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

Altered vitamin A homeostasis and increased size and adiposity in the rdh1-null mouse

Rat RoDH performs efficiently (V(m)/K(m)) in a pathway of all-trans-retinoic acid biosynthesis in cells and recognizes the physiological form of vitamin A, i.e., retinol bound with cellular retinol binding-protein, type I. Here we report that mouse embryo (e7.5 to e18.5) and liver (e12.5 to P2M) display inversely related mRNA expression of an Rodh ortholog, rdh1, and a major retinoic acid catabolic enzyme, cyp26a1, suggesting coordinate modulation of retinoic acid homeostasis. Rdh1 inactivation by homologous recombination produces mice with decreased liver cyp26a1 mRNA and protein and increased liver and kidney retinoid stores, when fed vitamin A-restricted diets. Thus, null mice autocompensate by down-regulating cyp26a1 and sparing retinoids, indicating that rdh1 metabolizes retinoids in vivo. Surprisingly, rdh1-null mice grow longer than wild type, with increased weight and adiposity, when restricted in vitamin A. Liver, kidney, and multiple fat pads increase in weight. Some differences reflect the larger sizes of rdh1-null mice, but mesentery, femoral, and inguinal fat pads grow disproportionately larger. These data reveal an unexpected contribution of Rdh1 to size and adiposity and provide the first genetic evidence of a candidate retinol dehydrogenase affecting either vitamin A-related homeostasis physiologically or vitamin A-related gene expression or biological function in vivo.

Mental and psychomotor development in Indonesian infants of mothers supplemented with vitamin A in addition to iron during pregnancy

Maternal nutrition is important for fetal development, but its impact on the functional outcome of infants is still unclear. The present study investigated the effects of vitamin A and Fe supplementation during gestation on infant mental and psychomotor development. Mothers of infants from five villages in Indonesia were randomly assigned to supervised, double-blind supplementation once per week from approximately 18 weeks of pregnancy until delivery. Supplementation comprised 120 mg Fe + 500 μg folic acid with (n94) or without (n94) 4800 μg retinol in the form of retinyl acetate. Mothers of infants who participated in the national Fe+folic acid supplementation programme, but whose intake of supplements was not supervised, were recruited from four other villages (n88). The mental and psychomotor development of infants was assessed, either at 6 or 12 months of age, using the Bayley Scales of Infant Development (BSID). We found no impact of vitamin A supplementation on mental or psychomotor development of infants. In addition, infants whose mothers had received weekly Fe supplementation had similar mental and psychomotor indices as those whose mothers had participated in the governmental Fe supplementation programme. The study population was moderately Fe and vitamin A deficient. The size of the treatment groups was large enough to detect a mean difference of 10 points on the BSID, which is less than 1 sd (15 points) of the average performance of an infant on the BSID. In conclusion, the present study did not find an impact of weekly supplementation of 4800 RE vitamin A in addition to Fe during gestation on functional development of Indonesian infants. However, smaller improvements in development may be seen if studied in a larger and/or more deficient population.

Spatial and temporal expression of glucocorticoid, retinoid, and thyroid hormone receptors is not altered in lungs of congenital diaphragmatic hernia

The degree of associated pulmonary hypoplasia and persistent pulmonary hypertension are major determination factors for survival in congenital diaphragmatic hernia (CDH) patients. Glucocorticoids, thyroid hormone, and vitamin A have been shown to be involved in human lung development. To determine their therapeutic potential in hypoplastic lungs of CDH patients, the temporal and spatial expression of glucocorticoid receptor, thyroid hormone receptors, retinoic acid receptors, and retinoid X receptors were evaluated in lungs of CDH patients, hypoplastic lungs from other causes, and normal lungs. As a series of supportive experiments, the expressions of these receptors were analyzed in lungs of nitrofen-induced CDH rats. Immunohistochemistry (human and rat) and in situ hybridization (rat) demonstrated no overt difference between CDH, hypoplastic, and control lungs, either in the localization nor the timing of the first expression of all analyzed receptors. The mRNA expression of each receptor was detected in all human CDH lungs by quantitative PCR. Our results suggest that, as far as receptors are concerned, hypoplastic lungs of fetuses and newborns with CDH are potentially as responsive to glucocorticoids, thyroid hormone, and retinoic acid as the lungs of normal children.

