Hedgehog signaling is required for commitment but not initial induction of slow muscle precursors

Abstract

In zebrafish, skeletal muscle precursors can adopt at least three distinct fates: fast, non-pioneer slow, or pioneer slow muscle fibers. Slow muscle fibers develop from adaxial cells and depend on Hedgehog signaling. We analyzed when precursors become committed to their fates and the step(s) along their differentiation pathway affected by Hedgehog. Unexpectedly, we find that embryos deficient in Hedgehog signaling still contain postmitotic adaxial cells that differentiate into fast muscle fibers instead of slow. We show that by the onset of gastrulation, slow and fast muscle precursors are already spatially segregated but uncommitted to their fates until much later, in the segmental plate when slow precursors become independent of Hedgehog. In contrast, pioneer and non-pioneer slow muscle precursors share a common lineage from the onset of gastrulation. Our results demonstrate that slow muscle precursors form independently of Hedgehog signaling and further provide direct evidence for a multipotent muscle precursor population whose commitment to the slow fate depends on Hedgehog at a late stage of development when postmitotic adaxial cells differentiate into slow muscle fibers.

Muscle‐specific expression of the smyd1 gene is controlled by its 5.3‐kb promoter and 5′‐flanking sequence in zebrafish embryos

“…Moreover, it also suggests that specification of adaxial cells does not require Hh signaling. These data are consistent with previous findings by Hirsinger and colleagues who showed that Hh signal is required for commitment but not initial induction of slow muscle precursors in zebrafish embryos (Hirsinger et al, 2004). Adaxial cells could form in the yot mutant, however, without Hh signaling, adaxial cells fail to differentiate into slow muscles, instead they differentiate into fast muscles.…”

Origin of the zebrafish endocrine and exocrine pancreas

“…A similar model has been proposed to explain how fast and slow muscle precursors acquire their different fates (Hirsinger et al, 2004). These authors reported that the fast and slow muscle progenitor pools derive from separate yet overlapping regions of the 6 hpf embryo (similar to the progenitor pools contributing to individual pancreatic buds).…”

Visualization, characterization and modulation of calcium signaling during the development of slow muscle cells in intact zebrafish embryos

“…To block the development of SMCs, wild-type embryos were incubated either in 0.1 mM cyclopamine (Calbiochem, EMD Chemical, Inc., Gibbstown, NJ, USA; Barresi et al, 2000;Hirsinger et al, 2004) dissolved in 1% DMSO or in 0.15 mM forskolin (Calbiochem; Barresi et al, 2000) dissolved in 2% DMSO in 30% Danieau's solution, from ~5.5 hpf to ~24 hpf. As a control, some embryos were incubated in 2% DMSO in 30 % Danieau's solution alone.…”