We identify the Caenorhabditis elegans myosin light-chain kinase, MLCK-1, required for contraction of spermathecae. During contraction, MLCK-1 moves from the apical cell boundaries to the basal actomyosin bundles, where it stabilizes myosin downstream of calcium signaling. MLCK and ROCK act in distinct subsets of cells to coordinate the timing of contraction.

SUMMARY Individually, dysfunction of both the endoplasmic reticulum (ER) and mitochondria has been linked to aging, but how communication between these organelles might be targeted to promote longevity is unclear. Here, we provide evidence that, in Caenorhabditis elegans , inhibition of the conserved unfolded protein response (UPR ER ) mediator, activating transcription factor ( atf ) -6 , increases lifespan by modulating calcium homeostasis and signaling to mitochondria. Atf-6 loss confers longevity via downregulation of the ER calcium buffer, calreticulin. ER calcium release via the inositol triphosphate receptor (IP 3 R/ itr-1 ) is required for longevity, while IP 3 R/ itr-1 gain of function is sufficient to extend lifespan. Highlighting coordination between organelles, the mitochondrial calcium import channel mcu-1 is also required for atf-6 longevity. IP 3 R inhibition leads to impaired mitochondrial bioenergetics and hyperfusion, which is sufficient to suppress long life in atf-6 mutants. This study reveals the importance of organellar calcium handling as a critical output for the UPR ER in determining the quality of aging.

The reproductive system of the hermaphroditic nematode C. elegans consists of a series of contractile cell types—including the gonadal sheath cells, the spermathecal cells and the spermatheca–uterine valve—that contract in a coordinated manner to regulate oocyte entry and exit of the fertilized embryo into the uterus. Contraction is driven by acto-myosin contraction and relies on the development and maintenance of specialized acto-myosin networks in each cell type. Study of this system has revealed insights into the regulation of acto-myosin network assembly and contractility in vivo.

Functional crosstalk between organelles is critical for maintaining cellular homeostasis.Individually, dysfunction of both endoplasmic reticulum (ER) and mitochondria have been linked to cellular and organismal aging, but little is known about how mechanisms of interorganelle communication might be targeted to extended longevity. The metazoan unfolded protein response (UPR) maintains ER health through a variety of mechanisms beyond its canonical role in proteostasis, including calcium storage and lipid metabolism.Here we provide evidence that in C. elegans, inhibition of the conserved UPR mediator, activating transcription factor (atf)-6 increases lifespan via modulation of calcium homeostasis and signaling to the mitochondria. Loss of atf-6 confers long life via downregulation of the ER calcium buffering protein, calreticulin. Function of the ER calcium release channel, the inositol triphosphate receptor (IP3R/itr-1), is required for atf-6 mutant longevity while a gain-of-function IP3R/itr-1 mutation is sufficient to extend lifespan. IP3R dysfunction leads to altered mitochondrial behavior and hyperfused morphology, which is sufficient to suppress long life in atf-6 mutants. Highlighting a novel and direct role for this inter-organelle coordination of calcium in longevity, the mitochondrial calcium import channel, mcu-1, is also required for atf-6 mutant longevity.Altogether this study reveals the importance of organellar coordination of calcium handling in determining the quality of aging, and highlights calcium homeostasis as a critical output for the UPR and atf-6 in particular.

H2O2 modulates RHO-1/Rho activity in the contractile tissue of the C. elegans spermatheca. Both exogenous and endogenously generated H2O2 decrease spermathecal contractility by inhibition of RHO-1 through oxidation of Cys 20. Regulation of H2O2 levels in the spermatheca depends on the activity of the cytosolic superoxide dismutase SOD-1.