Retinoic Acid is Required for Normal Morphogenetic Movements During Gastrulation

Abstract

Retinoic acid (RA) is a central regulatory signal that controls numerous developmental processes in vertebrate embryos. Although activation of Hox expression is considered one of the earliest functions of RA signaling in the embryo, there is evidence that embryos are poised to initiate RA signaling just before gastrulation begins, and manipulations of the RA pathway have been reported to show gastrulation defects. However, which aspects of gastrulation are affected have not been explored in detail. We previously showed that partial inhibition of RA biosynthesis causes a delay in the rostral migration of some of the earliest involuting cells, the leading edge mesendoderm (LEM) and the prechordal mesoderm (PCM). Here we identify several detrimental gastrulation defects resulting from inhibiting RA biosynthesis by three different treatments. RA reduction causes a delay in the progression through gastrulation as well as the rostral migration of the goosecoid-positive PCM cells. RA inhibition also hampered the elongation of explanted dorsal marginal zones, the compaction of the blastocoel, and the length of Brachet’s cleft, all of which indicate an effect on LEM/PCM migration. The cellular mechanisms underlying this deficit were shown to include a reduced deposition of fibronectin along Brachet’s cleft, the substrate for their migration, as well as impaired separation of the blastocoel roof and involuting mesoderm, which is important for the formation of Brachet’s cleft and successful LEM/PCM migration. We further show reduced non-canonical Wnt signaling activity and altered expression of genes in the Ephrin and PDGF signaling pathways, both of which are required for the rostral migration of the LEM/PCM, following RA reduction. Together, these experiments demonstrate that RA signaling performs a very early function critical for the progression of gastrulation morphogenetic movements.

Alcohol induces neural tube defects by reducing retinoic acid signaling and promoting neural plate expansion

“…These results were further supported by analysis of the pax8 expression pattern which has a very dynamic and informative expression pattern around NF19 ( Heller and Brändli, 1999 ), indicating that experimental and control embryos are at approximately the same developmental stage during NTC stages ( Figures 1F–J’ ). These data demonstrate, as previously described, that the reduction of RA signaling by EtOH exposure induces a transient developmental delay that is overcome during early neurula stages ( Yelin et al, 2007 ; Gur et al, 2022b ), and the NTDs observed in the EtOH-treated embryos are not the result of a developmental delay.…”

“…Previously we showed that the embryo is most sensitive to alcohol exposure close to the onset of gastrulation ( Yelin et al, 2005 ; Gur et al, 2022a ; Gur et al, 2022b ). In order to determine the sensitivity window for NTC defect induction by reduced RA signaling, we treated embryos with either EtOH or DEAB starting the treatments at different developmental stages.…”

“…Also in the rescue experiments, early gastrula showed the highest sensitivity for NTC defect induction by reduced RA signaling. The beginning of gastrulation marks the onset of RA signaling ( Ang and Duester, 1999 ; Niederreither et al, 1999 ; Grandel et al, 2002 ; Gur et al, 2022b ) and RA signaling onset follows the transcriptional activation of the retinaldehyde dehydrogenases, mainly aldh1a2 but also aldh1a3, at the initiation of gastrulation in the embryonic organizer ( Chen et al, 2001 ; Shabtai et al, 2018 ; Parihar et al, 2021 ; Gur et al, 2022a ; Lupo et al, 2005 ). In agreement, early RA signaling localizes to the embryonic organizer as shown in multiple vertebrate models ( Rossant et al, 1991 ; Hogan et al, 1992 ; Deltour et al, 1996 ; Yelin et al, 2005 ; Samarut et al, 2015 ).…”

“…At the onset of gastrulation in Xenopus embryos, cells from the Spemann-Mangold organizer involute and migrate rostrally forming the leading edge of the mesendoderm/prechordal mesendoderm (LEM/PCM) that secretes the anti-BMP and anti-Wnt signals necessary for neural induction ( Kaneda and Motoki, 2012 ; Huang and Winklbauer, 2018 ; Winklbauer, 2020 ). These cells also express one of the retinaldehyde dehydrogenases, aldh1a3 , and as a result, produce RA ( Lupo et al, 2005 ; Gur et al, 2022b ). We have recently shown that reduced RA signaling affects early gastrulation morphogenetic movements resulting in a transient delay in the rostral migration of the LEM/PCM ( Gur et al, 2022a ).…”

Essential Oils Produce Developmental Toxicity in Zebrafish Embryos and Cause Behavior Changes in Zebrafish Larvae

“…The reduced percent epiboly is indicative of a delay in the gastrulation process, in this case, probably caused by citral and thymol action. Citral is commonly used in pharmacology as an inhibitor of retinoic acid biosynthesis [24]. This acid plays a fundamental role in regulating early embryogenesis, especially during gastrulation and development of axis and limb formation [25].…”