Skeletal muscles arise from diverse embryonic origins in vertebrates, yet converge on extensively shared regulatory programs that require muscle regulatory factor (MRF)-family genes. Myogenesis in the tail of the simple chordate Ciona exhibits a similar reliance on its single MRF-family gene, and diverse mechanisms activate Ci-Mrf. Here, we show that myogenesis in the atrial siphon muscles (ASMs) and oral siphon muscles (OSMs), which control the exhalant and inhalant siphons, respectively, also requires Mrf. We characterize the ontogeny of OSM progenitors and compare the molecular basis of Mrf activation in OSM versus ASM. In both muscle types, Ebf and Tbx1/10 are expressed and function upstream of Mrf. However, we demonstrate that regulatory relationships between Tbx1/10, Ebf and Mrf differ between the OSM and ASM lineages. We propose that Tbx1, Ebf and Mrf homologs form an ancient conserved regulatory state for pharyngeal muscle specification, whereas their regulatory relationships might be more evolutionarily variable.
The authors declare no competing or financial interests.
T.T. contributed to conceptualization, investigation, original draft preparation, review and editing, visualization, and funding acquisition. L.C. contributed to conceptualization, resources, review and editing, visualization, supervision, and funding acquisition.
This work was supported by the National Institutes of Health/National Heart, Lung, and Blood Institute [grant number R01 HL108643 to L.C. and 2T32HD007520-16 to T.R.T. as part of the New York University Developmental Genetics Training Grant program (P.I.: Jessica Treisman)]. Deposited in PMC for release after 12 months.
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.136267.supplemental
- Received February 9, 2016.
- Accepted August 30, 2016.