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PubMed1995

Implication of inhibin and related proteins in fetal development.

Initial studies on inhibin, activin and follistatin focussed on their role as regulators of adult gonadal function via feedback regulation of anterior pituitary hormones and via intragonadal control of steroid hormones. The discovery of isoforms of follistatin which are either secreted or retained on the cell surface and which bind activin and, to a lesser extent, inhibin adds a further dimension to the regulation of these peptides. More recently, the cloning of inhibin and activin, and the observation of their close homology to the transforming growth factor-beta family of peptides, has led to an interest in their possible role as growth and differentiation factors. Activin, inhibin and follistatin are expressed in embryonic and fetal tissues, as well as in the placenta. However, although activin is a potent regulator of growth and differentiation in a number of cell types, their role in embryonic and fetal development has yet to be established. High concentrations of inhibin have been observed in the fetal gonads, particularly the testes, and in the fetal adrenals of a number of species and a sex difference in fetal plasma concentrations has also been observed. Although the stimulus for high concentrations of inhibin in the fetus is not know, they are associated with decreased testicular testosterone and a decrease in the concentration of circulating follicle-stimulating hormone (FSH); this suggests that, as in the adult, inhibin may be involved in the regulation of fetal testicular androgen and pituitary FSH secretion during late gestation. The recent reports of elevated concentrations of inhibin and, particularly, activin in amniotic fluid during late gestation and its ability to stimulate the production of prostaglandin E2 by fetal membranes provides yet another potential role for this hormone in the regulation of events leading to parturition.

Activins↗

PubMed1988

Characterization of prenatal growth and development in the crab-eating macaque (Macaca fascicularis) by ultrasound.

Diagnostic ultrasound is a valuable tool for the examination of various anatomical structures in vivo. Improvements in technology have increased its effectiveness and provided a noninvasive method for the in utero observation of a variety of structural and functional events. Ultrasound is utilized in our laboratory to monitor a variety of studies during embryonic and fetal development. Basic to these evaluations is the ability to assess normal growth and development. The cynomolgus, or crab-eating macaque (Macaca fascicularis), has been observed in utero by ultrasound from early gestation to term. The earliest detection of implantation is by the identification of a developing gestational sac (GS), which may be visualized on gestational day (GD) 14-15. Positive identification of the GS on GD 16-18 and appearance of the embryo, yolk sac, and cardiac motion on GD 21-25 confirms pregnancy. Once the embryo is evident, measurements of the greatest length (GL) may be used to assess normal growth or to aid in the prediction of gestational age. During the fetal period, a variety of growth parameters aid in fetal evaluation. The gender of the fetus can be accurately identified as early as GD 70-75. An assessment of viability and condition can be determined by the observation of embryonic and fetal heart rates and gross body movement.

Animals↗

PubMed1999

Sequence and expression analysis of Nhlh1: a basic helix-loop-helix gene implicated in neurogenesis.

Nhlh1 is a basic helix-loop-helix (bHLH) gene that has been implicated in mouse neurogenesis. Previous studies have shown it to be expressed in regions in which there are differentiating neurons during late embryonic and fetal development, but detailed studies of the role of Nhlh1 earlier in embryonic development have not been performed. In this paper, we examine the expression of Nhlh1 transcripts at early embryonic stages (E8.5-E10.5), at the onset of neurogenesis, and compare the pattern of expression with that of Islet-1, a marker of postmitotic neurons. We show that Nhlh1 is expressed in early postmitotic neurons but is down-regulated as these cells migrate from the ventricular zone. We have also determined the genomic structure of mouse Nhlh1 and have characterised the promoter sequence, as a first step towards identifying factors that may control Nhlh1 expression. Nhlh1 has been implicated previously as a candidate for the neural tube defect mutant loop-tail (Lp); here, we present sequence and expression data indicating that Nhlh1 is unlikely to be responsible for the Lp mutation.

Amino Acid Sequence↗

PubMed1989

A developmental study of the abnormal expression of alpha-cardiac and alpha-skeletal actins in the striated muscle of a mutant mouse.

