The expression patterns of alx genes in ambulacraria.

(A–D) The expression pattern of starfish alx1 (Apalx1). (A–C) Expression was barely evident prior to the bipinnaria stage. (D) Expression was evident in mesenchyme cells of the posterior region of late bipinnarial larvae. (E-H) The expression pattern of brittle star alx1 (Akalx1). (E) Expression was evident in the putative vegetal plate of the blastula (F) and in mesenchyme cells that ingressed from the vegetal plate. (G) At the gastrula stage, expression was evident in mesenchyme cells located bilaterally to the archenteron. (H) In plutei, expression was evident in mesenchyme cells located along the arms. (I-K) The expression pattern of sea cucumber alx1 (Hlalx1). (I) Expression was not evident prior to the gastrula stage. (J) In mesenchyme of the gastrula, expression was evident in a few cells located in the posterior larval region. (K) In auricularia larvae, expression was evident in mesenchyme cells. (L-N) The expression pattern of starfish Calx (ApCalx). (L) Expression was evident in the vegetal plate of the blastula. (M) Expression was noted at the tip of the archenteron of the gastrula. (N) In early bipinnariae, expression persisted in the coelom and de novo expression was evident in the posterior enterocoel that invaginated from the left side of the gut. (O-Q) The expression pattern of sea urchin Calx (HpCalx). Red fluorescent signals indicate HpCalx transcripts and blue signals denote nuclei stained by DAPI. (O) Expression was evident in ingressed primary mesenchyme cells (PMCs) of the blastula mesenchyme. (P) In late-stage gastrulae, signals disappeared from PMCs but were observed in secondary mesenchyme cells (SMCs) located around the tip of the archenteron. (Q) Expression was restricted to the coelomic pouches of prism larvae. (R, S) The expression pattern of acorn worm alx (Bsimalx). (R) In the mid-gastrula, expression was evident in cells at developing protocoel. (S) At a later stage of gastrula, expression was observed in the proximal part of the protocoel. Scale bars: 50 μm.