The biological activity of retinoic acid in the domestic fowl and the effects of vitamin A deficiency on the chick embryo

Leg disorders in broiler chickens: a review of current knowledge

Ensuring improved leg health is an important prerequisite for broilers to achieve optimal production performance and welfare status. Broiler leg disease is characterized by leg muscle weakness, leg bone deformation, joint cysts, arthritis, femoral head necrosis, and other symptoms that result in lameness or paralysis. These conditions significantly affect movement, feeding and broiler growth performance. Nowadays, the high incidence of leg abnormalities in broiler chickens has become an important issue that hampers the development of broiler farming. Therefore, it is imperative to prevent leg diseases and improve the health of broiler legs. This review mainly discusses the current prevalence of broiler leg diseases and describes the risk factors, diagnosis, and prevention of leg diseases to provide a scientific basis for addressing broiler leg health problems.

Spermatogonia differentiation requires retinoic acid receptor γ

Vitamin A is instrumental to mammalian reproduction. Its metabolite, retinoic acid (RA), acts in a hormone-like manner through binding to and activating three nuclear receptor isotypes, RA receptor (RAR)α (RARA), RARβ, and RARγ (RARG). Here, we show that 1) RARG is expressed by A aligned (A(al)) spermatogonia, as well as during the transition from A(al) to A(1) spermatogonia, which is known to require RA; and 2) ablation of Rarg, either in the whole mouse or specifically in spermatogonia, does not affect meiosis and spermiogenesis but impairs the A(al) to A(1) transition in the course of some of the seminiferous epithelium cycles. Upon ageing, this phenomenon yields seminiferous tubules containing only spermatogonia and Sertoli cells. Altogether, our findings indicate that RARG cell-autonomously transduces, in undifferentiated spermatogonia of adult testes, a RA signal critical for spermatogenesis. During the prepubertal spermatogenic wave, the loss of RARG function can however be compensated by RARA, as indicated by the normal timing of appearance of meiotic cells in Rarg-null testes. Accordingly, RARG- and RARA-selective agonists are both able to stimulate Stra8 expression in wild-type prepubertal testes. Interestingly, inactivation of Rarg does not impair expression of the spermatogonia differentiation markers Kit and Stra8, contrary to vitamin A deficiency. This latter observation supports the notion that the RA-signaling pathway previously shown to operate in Sertoli cells also participates in spermatogonia differentiation.

Retinoic acid and the heart

Retinoic acid (RA), the active derivative of vitamin A, by acting through retinoid receptors, is involved in signal transduction pathways regulating embryonic development, tissue homeostasis, and cellular differentiation and proliferation. RA is important for the development of the heart. The requirement of RA during early cardiovascular morphogenesis has been studied in targeted gene deletion of retinoic acid receptors and in the vitamin A-deficient avian embryo. The teratogenic effects of high doses of RA on cardiovascular morphogenesis have also been demonstrated in different animal models. Specific cardiovascular targets of retinoid action include effects on the specification of cardiovascular tissues during early development, anteroposterior patterning of the early heart, left/right decisions and cardiac situs, endocardial cushion formation, and in particular, the neural crest. In the postdevelopment period, RA has antigrowth activity in fully differentiated neonatal cardiomyocytes and cardiac fibroblasts. Recent studies have shown that RA has an important role in the cardiac remodeling process in rats with hypertension and following myocardial infarction. This chapter will focus on the role of RA in regulating cardiomyocyte growth and differentiation during embryonic and the postdevelopment period.

Effects of high dietary vitamin A supplementation on tibial dyschondroplasia, skin pigmentation and growth performance in avian broilers

An experiment was conducted to study high dietary vitamin A on tibial dyschondroplasia, growth performance and skin pigmentation in broilers. One hundred and twenty Avian commercial broilers were randomly allotted to three treatments: group C (control group), in which broilers were fed basic diet containing vitamin A 5512IU/kg diet; group A, in which broilers were fed basic diet with addition vitamin A 35512IU/kg; group B, broilers were fed basic diet with supplement vitamin A 65512IU/kg. The experiment lasted 35d and at the end of the trial, broilers were killed and the right proximal tibiotarsi were dissected in longitudinal section for the assessment of TD incidence and TD index, skin from the same area of breast and tibia in broilers were collected to determine pigmentation. The results showed that a high level vitamin A significantly increased the rate of TD incidence and TD index, but middle level vitamin A did not have a significant effect on that. Both low and high retinoic acid decreased growth performance and skin pigmentation in broilers. It suggests that a high dietary vitamin A cause tibial dyschondroplasia in broilers, decreased growth performance and skin pigmentation. It is likely that the effect of vitamin A on TD is mediated through a depression of vitamin D status.

Retinoid requirements in the reproduction of zebrafish

This study examines whether retinoids are essential in the reproduction of zebrafish. Using RT-PCR, it was shown that the ovaries and testes express enzymes that synthesize and metabolize the hormone retinoic acid (RA) (raldh2 and cyp26a, respectively), and RA receptors (raraa, rarga, rxrba, rxrbb, rxrga but not rxrab). Three new isoforms of rxrba were also observed in a variety of tissues. In other experiments, zebrafish were exposed for 11 d to diethylaminobenzaldehyde (DEAB), an inhibitor of RA synthesis, or fed a retinoid deficient diet for 130 d in order to evaluate the functional requirements of retinoids in reproduction. DEAB altered cyp26a transcript numbers in the gonads, suggesting an impact on RA, and decreased the number of spawned eggs by 95%. The retinoid deficient diet decreased whole body retinoids (retinol and retinal) by 68% in females and 33% in males. Females fed the retinoid deficient diet also produced 73% fewer eggs that contained 78% less retinal than controls. Fertilization rates were not affected. These studies have shown that the RA receptors are expressed in zebrafish gonads, and RA is required for the spawning of eggs. Dietary retinoid content influences reproduction, while retinyl ester storage levels appear to be of little significance. Females were more susceptible to retinoid perturbation than males, likely due to the cost of retinal deposition in the eggs. Overall, these studies have shown retinoids play a fundamental role in the reproduction of zebrafish, and the lack of retinyl ester stores in controls that successfully spawned illustrates that we have only a limited understanding of the retinoid physiology and requirements of fish.

The expanding role for retinoid signaling in heart development

The importance of retinoid signaling during cardiac development has long been appreciated, but recently has become a rapidly expanding field of research. Experiments performed over 50 years ago showed that too much or too little maternal intake of vitamin A proved detrimental for embryos, resulting in a cadre of predictable cardiac developmental defects. Germline and conditional knockout mice have revealed which molecular players in the vitamin A signaling cascade are potentially responsible for regulating specific developmental events, and many of these molecules have been temporally and spatially characterized. It is evident that intact and controlled retinoid signaling is necessary for each stage of cardiac development to proceed normally, including cardiac lineage determination, heart tube formation, looping, epicardium formation, ventricular maturation, chamber and outflow tract septation, and coronary arteriogenesis. This review summarizes many of the significant milestones in this field and particular attention is given to recently uncovered cross-talk between retinoid signaling and other developmentally significant pathways. It is our hope that this review of the role of retinoid signaling during formation, remodeling, and maturation of the developing heart will serve as a tool for future discoveries.

