Distribution of cellular retinoic acid-binding proteins I and II in the chick embryo and their relationship to teratogenesis.

The distribution of cellular retinoic acid-binding proteins I and II (CRABP I and II) during the first 6 days of chick development has been investigated using immunoblotting. Since retinoic acid (RA) is teratogenic to some parts of the embryo, stimulatory to other parts, and has no effect on others it may be that the distribution of cytoplasmic proteins such as CRABP I and II plays some role in this differential activity. Neither protein is expressed in the day 2 embryo, but from day 3 onwards both proteins are expressed and CRABP I is in considerable excess over CRABP II.

The kreisler mouse: a hindbrain segmentation mutant that lacks two rhombomeres.

kreisler is a recessive mutation resulting in gross malformation of the inner ear of homozygous mice. The defects in the inner ear are related to abnormalities in the hindbrain of the embryo, adjacent to the ear rudiments. At E9.

Retinoic acid gradients during limb regeneration.

Retinoids have been implicated in pattern formation processes in both developing chick limbs and in the regenerating limbs of urodele amphibians as well as in other aspects of embryonic development. Since chick wing buds have been shown to have a higher concentration of all-trans-retinoic acid (RA) in the posterior region than in the anterior region, we set out to look for a gradient of RA in the regenerating limb of the axolotl, Ambystoma mexicanum. We used high-performance liquid chromatography to separate, identify, and measure the concentration of retinoids present in the tissues.

Biolistics. The retinoic acid supergun affair.

By using biolistics to transfect the regenerating amphibian limb with cDNAs encoding chimeric receptors, the functions of individual retinoic acid receptors have been pinpointed.

The effect of vitamin A (retinoids) on pattern formation implies a uniformity of developmental mechanisms throughout the animal kingdom.

Retinoids are low molecular weight, lipophilic derivatives of vitamin A which have a profound effect upon the development of a diverse array of animals. Here, I review these effects on Invertebrates: a colonial hydroid, a colonial ascidian, and Vertebrates: the regenerating amphibian limb, the developing chick limb bud, the regenerating amphibian tail, the anteroposterior axis of the early embryo, the developing chick embryo skin. There is a striking uniformity of effect of retinoids on pattern formation when applied to these diverse organisms.

The homeotic transformation of tails into limbs in Rana temporaria by retinoids.

The most remarkable of all the effects of retinoids on embryonic systems is the homeotic transformation of tails into legs which was recently reported using an Indian species of frog. Since then several attempts have been made to repeat these results on other species, notably Xenopus, with no success. Here I report the successful repetition of this homeotic transformation using Rana temporaria tadpoles treated with retinyl palmitate.

The distribution of cellular retinoic acid-binding protein I during odontogenesis in the rat incisor.

Retinoids are important molecules in various aspects of embryological development. Here the distribution of cellular retinoic acid-binding protein I (CRABPI) was studied in the continuously growing incisor of adult rats using an affinity-purified rabbit polyclonal antibody. CRABPI was present throughout the presecretory and secretory ameloblast layer.

Cellular Retinole Acid Binding Protein In the Periodontal Ligament.

As retinoic acid is an important signaling molecule during embryological development. Since periodontal tissues are thought to have fetal-like properties, the present study was to determine the presence and distribution of cellular retinoic acid-binding protein I(CRABP I) in the periodontal tissues of the rat. Following demineralization, wax sections of the molar teeth of four adult male rats were cut in a plane parallel to the molar tooth row.

Cellular retinoic acid binding protein in the periodontal ligament.

As retinoic acid is an important signaling molecule during embryological development. Since periodontal tissues are thought to have fetal-like properties, the present study was to determine the presence and distribution of cellular retinoic acid-binding protein I(CRABPI) in the periodontal tissues of the rat. Following demineralization, wax sections of the molar teeth of four adult male rats were cut in a plane parallel to the molar tooth row.

Zebrafish pax[b] is involved in the formation of the midbrain-hindbrain boundary.

Among the genes thought to be involved in patterning the nervous system are a family of developmentally regulated paired box-containing (Pax) genes. Mutations in some of these Pax genes lead to severe developmental abnormalities. Zebrafish pax[b](pax[zf-b]) is a member of the Pax gene family that is expressed in the presumptive posterior midbrain from the end of gastrulation and, at later stages, in other localized regions of the developing embryo.

Retinoic acid and development of the central nervous system.

We consider the evidence that RA, the vitamin A metabolite, is involved in three fundamental aspects of the development of the CNS: 1) the stimulation of axon outgrowth in particular neuronal sub-types; 2) the migration of the neural crest; and 3) the specification of rostrocaudal position in the developing CNS (forebrain, midbrain, hindbrain, spinal cord). The evidence we discuss involves RA-induction of neurites in cell cultures and explants of neural tissue; the teratological effects of RA on the embryo's nervous system; the observation that RA can be detected endogenously in the spinal cord; and the fact that the receptors and binding proteins for RA are expressed in precise domains and neuronal cell types within the nervous system.

Domains of cellular retinoic acid-binding protein I (CRABP I) expression in the hindbrain and neural crest of the mouse embryo.

We describe here the distribution of cellular retinoic acid-binding protein I (CRABP I) in the head of the early mouse embryo from day 8 to day 13 of gestation, using both in situ hybridisation to localise mRNA and immunocytochemistry to localise protein. The distribution of mRNA and protein was found to be identical. CRABP I first appeared in part of the presumptive hindbrain of the presomite embryo and then became localised to rhombomeres 2, 4, 5 and 6.

