Austin, J. D. | Search bioRxiv

bioRxiv2024

Mylpf dosage is proportionate to fast-twitch myofibril size in the zebrafish embryo

Muscle becomes stronger by expanding sarcomeres from the cells edge to its center. Here we investigate how Mylpf (Myosin Light Chain Phosphorylatable Fast) abundance impacts sarcomere growth. The two zebrafish Mylpf genes (mylpfa and mylpfb) are exclusively expressed in fast-twitch muscle, with mylpfa expressed more abundantly than mylpfb. Mutations in both genes cause full mRNA and protein loss, and loss of sarcomere formation. The degree of sarcomere reduction in fast-twitch muscle is predicted by Mylpf protein dosage using a high-slope Hill equation. The sarcomere defect may be driven by thick filament localization, which is impaired in mylpfa-/-and obliterated in mylpfa-/-;mylpfb-/-. Slow-twitch muscle is spared, becoming larger and more active in the mutants. The mylpfa-/- defects can be rescued by Mylpfa-GFP, Mylpfb-GFP, and by human MYLPF-GFP with equivalent efficiency, but not by a MYLPF protein variant that causes Distal Arthrogryposis. These effects indicate that Mylpf dosage strengthens muscle by mediating myofilament localization, and thereby sarcomere and myofibril growth.

developmental biology↗

bioRxiv2023

Exploring The Role Of Isolation By Distance, Isolation By Environment, And Hybridization In Campylorhynchus Wrens Along A Precipitation Gradient In Western Ecuador

Climate variability can cause genetic and phenotypic diversity within species, which affects the evolution of biodiversity. A balance between gene flow and selection maintains changes in the frequency of genetic and phenotypic variants along an environmental gradient. In this study, we investigated a hybrid zone in western Ecuador involving two species of wrens (Aves: Troglodytidae), Campylorhynchus zonatus and C. fasciatus, and their admixed populations. We hypothesized that isolation by distance (IBD) and different ecological preferences, isolation by environment (IBE), result in limited dispersal between populations along the precipitation gradient in western Ecuador. We asked two main questions: (1) What is the relative contribution of IBD and IBE to patterns of genetic differentiation of these species along the environmental gradient in western Ecuador? And (2) Is there evidence of genetic admixture and introgression between these taxa in western Ecuador? We analyzed 4,409 SNPs from the blood of 112 individuals sequenced using ddRadSeq. The most likely clusters ranged from K=2-4, corresponding to categories defined by geographic origins, known phylogenetics, and physical or ecological constraints. Evidence for IBD was strong across all models, and evidence for IBE was less strong but still significant for annual mean precipitation and precipitation seasonality. We observed gradual changes in genetic admixture between C. f. pallescens and C. zonatus along the environmental gradient. Genetic differentiation of the two populations of C. f. pallescens could be driven by a previously undescribed potential physical barrier near the center of western Ecuador. Lowland habitats in this region may be limited due to the proximity of the Andes to the coastline, limiting dispersal and gene flow, particularly among dry-habitat specialists. We do not propose taxonomic changes, but the admixture observed in C. f. pallescens suggests that this described subspecies could be a hybrid between C. z. brevirostris and C. fasciatus, with different degrees of admixture along western Ecuador and northwestern Peru. This study contributes to the knowledge of avian population genomics in the tropics.

evolutionary biology↗