CYP26A1 and CYP26C1 cooperatively regulate anterior-posterior patterning of the developing brain and the production of migratory cranial neural crest cells in the mouse

The appropriate regulation of retinoic acid signaling is indispensable for patterning of the vertebrate central nervous system along the anteroposterior (A-P) axis. Although both CYP26A1 and CYP26C1, retinoic acid-degrading enzymes that are expressed at the anterior end of the gastrulating mouse embryo, have been thought to play an important role in central nervous system patterning, the detailed mechanism of their contribution has remained largely unknown. We have now analyzed CYP26A1 and CYP26C1 function by generating knockout mice. Loss of CYP26C1 did not appear to affect embryonic development, suggesting that CYP26A1 and CYP26C1 are functionally redundant. In contrast, mice lacking both CYP26A1 and CYP26C1 were found to manifest a pronounced anterior truncation of the brain associated with A-P patterning defects that reflect expansion of posterior identity at the expense of anterior identity. Furthermore, Cyp26a1-/-Cyp26c1-/- mice fail to produce migratory cranial neural crest cells in the forebrain and midbrain. These observations, together with a reevaluation of Cyp26a1 mutant mice, suggest that the activity of CYP26A1 and CYP26C1 is required for correct A-P patterning and production of migratory cranial neural crest cells in the developing mammalian brain.

Retinoic acid and hindbrain patterning

Retinoid signaling plays an important role in the developmental patterning of the hindbrain. Studies of the teratogenic effects of retinoids showed early on that the hindbrain suffered patterning defects in cases of retinoid excess or deficiency. Closer examination of these effects in animal models suggested that retinoids might play a physiological role in specifying the antero-posterior axis of the hindbrain. This idea was supported by the localization of retinoid synthetic and degradative enzymes, binding proteins, and receptors to the hindbrain and neighboring regions of the neuroepithelium and the mesoderm. In parallel, it became clear that the molecular patterning of the hindbrain, in terms of the regionalized expression of Hox genes and other developmental regulatory genes, is profoundly influenced by retinoid signaling.

LEDGF regulation of alcohol and aldehyde dehydrogenases in lens epithelial cells: stimulation of retinoic acid production and protection from ethanol toxicity

Retinoic acid (RA) is required for the normal growth and maintenance of many cell types, including lens epithelial cells (LECs). Alcohol (ADH) and aldehyde (ALDH) dehydrogenases are implicated in cellular detoxification and conversion of vitamin A to RA. Lens epithelium-derived growth factor (LEDGF) provides cellular protection against stress by transactivating stress-associated genes. Here we show evidence that LEDGF binds and transactivates heat shock (nGAAn) and stress response (A/TGGGGA/T) elements in the promoters of ADH1, ADH4, and retinaldehyde 2 (RALDH2) genes. Electrophoretic mobility and supershift assays disclosed specific binding of LEDGF to nGAAn and A/TGGGGA/T elements in these gene promoters. Transfection experiments in LECs with promoters linked to a chloramphenicol acetyltransferase (CAT) reporter gene along with LEDGF cDNA revealed higher CAT activity. RT-PCR results confirmed that LECs overexpressing LEDGF contained increased levels of ADH1, ADH4, and RALDH2 mRNA. Notably, LECs displayed higher LEDGF mRNA and protein expression during ethanol stress. Cells overexpressing LEDGF typically exhibited elevated RA levels and survived well during ethanol stress. The present findings indicate that LEDGF is one of the transcriptional activators of these genes that facilitates cellular protection against ethanol stress and plays a role in RA production.

Regulation of retinoic acid distribution is required for proximodistal patterning and outgrowth of the developing mouse limb

Exogenous retinoic acid (RA) induces marked effects on limb patterning, but the precise role of endogenous RA in this process has remained unknown. We have studied the role of RA in mouse limb development by focusing on CYP26B1, a cytochrome P450 enzyme that inactivates RA. Cyp26b1 was shown to be expressed in the distal region of the developing limb bud, and mice that lack CYP26B1 exhibited severe limb malformation (meromelia). The lack of CYP26B1 resulted in spreading of the RA signal toward the distal end of the developing limb and induced proximodistal patterning defects characterized by expansion of proximal identity and restriction of distal identity. CYP26B1 deficiency also induced pronounced apoptosis in the developing limb and delayed chondrocyte maturation. Wild-type embryos exposed to excess RA phenocopied the limb defects of Cyp26b1(-/-) mice. These observations suggest that RA acts as a morphogen to determine proximodistal identity, and that CYP26B1 prevents apoptosis and promotes chondrocyte maturation, in the developing limb.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Retinoid metabolism (LRAT, REH) in the yolk-sac membrane of Japanese quail eggs and effects of mono-ortho-PCBs

Retinoids stored in the avian egg are essential for normal development, however, laboratory and field experiments suggest that they are affected by environmental contaminants. Lecithin:retinol acyltransferase (LRAT) activity was detected in the microsomal fraction of the yolk-sac membrane of the Japanese quail at day 6 of development. LRAT activity was maximal at pH 7.0 having apparent kinetic parameters of K(m)=1.35 microM and V(max)=0.21 nmol/mg protein/h and was inhibited by the sulfhydryl modifying agent N-ethyl-maleimide. Retinol ester hydrolase (REH) activity in the microsomal fraction of the yolk-sac membrane was stimulated by the bile salt analogue 3-[(3-cholamidopropyl) dimethyl-ammonio]-1-propane sulfonate and was maximal at pH 9.0 with apparent K(m)=77 microM and V(max)=34.3 nmol/mg protein/h. Injection of the PCB congener 2,3,3',4,4'-pentachlorobiphenyl increased both REH and LRAT activities, whereas 2,3,3',4-tetrachlorobiphenyl stimulated LRAT. Yolk retinol concentration and the molar ratio retinol:retinyl palmitate were lower in the exposed eggs. Yolk retinol concentration decreased as LRAT increased (R(2)=0.89) suggesting that certain PCB congeners may affect vitamin A mobilization in ovo by increasing LRAT activity in the yolk-sac membrane.

