Effects of retinoic acid upon eye field morphogenesis and differentiation

Abstract

This study describes a whole embryo and embryonic field analysis of retinoic acid's (RA) effects upon Xenopus laevis forebrain development and differentiation. By using in situ and immunohistochemical analysis of pax6, Xbf1, and tyrosine hydroxylase (TH), gene expression during eye field, telencephalon field, and retinal development was followed with and without RA treatment. These studies indicated that RA has strong effects upon embryonic eye and telencephalon field development with greater effects upon the ventral development of these organ fields. The specification and determination of separate eye primordia occurred at stage-16 when the prechordal plate reaches its most anterior aspect in Xenopus laevis. Differentiation of the dopaminergic cells within the retina was also affected in a distinct dorsoventral pattern by RA treatment, and cell type differentiation in the absence of distinct retinal laminae was also observed. It was concluded that early RA treatments affected organ field patterning by suppression of the upstream elements required for organ field development, and RA's effects upon cellular differentiation occur downstream to these organ determinants' expression within a distinct dorsoventral pattern.

Axes establishment during eye morphogenesis in Xenopus by coordinate and antagonistic actions of BMP4, Shh, and RA

“…Though our results showed that Shh could act as a ventral signal in Xenopus eyes, RA has been well known as a strong effecter upon anterior field including eye with great influence on the ventral development of these organs of Xenopus (Durston et al, 1989;Drysdale and Crawford, 1994;Eagleson et al, 2001), zebrafish (MarshArmstrong et al, 1994;Hyatt et al, 1996), and mouse (McCaffery et al 1992(McCaffery et al ,1999Kastner et al, 1994Kastner et al, ,1997. We thus examined whether the ventralizing pathways of RA and Shh are mutually correlated.…”

“…Thereafter, the axes establishment is achieved by their mutual attenuation via downstream cascade rather than their direct interaction. Concerning RA, another possible ventralization factor of the optic vesicle (Hyatt et al, 1996;McCaffery et al, 1999;Eagleson et al, 2001), RA treatment indeed upregulated the expression of ventral marker vax2 but could not repress the expression of dorsal markers tbx2/3/5 or bmp4. We also noticed that shh expression in the forebrain was not repressed by RA treatment, whereas it was severely repressed in the midand hindbrain and anterior neural tube.…”

“…It has been shown that the postgastrula stage is the critical period for ocular development, and RA treatment in the earlier stages results in the loss of the anterior head including the eyes (Hyatt et al, 1996;Eagleson et al, 2001). That is why we administered RA on Xenopus embryos from a postgastrula stage (stage 16).…”

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

“…The role of RA in specifying subtypes of cells has been discussed for the vertebrate central nervous system (42,43), retina (44), limb bud mesenchyme (45), heart (46), kidney (47), lung (48), and skin (49,50). Similarly, for amphioxus, the present results suggest that RA (signaling through Hox genes) may also be involved in the differentiation of neurons into subtypes within the epidermal ectoderm.…”

Characterizing gene expression during lens formation in Xenopus laevis: Evaluating the model for embryonic lens induction

“…Perhaps there is a key distinction in the timing of these different interactions, and planar lens induction does not begin until stage 13-14. In fact, regionalization of anterior neural structures is a progressive process Sive, 2000, 2001), and complete separation of the embryonic eye primordia does not occur until stage 16 in Xenopus (Eagleson et al, 2001).…”