Bunker, M. | Search bioRxiv

bioRxiv2026

Neural Crest-Derived Endocardial Cells Required for Heart Valve Development

Abnormalities in cardiac valves, which maintain unidirectional blood flow through the heart, affect 2-3% of people worldwide and are the most common form of structural heart disease (1).Yet the cell types that make up the valve, and how they communicate to direct development and homeostasis, remain poorly understood. Here, we identify a rare, essential population of highly secretory valve endocardial cells in mouse and human that derive from migrating neural crest cells. Ablation of these cells in mice caused perinatal lethality with thickened leaflets, stenosis, and regurgitation, mirroring human valve disease. This subset of endocardial cells uniquely expresses the secreted signaling protein parathyroid hormone-like hormone (Pthlh). Global disruption of Pthlh caused valve stenosis and lethality and neural crest-specific deletion produced similar valve disease, with impaired maturation of valvular interstitial cells and disrupted bone morphogenetic protein signaling. These findings identify a previously unrecognized cell type and signaling pathway essential for valve morphogenesis, with implications for the pathogenesis and treatment of human valve defects.

developmental biology↗

bioRxiv2020

Parallel evolution in the integration of a co-obligate aphid symbiosis

Insects evolve dependencies - often extreme - on microbes for nutrition. These include cases where insects harbour multiple endosymbionts that function collectively as a metabolic unit. How do these metabolic co-dependencies originate, and is there a predictable sequence of events leading to the integration of new symbionts? While dependency on multiple nutrient-provisioning symbionts has evolved numerous times across sap-feeding insects, there is only one known case of metabolic co-dependency in aphids, between Buchnera aphidicola and Serratia symbiotica in the Lachninae subfamily. Here we identify three additional independent transitions to the same co-obligate symbiosis in different aphids. A comparison of recent and ancient associations allows us to investigate intermediate stages of metabolic and physical integration between the typically facultative symbiont, Serratia, and the ancient obligate symbiont Buchnera. We find that these uniquely replicated evolutionary events support the idea that co-obligate associations initiate in a predictable manner, through parallel evolutionary processes. Specifically, we show (i) how the repeated losses of the riboflavin pathway in Buchnera leads to dependency on Serratia, (ii) evidence of a stepwise process of symbiont integration, whereby dependency evolves first, then essential amino acid pathways are lost (at ~30-60MYA), which coincides with increased physical integration of the companion symbiont; and (iii) dependency can evolve prior to specialised structures (e.g. bacteriocytes), and in one case with no direct nutritional basis. More generally, our results suggest the energetic costs of synthesising nutrients may provide a unified explanation for the sequence of gene loses that occur during the evolution of co-obligate symbiosis.

evolutionary biology↗