GAL80ts inhibitor, which allows EDTP expression to be switched on at different stages of the life cycle.
DJ694 homozygotes had no developmental defects, but laid significantly fewer eggs than the w1118 control and DJ694/+ heterozygotes. The defect was recessive and temperature-independent. DJ694 males also had reduced fertility: eggs fertilized by them less often produced adult flies, even though their mating frequency was higher than that of wild type. The lifespan of DJ694 homozygotes was 2–29% shorter depending on sex and genetic background. No locomotor or muscle defects were found. Ovaries in young DJ694 females looked normal. Genetic rescue with three independent UAS-EDTP insertions fully restored fertility and lifespan. Temporal rescue showed that EDTP is needed both during development and in adulthood for normal fertility. In the eye, co-expression of EDTP reduced the number of polyglutamine aggregates, but no such effect occurred in muscles, and EDTP did not affect the lifespan shortening caused by aggregates.
The results show that EDTP is critically important for reproductive function and longevity in adult Drosophila, but its role in muscles is not tied to clearing protein aggregates. This challenges the hypothesis that EDTP regulates lifespan through autophagy in muscles. The tissue-specific effects (eye versus muscle) point to different mechanisms of action of the protein in different cellular contexts.
Further research could aim to uncover the molecular mechanisms linking EDTP to fertility and aging. EDTP may influence juvenile hormone signaling or the function of muscle cells in the oviduct and ejaculatory duct. It would also be interesting to study which particular lipid substrates of EDTP are critical in these processes and how its activity is regulated with age.
The work matters for understanding the role of myotubularins in whole-organism physiology, especially in the context of reproductive aging and muscle diseases. The findings could be useful for developing models to study MTMR14-associated myopathies in humans.
The next step could be a detailed study of spermatogenesis and oviduct function in DJ694 flies, as well as an analysis of sperm transfer after mating. It is also worth checking whether EDTP affects juvenile hormone signaling in the ovaries and how this relates to fertility.
The work addresses the fundamental problem of how lipid phosphatases regulate aging and reproductive health. The question of the tissue-specific mechanisms of EDTP action remains open, as does why its effect on aggregates differs between the eye and muscle. This ties into the broader problem of understanding the role of phosphoinositide metabolism in the physiology of aging.
The human homolog of EDTP was named hJumpy because of the jumpy behavior of flies with a mutation in this gene. DJ694 flies indeed show hyperactivity when startled and have trouble stopping their wing buzzing after landing.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.