Unique Features of River Lamprey (Lampetra fluviatilis) Myogenesis

Abstract

The river lamprey (L. fluviatilis) is a representative of the ancestral jawless vertebrate group. We performed a histological analysis of trunk muscle fiber differentiation during embryonal, larval, and adult musculature development in this previously unstudied species. Investigation using light, transmission electron (TEM), and confocal microscopy revealed that embryonal and larval musculature differs from adult muscle mass. Here, we present the morphological analysis of L. fluviatilis myogenesis, from unsegmented mesoderm through somite formation, and their differentiation into multinucleated muscle lamellae. Our analysis also revealed the presence of myogenic factors LfPax3/7 and Myf5 in the dermomyotome. In the next stages of development, two types of muscle lamellae can be distinguished: central surrounded by parietal. This pattern is maintained until adulthood, when parietal muscle fibers surround the central muscles on both sides. The two types show different morphological characteristics. Although lampreys are phylogenetically distant from jawed vertebrates, somite morphology, especially dermomyotome function, shows similarity. Here we demonstrate that somitogenesis is a conservative process among all vertebrates. We conclude that river lamprey myogenesis shares features with both ancestral and higher vertebrates.

Shared features of blastula and neural crest stem cells evolved at the base of vertebrates

“…HCR-FISH probe sets targeting were custom-designed by Molecular Instruments. Immediately after HCR-FISH, lamprey embryos were rinsed in PBS-T (1x PBS, 0.1% Tween 20), blocked (PBS-T, 10% fetal bovine serum), and then rocked overnight at 4°C in anti-Pax3 primary antibody that has been previously validated in lamprey 70 (DSHB #528426, 1:5). After several rinses in PBS-T, samples were incubated in goat anti-mouse IgG Alexa Fluor™ 546 secondary antibody (ThermoFisher A28182), rinsed again several times in PBS-T, and incubated with SYTOX Green nucleic acid stain (ThermoFisher S7020).…”