Fig. 2.

Afi-pplx is expressed similar to sea urchin Spu-pmar1, but does not function as repressor. a Phylogeny of Pplx and Pmar1 proteins suggesting orthology of these genes. Other paired-like homeodomains are use as outgroup. First value on branch is bootstrap support and second value is posterior probability. Tree is the consensus of differently constructed trees, using different initial alignments as well as different methodologies (Additional file 1: Figure S3). b WMISH showing the expression of Afi-pplx during A. filiformis development. c Time-line comparison of Spu-pmar1 and Afi-pplx transcript abundance adjusted for the stages of development (see Additional file 1: Figure S10) and normalized to their individual maximum of expression shows high correlation of expression dynamic (cross-correlation: 0.801). For brittle star, error bars represent standard deviation of two biological replicas. Sea urchin data were obtained from [59]. d Schematic representation of the double negative gate in euechinoid, showing how the large micromeres are specified to be skeletogenic. e S. purpuratus embryos injected with synthetic mRNA for Spu-pmar1, Afi-pplx, and GFP control (see Additional file 1: Figure S4 for details). No phenotype is observable in Afi-pplx-mRNA embryos or GFP controls, while injection of Spu-pmar1-mRNA induces skeletogenic fate in all cells. WMISH of Spu-delta in embryos injected with Afi-pplx-mRNA or Spu-pmar1-mRNA, which show expansion of Spu-delta expression to the whole embryo in Spu-pmar1-mRNA-injected embryos. Bfl Branchiostoma floridae, Lva Lytechinus variegatus, Pli Paracentrotus lividus, Hpu Hemicentrotus pulcherrimus, Spu Strongyloncentrotus purpuratus, Afi Amphiura filiformis, Pmi Patiria miniata, Sko Saccoglossus kowalevskii, VV vegetal view, Cl cleavage, EBl early blastula, Bl blastula, MBl mesenchyme blastula