Retinoic acid repatterns axolotl lateral line receptors.

Abstract

The effects of all-trans retinoic acid on the development of the lateral line placodes of axolotls was studied. Late gastrula and early neurula were exposed to 10 -7 to 10 -5 M retinoic acid for one hour and then reared until they would normally be feeding larvae. As in other vertebrates, the extent of the developmental abnormalities is concentration dependent. Those embryos exposed to the highest concentration of retinoic acid failed to form much of the forebrain and midbrain, including the olfactory, optic and otic organs, which were reduced or absent. Although all lateral line placodes continued to generate fully formed receptors and cranial nerves, the production of neuromasts and the organization of these receptors into lines were markedly reduced. Equally important, all of the placodes at the highest concentration of retinoic acid failed to generate ampullary organs, thereby indicating a strong posteriorizing effect of retinoic acid on these placodes.

Retinoic acid influences anteroposterior positioning of epidermal sensory neurons and their gene expression in a developing chordate (amphioxus)

“…First, RA response elements are present in the regulatory regions of Hox genes generally (41). Moreover, RA signaling can influence the anteroposterior positioning and͞or cytodifferentiation of some placodes in the developing vertebrate epidermis (10)(11)(12), although Hox genes were not considered in these studies.…”

“…The presence of a similar RA-dependent Hox code in the developing vertebrate epidermis remains a definite possibility. However, for vertebrates, the degree of autonomy of epidermal development needs further study because the positioning of epidermal neurons may be influenced strongly by factors from the nearby central nervous system and͞or mesoderm (10)(11)(12). If epidermal development turns out to be more autonomous in amphioxus than in vertebrates, it could reflect either an independent loss or a gain of autonomy, respectively, in the vertebrate or amphioxus lines of descent.…”

“…The involvement of RA signaling in global patterning is best known for the neural ectoderm (3,5,6), endoderm (3,7,8), and mesoderm (9) but has been less studied for the epidermal ectoderm (so designated to emphasize its distinction from the neural ectoderm). To date, the only structures known to be patterned by RA signaling within the vertebrate epidermal ectoderm are some of the placodes (10)(11)(12).…”

Retinoic acid signaling in development: Tissue‐specific functions and evolutionary origins

“…foxc1 and pitx2) (Matt et al, 2005). RA signaling is also implicated in the development of other placodes, such as the olfactory (Anchan et al, 1997;Mic et al, 2000), the otic (Dupé et al, 1999;Romand et al, 2006;White et al, 2000), and the lateral line placodes (Gibbs and Northcutt, 2004) (see Fig. 3).…”

“…Treatments with RA and RA antagonist shift the AP distribution of sensory neurons in the general ectoderm and alter the combinatorial code of proneural genes expressed in these cells (Schubert et al, 2004). The effect of RA on the distribution of sensory neurons in the amphioxus general ectoderm is reminiscent of the posteriorizing action of exogenous RA on the lateral line neurons of axolotls (Gibbs and Northcutt, 2004).…”