Whole-body gene expression atlas of an adult metazoan

Gene activity defines cell identity, drives intercellular communication, and underlies the functioning of multicellular organisms. We present the single-cell resolution atlas of gene activity of a fertile adult metazoan: Caenorhabditis elegans. This compendium comprises 180 distinct cell types and 19,657 expressed genes. We predict 7541 transcription factor expression profile associations likely responsible for defining cellular identity. We predict thousands of intercellular interactions across the C. elegans body and the ligand-receptor pairs that mediate them, some of which we experimentally validate. We identify 172 genes that show consistent expression across cell types, are involved in basic and essential functions, and are conserved across phyla; therefore, we present them as experimentally validated housekeeping genes. We developed the WormSeq application to explore these data. In addition to the integrated gene-to-systems biology, we present genome-scale single-cell resolution testable hypotheses that we anticipate will advance our understanding of the molecular mechanisms, underlying the functioning of a multicellular organism and the perturbations that lead to its malfunction.

Vibrometry as a noncontact alternative to dynamic and viscoelastic mechanical testing in cartilage

Physiological loading of knee cartilage is highly dynamic and may contribute to the progression of osteoarthritis. Thus, an understanding of cartilage's dynamic mechanical properties is crucial in cartilage research. In this study, vibrometry was used as a fast (2 h), noncontact and novel alternative to the slower (30 h), traditional mechanical and biochemical assays for characterization of cartilage from the condyle, patella, trochlear groove and meniscus. Finite-element models predicted tissue resonant frequencies and bending modes, which strongly correlated with experiments (R2 = 0.93). Vibrometry-based viscoelastic properties significantly correlated with moduli from stress relaxation and creep tests, with correlation strengths reaching up to 0.78. Loss modulus also strongly correlated with glycosoaminoglycan (GAG) content. Dynamic properties measured by vibrometry significantly differed among various knee cartilages, ranging between 6.1 and 56.4 MPa. Interestingly, meniscus viscoelastic properties suggest that contrary to common belief, it may lack shock absorption abilities; instead, condylar hyaline cartilage may be a better shock absorber. These data demonstrate for the first time that vibrometry is a noncontact approach to dynamic mechanical characterization of hyaline and fibrocartilage cartilage with concrete relationships to standard quasi-static mechanical testing and biochemical composition. Thus, with a single tool, vibrometry greatly facilitates meeting multiple regulatory recommendations for mechanical characterization of cartilage replacements.

Targetable cellular signaling events mediate vascular pathology in vascular Ehlers-Danlos syndrome

Vascular Ehlers-Danlos syndrome (vEDS) is an autosomal-dominant connective tissue disorder caused by heterozygous mutations in the COL3A1 gene, which encodes the pro-α 1 chain of collagen III. Loss of structural integrity of the extracellular matrix is believed to drive the signs and symptoms of this condition, including spontaneous arterial dissection and/or rupture, the major cause of mortality. We created 2 mouse models of vEDS that carry heterozygous mutations in Col3a1 that encode glycine substitutions analogous to those found in patients, and we showed that signaling abnormalities in the PLC/IP3/PKC/ERK pathway (phospholipase C/inositol 1,4,5-triphosphate/protein kinase C/extracellular signal-regulated kinase) are major mediators of vascular pathology. Treatment with pharmacologic inhibitors of ERK1/2 or PKCβ prevented death due to spontaneous aortic rupture. Additionally, we found that pregnancy- and puberty-associated accentuation of vascular risk, also seen in vEDS patients, was rescued by attenuation of oxytocin and androgen signaling, respectively. Taken together, our results provide evidence that targetable signaling abnormalities contribute to the pathogenesis of vEDS, highlighting unanticipated therapeutic opportunities.