Multipotent Adult Progenitor Cells from Swine Bone Marrow

We show that multipotent adult progenitor cells (MAPCs) can be derived from both postnatal and fetal swine bone marrow (BM). Although swine MAPC (swMAPC) cultures are initially mixed, cultures are phenotypically homogenous by 50 population doublings (PDs) and can be maintained as such for more than 100 PDs. swMAPCs are negative for CD44, CD45, and major histocompatibility complex (MHC) classes I and II; express octamer binding transcription factor 3a (Oct3a) mRNA and protein at levels close to those seen in human ESCs (hESCs); and have telomerase activity preventing telomere shortening even after 100 PDs. Using quantitative-reverse transcription-polymerase chain reaction (Q-RT-PCR), immunofluorescence, and functional assays, we demonstrate that swMAPCs differentiate into chondrocytes, adipocytes, osteoblasts, smooth muscle cells, endothelium, hepatocyte-like cells, and neuron-like cells. Consistent with what we have shown for human and rodent MAPCs, Q-RT-PCR demonstrated a significant upregulation of transcription factors and other lineage-specific transcripts in a time-dependent fashion similar to development. When swMAPCs were passaged for 3-6 passages at high density (2,000-8,000 cells per cm(2)), Oct3a mRNA levels were no longer detectable, cells acquired the phenotype of mesenchymal stem cells (CD44(+), MHC class I(+)), and could differentiate into typical mesenchymal lineages (adipocytes, osteoblasts, and chondroblasts), but not endothelium, hepatocyte-like cells, or neuron-like cells. Even if cultures were subsequently replated at low density (approximately 100-500 cells per cm(2)) for >20 PDs, Oct3a was not re-expressed, nor were cells capable of differentiating to cells other than mesenchymal-type cells. This suggests that the phenotype and functional characteristics of swMAPCs may not be an in vitro culture phenomenon.

Retinoic acid signalling is required for specification of pronephric cell fate

The mechanisms by which a subset of mesodermal cells are committed to a nephrogenic fate are largely unknown. In this study, we have investigated the role of retinoic acid (RA) signalling in this process using Xenopus laevis as a model system and Raldh2 knockout mice. Pronephros formation in Xenopus embryo is severely impaired when RA signalling is inhibited either through expression of a dominant-negative RA receptor, or by expressing the RA-catabolizing enzyme XCyp26 or through treatment with chemical inhibitors. Conversely, ectopic RA signalling expands the size of the pronephros. Using a transplantation assay that inhibits RA signalling specifically in pronephric precursors, we demonstrate that this signalling is required within this cell population. Timed antagonist treatments show that RA signalling is required during gastrulation for expression of Xlim-1 and XPax-8 in pronephric precursors. Moreover, experiments conducted with a protein synthesis inhibitor indicate that RA may directly regulate Xlim-1. Raldh2 knockout mouse embryos fail to initiate the expression of early kidney-specific genes, suggesting that implication of RA signalling in the early steps of kidney formation is evolutionary conserved in vertebrates.

Ontogeny of mRNA abundance of nuclear receptors and nuclear receptor target genes in young cattle

After birth the development of appropriate detoxification mechanisms is important. Nuclear receptors (NR), such as constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor-alpha (PPARalpha), retinoid receptors (RAR, RXR), and NR target genes are involved in the detoxification of exogenous and endogenous substances. We quantified abundances of hepatic mRNA of NR and several NR target genes (cytochromes, CYP; cytochrome P450 reductase, CPR; UDP-glucuronosyl transferase, UDP) in calves at different ages. Gene expression was quantified by real-time RT-PCR. Abundance of mRNA of CAR and PXR increased from low levels at birth in pre-term calves (P0) and full-term calves (F0) to higher levels in 5-day-old calves (F5) and in 159-day-old veal calves (F159), whereas mRNA levels of PPARalpha did not exhibit significant ontogenetic changes. RARbeta mRNA levels were higher in F5 and F159 than in F0, whereas no age differences were observed for RARalpha levels. Levels of RXRalpha and RXRbeta mRNA were lower in F5 than in P0 and F0. Abundance of CYP2C8 and CYP3A4 increased from low levels in P0 and F0 to higher levels in F5 and to highest levels in F159. Abundance of CPR was transiently decreased in F0 and F5 calves. Levels of UGT1A1 mRNA increased from low levels in P0 and F0 to maximal level in F5 and F159. In conclusion, mRNA levels of NR and NR target genes exhibited ontogenetic changes that are likely of importance for handling of xeno- and endobiotics with increasing age.

