Vf. Hinman et Bm. Degnan, RETINOIC ACID DISRUPTS ANTERIOR ECTODERMAL AND ENDODERMAL DEVELOPMENTIN ASCIDIAN LARVAE AND POSTLARVAE, Development, genes and evolution, 208(6), 1998, pp. 336-345
In vertebrates, excess all-trans retinoic acid (RA) applied during axi
s formation leads to the apparent truncation of anterior structures. I
n this study we sought to determine the type of defects caused by ecto
pic RA on the development of the ascidian Herdmania curvata. We demons
trate that H. curvata embryos cultured in the presence of RA develop i
nto larvae whose trunks are shortened and superficially resemble those
of early metamorphosing postlarvae. Despite RA-treated larvae lacking
papillar structures they respond normally to natural cues that induce
metamorphosis, indicating that chemosensory functionality previously
mapped to the most anterior region of normal larvae is unaffected by R
A. Excess RA applied during postlarval development leads to a graded l
oss of the juvenile pharynx, apparently by respecifying anterior endod
erm to a more posterior fate. This structure is considered homologous
to the gill slits of amphioxus. which are also lost upon RA treatment.
This suggests that RA may have had a role in the development of the p
harynx of the ancestral chordate and that this function has been maint
ained in ascidians and cephalochordates and lost in vertebrates.