BALB/c mice possess a 5' duplication of the alpha-cardiac actin gene which is associated with abnormal levels of alpha-cardiac and alpha-skeletal actin mRNAs in adult cardiac tissue. This mutation therefore provides a potential tool for the study of the inter-relationship between the striated muscle actins. We have examined the expression of this actin gene pair throughout the development of skeletal and cardiac muscle in BALB/c mice. During embryonic and fetal development, the expression of these two genes is indistinguishable from that in normal mice, as determined by in situ hybridization. A quantitative postnatal study demonstrates that in the hearts of normal mice the level of alpha-cardiac actin mRNA declines, whereas that of alpha-skeletal actin increases. In mutant mice, these trends are exaggerated so that whereas normal mice have 95.8% alpha-cardiac mRNA and 4.2% alpha-skeletal mRNA in the adult heart, BALB/c mice have 52.4 and 47.6% of these mRNAs, respectively. This difference is also reflected at the protein level. In developing skeletal muscle, the expression of these genes follows kinetics similar to that observed in the heart with a decrease in the relative level of alpha-cardiac mRNA as the muscle matures. Cardiac actin mRNA levels are again lower in the mutant mouse, but here the effect is less striking because skeletal actin is the predominant isoform. These results are discussed in the context of the interaction between this actin gene pair in developing and adult striated muscle.

Actins↗

PubMed1985

Prenatal hamster development following maternal administration of PGE2 at midterm.

The effects of PGE2 on embryonic and fetal development were studied in the golden Syrian hamster. Pregnant hamsters were treated on day 8 of gestation with either 0.2, 0.5, 0.75, or 1.0 mg/kg PGE2 delivered I.P. and the near term litters were compared to those of untreated and vehicle treated controls. Fetuses from the treated litters showed significantly higher frequencies of mortality, lower weights, malformations, and missing ossification centres in comparison to control litters. The results demonstrate that PGE2 is teratogenic in the hamster and the developing neural tube and the fetal skeleton are particularly susceptible to the effects of this teratogen.

Abnormalities, Drug-Induced↗

PubMed2002

Three-dimensional sonoembryology.

Three-dimensional (3D) ultrasound plays an important role in obstetrics, predominantly for assessing fetal anatomy. Presenting volume data in a standard anatomic orientation valuably assists both ultrasonographers and pregnant patients to recognize the anatomy more readily. Three-dimensional ultrasound is advantageous in studying normal embryonic and/or fetal development, as well as providing information for families at risk for specific congenital anomalies by confirming normality. This method offers advantages in assessing the embryo in the first trimester due to its ability to obtain multiplanar images through endovaginal volume acquisition. Rotation allows the systematic review of anatomic structures and early detection of fetal anomalies. Three-dimensional ultrasound imaging in vivo compliments pathologic and histologic evaluation of the developing embryo, giving rise to a new term: 3D sonoembryology. Rapid technological development will allow real-time 3D ultrasound to provide improved and expanded patient care on the one side, and increased knowledge of developmental anatomy on the other.

Congenital Abnormalities↗

PubMed1997

The oncoproteins c-erb-B2, c-fos and the tumour suppressor protein p53 in human embryos and fetuses.

Oncoproteins and tumour-suppressor proteins are thought to possess an antagonistic function in the regulation of growth and differentiation processes during embryonic and fetal development. In contrast, in the adult, tumour growth is associated with the overexpression of oncoproteins or the malfunction of tumour-suppressor proteins. We examined the occurrence of the tumour proteins c-erb-B2 and c-fos and the tumour-suppressor protein p53 in 17 human embryos and fetuses with the help of immunohistochemistry. C-erb-B2 was detected mainly in embryonic tissue that are not known for c-erb-B2-overexpression in tumours in the adult. In contrast, c-fos was almost always located in fetal tissues corresponding to its location in adult tumours. Staining for p53 was found in a wide variety of embryonic and fetal tissues. C-erb-B2 and p53 were localized in the same tissue structures of the developing skin, heart and muscle. In other tissues, e.g. muscle and bone, c-fos was found together with p53, suggesting an antagonistic action of these proliferative and antiproliferative factors. Furthermore, c-erb-B2. c-fos and p53 appear to be important for growth and differentiation processes in human development as the occurrence of these proteins was not only restricted to specific tissues but also to specific stages of development of these tissues.

Embryo, Mammalian↗

PubMed1996

Ontogeny of 5 alpha-reductase (type 1) messenger ribonucleic acid expression in rat brain: early presence in germinal zones.