Effects of dietary vitamin A intake on acrosin- and plasminogen-activator activity of ram spermatozoa

Acrosin and plasminogen activators are proteolytic enzymes of ram spermatozoa that play an essential role in the induction of the acrosome reaction, as well as the binding of spermatozoa to the oocyte and their penetration through the layers that surround the oocyte. Since vitamin A can alter gene expression in various tissues, testis included, this study was undertaken to evaluate the possible effect of vitamin A intake on acrosin- and plasminogen-activator activity. During a 20-week experiment, 15 rams of the Greek breed Karagouniki, divided to three groups, received different amounts of vitamin A per os in retinyl acetate capsules (group A, controls, 12,500 iu/animal per day; group B, 50,000 iu/animal per day; group C, 0 iu/animal per day up to the 13th week, then 150,000 iu/animal per day until the end of the experiment). Acrosin- and plasminogen-activator activity were determined by spectrophotometric methods. Vitamin A was determined in blood plasma by HPLC. No statistical differences were detected regarding the body weight of the rams or the qualitative and quantitative parameters of their ejaculate throughout the whole experiment. No statistically significant alterations of enzyme activity were detected in group B. In group C, both enzyme activities started declining in week 9. Compared with controls, maximum reduction for acrosin was 49% on week 11 and for plasminogen activators 51% in week 14. Activities returned to normal rates after vitamin A re-supplementation. To date, the main result of vitamin A deficiency was known to be arrest of spermatogenesis and testicular degeneration. A new role for vitamin A may be suggested, since it can influence factors related to male reproductive ability before spermatogenesis is affected.

Interactions of ultraspiracle with ecdysone receptor in the transduction of ecdysone- and juvenile hormone-signaling

Analyses of integration of two-hormone signaling through the vertebrate nuclear hormone receptors, for which the retinoid X receptor is one partner, have generated a number of mechanistic models, including those described as 'subordination' models wherein ligand-activation of one partner is subordinate to the liganded state of the other partner. However, mechanisms by which two-hormone signaling is integrated through invertebrate nuclear hormone-binding receptors has not been heretofore experimentally elucidated. This report investigates the integration of signaling of invertebrate juvenile hormone (JH) and 20-OH ecdysone (20OHE) at the level of identified nuclear receptors (ultraspiracle and ecdysone receptor), which transcriptionally activate a defined model core promoter (JH esterase gene), through specified hormone response elements (DR1 and IR1). Application of JH III, or 20OHE, to cultured Sf9 cells transfected with a DR1JHECoreLuciferase (or IR1JHECoreLuciferase) reporter promoter each induced expression of the reporter. Cotreatment of transfected cells with both hormones yielded a greater than additive effect on transcription, for especially the IR1JHECoreLuciferase reporter. Overexpression in Sf9 cells of recombinant Drosophila melanogaster ultraspiracle (dUSP) fostered formation of dUSP oligomer (potentially homodimer), as measured by coimmunoprecipitation assay and electrophoretic mobility assay (EMSA) on a DR1 probe, and also increased the level of transcription in response to JH III, but did not increase the transcriptional response to either 20OHE treatment alone or to the two hormones together. Inapposite, overexpression of recombinant D. melanogaster ecdysone receptor (dEcR) in the transfected cells generated dUSP/dEcR heterodimer [as measured by EMSA (supershift) on a DR1 probe] and increased the transcriptional response to 20OHE-alone treatment, but did not increase the transcriptional response to the JH III-alone treatment. Our studies provide evidence that in this model system, JH III-activation of the reporter promoter is through USP oligomer (homodimer) that does not contain EcR, while the 20OHE-activation is through the USP/EcR heterodimer. These results also show that the integration of JH III and 20OHE signaling is through the USP/EcR heterodimer, but that when the EcR partner is unliganded, the USP partner in this system is unable to transduce the JH III-activation.

Different effect of beta-carotene on proliferation of prostate cancer cells

It was shown that high doses of beta-carotene (>30 microM) decrease proliferation of prostate cancer cells in vitro. However, it is rather doubtful whether such concentration of beta-carotene is really accessible at cellular level. We studied the effect of 3 and 10 microM beta-carotene on proliferation and gene expression in LNCaP and PC-3 prostate cancer cell lines. Beta-carotene--more efficiently absorbed from medium by androgen-sensitive LNCaP cells--increased proliferation of LNCaP cells whereas it had weaker effect on PC-3 cells. Initial global analysis of expression of genes in both cell lines treated with 10 microM beta-carotene (Affymetrix HG-U133A) showed remarkable differences in number of responsive genes. Their recognition allows for conclusion that differences between prostate cancer cell lines in response to beta-carotene treatment are due to various androgen sensitivities of LNCaP and PC-3 cells. Detailed analysis of expression of selected genes in beta-carotene treated LNCaP cells at the level of mRNA and protein indicated that the observed increase of proliferation could have been the result of slight induction of a few genes affecting proliferation (c-myc, c-jun) and apoptosis (bcl-2) with no significant effect on major cell cycle control genes (cdk2, RB, E2F-1).