Vitamin A deficiency reduces insulin-like growth factor (IGF)-I gene expression and increases IGF-I receptor and insulin receptor gene expression in tissues of Japanese quail (Coturnix coturnix japonica)

The insulin-like growth factor (IGF) system is regulated by various stimuli, including hormones, growth factors and nutritional status. We examined the effects of vitamin A on components of the IGF system in Japanese quail. Male quail (1 d old) fed a vitamin A-deficient diet for 14 or 21 d developed vitamin A deficiency, as confirmed by a depletion of serum retinol and hepatic retinyl palmitate. Consuming the vitamin A-deficient diet for 14 d did not affect growth rate, but decreased the serum IGF-I concentrations by 22% compared with the control group. The decreased serum IGF-I levels were accompanied by 21-52% lower levels of IGF-I mRNA in the testis, lung, liver and heart, whereas IGF-I receptor (IGF-IR) and insulin receptor (IR) gene expressions were unaffected in these tissues. Continuous feeding of the vitamin A-deficient diet for 21 d retarded growth and further decreased the levels of serum IGF-I and tissue IGF-I mRNA. Serum IGF-I levels were reduced by approximately 50%; IGF-I mRNA levels were > 90% lower in the liver and lung and approximately 60% lower in the heart and testis. In contrast, levels of the IGF-IR and IR mRNAs were approximately 100% greater in some tissues examined. When vitamin A-deficient quail received a single injection of retinol or retinoic acid (0.1 mg/bird), tissue IGF-I, IGF-IR and IR gene expressions did not change after 4 h. These results suggest a possible physiologic role of the IGF system in mediating vitamin A-supported growth of Japanese quail.

Cloning of complementary deoxyribonucleic acids encoding quail (Coturnix coturnix japonica) retinoic acid receptor ss isoforms and changes in their gene expression during gonadotropic growth

Retinoids have important effects on the development of the reproductive system, where they act via their specific nuclear receptors: retinoic acid receptors (RARalpha, ss, gamma) and retinoid X receptors (RXRalpha, ss, gamma). The research reported here was conducted in an effort to clone quail RARbeta+ cDNA (qRARbeta) and to evaluate the expression of qRARbeta+ mRNAs in different tissues and during the development of gonadotropic organs. Two complete cDNAs of qRARbeta1 and qRARbeta2 were isolated by a combination of reverse transcription-polymerase chain reaction and 5'- and 3'-rapid amplification of cDNA ends techniques. An RNase protection assay revealed the widespread expression of qRARbeta1 and beta2 with large tissue-specific variations. The qRARbeta1 isoform was predominant in the testis, whereas qRARbeta2 was dominant in the other tissues examined with the exception of the brain, where both isoforms were almost equally expressed. In the developing testes, the qRARbeta1 mRNA level was high between 30 and 40 days of age, the period during which the testes grew rapidly. The level declined thereafter to its initial level. In contrast, qRARbeta2 mRNA did not exhibit obvious changes. In the developing oviducts, both qRARbeta1 and beta2 mRNAs reached their peak levels by 30 days of age, just before the rapid development of the oviduct occurred, and then decreased to almost undetectable levels when the oviduct developed to the laying stage (over 2.88 g in weight). Similar expression patterns of qRARbeta1 and beta2 were also observed in the developing follicles from the prehierarchical (<2-mm diameter) to the largest preovulatory follicle. In contrast, neither qRARbeta1 nor beta2 mRNA exhibited developmental changes in the brain. These results suggest that RARbeta+ may play an important role in the development of the reproductive systems of birds.

Retinoic acid accelerates the development of reproductive organs and egg production in Japanese quail (Coturnix coturnix japonica)

The effects of retinoic acid on the development of reproductive organs and egg production in female Japanese quail (Coturnix coturnix japonica) were investigated. Female quail were fed a diet containing retinoic acid at 4 mg/kg (RA) or two diets containing retinyl acetate at 5000 IU/kg (VA1) or 14 000 IU/kg (VA2) after being fed a vitamin A-free diet for 2 wk (experiment 1). The oviduct and ovary grew more rapidly (P < 0.05) in RA-treated quail than in VA-treated quail at 5 wk of age. In addition, the body weight of RA-fed quail was also greater (P: < 0.05) than that of VA-fed quail at 5 wk. The RA-treated quail laid their first eggs approximately 5 days earlier (P < 0.05) than the VA-treated quail. Furthermore, these RA-fed quail laid more eggs (P < 0.05) than those VA-fed quail during the experimental period. To confirm the results of experiment 1, a similar experiment was conducted to record the first egg and total eggs laid by quail fed VA2 or RA (experiment 2). The early onset of oviposition was again observed in the RA-treated group (P < 0.01). These results suggest that retinoic acid has a stimulating effect on the reproductive system of female Japanese quail, as has been previously shown in the reproductive system of male Japanese quail.

Retinoids in embryonal development

The key role of vitamin A in embryonal development is reviewed. Special emphasis is given to the physiological action of retinoids, as evident from the retinoid ligand knockout models. Retinoid metabolism in embryonic tissues and teratogenic consequences of retinoid administration at high doses are presented. Physiological and pharmacological actions of retinoids are outlined and explained on the basis of their interactions as ligands of the nuclear retinoid receptors. Immediate target genes and the retinoid response elements of their promoters are summarized. The fundamental role of homeobox genes in embryonal development and the actions of retinoids on their expression are discussed. The similarity of the effects of retinoid ligand knockouts to effects of compound retinoid receptor knockouts on embryogenesis is presented. Although much remains to be clarified, the emerging landscape offers exciting views for future research.

The role of retinoic acid in embryonic and post-embryonic development

Retinoic acid (RA) is the bioactive metabolite of vitamin A (retinol) which acts on cells to establish or change the pattern of gene activity. Retinol is converted to RA by the action of two types of enzyme, retinol dehydrogenases and retinal dehydrogenases. In the nucleus RA acts as a ligand to activate two families of transcription factors, the RA receptors (RAR) and the retinoid X receptors (RXR) which heterodimerize and bind to the upstream sequences of RA-responsive genes. Thus, in addition to the well-established experimental paradigm of depriving animals of vitamin A to determine the role of RA in embryonic and post-embryonic development, molecular biology has provided us with two additional methodologies: knockout the enzymes or the RAR and RXR in the mouse embryo. The distribution of the enzymes and receptors, and recent experiments to determine the endogenous distribution of RA in the embryo are described here, as well as the effects on the embryo of knocking out the enzymes and receptors. In addition, recent studies using the classical vitamin A-deprivation technique are described, as they have provided novel insights into the regions of the embryo which crucially require RA, and the gene pathways involved in their development. Finally, the post-embryonic or regenerating systems in which RA plays a part are described, i.e. the regenerating limb, lung regeneration, hair cell regeneration in the ear and spinal cord regeneration in the adult.