The physiological significance of androgens and neurosteroids in the development of the central nervous system (CNS) is still unclear. One way to address this question is to examine the regional and developmental expression of enzymes involved in the biosynthesis of these compounds. As 5alpha-reduction is a key step in the formation of dihydrotestosterone and some neurosteroids, we investigated the distribution of 5alpha-reductase (type 1) messenger RNA (mRNA) in the brain of fetuses and offspring of time pregnant Long-Evan rats by means of in situ hybridization. Our results indicate that during ontogeny, 5alpha-reductase mRNA is expressed in three distinct patterns. 1) During late embryonic and fetal development, on gestational days 12-18, specific 5alpha-reductase mRNA was detected in germinal and ventricular zones of the developing CNS. Specific labeling was also detected in the liver and certain ganglia, such as those of the trigeminal and spinal nerves. 2) During late fetal and early postnatal development, 5alpha-reductase mRNA levels in the ventricular zones gradually decreased, but specific mRNA newly appeared in differentiating regions of the brain, such as the cortical plate and the thalamus. 3) On postnatal day 15 and in adult animals, low levels of 5alpha-reductase mRNA were detected in typical white matter structures, such as optical chiasm, lateral olfactory tract, and corpus callosum. Expression of 5alpha-reductase mRNA in germinal zones and differentiating fields of the pre- and early postnatal rat CNS has not been described; this suggests that 5alpha-reductase might serve a function in general aspects of brain development, e.g. proliferation and differentiation. As several types of steroid hormones can serve as substrates for 5alpha-reductase, it remains to be elucidated which metabolite(s) mediates the possible actions of the_ enzyme in CNS development.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed1989

Role of cumulus cells and serum on the in vitro maturation, fertilization, and subsequent development of rat oocytes.

Immature oocytes were collected from immature female rats (60-65 g) 40 h after injection with 6 IU pregnant mare's serum gonadotropin (PMSG). Oocytes were matured cumulus-intact (CI) or cumulus-free (CF) in medium supplemented with 0.5% bovine serum albumin (BSA) or 5-20% serum for periods of up to 24 h. After assessment for nuclear maturation, the oocytes were exposed to epididymal sperm for fertilization in vitro. In vitro-matured and ovulated oocytes undergoing fertilization were transferred to unilaterally pregnant recipients for embryonic and fetal development. The presence of cumulus cells and serum shortened (by 2 h) the time required for polar body emission by in vitro-matured oocytes and also helped to increase significantly the penetrability of the oocytes by spermatozoa. A high proportion (45.6%) of fertilized oocytes showed evidence of abnormal fertilization following maturation in the absence of cumulus cells. Oocytes matured CI before fertilization were able to develop to viable fetuses (57.8%) in proportions similar to ovulated oocytes (55.0%) after in vitro fertilization. These findings indicate an essential role for cumulus cells in promoting normal cytoplasmic maturation of oocytes necessary for pronuclear formation and subsequent developmental capability.

Animals↗

PubMed1998

First trimester utero-placental circulation: maternal-fetal interaction.

Progressive development of embryonal and maternal circulations is essential for normal pregnancy outcome. The early embryo and trophoblast are very sensitive to the conditions under which they grow and differentiate. The most crucial event in human ontogeny is trophoblast invasion, a process that will enable chorionic and maternal circulations to develop in a synchronized fashion, balancing the metabolic needs with the capability to defend against oxidative stress. Trophoblast invasion transforms the spiral arteries into low resistance vessels, a change necessary for establishment of continuous forward blood flow once the villi are anchored and have obtained defense mechanisms against oxidative insult. Based on a review of current knowledge of human trophoblast and embryonic growth and development of embryonic and maternal placental circulations it seems that human ontogeny occurs in a low oxygen environment during the initial stages of pregnancy. This is similar to the environment in which the first single cell organisms appeared and it remains to be seen if the development process of the primitive single cell organisms, and its energy generating processes, is an appropriate model for studying early human ontogeny.

Cell Differentiation↗

PubMed2001

Neurochemical differentiation of functionally distinct populations of autonomic neurons.