Peroxisome proliferator-activated receptor-binding protein null mutation results in defective mammary gland development

A conditional null mutation of peroxisome proliferator-activated receptor-binding protein (PBP) gene was generated to understand its role in mammary gland development. PBP-deficient mammary glands exhibited retarded ductal elongation during puberty, and decreased alveolar density during pregnancy and lactation. PBP-deficient mammary glands could not produce milk to nurse pups during lactation. Both the mammary ductal elongation in response to estrogen treatment and the mammary lobuloalveolar proliferation stimulated by estrogen plus progesterone were attenuated in PBP-deficient mammary glands. The proliferation index was decreased in PBP-deficient mammary glands. PBP-deficient mammary epithelial cells expressed abundant beta-casein, whey acidic protein, and WDNM1 mRNA, indicating a relatively intact differentiated function. PBP-deficient epithelial cells were unable to form mammospheres, which were considered to be derived from mammary progenitor/stem cells. We conclude that PBP plays a pivotal role in the normal mammary gland development.

Coxsackievirus and adenovirus receptor is essential for cardiomyocyte development

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that is known to be a site of viral attachment and entry, but its physiologic functions are undefined. CAR expression is maximal in neonates and wanes rapidly after birth in organs such as heart, muscle, and brain, suggesting that CAR plays a role in the development of these tissues. Here, we show that CAR deficiency resulted in an embryonic lethal condition associated with cardiac defects. Specifically, commencing approximately 10.5 days postconception (dpc), CAR-/- cardiomyocytes exhibited regional apoptosis evidenced by both histopathologic features of cell death and positive staining for the apoptotic marker cleaved caspase 3. CAR-/- fetuses invariably suffered from degeneration of the myocardial wall and thoracic hemorrhaging, leading to death by 11.5 dpc. These findings are consistent with the view that CAR provides positive survival signals to cardiomyocytes that are essential for normal heart development.

Moderate maternal vitamin A deficiency alters myogenic regulatory protein expression and perinatal organ growth in the rat

Vitamin A deficiency is one of the most common dietary deficiencies in the developing world and is a major health concern where it is associated with increased risk of fetal and infant mortality and morbidity. Early studies in the rat demonstrated that, in addition to respiratory problems, neonates showed evidence of mobility problems in response to moderate vitamin A deficiency. This study investigated whether moderate deficiency of this vitamin plays a role in regulating key skeletal muscle regulatory pathways during development. Thirty female rats were fed vitamin A-moderate (VAM) or vitamin A-sufficient diets from weaning and throughout pregnancy. Fetal and neonatal hindlimb and muscle samples were collected on days 13.5, 15.5, 17.5, and 19.5 of pregnancy and 1 day following birth. Mothers fed the VAM diet had reduced retinol concentrations at all time points studied (P < 0.01), and neonates had reduced relative lung weights (P < 0.01). Fetal weight and survival did not differ between groups but neonatal survival was lower in the VAM group where neonates had increased relative heart weights (P < 0.05). Analysis of myogenic regulatory factor expression and calcineurin signaling in fetuses and neonates demonstrated decreased protein levels of myf5 [50% at 17.5 dg (P < 0.05)], myogenin [70% at birth (P < 0.001)], and myosin heavy chain fast [50% at birth (P < 0.05)] in response to moderate vitamin A deficiency. Overall, these changes suggest that vitamin A status during pregnancy may have important implications for fetal muscle development and subsequent muscle function in the offspring.