Heads or tails? Retinoic acid will decide

A recent study (Niederreither et al. Nat Genet 1999;21:444-448 [Ref. 1]) describes the phenotype of a gene knockout for an enzyme, retinaldehyde dehydrogenase 2 (RALDH-2), that synthesizes retinoic acid (RA) in the early embryo. The effects generated by this single enzyme mutation are remarkably similar to those previously described in vitamin A-deprivation studies and compound retinoic acid receptor knockouts, which involve multiple systems of the embryo. With other data on the distribution of RA, its role in axial specification of the early embryo is considerably clarified. Surprisingly, it seems that head development is unaffected in these RALDH-2 knockout embryos; thus, the anterior of the embryo does not require RA, despite the observations that the hindbrain seems exquisitely sensitive to RA perturbation. Head development may be realised by a cytochrome P450 enzyme (CYP26), which has been described recently. Between these two opposing forces, the hindbrain develops.

Storage of retinoids and beta-carotene in the genital organs of Japanese quail

The present study was designed to investigate the effect of a one-month feeding of retinyl acetate (RA) on the retinol (ROL), retinyl palmitate (RP) and beta-carotene (BC) levels in the blood, testicles and ovarian follicles of adult Japanese quails. The basal diet (containing vitamin A at 10 x 10(3) IU/kg) was supplemented with 100 x, 500 x and 1000 x 10(3) IU/kg RA in Groups I, II and III in both sexes. Plasma vitamin A levels rose in all groups. The elevations were caused basically by the RP fraction. The ROL concentration increased only slightly, indicating saturation of the blood binding/transport system. Plasma BC was depressed in both sexes. RA feeding resulted in high RP concentration in the genital organs (testicles and ovarian follicles), indicating subclinical hypervitaminosis, while the BC content of genital organs decreased considerably. The retinoid and BC concentration of ovarian follicles (F1-F5) was in the same range, indicating continuous retinoid and carotene transport during the fast maturation period. Retinoid content of the genital organs was higher in layers than in roosters. BC deposition was decreased both in the testicles and in the follicles, indicating a competition between RP and BC for the storage capacity of organs.

Abnormal anteroposterior and dorsoventral patterning of the limb bud in the absence of retinoids

We describe here how the early limb bud of the quail embryo develops in the absence of retinoids, including retinoic acid. Retinoid-deficient embryos develop to about stage 20/21, thus allowing patterns of early gene activity in the limb bud to be readily examined. Genes representing different aspects of limb polarity were analysed. Concerning the anteroposterior axis, Hoxb-8 was up-regulated and its border was shifted anteriorly whereas shh and the mesodermal expression of bmp-2 were down-regulated in the absence of retinoids. Concerning the apical ectodermal genes, fgf-4 was down-regulated whereas fgf-8 and the ectodermal domain of bmp-2 were unaffected. Genes involved in dorsoventral polarity were all disrupted. Wnt-7a, normally confined to the dorsal ectoderm, was ectopically expressed in the ventral ectoderm and the corresponding dorsal mesodermal gene Lmx-1 spread into the ventral mesoderm. En-1 was partially or completely absent from the ventral ectoderm. These dorsoventral patterns of expression resemble those seen in En-1 knockout mouse limb buds. Overall, the patterns of gene expression are also similar to the Japanese limbless mutant. These experiments demonstrate that the retinoid-deficient embryo is a valuable tool for dissecting pathways of gene activity in the limb bud and reveal for the first time a role for retinoic acid in the organisation of the dorsoventral axis.

Kinetic properties of the human liver cytosolic aldehyde dehydrogenase for retinal isomers

Retinoic acid exerts pleiotropic effects by acting through two families of nuclear receptors, RAR and RXR. All-trans and 9-cis retinoic acid bind RARs, whereas 9-cis retinoic acid binds and activates only the RXRs. To understand the role of human liver cytosolic aldehyde dehydrogenase (ALDH1) in retinoic acid synthesis, we examined the ability of ALDH 1 to catalyze the oxidation of the naturally occurring retinal isomers. ALDH1 catalyzed the oxidation of all-trans, 9-cis, and 13-cis retinal with equal efficiency. However, the affinity to all-trans retinal (Km = 2.2 microM) was twofold higher than to 9-cis (Km = 5.5 microM) and 13-cis (Km = 4.6 microM) retinal. All-trans retinol was a potent inhibitor of ALDH1 activity, and inhibited all-trans retinal oxidation uncompetitively. Comparison of the kinetic properties of ALDH1 for retinal isomers with those of previously reported rat kidney retinal dehydrogenase showed distinct differences, suggesting that ALDH1 may play a different role in retinal metabolism in liver.

Initial retinoid requirement for early avian development coincides with retinoid receptor coexpression in the precardiac fields and induction of normal cardiovascular development

Vitamin A requirement for early embryonic development is clearly evident in the gross cardiovascular and central nervous system abnormalities and an early death of the vitamin A-deficient quail embryo. This retinoid knockout model system was used to examine the biological activity of various natural retinoids in early cardiovascular development. We demonstrate that all-trans-, 9-cis-, 4-oxo-, and didehydroretinoic acids, and didehydroretinol and all-trans-retinol induce and maintain normal cardiovascular development as well as induce expression of the retinoic acid receptor beta2 in the vitamin A-deficient quail embryo. The expression of RARbeta2 is at the same level and at the same sites where it is expressed in the normal embryo. Retinoids provided to the vitamin A-deficient embryo up to the 5-somite stage of development, but not later, completely rescue embryonic development, suggesting the 5-somite stage as a critical retinoid-sensitive time point during early avian embryogenesis. Retinoid receptors RARalpha, RARgamma, and RXRalpha are expressed in both the precardiac endoderm and mesoderm in the normal and the vitamin A-deficient quail embryo, while the expression of RXRgamma is restricted to precardiac endoderm. Vitamin A deficiency downregulates the expression of RARalpha and RARbeta. Our studies provide strong evidence for a narrow retinoid-requiring developmental window during early embryogenesis, in which the presence of bioactive retinoids and their receptors is essential for a subsequent normal embryonic development.

Alcohol dehydrogenase as a critical mediator of retinoic acid synthesis from vitamin A in the mouse embryo

Vitamin A (retinol) must be metabolized to an active retinoid ligand in order to fulfill all of its roles in vertebrate development. During retinoid signaling, retinol is first converted to retinal followed by conversion of retinal to the active ligand retinoic acid, which modulates nuclear retinoic acid receptors (RAR). The alcohol dehydrogenase (ADH) enzyme family may function in the metabolism of retinol, the alcohol form of vitamin A, as well as ethanol metabolism. Some members of the ADH family prefer retinol as a substrate over ethanol, and their ability to oxidize retinol is competitively inhibited by intoxicating levels of ethanol. Likewise, there exists an aldehyde dehydrogenase (ALDH) family containing several members preferring retinal as a substrate over acetaldehyde. The spatiotemporal expression patterns of ADH-IV and two forms of ALDH match the spatiotemporal detection of retinoic acid during mouse embryogenesis, i.e., no detection at 6.5 d of embryogenesis (E6.5), followed by detection at E7.5 in the primitive streak, and then detection in numerous tissues later in development. This suggests that certain forms of ADH and ALDH may cooperate to upregulated retinoic acid synthesis during development. Treatment of mouse embryos at E7.5 with an intoxicating amount of ethanol leads to a reduction in retinoic acid levels. At E7.5, two other mouse enzymes known to metabolize ethanol (ADH-I and P450 2E1) are not expressed, indicating that ADH-IV may be the only enzyme available at this stage to metabolize both ethanol and retinol. These findings suggest that ADH-IV participates in the initiation of retinoid signaling by functioning as a retinol dehydrogenase and that this can be inhibited by ethanol intoxication.

