The measurement of lifespan pervades aging research. Because lifespan results from complex interactions between genetic, environmental and stochastic factors, it varies widely even among isogenic individuals. The action of molecular mechanisms on lifespan is therefore visible only through their statistical effects on populations. Survival assays in C. elegans provided critical insights into evolutionarily conserved determinants of aging. To enable the rapid acquisition of survival curves at arbitrary statistical resolution, we developed a scalable imaging and analysis platform to observe nematodes over multiple weeks across square meters of agar surface at 8 μm resolution. The method generates a permanent visual record of individual deaths from which survival curves are constructed and validated, producing data consistent with the manual method for several mutants in both standard and stressful environments. Our approach allows rapid, detailed reverse-genetic and chemical screens for effects on survival and enables quantitative investigations into the statistical structure of aging.

Ulmschneider et al. demonstrate that intracellular pH increases during differentiation of Drosophila ovarian epithelial stem cells and mouse embryonic stem cells, that blocking this increase impairs differentiation, and that intracellular pH may regulate the strength of Hedgehog signaling in epithelial stem cells.

Caenorhabditis elegans defecation is a rhythmic behavior, composed of three sequential muscle contractions, with a 50-s periodicity. The motor program is driven by oscillatory calcium signaling in the intestine. Proton fluxes, which require sodium-proton exchangers at the apical and basolateral intestinal membranes, parallel the intestinal calcium flux. These proton shifts are critical for defecation-associated muscle contraction, nutrient uptake, and longevity. How sodium-proton exchangers are activated in time with intestinal calcium oscillation is not known. The posterior body defecation contraction mutant (pbo-1) encodes a calcium-binding protein with homology to calcineurin homologous proteins, which are putative cofactors for mammalian sodium-proton exchangers. Loss of pbo-1 function results in a weakened defecation muscle contraction and a caloric restriction phenotype. Both of these phenotypes also arise from dysfunctions in pH regulation due to mutations in intestinal sodium-proton exchangers. Dynamic, in vivo imaging of intestinal proton flux in pbo-1 mutants using genetically encoded pH biosensors demonstrates that proton movements associated with these sodium-proton exchangers are significantly reduced. The basolateral acidification that signals the first defecation motor contraction is scant in the mutant compared with a normal animal. Luminal and cytoplasmic pH shifts are much reduced in the absence of PBO-1 compared with control animals. We conclude that pbo-1 is required for normal sodium-proton exchanger activity and may couple calcium and proton signaling events.

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The Caenorhabditis elegans defecation cycle is a 3‐step motor program. Cycle timing is controlled by intestinal calcium flux. The first step, posterior body wall muscle contraction (pBoc), is elicited by protons1,2. Protons are transported from the intestine into the pseudocoelomic space via the sodium‐proton exchanger 7 (NHX‐7) and activate ion channels in body wall muscles, resulting in contraction1. A second exchanger, NHX‐2, allows proton movements between the lumen and intestinal cells2. We hypothesize calcineurin homologous protein (CHP), a calcium responsive co‐factor for sodium‐proton exchangers, activates these NHXs in response to calcium flux. Two CHP mutants that alter calcium binding motifs exhibit pBoc defects. Genetically encoded pH indicator proteins were used to monitor pH levels in vivo. CHP mutants display altered pseudocoelomic, cytoplasmic, and lumenal proton fluxes. Cumulatively, chp mutants' pH phenotypes encompass both nhx‐2's and nhx‐7's mutant traits, suggesting CHP activates these exchangers to coordinate the calcium wave and pBoc initiation. Support is from the NSF.

Histone 3 lysine 9 tri‐methylation (H3K9me3) is a hallmark of heterochromatin, a repressive structure found at repetitive and telomeric regions in the genome. This histone modification plays a critical role in the temporal control of heterochromatic replication and the regulation of euchromatic gene expression. Alterations in H3K9me3 and heterochromatin are directly associated with the onset of genomic instability and cancer. The lack of H3K9me3 has also been shown to be a contributor to the premature aging disease Hutchinson‐Gilford Progeria Syndrome. These few examples highlight an important link between the levels of H3K9me3, cancer, and premature aging. Identifying factors that influence H3K9me3 and heterochromatin dynamics will have profound implications in pathophysiology. We recently identified the first histone lysine‐specific tri‐demethylase family (JMJD2A‐D) in human and C. elegans (JMJD‐2) that regulate H3K9me3 and H3K36me3 levels. We uncovered a novel and highly conserved role for the JMJD2 proteins in multiple DNA‐templated processes. We have also demonstrated that the phenotypes are a reflection of altered chromatin structure. Our observations suggest that JMJD2 proteins are important regulators of the chromatin state from worm to human. We will present these findings as well as our most recent advances into understanding the molecular basis of the JMJD‐2‐related phenotypes.