Effects of Retinol on the in vitro Development of Bos Indicus Embryos to Blastocysts in Two Different Culture Systems

The objective of this study was to evaluate the effect of retinol on the in vitro development of early embryos of cultured Bos indicus (Expt 1) to the blastocyst stage in medium simplex of optimization (KSOM) or sintetic fluid of oviduct (SOF) or co-cultured (Expt 2) with an oviduct cell monolayer (OCM) in KSOM or SOF. A total of 3149 cumulus-oocyte complexes obtained by aspirating follicles (2-5 mm diameter) from ovaries of slaughtered animals were selected for IVM and incubated in TCM 199 supplemented with 25 mM HEPES at 39 degrees C in air with 5% CO(2) and maximum humidity for 24 h. In vitro fertilization (IVF) was performed in modified defined medium (mDM) medium. Eighteen hours after IVF, cumulus cells were removed and presumptive zygotes were randomly allocated to the experimental groups. Zygotes cultured (Expt 1) in KSOM + retinol, KSOM, SOF + retinol and SOF were incubated in maximum humidity at 39 degrees C, 5% CO(2), 5% O(2) and 90% N(2). Zygotes co-cultured (Expt 2) in KSOM + retinol + OCM, KSOM + OCM, SOF + retinol + OCM and SOF + OCM were incubated at 39 degrees C, 5% CO(2). In both experiments media were partially changed 48 h after IVF and unfertilized ova were removed. Afterwards embryos were kept in culture or co-culture for further 9 days. In Expt 1, blastocyst rates (day 7) were 14.6% (KSOM + retinol), 15.8% (KSOM), 16.4% (SOF + retinol) and 15.9% (SOF). In Expt 2, the blastocyst rates (day 7) were 25.4% (KSOM + retinol + OCM) 14.2% (KSOM + OCM), 24.3% (SOF + retinol + OCM) and 15.9% (SOF + OCM). The same influence profile of retinol was observed in the formation of the expanded (day 9) and hatched (day 11) blastocysts. The results obtained in Expt 2 demonstrated that the addition of 0.28 microg/ml retinol to the embryo culture media used in this study had a significant (p < 0.05) positive effect on bovine early embryonic development, under the conditions tested, and can be used to enhance in vitro embryo production.

Differentiation of embryonic stem cells to a neural fate: A route to re-building the nervous system?

The many and varied proposed applications of cell replacement therapies in the treatment of human disease states, particularly those arising from cell loss or dysfunction, have been discussed widely in both the scientific and popular press. Although an attractive concept, cell therapies require the development of a readily available source of donor cells suitable for transplantation. Embryonic stem (ES) cells, with proven ability to differentiate to all cell populations of the embryo and adult in vitro, provide a potential source of therapeutic cells. The differentiation capability of mouse ES cells in vitro has been studied extensively over the last 20 years and the formation of neural precursors and neural cell lineages from mouse ES cells is well established. Cell populations highly enriched/homogenous in neural precursors have been achieved using a variety of chemical or biological inducing agents coupled with selective growth conditions. Preliminary reports suggest that similar neural enrichment is seen when these methodologies are applied to primate and human ES cells. ES cell-derived neural precursors have been analyzed in vitro and in vivo and found to be functionally normal and, after introduction into rodent models of human neurodegenerative diseases, capable of effecting measurable disease recovery. We review progress in the formation of neural precursors from mouse ES cells, particularly the recent reports of directed differentiation of ES in response to biological inductive factors, and assess the transfer of these approaches to human ES cells.

Feedback mechanisms regulate retinoic acid production and degradation in the zebrafish embryo

Retinoic acid (RA) signaling in vertebrate embryos occurs in a distinct physical and temporal pattern. Regulating this spatial distribution is crucial to the development of the embryo, as RA in excess or in inappropriate tissues is teratogenic. In order to understand how RA availability is determined in zebrafish we have investigated the expression of cyp26a1, an enzyme that inactivates RA, and its relationship to raldh2, one of the enzymes that produce RA from retinal. cyp26a1 expression follows three phases: in presumptive anterior neurectoderm and in a circumblastoporal ring during gastrulation, in the tailbud throughout somitogenesis, and in multiple specific tissue types beginning at mid-somitogenesis and continuing through 48 h postfertilization (hpf). This expression was either adjacent or opposite to those tissues expressing raldh2. We then investigated how RA production might regulate these relationships. Endogenous RA produced by raldhs did not play a role in setting cyp26a1 expression in most tissues. However, exogenous RA regulates expression of both enzymes. cyp26a1 is up regulated in the embryo in a time, concentration, and tissue-dependent manner. Conversely, raldh2 expression is reduced with RA treatment. Tests of the raldh2 promoter in cell transfections proved that RA directly represses its activity. These data demonstrate that the feedback mechanisms regulating production and degradation of RA must be considered in any experiments altering levels of RA in the developing vertebrate embryo.