The role of vitamin A in the development of the central nervous system

We describe here the defects that arise in the central nervous system (CNS) of quail embryos when they develop in the absence of vitamin A. It has been assumed that because of the effects of excess vitamin A and its metabolites, particularly retinoic acid (RA), on the CNS they are involved in various aspects of CNS development. We show that this is indeed the case, because these deficient quail embryos have three defects in their CNS. First, the posterior hindbrain fails to develop because the cells fated to form this part of the CNS in the very early embryo die by apoptosis. Second, the neural tube fails to extend neurites into the periphery both in vivo and in vitro. Third, the neural crest cells throughout the embryo die by apoptosis. These results demonstrate a crucial requirement for vitamin A in CNS development.

Retinoids and their receptors in vertebrate embryogenesis

Vitamin A and its derivatives, the retinoids, participate in formation of diverse embryonic structures, including face, heart, eye, limb and nervous system. Studies of retinoid-deficient and -treated embryos, and of receptor null mutants, provide evidence that this participation involves interactions between retinoids and their receptors. Targeted retinoid application and retinoid deficiency, using in ovo avian embryos, has identified early cardiogenic contributions, including cardiocyte gene expression and differentiation, heart tube fusion and laterality, and segmental identity. Also useful is a mammalian model, which targets retinoid deficiency to distinct gestational windows, circumventing limitations of traditional deficiency studies and current null mutant technologies. Rat embryos made deficient in retinoids during gestational d 11.5-13.5 exhibit specific cardiac, limb, ocular and nervous system deficits. That many of the anomalies previously reported in retinoid receptor null mutants are observed in deficiency confirms that ligand-receptor interactions are essential for embryonic development. Other defects are novel, reemphasizing the functional redundancy of retinoid receptors and that retinoid receptors have multiple and overlapping contributions to morphogenesis.

Positional apoptosis during vertebrate CNS development in the absence of endogenous retinoids

We have previously shown that quail embryos that develop in the absence of vitamin A have severe defects in their central nervous system. One defect is a completely missing posterior hindbrain. Here we have studied how this comes about by examining cell death using a wholemount technique. In these A- embryos we observe two narrow bands of ectopic apoptosis. One is in the mesenchyme in the region of the first somite and occurs at the 4–6 somite stage, before neural tube closure. The second band follows immediately afterwards and occurs in the neuroepithelium of the presumptive posterior hindbrain at the 6–8 somite stage. Electron microscopy shows that the dying neuroepithelial cells exhibit the characteristics of apoptosis. Rescuing the embryos by injecting retinol before gastrulation completely prevents these apoptotic events. In an effort to identify some of the genes that may be involved in the apoptotic pathway we show that Msx-2 is upregulated in the apoptotic neuroepithelium and thus may be involved, whereas Bmp-4 is not altered and thus presumably not involved. Since these apoptotic event take place at the time of specification of axial identity and segmentation in the mesenchyme and neuroepithelium we conclude that these cells die because they are wrongly specified in terms of their rostrocaudal position, a novel phenomenon which we refer to as positional apoptosis.

Retinoic acid and alcohol/retinol dehydrogenase in the mouse adrenal gland: a potential endocrine source of retinoic acid during development

Retinoid signaling requires the conversion of retinol to retinoic acid by a two-step process, the first of which can be catalyzed in vitro by class I and class IV alcohol dehydrogenases (ADH). These enzymes may participate in local retinoic acid synthesis in some target tissues, although other studies suggest retinoic acid may also be supplied to tissues via the bloodstream, much like an endocrine hormone. Here we have analyzed the expression of these two ADHs as well as retinoic acid production in the adrenal gland, an organ known to be an endocrine source of other hormones. In situ hybridization revealed high levels of both class I and class IV ADH messenger RNAs in adrenal glands of 16.5-day mouse embryos and adults. Class I ADH protein was immunohistochemically detected in embryonic and adult adrenal glands, the latter primarily in the zona fasiculata of the cortex. Abundant class IV ADH protein was detected in the embryonic adrenal as well as in the zona glomerulosa and zona fasiculata of the adult adrenal cortex. Interestingly, class IV ADH protein was found in only a subset of adult cortical cells arranged in radial columns, thus providing further evidence for centripetal cell migration during adrenocortical differentiation. Using a retinoic acid bioassay, adrenal glands from 16.5 day embryos were found to have significantly higher levels of retinoic acid than embryonic liver. The adult adrenal was found to have approximately 15.5 pmol/g of retinoic acid, whereas the adult liver had 24.8 pmol/g, and brain, heart, and spleen each had less than 1.0 pmol/g. Because previous findings indicate that the adrenal gland is not a retinoid target tissue, our detection of both alcohol/retinol dehydrogenases and significant amounts of retinoic acid in this organ suggests that it functions as a potential endocrine source of this hormone during mouse development.

Initiation of retinoid signaling in primitive streak mouse embryos: spatiotemporal expression patterns of receptors and metabolic enzymes for ligand synthesis

The requirement of vitamin A (retinol) for successful completion of vertebrate embryogenesis is well established. Retinoid signaling involves a two-step metabolic event in which retinol is first converted to retinal, and then retinal is converted to the active ligand retinoic acid, which modulates the transcriptional activity of a nuclear retinoic acid receptor (RAR). During mouse embryogenesis, retinoic acid is not detected at 6.5 days of embryonic development (E6.5) when gastrulation first initiates, but it is detected at E7.5 and later. This suggests that retinoid signaling during embryogenesis may be initiated during the primitive streak stage. Here we have used whole-mount in situ hybridization to examine E6.5-E8.5 mouse embryos for expression of RAR alpha, RAR beta, RAR gamma, and two enzymes, class IV alcohol dehydrogenase (ADH-IV) and class I aldehyde dehydrogenase (ALDH-I), which have been shown to have retinol and retinal dehydrogenase activities, respectively. At E6.5, RAR alpha mRNA was expressed ubiquitously in embryonic and extraembryonic tissues, RAR gamma mRNA was detected throughout all embryonic tissues, but mRNAs for RAR beta, ADH-IV, and ALDH-I were not detected. By E7.5, RAR alpha mRNA was still ubiquitous, RAR beta mRNA was now observed in presumptive hindbrain ectoderm and adjacent mesenchyme, RAR gamma mRNA was still observed in all embryonic tissues, and ADH-IV as well as ALDH-I mRNAs were now both expressed in primitive streak mesoderm. In E8.5 embryos, RAR alpha mRNA was still ubiquitous, RAR beta mRNA was present in the caudal hindbrain as well as the closed neural tube and foregut, RAR gamma mRNA was widespread but most prevalent in caudal embryonic tissues, and mRNAs for both ADH-IV and ALDH-I were expressed in cranial mesenchyme, somites, and paraxial mesoderm. Thus, ADH-IV and ALDH-1, two metabolic enzymes able to convert retinol to retinoic acid, are both initially expressed in primitive streak mesoderm at E7.5 when retinoic acid is first detectable. On the other hand, RAR alpha and RAR gamma expression is widespread and present at E6.5 prior to retinoic acid detection. These results suggest that upregulation of ADH-IV and ALDH-I gene expression in primitive streak mesoderm may lead to retinoic acid synthesis and initiation of retinoid signaling during mouse embryogenesis.