The coeliac ganglion of guinea pigs displays a unique topographical arrangement of neurochemically and functionally distinct populations of sympathetic neurons. The authors used multiple-labeling immunohistochemistry to investigate the neurochemical differentiation of these neurons during embryonic and fetal development. Sympathoadrenal precursors, located on either side of the abdominal aorta, were intensely immunoreactive for tyrosine hydroxylase (TH-IR), neurofilament, and the human natural killer 1 antibody at midembryonic stages (Carnegie stages 16-19). During late embryonic stages (stages 20-23), a single bilobed ganglion had formed. At this time, neuropeptide Y immunoreactivity (NPY-IR) was widely expressed in sympathetic neurons (with moderate TH-IR) and chromaffin cells (with intense TH-IR). The onset of somatostatin (Som-IR) expression followed that of NPY-IR and was restricted to sympathetic neurons. However, at late embryonic stages, most TH-IR neurons with Som-IR also expressed NPY-IR (a combination of peptides not found in the mature coeliac ganglion). Between late embryonic stages and the end of the early fetal period, there was a significant increase in the proportion of neurons in lateral regions that had both NPY-IR and TH-IR. At the same time, there was an increase in the proportion of neurons in medial regions that had both Som-IR and TH-IR. Neurons expressing both Som-IR and TH-IR were rarely observed in lateral regions of the coeliac ganglion. Thus, a clear topography within the coeliac ganglion is established during late embryonic and early fetal stages of development and reflects that found in the mature animal by the end of the early fetal period.

Adrenal Glands↗

PubMed2004

Bystander effects, adaptive response and genomic instability induced by prenatal irradiation.

The developing human embryo and fetus undergo very radiosensitive stages during the prenatal development. It is likely that the induction of low dose related effects such as bystander effects, the adaptive response, and genomic instability would have profound effects on embryonic and fetal development. In this paper, I review what has been reported on the induction of these three phenomena in exposed embryos and fetuses. All three phenomena have been shown to occur in murine embryonic or fetal cells and structures, although the induction of an adaptive response (and also likely the induction of bystander effects) are limited in terms of when during development they can be induced and the dose or dose-rate used to treat animals in utero. In contrast, genomic instability can be induced throughout development, and the effects of radiation exposure on genome instability can be observed for long times after irradiation including through pre- and postnatal development and into the next generation of mice. There are clearly strain-specific differences in the induction of these phenomena and all three can lead to long-term detrimental effects. This is true for the adaptive response as well. While induction of an adaptive response can make fetuses more resistant to some gross developmental defects induced by a subsequent high dose challenge with ionizing radiation, the long-term effects of this low dose exposure are detrimental. The negative effects of all three phenomena reflect the complexity of fetal development, a process where even small changes in the timing of gene expression or suppression can have dramatic effects on the pattern of biological events and the subsequent development of the mammalian organism.

Animals↗

PubMed2003

From the germinal cells to the newborn animal: the transmission of genes and life through the generations.

The technology of reproduction progressed considerably during the last decade, leading to a certain availability of in vitro methods for fertilisation, oocyte maturation and embryo culture. The most spectacular manipulations are cloning and transgenesis. This review focuses on the early appearance of germinal cell precursors and the long-standing fate of gametes in mammals. The evident complexity and long-term programming of events in gametes and early embryos explain part of the difficulties encountered during the development of in vitro and in vivo methods such as multiple ovulation and embryo transfer (MOET), oestrus synchronisation, ovulation induction, superovulation, in vitro maturation and fertilisation, cryopreservation, transgenesis, nuclear transfer and cloning) and the occurrence of unexpected alterations of development, e.g. embryonic or fetal mortality, large-weight newborn syndrome and other dysregulations in imprinting or DNA transmission.

Animals↗

PubMed1994

Polysialic acid of the neural cell adhesion molecule (N-CAM) is widely expressed during organogenesis in mesodermal and endodermal derivatives.