Hyperglycaemia potentiates the teratogenicity of retinoic acid in diabetic pregnancy in mice

AIMS/HYPOTHESIS

We recently showed in mice that maternal diabetes increases embryonic susceptibility to caudal regression induced by vitamin A metabolite retinoic acid. Here we tested whether in the maternal diabetic milieu hyperglycaemia is the critical factor responsible for mediating this increased susceptibility.

METHODS

Non-diabetic pregnant mice were made hyperglycaemic by subcutaneous injections of glucose at regular intervals. Conversely, diabetic pregnant mice were treated with phlorizin to induce renal glucosuria and thus reduce blood glucose concentrations. Pregnant mice were treated with retinoic acid and the extent of caudal regression in mouse embryos, measured in terms of the ratio of tail length to crown-rump length was assessed. Embryos were also examined for Wnt-3a expression and cell death.

RESULTS

Embryos of mice treated with glucose had a greater extent of caudal regression induced by retinoic acid than saline-treated controls, with enhanced down-regulation of Wnt-3a expression and exacerbated cell death specifically at the caudal end of the embryo. Embryos of diabetic mice treated with phlorizin had a similar extent of caudal regression to embryos of non-diabetic mice after treatment with retinoic acid.

CONCLUSIONS/INTERPRETATION

Hyperglycaemia increases embryonic susceptibility to caudal regression induced by retinoic acid, with the underlying cellular and molecular changes closely mimicking those that occur in maternal diabetes. Reduction of blood glucose concentrations in diabetic mice completely abolishes this increased susceptibility to retinoic acid. These results suggest that in maternal diabetes hyperglycaemia is the critical factor responsible for potentiating the teratogenic effect of retinoic acid.

Cellular and molecular mechanisms of development of the external genitalia

The limb and external genitalia are appendages of the body wall. Development of these structures differs fundamentally in that masculine development of the external genitalia is androgen dependent, whereas development of the limb is not. Despite this fundamental difference in developmental regulation, epithelial-mesenchymal interactions play key roles in the development of both structures, and similar regulatory molecules are utilized as mediators of morphogenetic cell-cell interactions during development of both the limb and external genitalia. Given the relatively high incidence of hypospadias, a malformation of penile development, it is appropriate and timely to review the morphological, endocrine, and molecular mechanisms of development of the genital tubercle (GT), the precursor of the penis in males and the clitoris in females. Morphological observations comparing development of the GT in humans and mouse emphasize the validity of the mouse as an animal model of GT development and validate the results of experimental studies. Accordingly, the use of mutant mice provides important insights into the roles of specific regulatory molecules in development of the external genitalia. While our current understanding of the morphological and molecular mechanisms of mammalian external genitalia development is still rudimentary, this review summarizes the current state of our knowledge and whenever possible draws from the rich experimental embryology literature on other relevant organs such as the developing limb. Future research on the hormonal and molecular mechanisms of GT development may yield strategies to prevent or reduce the incidence of hypospadias and to elucidate the molecular genetic mechanisms of GT morphogenesis, especially in relation to common organogenetic pathways utilized in other organ systems.

Identification of novel roles of the cytochrome p450 system in early embryogenesis: effects on vasculogenesis and retinoic Acid homeostasis

The cytochrome P450-dependent monooxygenase system catalyzes the metabolism of xenobiotics and endogenous compounds, including hormones and retinoic acid. In order to establish the role of these enzymes in embryogenesis, we have inactivated the system through the deletion of the gene for the electron donor to all microsomal P450 proteins, cytochrome P450 reductase (Cpr). Mouse embryos homozygous for this deletion died in early to middle gestation (approximately 9.5 days postcoitum [dpc]) and exhibited a number of novel phenotypes, including the severe inhibition of vasculogenesis and hematopoiesis. In addition, defects in the brain, limbs, and cell types where CPR was shown to be expressed were observed. Some of the observed abnormalities have been associated with perturbations in retinoic acid homeostasis in later embryogenesis. Consistent with this possibility, embryos at 9.5 dpc had significantly elevated levels of retinoic acid and reduced levels of retinol. Further, some of the observed phenotypes could be either reversed or exacerbated by decreasing or increasing maternal retinoic acid exposure, respectively. Detailed analysis demonstrated a close relationship between the observed phenotype and the expression of genes controlling vasculogenesis. These data demonstrate that the cytochrome P450 system plays a key role in early embryonic development; this process appears to be, at least in part, controlled by regional concentrations of retinoic acid and has profound effects on blood vessel formation.

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.

