Trunk muscle differentiation-a lesson from the Chinese fire-bellied newt (Hypselotriton orientalis)

Extant amphibians are divided into three distinct lineages: Gymnophiona, Urodela, and Anura. Owing to their diversity, they are widely used in research concerning, among others, tissue regeneration. Here, we describe larval myotomal myogenesis in the Chinese fire-bellied newt, Hypselotriton orientalis. Morphological, ultrastructural, cytochemical, and immunohistochemical analyses showed that trunk muscles grow through hypertrophy and hyperplasia mediated by the expression of typical myogenic factors, such as Pax7, from muscle progenitor cells. Our findings also suggest a third alternative mechanism for muscle growth involving the muscle splitting or fragmentation of preexisting larval myotubes.