We have studied the expression of homopolymers of alpha 2,8-linked sialic acid (polySia) and the neural cell adhesion molecule (N-CAM) during the embryonic and fetal development of rat, chicken and man using immunocytochemistry and immunoblotting. During development, polySia and N-CAM were widely expressed in mesodermally and neuro-ectodermally derived elements. In specific developmental processes, cells of endodermal and ectodermal (non-neural) origin were also immunoreactive for these molecules. Loss of polySia and N-CAM immunoreactivity often accompanied differentiation of mesodermally derived cells. In cartilage formation for instance, cells in precartilaginous mesenchymal condensations stained for N-CAM and polySia until the first appearance of specific chondrocyte function, independent of the stage of development. Transient de novo expression of polySia, in newly induced ectodermal cells, paralleled the reciprocal inductive interactions of mesodermally derived cells with cells of ectodermal origin during hair follicle formation. All ectodermally derived hair follicle cells, except the putative stem cells, later ceased expression of these molecules. Ectodermal expression of polySia and N-CAM was otherwise rare. The endodermally derived epithelium of the digestive and respiratory tracts were polySia and N-CAM immunoreactive early in organogenesis (embryonic day 12 in mouse). Cells of this derivation later all became unreactive, although decrease in immunoreactivity during development was faster in derivatives of more cranial portions of the endoderm. In general, during organogenesis, epithelial elements showed polySia and N-CAM expression before and during epithelium formation, thereafter losing immunoreactivity, irrespective of the developmental origin of the epithelial cells. PolySia and N-CAM staining in the chicken respiratory tract epithelium was more wide-spread and lasted significantly longer than in either man or rat. Cells that expressed N-CAM, but not polySia, were found during the development of both skin and pancreas, indicating independent control of polySia expression. Outside the nervous system no cells that expressed polySia but not N-CAM were observed.

Animals↗

PubMed1992

Embryology of the eye and its adnexae.

The embryonal and fetal development of the human eye includes a series of sequential events starting with the fertilization of the ovum and culminating in the birth of a normal baby. Three main periods can be distinguished in the prenatal development of the eye. The first period called embryogenesis is characterized by the establishment of the primary organ rudiments and ends at the end of the 3rd week with the appearance of the optic sulci on both sides of the midline at the expanded cranial end of the still open neural folds. The second period called organogenesis includes the development of the primary organ rudiments and extends till the end of the 8th week. The third period involves the differentiation of each of the primitive organs into a fully or partially active organ and is called differentiation. The period of embryogenesis is characterized by the appearance and migration of the neural crest cells and by the formation of the primary brain vesicles. The period of organogenesis extends from the 4th week till the end of the 8th week. The 4th week shows the closure of the neural canal anteriorly with the subsequent evagination of its lateral wall into optic vesicles, the invagination of the lower nasal wall of the optic vesicle causing the formation of the optic cup, and the development of the lens plate, retinal disk and embryonic fissure. The embryonic fissure extends into the optic stalk which connects the cavity of the optic vesicle with the cavity of the neural canal; the hyaloid artery penetrates into the optic cup through the embryonic fissure. During the 5th week, the optic cup is concluded, and the cells of its external layer acquire pigmentation as a result of contact with developing capillaries in the periocular mesenchyme; these capillaries anastomose with each other and form anteriorly the annular vessel. The lens plate develops into a lens pit and later into a lens vesicle which separates soon thereafter from the surface ectoderm. Inside the optic cup, the hyaloid vessels form the capillaries of the posterior tunica vasculosa lentis and through the capillaries of the lateral tunica vasculosa lentis anastomose with the annular vessel. The primary vitreous forms and the surface ectoderm overlying the lens vesicle differentiates into a primitive corneal epithelium. The facial and orbital structures also develop at this stage. The 6th week shows the incipient differentiation of the inner layer of the optic cup into a sensory retina, the formation of the secondary vitreous, the transformation of the posterior cells of the lens vesicle into primary lens fibers, the development of the periocular vasculature and the appearance of the first eyelid folds and of the anlage of the nasolacrimal duct. However, the dominating factor is the closure of the embryonic fissure.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Differentiation↗

PubMed2003

Lack of developmental toxicity of D-003: a mixture of long-chain fatty acids in rats.

D-003 is a mixture of long-chain fatty acids isolated and purified from sugar cane wax, the major component of which is 1-octacosanoic acid and which possesses effective antiplatelet, antithrombotic and cholesterol-lowering effects. D-003 was suspended in 1% acacia gum solution, and given daily by gavage to rats at dose levels of 5, 100 and 1000 mg/kg/day on days 6 through 15 of gestation. Cyclophosphamide, serving as a positive control, was given at the dose of 50 mg/kg/day on day 15 of gestation. Evidence of maternal or developmental toxicity was not observed in the groups treated with D-003. Maternal clinical signs of toxicity were not observed and the analysis of initial body weight and the body weight gain during the treatment period was comparable among the groups treated with D-003 and control. As expected, cyclophosphamide caused both embryotoxic and teratogenic effects in rats. Meanwhile, no adverse effects on reproductive performance, or on embryonic or fetal development, including visceral and skeletal examination, were seen in any of the groups administered D-003. It is concluded that D-003 administered up to 1000 mg/kg/day did not induce any evidence of developmental toxicity.