Reduction of all-trans-retinal in the mouse liver peroxisome fraction by the short-chain dehydrogenase/reductase RRD: induction by the PPAR alpha ligand clofibrate

The mouse liver 16,000 g fraction, which contains peroxisomes, reduces all-trans-retinal, but has limited ability to dehydrogenate retinol enzymatically. Feeding mice for 2 weeks with a diet containing clofibrate (0.5%, w/w), a PPAR alpha ligand and peroxisome proliferator, increased the 16,000 g fraction approximately 2-fold in protein, approximately 2-fold in specific activity of retinal reduction, and approximately 4-fold in retinal reductase units compared to controls, and caused a 50% decrease in liver retinol. An increase in both reductase specific activity and units indicates that clofibrate/PPAR alpha induced expression of retinal-reducing enzymes(s), in addition to increasing reductase(s) content. We expressed a cDNA from the NCBI data bank that encodes a peroxisome short-chain dehydrogenase/reductase. The enzyme, mouse retinal reductase (RRD, also known as human 2,4-dienoyl-CoA reductase), reduces all-trans-retinal [V(m) = 40 nmol min(-1) (mg of protein)(-1); K(0.5) = 2.3 microM] and has 4- and 60-fold less activity with 13-cis-retinal and 9-cis-retinal, respectively. Recombinant RRD functions with both unbound and CRBP(I) (cellular retinol-binding protein)-bound retinal, but apo-CRBP(I) inhibits the reductase. RRD mRNA expression was initiated on embryo day 7. Most adult tissues assayed expressed the mRNA. Liver, kidney, and heart had the most intense expression, with much less intense expression in brain, spleen, and lung. Clofibrate feeding increased the amount of RRD protein in the 16,000 g fraction of liver, consistent with the clofibrate-induced increase in reductase activity. These data relate retinoid metabolism, PPAR alpha, peroxisomes, and RRD, and are consistent with a further function of CRBP(I) in retinoid metabolism.

2,3,7,8-tetrachlorodibenzo-p-dioxin induces lecithin: retinol acyltransferase transcription in the rat kidney

Vitamin A (retinoids) has an essential role in development and throughout life of humans and animals. Consequently, effects of the environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on retinoid metabolism may be contributory to its toxicity. This study was performed to clarify the mechanism behind dioxin-induced retinyl ester formation in the rat kidney. In addition we investigated the possible role of CYP1A1 in dioxin-induced all-trans-retinoic acid (atRA) formation. Male Sprague-Dawley rats were exposed to a single oral dose of TCDD in a combined dose-response and time-course study, with doses ranging from 0.1 to 100 microg/kg bw and time points from 1 to 28 days. Levels of atRA and the expression of two potentially retinoic acid (RA)-controlled proteins critically involved in retinoid storage regulation, lecithin: retinol acyltransferase (LRAT) and cellular retinol binding protein I (CRBP I), were analyzed in liver and kidney. The expression and activity of cytochrome P4501A1 (assayed as ethoxyresorufin-O-deethylase activity) was assessed to gain insight into its potential role in RA synthesis. There was a significant increase in LRAT mRNA expression in the kidney, whereas no such increase could be observed in the liver, despite significantly increased atRA levels in both tissues. This suggests a tissue-specific regulation of LRAT by TCDD that may be dependent on other factors than atRA. Neither CRBP I mRNA nor protein levels were altered by TCDD. The time-course relationship between CYP1A1 activity and atRA levels in liver and kidney does not exclude a role of CYP1A1 in TCDD-induced RA synthesis. The observed altered regulation of the retinoid-metabolizing enzyme LRAT, together with the low doses and short time required by TCDD to change tissue RA levels, suggest that enzymes involved in retinoid metabolism are specific and/or direct targets of TCDD.