Expression and retinoid modulation of N-arginine dibasic convertase and an aminopeptidase-B in human neuroblastoma cell lines

Under retinoic acid exposure, the three SK-N-BE(2)-derived human neuroblastoma cell lines, BE(2)-NA, BE(2)-SA and BE(2)-M17 undergo mainly differentiation, apoptosis or continue to proliferate, respectively. We have used this model system to study the modulation of the transcriptional expression of putative processing enzymes, two novel metallopeptidases; i.e. N-arginine dibasic convertase (NRD convertase; EC 3.4,24,61) and an aminopeptidase-B after exposure of the cells either to retinoic acid or to synthetic retinoid analogs. The data indicate that the two respective enzymes are differently modulated in the various cell lines. Whereas aminopeptidase-B expression is enhanced in most cases, NRD convertase appears to undergo opposite regulation in proliferating versus differentiating neuroblastoma cells. It is concluded that both genes might contain retinoic acid regulatory elements (RARE) in their promoters.

Retinoid receptor expression and all-trans retinoic acid-mediated growth inhibition in vascular smooth muscle cells

BACKGROUND

Retinoids have been used in the successful treatment of a variety of human hyperproliferative diseases. Their role in smooth muscle cell (SMC) growth control, however, has not been clearly established. The present study was designed to assess the retinoid receptor mRNA expression profile in SMCs and to determine whether retinoids exert a growth-inhibitory effect in these cells.

METHODS AND RESULTS

Five of the six retinoid receptors were expressed in both cultured SMCs and aorta as determined by Northern blotting or reverse transcriptase-polymerase chain reaction. Receptor activity was demonstrated in SMCs with the use of a reporter assay with a retinoid receptor DNA binding sequence linked to a chloramphenicol acetyltransferase reporter gene. DNA synthesis and cell proliferation assays were performed to show that all-trans retinoic acid (atRA) antagonized platelet-derived growth factor-BB and serum-stimulated SMC growth. Growth inhibition was distal to early growth-signaling events because induction of c-fos, c-jun, and egr-1 mRNA was unaffected by atRA. However, with an activated protein-1-linked chloramphenicol acetyltransferase reporter, atRA was shown to inhibit the activity of activated protein-1-dependent transcription in a transient transfection assay.

CONCLUSIONS

These results establish the presence of functional retinoid receptors in SMCs and document the growth-inhibitory action of atRA on these cells. Retinoid compounds, already in clinical use as antiproliferative agents for nonvascular indications, should be assessed further in in vivo models of intimal disease.

Selective regulation of cardiomyocyte gene expression and cardiac morphogenesis by retinoic acid

Early heart development is known to be sensitive to retinoid concentrations; a specific pattern of malformations is observed in both vitamin A-deficiency and retinoid-toxicity states. While the influence of retinoids on early cardiac morphogenesis has been described previously, the effect of retinoids upon cardiomyocyte differentiation and gene expression is largely uncharacterized. We have established an in ovo chick embryo model in which slow-release retinoic acid (RA) induces four distinct cardiac malformations in a dose-dependent fashion. Late primitive streak-stage chick embryos were treated with all-trans-retinoic acid released from anion exchange beads placed on the embryo's left side and then allowed to develop further for 20-24 hr. At low doses (10 and 25 micrograms/ml RA) an abnormal loop structure was observed. At higher doses (50 and 100 micrograms/ml RA) cardia bifida and clustered heart tissue were noted. Situs inversus only occurred after treatment with 100 micrograms/ml RA. RA-treated embryos were subsequently analyzed for appropriate cardiac myocyte differentiation using antibody staining and ELISA analysis to detect sarcomeric myosin heavy chain, tropomyosin, titin, and alpha-actinin protein expression. Alpha-actinin expression was significantly decreased in RA-treated embryos, as compared to DMSO-treated controls. Also, heart contraction rate was depressed after RA exposure. RA exposure did not alter the protein expression levels of sarcomeric myosin heavy chain or tropomyosin. The observed alterations are consistent with suggestions that retinoids may affect both morphogenesis and myofibril formation in the developing heart.

Vitamin A-deficient quail embryos have half a hindbrain and other neural defects

BACKGROUND

Retinoic acid (RA) is a morphogenetically active signalling molecule thought to be involved in the development of severely embryonic systems (based on its effect when applied in excess and the fact that it can be detected endogenously in embryos). Here, we adopt a novel approach and use the vitamin A-deficient (A-) quail embryo to ask what defects these embryos show when they develop in the absence of RA, with particular reference to the nervous system.

RESULTS

We have examined the anatomy, the expression domains of a variety of genes and the immunoreactivity to several antibodies in these A- embryos. In addition to the previously documented cardiovascular abnormalities, we find that the somites are smaller in A- embryos, otic vesicle development is abnormal and the somites continue up to and underneath the otic vesicle. In the central nervous system, we find that neural crest cells need RA for normal development and survival, and the neural tube fails to extend any neurites into the periphery. Using general hindbrain morphology and the expression patterns of Hoxa-2, Hoxb-1, Hoxb-4, Krox-20 and FGF-3 as markers, we conclude that segmentation in the myelencephalon (rhombomeres 4-8) is disrupted. In contrast, the dorsoventral axis of the neural tube using Shh, islet-1 and Pax-3 as markers is normal.

CONCLUSIONS

These results demonstrate at least three roles for RA in central nervous system development: neural crest survival, neurite outgrowth and hindbrain patterning.

