Fig. 10.

Oral siphon muscle development in Ciona. a Diagram depicting the development of oral siphon muscles (OSMs) in Ciona robusta, adapted from [332]. OSM precursors (OSMPs) are derived from an OSM founder cell (OSMF), which in turn derives from the anterior trunk lateral cell (aTLC). Trunk lateral cells (TLCs) are in turn derived the A7.6 blastomere of the 110-cell-stage embryo. Timing is given in hours post-fertilization (hpf) at 18 °C. Atrial siphon muscles (ASMs) derive from the B7.5 blastomeres. b Diagram of the A7.6 lineage, with precursors of non-OSM contributions (blood, tunic cells, part of stomach, part of gill slit epithelium, etc.) depicted as white circles. At bottom is a diagram depicting the timing of expression of the transcription factors that are central to the OSM gene regulatory network, relative to each cell fate decision. Refer a for developmental timing of cell fate decisions in hours post-fertilization. c Common siphon muscle gene regulatory network, showing OSM-specific, ASM-specific, or shared hierarchical regulatory relationships. Putative, untested regulatory connections show as dotted lines. Re-wiring of the network must have occurred in either the OSM or ASM lineage, changing the hierarchy between Tbx1/10 and Ebf, and the mechanism of Mrf regulation