The molecular basis of positional information.

Embryologists have dreamed of their own particular philosophers stone for 100 years. During that time they have repeatedly demonstrated the likely existence of signalling molecules or morphogens that control the pattern of development in the embryo. Now at last seems possible that some of these morphogens may have been identified.

Retinoic acid stimulates neurite outgrowth in the amphibian spinal cord.

There is increasing evidence that retinoic acid (RA), a vitamin A metabolite, plays a role in the development of the nervous system. Here we specifically test this notion by examining the effect of RA on neurite outgrowth from explanted segments of the axolotl spinal cord. We show that there is a threshold concentration in the region of 0.

The murine Hox-2 genes display dynamic dorsoventral patterns of expression during central nervous system development.

This report demonstrates that the genes in the murine Hox-2 cluster display spatially and temporally dynamic patterns of expression in the transverse plane of the developing CNS. All of the Hox-2 genes exhibit changing patterns of expression that reflect events during the ontogeny of the CNS. The observed expression correlates with the timing and location of the birth of major classes of neurons in the spinal cord.

The respecification of limb pattern by new synthetic retinoids and their interaction with cellular retinoic acid-binding protein.

We describe here experiments to examine the role of cellular retinoic-acid-binding protein (CRABP) during the induction of limb duplication in the chick limb bud and regenerating axolotl limb by retinoids. A newly synthesised class of retinoic acid analogues have been used because among them, some have been specifically designed with the property of binding to the retinoic acid receptors, but not to CRABP. We can thus test whether binding to CRABP is an obligatory step during limb respecification.

The involvement of retinoic acid in the development of the vertebrate central nervous system.

We discuss here both previously published data and our current experiments which suggest that the vitamin A derivative, retinoic acid (RA), may play a role in the development of the vertebrate central nervous system (CNS). This evidence comes from the following: both an excess and a deficiency of vitamin A causes embryonic defects of the CNS; RA has been detected endogenously in the CNS; RA stimulates neurite outgrowth; the retinoic acid receptors have been detected with interesting distributions in the CNS; the binding protein for retinol, namely cellular retinol binding protein (CRBP) is found in the radial glia of the ventral floor plate; the binding protein for RA, namely, cellular retinoic acid binding protein (CRABP) is found in particular sets of axons in the developing spinal cord, in particular rhombomeres in the developing hindbrain and in the neural crest. Some hypotheses for the possible role of RA in various aspects of CNS development are discussed.

Retinoic acid-binding protein, rhombomeres and the neural crest.

We have investigated by immunocytochemistry the spatial and temporal distribution of cellular retinoic acid-binding protein (CRABP) in the developing nervous system of the chick embryo in order to answer two specific questions: do neural crest cells contain CRABP and where and when do CRABP-positive neuroblasts first arise in the neural tube? With regard to the neural crest, we have compared CRABP staining with HNK-1 staining (a marker of migrating neural crest) and found that they do indeed co-localise, but cephalic and trunk crest behave slightly differently. In the cephalic region in tissues such as the frontonasal mass and branchial arches, HNK-1 immunoreactivity is intense at early stages, but it disappears as CRABP immunoreactivity appears. Thus the two staining patterns do not overlap, but are complementary.

Retinoid-binding protein distribution in the developing mammalian nervous system.

We have analysed the distribution of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) in the day 8.5-day 12 mouse and rat embryo. CRBP is localised in the heart, gut epithelium, notochord, otic vesicle, sympathetic ganglia, lamina terminalis of the brain, and, most strikingly, in a ventral stripe across the developing neural tube in the future motor neuron region.

Retinoic acid, a developmental signalling molecule.

Retinoic acid has been used as a tool both by embryologists studying the spatial organization of cells in the embryo and by molecular biologists studying the control of gene expression in the nucleus. Embryologists have shown that retinoic acid can modify the pattern of cell differentiation so as to duplicate complete parts of the embryo in a well-organized way; molecular biologists have shown that retinoic acid can act as the switch starting the sequence of differential gene expression that results in cell differentiation. In the past year these two approaches have converged so that there now seems a real possibility that we may soon for the first time understand how a particular vertebrate development system works.

Cellular retinoic acid-binding protein and the role of retinoic acid in the development of the chick embryo.

The distribution of cellular retinoic acid-binding protein (CRABP) in four stages of chick development is described using an affinity-purified antibody against rat CRABP. CRABP is the protein to which retinoic acid (RA) binds when it enters cells and may reflect the requirement of those cells for RA. We found several discrete cell populations which showed high levels of immunoreactivity.

The relationship among retinoid structure, affinity for retinoic acid-binding protein, and ability to respecify pattern in the regenerating axolotl limb.

To further our understanding of the action of retinoids on the respecification of pattern in the regenerating axolotl limb we have studied the relative potencies of a range of synthetic and natural retinoids administered locally to the blastema. Alterations in the polar end group of the retinoic acid (RA) molecule to produce esters, the alcohol, or the aldehyde abolish the ability of the molecule to respecify pattern. On the other hand, alterations of the ring or side chain to produce the synthetic retinoids arotinoid and TTNPB considerably increases the potency of the molecule to respecify pattern--TTNPB is at least 100X more potent than retinoic acid.