Retinoic acid response elements as positive and negative regulators of the expression of the homeobox b-1 gene

Retinoic acid-dependent homeobox Hoxb-1 gene expression offers an unanticipated example of both a positive and a negative transcriptional activity of RA, as exerted at different times during embryogenesis. A paradigm for the transduction of positive and negative signaling is the discovery that retinoic acid response elements (RAREs), positioned in the 3' enhancer and 5' promoter of the Hoxb-1 gene, may function respectively as positive and negative regulators, thereby permitting a diffused (early positive) as well as segmentally specified and limited (late negative) expression of the gene. This molecular action of retinoic acid may provide a mechanism for our understanding of normal embryogenesis and of the interference with this process by ectopic retinoic acid, thereby leading to teratogenesis.

All-trans retinoic acid stimulates and maintains neurite outgrowth in nerve growth factor-supported developing chick embryonic sympathetic neurons

In explanted embryonic chick sympathetic neurons, all-trans retinoic acid (RA) as well as nerve growth factor (NGF) were found to be required for neuronal survival and neurite outgrowth at early stages of development (day 6.5-7) in agreement with previous work (Rodriguez-Tébar and Rohrer [1991] Development 112:813-820). The dependence of neurons on all-trans RA for survival diminished at later stages of development. However, all-trans RA was found to be needed at all stages of development in order to maximize neurite outgrowth. Further, removal of all-trans RA from the cultures led to a rapid degeneration of the formed neurites, demonstrating the essentiality of all-trans RA for both the development of neurites, and for the maintenance of existing neurites in cultured embryonic sympathetic neurons. The mechanism whereby all-trans RA exerts its effects on embryonic sympathetic neurons may involve activation of the nuclear retinoic acid and retinoid-X receptor (RAR and RXR) families. The results of Northern blot analyses and/or reverse transcriptase-polymerase chain reaction (RT-PCR) studies show that embryonic sympathetic ganglia express RAR beta, RAR gamma and RXR gamma mRNAs. RXR gamma mRNA is expressed at highest levels in immature neurons that are not yet responsive to NGF (day 6.5-7) and message levels decline with increasing developmental age. In contrast, RAR beta transcript levels are barely detectable at day 6.5-7, and increase approximately 4-fold in ganglia from embryos at day 8.5-9 and decline thereafter. RT-PCR studies show that RAR gamma mRNA is expressed both early (day 6.5-7) and late (day 15) in ganglionic development. Transcripts for the NGF receptors, p75NGFR and p140trk were also examined. The appearance of a single 2.7 kb p140trk transcript coincides with the time when RAR beta mRNA is maximally expressed, raising the possibility that NGF receptors may be targets of retinoid action. Evidence is also presented that all-trans RA may enhance neurite outgrowth by mechanisms other than simply inducing NGF-responsiveness of neurons.

Comparative study of Msx-1 expression in early normal and vitamin A-deficient avian embryos

Homeobox-containing genes may play an important role in establishing embryonic patterns during development of vertebrates. Retinoic acid is able to induce expression of Hox genes in cells in culture and to alter expression patterns in the developing vertebrate embryos. Using wholemount in situ hybridization, we have examined and compared the expression patterns of a homeobox-containing gene, Msx-1, in early normal and vitamin A-deficient quail embryos. At gastrulation stage, Msx-1 is primarily expressed in the posterior half of both normal and vitamin A-deficient embryos. However, the gene is expressed wider and stronger in the vitamin A-deficient embryos. At neurulation stages, Msx-1 is continuously expressed in the posterior region up to Hensen's node and in the edge of the neural fold in both normal and vitamin A-deficient embryos. Notably, in the vitamin A-deficient embryos, Msx-1 is expressed more strongly and is also expressed ectopically in the anterior and precardiac regions. These results provide evidence that endogenous retinoids are involved in the normal expression of Msx-1 in avian embryo and that the expression of Msx-1 is downregulated by endogenous and physiological retinoids in vivo during early avian embryogenesis.

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. Within the day 4 embryo there is some significant variation in the distribution according to tissue type. Neural tissues, neural crest derivatives, and limb buds most strongly express CRABP I whilst other tissues contain only moderate levels, and heart and epidermis do not express CRABP I at all. CRABP II has a widespread distribution, although at a lower level than CRABP I, with the exception of somites and ectoderm which do not express it at all. In the limb buds, there is a significant variation in CRABP I levels across the anteroposterior axis which suggests that these two CRABPs may have different functions during development. The relationship of these distributions in the embryo to the role of endogenous RA and the teratogenic effects of RA is discussed.

Retinoic acid enhances adhesiveness, laminin and integrin beta 1 synthesis, and retinoic acid receptor expression in F9 teratocarcinoma cells

The teratocarcinoma-derived F9 cells respond to retinoic acid (RA) and RA plus dibutyrylcyclic adenosine monophosphate (dcAMP) by differentiating into endoderm cells, which elaborate a laminin and type IV collagen-rich matrix. We found that the induction of differentiation is accompanied by a small but consistent increase in cell adhesiveness to a variety of substrates, including laminin. Therefore we investigated biochemical mechanisms involved in this phenomenon. Endoglycosidase treatment showed that laminin contains complex and hybrid oligosaccharide structures. RA enhanced general biosynthesis of laminin without a specific increase in galactose incorporation: this sugar was mainly in polylactosamine structures in the A chain of laminin and as terminal galactose alpha 1,3 galactose in the B chain. Laminin receptor analysis showed that RA decreased laminin binding protein-37 (LBP-37) but increased the amount of beta 1 integrin, suggesting the involvement of beta 1 integrin in the attachment process. Northern blot analysis showed increased expression of retinoid receptors within hours of RA exposure. These studies demonstrate that RA increases cell to substrate interactions by increasing the biosynthesis of laminin and beta 1 integrin. These effects are most likely subsequent to the RA-induced biosynthesis of the retinoid receptors.

Transport and uptake of retinol during chicken oocyte growth

Most, if not all, components found in the yolk of a chicken egg are extracted from the plasma compartment during the rapid growth phase of the oocyte. Uptake of the major yolk constituents, very-low-density lipoprotein and vitellogenin, has been shown to be mediated by a specific receptor in the plasma membrane of the oocyte (Barber, D.L., Aebersold, R., Sanders, E.J. and Schneider, W.J. (1991) J. Biol. Chem. 266, 18761-18770). In the current study, we sought biochemical evidence for the uptake into oocytes of a minor but biologically very important component, the vitamin retinol. For transport in serum, retinol is bound to retinol-binding protein (RBP), which in turn forms a complex with transthyretin (TTR). In order to gain insight into the biochemical details of transport of the vitamin, we have identified, purified and characterized RBP, TTR, and RBP-TTR complexes from chicken serum and yolk. The results demonstrate that both serum and yolk contain the tertiary retinol-RBP-TTR complexes as well as free RBP and TTR. Western blots of yolk collected from oocytes at different stages of growth show that both RBP and TTR, but not albumin, are more abundant at early stages relative to total yolk protein. In addition, we find both RBP and TTR in endocytic clathrin-coated vesicles of the oocyte. Our results support the hypothesis that retinol, which must be imported by the oocyte for proper embryonic development, is internalized by the chicken oocyte bound to its serum protein-transport complex.