Abnormalities, Drug-Induced↗

PubMed2006

Medical treatment for early fetal death (less than 24 weeks).

BACKGROUND: In most pregnancies that miscarry, arrest of embryonic or fetal development occurs some time (often weeks) before the miscarriage occurs. Ultrasound examination can reveal abnormal findings during this phase by demonstrating anembryonic pregnancies or embryonic or fetal death. Treatment before 14 weeks has traditionally been surgical but medical treatments may be effective, safe, and acceptable, as may be waiting for spontaneous miscarriage. OBJECTIVES: To assess the effectiveness, safety and acceptability of any medical treatment for early pregnancy failure (anembryonic pregnancies or embryonic and fetal deaths before 24 weeks). SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group Trials Register (30 November 2005). SELECTION CRITERIA: Randomised trials comparing medical treatment with another treatment (e.g. surgical evacuation), or placebo, or no treatment for early pregnancy failure. Quasi-random studies were excluded. DATA COLLECTION AND ANALYSIS: Data were extracted unblinded. MAIN RESULTS: Twenty four studies (1888 women) were included. Vaginal misoprostol hastens miscarriage (complete or incomplete) when compared with placebo: e.g. miscarriage less than 24 hours (two trials, 138 women, relative risk (RR) 4.73, 95% confidence interval (CI) 2.70 to 8.28), with less need for uterine curettage (two trials, 104 women, RR 0.40, 95% CI 0.26 to 0.60) and no significant increase in nausea or diarrhoea. Lower-dose regimens of vaginal misoprostol tend to be less effective in producing miscarriage (three trials, 247 women, RR 0.85, 95% CI 0.72 to 1.00) with similar incidence of nausea. There seems no clear advantage to administering a 'wet' preparation of vaginal misoprostol or of adding methotrexate, or of using laminaria tents after 14 weeks. Vaginal misoprostol is more effective than vaginal prostaglandin E in avoiding surgical evacuation. Oral misoprostol was less effective than vaginal misoprostol in producing complete miscarriage (two trials, 218 women, RR 0.90, 95% CI 0.82 to 0.99). Sublingual misoprostol had equivalent efficacy to vaginal misoprostol in inducing complete miscarriage but was associated with more frequent diarrhoea. The two trials of mifepristone treatment generated conflicting results. There was no statistically significant difference between vaginal misoprostol and gemeprost in the induction of miscarriage for fetal death after 13 weeks. AUTHORS' CONCLUSIONS: Available evidence from randomised trials supports the use of vaginal misoprostol as a medical treatment to terminate non-viable pregnancies before 24 weeks. Further research is required to assess effectiveness and safety, optimal route of administration and dose. Conflicting findings about the value of mifepristone need to be resolved by additional study.

Abortifacient Agents↗

PubMed1992

Multiple sites of Hox-7 expression during mouse embryogenesis: comparison with retinoic acid receptor mRNA localization.

We report results from a study of Hox-7 expression during mouse embryonic and fetal development and compare the localization of Hox-7 transcripts with those of the retinoic acid receptors. Transcripts were detected by in situ hybridization. Hox-7 expression occurs in (1) cephalic neural crest and its derivatives, (2) sites of ectomesodermal interaction, (3) extraembryonic tissues, and (4) endocardial cells. Hox-7 does not seem to be involved in defining rostrocaudal boundaries, but instead appears to be expressed along the proximodistal axes at these sites. We further investigated the active sites of morphogenesis, which involve an ectomesodermal interaction (e.g., limb buds, visceral arches), including genital tubercle and tail ridge. These are regions highly positive for Hox-7 transcripts, and many are known to be sites for the expression of gamma-retinoic acid receptors (RARs) and cellular retinoic acid binding proteins. Most regions that express Hox-7 are subregions of gamma-RAR expression. In the developing limb bud, expression of Hox-7 takes place in the interdigital region, where it overlaps areas of beta-RAR expression.

Animals↗