Expression of Hox4 during development of the pentamerous juvenile sea star, Parvulastra exigua

Abstract

Expression of Hox4 during development of the bilateral larva and pentameral juvenile sea star was investigated in Parvulastra exigua. The role of Hox4, possibly the anterior-most gene in the echinoderm Hox cluster, in the formation of the echinoderm adult body plan has not been examined previously. In the larva of P. exigua, PeHox4 is expressed in the developing coeloms-the anterior and the right and left coeloms that generate the aboral and oral coeloms of the juvenile. At the rudiment stage, PeHox4 was expressed in the five primary lobes of the hydrocoel that give rise to primary podia, the foundation of the adult body plan. This suggests a role for this gene in the development of the echinoderm body plan. In contrast to other bilaterians, Hox4 was not expressed in the developing asteroid central nervous system.

The sea cucumber genome provides insights into morphological evolution and visceral regeneration

“…japonicus genome. Generally, Hox4 is conserved in Asteroidea, and its expression is characterized in the dwarf cushion star Parvulastra exigua [35]. However, Hox4 is lost in S .…”

How Hox genes can shed light on the place of echinoderms among the deuterostomes

“…Hox1 is expressed in the radial nerve cord and in the circumoral nerve ring of Asterias rubens [38]. Hox4 expression was detected in Parvulastra exigua , an asterinid starfish with abbreviated development [36]. The Hox4 gene expresses successively in the larval coeloms and in the rudiment of the juvenile in the epithelium of the anterior coelom and archenteron of the larva and then in the hydrocoel (including the primary lobes).…”

“…Hox3 is expressed at the level of the hyponeural sinus (echinoid dental sacs) [97], and in asteroids Hox4 has been detected in the hydrocoel [36]. Hox5 is expressed in close relationship with the hydrocoel in echinoids [41], but also at the anterior tip of the somatocoels in crinoids [25], and to a lesser degree in asteroids.…”

Echinodermata

“…Several studies document expression of signaling and homeobox genes in the coeloms (e.g., eng , wnt , hox4 ), indicating a role for these genes in early development of the juvenile (Peterson et al 2000a ;Ferkowicz and Raff 2001 ;Byrne et al 2005 ;Cisternas and Byrne 2009 ). Hox genes are expressed in a spatial and collinear sequence in the coeloms of sea urchin and crinoid larvae (Table 1.2 ; see Peterson et al 2000a ;Hara et al 2006 ).…”