The fly muscles lab
at Dalhousie University Biology Department Nova Scotia, Canada
Latest Projects
1: Filamin holds the sarcomere together
Filamins are elastic molecular sensors that detect pulling strains in the actin cytoskeleton and transduce them into molecular signaling cascades. Flies have a single typical filamin gene called Cheerio. In muscles, Cheerio localizes to the Z-disc and is required for myofibril stability. Cheerio mutants that are unable to sense pulling or stretching forces have fragile muscles that break upon contraction. A dominant mutant that mimics the activated, stretched version of Cheerio develops large aggregates, which we interpret as a gain of function in the signaling cascade.
We do not yet know the proteins that are signaled through the activation of Cheerio in muscles, so we are identifying them using proteomics and protein modeling (AlphaFold). We have identified several hits, which we are currently characterizing in vivo using RNAi and mutant alleles. Our goal is to map the full sequence of molecular events triggered by filamin mechanical activation in muscles and to understand how these events contribute to myofibril and muscle stability.
2: Muscle damage and repair in insects
Mechanically overloaded muscles break at the myofibril level. In vertebrates, this is the starting point of muscle hypertrophy. In insects, the repair mechanism is largely unknown. We have developed techniques to induce muscle damage using light-gated ion channels, which cause the complete disintegration of myofibrils. We have demonstrated that these muscles completely repair themselves within a few days. We are now characterizing the molecular mechanisms involved using confocal and transmission electron microscopy, and we are exploring other methods of inducing muscle damage.
Image below: TEM images of muscles before muscle damage (left) and after muscle damage (right). A few days later, the myofibril structure will regenerate completely.
2: Metabolic regulation of sarcomere size
Using a bioinformatics approach, we searched for proteins that share an evolutionary path with the main Z-disc components, Zasp and α-actinin. This led us to a key enzyme of the TCA cycle, oxoglutarate dehydrogenase (OGDH). While OGDH is expected to be confined to mitochondria, we found it localized not only in mitochondria but also at the myofibrils in the Z-disc.
Expanding on this discovery, a biotinylation screen for Z-disc-associated proteins revealed several other energy metabolism enzymes at the Z-disc, many of which are typically linked to mitochondria. This suggests that the Z-disc may serve as a hub for energy-related enzymes, potentially playing a role in enzymatic regulation in muscle. Given the tight control muscles exert over their energy metabolism, this localization could be a key regulatory mechanism.
Image below: Confocal microscopy images of indirect flight muscles in control flies (a) and in flies with CRISPR-induced mutations in the three subunits of the oxoglutarate dehydrogenase complex (b–d). In the mutant conditions, myofibrils fail to grow, and mini Z-discs are observed throughout the muscle. Actin is shown in green, and the Z-disc is in magenta.