High postnatal lethality and testis degeneration in retinoic acid receptor alpha mutant mice

Retinoic acid (RA) plays a critical role in normal development, growth, and maintenance of certain tissues. The action of RA is thought to be mediated in part by the three nuclear receptors (RAR alpha, -beta, and -gamma), each of which is expressed as multiple isoforms. To investigate the function of the RAR alpha gene, we have disrupted, in the mouse, the whole gene or the isoform RAR alpha 1. Although RAR alpha 1 is the predominant isoform and is highly conserved among vertebrates, RAR alpha 1-null mice appeared normal. However, targeted disruption of the whole RAR alpha gene resulted in early postnatal lethality and testis degeneration. These results, showing that RAR alpha is indeed involved in the transduction of the RA signal, also suggest an unexpected genetic redundancy.

Incidence and classification of early embryonic mortality in broiler breeder chickens

1. Unusually high early embryonic mortality (EEM) was observed in hatching eggs from broiler compared with white or brown table-egg breeders in Atlantic Canada. Broiler breeder EEM in Atlantic Canada was twice the EEM in broiler breeders from other areas of North America. 2. Comparisons of holding temperatures (18 and 30 degrees C) for 24 h after egg collection, in combination with a storage time of 0 or 7 d at 18 degrees C prior to incubation, were made using the criteria: embryo development (stage), and size at 0, 3, 6 and 9 d incubation, EEM, late embryonic mortality (LEM) and hatchability (HAT). 3. Stage of development of embryos, at 0 d incubation, was highest for eggs held for 24 h at 30 degrees C and stored for 7 d. Embryo stage, weight and length at 3, 6 and 9 d incubation were positively correlated. 4. Hatchability of fertile eggs was lowest (66.5%) for eggs held for 24 h at 30 degrees C and stored for 7 d and highest (87.2%) for eggs held for 24 h at 18 degrees C and stored for 0 d. Holding temperature and storage time significantly influenced EEM and LEM. 5. EEM classification differed for strain of breeder. In broiler breeders the majority of the EEM was at a relatively late stage of development (exhibiting an obvious blood ring with a visible embryo). In comparison, EEM from table egg breeders was distributed equally among three categories.

Induction of thrombospondin 1 by retinoic acid is important during differentiation of neuroblastoma cells

Neuroblastoma, a malignant neoplasm that arises in the adrenal medulla or sympathetic ganglion, is one of the most common solid tumors of childhood. Reports that neuroblastomas spontaneously mature to form benign ganglioneuromas have prompted investigations into the efficacy of using agents that induce neuronal differentiation in the treatment of this malignancy. Retinoic acid is one agent in particular that has been shown to induce growth inhibition and terminal differentiation of neuroblastoma cell lines in vitro. Using the human neuroblastoma cell line SMH-KCNR, we have investigated the role of the extracellular matrix protein thrombospondin in retinoic acid induced neuroblastoma differentiation. Treatment with retinoic acid results in a rapid induction (within 4 h) of thrombospondin (TSP) message which is independent of intervening protein synthesis and superinducible in the presence of cycloheximide. This suggests that TSP functions as a retinoic acid inducible immediate early response gene. A concomitant increase in both cell associated and soluble forms of TSP protein can be detected within 24 h of retinoic acid treatment. A functional role for TSP in SMH-KCNR differentiation was established in experiments which showed that exposure to anti-TSP monoclonal antibodies delay retinoic acid differentiation for 48 h. At the time the cells overcome the effects of TSP inhibition, laminin production becomes maximal. Treatment of the cells with a combination of anti-TSP and antilaminin antibodies results in complete inhibition of differentiation.

A hypothetical mechanism for fetal alcohol syndrome involving ethanol inhibition of retinoic acid synthesis at the alcohol dehydrogenase step

Ethanol acts as a teratogen causing brain, craniofacial, and limb abnormalities in those suffering from fetal alcohol syndrome. Normal embryonic development of the vertebrate nervous system and limbs has recently been shown to be governed by retinoic acid, the active form of vitamin A. Retinol dehydrogenase is an enzyme needed to convert vitamin A (retinol) to retinoic acid, a molecule that specifies embryonic pattern formation by controlling gene expression. Ethanol acts as a competitive inhibitor of the retinol dehydrogenase activity attributed to mammalian alcohol dehydrogenase (ADH), an enzyme that uses both retinol and ethanol as substrates. An hypothesis is presented in which many of the abnormalities observed in fetal alcohol syndrome may be caused by high levels of ethanol acting as a competitive inhibitor of ADH-catalyzed retinol oxidation in the embryo or fetus. This would presumably result in a reduction of retinoic acid synthesis in embryonic tissues such as the nervous system and limbs that require critical levels of this molecule to specify spatial patterns.

Retinol-induced modification of the extracellular matrix of endothelial cells: its role in growth control

The growth of the endothelial cell (EC) is tightly regulated throughout the body. Many factors have been implicated in modulating EC growth including diffusible compounds, cell-to-cell interactions, and the extracellular matrix (ECM). Retinol, or vitamin A alcohol, has recently been shown to inhibit the growth of bovine capillary ECs, in vitro. Retinoids are known to modify ECM in other cell systems, and pure ECM components have been shown to effect EC growth rates. We, therefore, examined the role of the matrix in the retinol-induced inhibition of ECs. Cell-free matrices from control and vitamin A-treated ECs were prepared by removing cells with EGTA treatment after 7 d of culture. Matrix proteins were analyzed by solubilizing the matrices in 5 M guanidine-HCl and performing Western blot analysis using specific antibodies to matrix proteins. In isolating the ECM, we observed that retinol-treated cultures of ECs were resistant to EGTA removal; retinol-treated ECs required twice the exposure time to EGTA to detach from their matrix than did controls cells. Western blot analysis of matrix proteins derived from control and retinol-treated EC cultures demonstrated a 1.6-fold increase in laminin beta chains and a 2.5-fold increase in fibronectin in the ECM of retinol-treated EC compared to control cell matrix. Functional properties of these matrices were assessed by plating control and Day 6 retinol-treated ECs onto the matrices and measuring attachment and growth by determining cell numbers at 24, 72, and 144 h. These studies revealed that control cells attached in greatest numbers to a control matrix whereas retinol-treated ECs preferentially attached to a matrix derived from retinol-treated cells. Furthermore, control ECs which grew rapidly on a control matrix were growth inhibited on a retinol-derived matrix. These data indicate that vitamin A treatment of ECs effects both their phenotype and influences the composition and the functional properties of their underlying ECM. These studies also demonstrate that alterations of the matrix are at least in part responsible for the growth inhibition of EC by retinol.