Gene structure and minimal promoter of mouse rdh1

Mouse rdh1 encodes retinol dehydrogenase type 1 (RDH1), a short-chain dehydrogenase, which recognizes as substrates all-trans-retinol, 9-cis-retinol, 5alpha-androstan-3,17-diol and 5alpha-androstan-3-ol-17-one. RDH1 is the most efficient known mouse short-chain dehydrogenase that catalyzes dehydrogenation of all-trans-retinol, and contributes to a reconstituted path of all-trans-retinoic acid biosynthesis, when coexpressed in reporter cells with any one of three retinal dehydrogenases. Rdh1 shows widespread, if not ubiquitous, mRNA expression in the mouse beginning no later than embryo day 7. Here we report genomic organization, chromosomal localization and analysis of a minimum promoter of mouse rdh1. Rdh1 consists of four exons and three introns and spans approximately 14412 bp. Rdh1 is a single copy gene that maps to chromosome 10D3 with rdh5-9, but no known disorder maps precisely to rdh1. Rdh1 has three transcription start sites in kidney and one start site in liver. The rdh1 5'-region between -424 and +43 induces transcription maximally in COS7, mouse kidney RAG, and mouse liver NMu3Li cells. This section has no TATA box, but has a CCAAT box beginning 65 bp upstream of the major transcription start site, which is required for transcription of transfected reporter constructs. An AP1 binding site at -119 also activates transfected reporter constructs, and mediates 2-O-tetradecanoylphorbol-13-acetate (TPA) induced transcription. All-trans-retinoic acid antagonizes the TPA affect; however, no RARE or RXRE was found in the proximal promoter region, consistent with indirect regulation by all-trans-retinoic acid.

Differential recognition of the free versus bound retinol by human microsomal retinol/sterol dehydrogenases: characterization of the holo-CRBP dehydrogenase activity of RoDH-4

All-trans-retinol is the precursor for all-trans-retinoic acid, the activating ligand for nuclear transcription factors retinoic acid receptors. In the cytosol of various cells, most retinol exists in a bound form, complexed with cellular retinol binding protein type I (holo-CRBP). Whether retinoic acid is produced from the free or bound form of retinol is not yet clear. Here, we present evidence that holo-CRBP is recognized as substrate by human microsomal short-chain dehydrogenase/reductase (SDR) RoDH-4 with the K(m) value close to the liver concentration of holo-CRBP. The ability to utilize holo-CRBP differentiates RoDH-4 from a related enzyme, RoDH-like 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), which is 3-fold more active with free retinol than RoDH-4 but is 15-fold less active toward holo-CRBP. Recognition of the cytosolic holo-CRBP as substrate is consistent with RoDH-4 orientation in the membrane. As established by immunoprecipitation and glycosylation scanning, RoDH-4 faces the cytosolic side of the membrane. Purified RoDH-4, stabilized by reconstitution into proteoliposomes, exhibits the apparent K(m) values for substrates and NAD(+) similar to those of the microsomal enzyme and oxidizes holo-CRBP with the catalytic efficiency (k(cat)/K(m)) of 59 min(-1) mM(-1). Apo-CRBP acts as a strong competitive inhibitor of holo-CRBP oxidation with an apparent K(i) value of 0.2 microM. The results of this study suggest that the human retinol-active SDRs are not functionally equivalent and that, in contrast to RoDH-like 3alpha-HSD, RoDH-4 can access the bound form of retinol for retinoic acid production and is regulated by the apo-/holo-CRBP ratio.

Expression of PPAR and RXR isoforms in the developing rat and human term placentas

Placental fatty acid transfer is critical to meet the foetal requirements necessary for the biosynthesis of biological membranes, myelin, and various signaling molecules. The primary objective of this research was to elucidate the placental expression patterns of genes that may potentially regulate placental fatty acid transfer and homeostasis. In this study, we have elucidated the temporal and spatial patterns of expression of peroxisome proliferator-activated receptor (PPAR) and 9-cis retinoic acid receptor (RXR) isoforms in the junctional and labyrinth zones of the developing rat chorioallantoic placenta and in human term placenta. PPAR (alpha, beta, and gamma) and RXR (alpha, beta, and gamma) isoforms are nuclear hormone receptors that are known to regulate gene transcription and protein expression levels of fatty acid transport and metabolism mediating proteins through the formation of a DNA binding heterodimer complex. In the present study, the expression patterns of PPAR and RXR isoforms were determined in developing rat placenta and human term placenta using RT-PCR and immunohistochemical analyses. PPARalpha, beta, gamma, RXRalpha, beta and gamma were expressed in both junctional (invasive/endocrine function) and labyrinth (transport barrier) zones of the rat placenta, from day 13 to day 21 of gestation. In the human term placenta, PPARalpha, beta, gamma, RXRalpha and gamma were observed, while RXRbeta was not detected. Immunocytochemistry staining results determined the presence of PPARalpha, beta, gamma, RXRalpha and gamma to be specific to the syncytial trophoblast layer of the human chorionic villi. The presence of PPAR and RXR isoforms in both the rat and human placentas suggest that PPAR and RXR isoforms are potential regulators of placental lipid transfer and homeostasis. Our work provides a framework for the further investigation of PPAR and RXR isoform specific regulation of placental fatty acid uptake, transport and metabolism.

Developmental signaling in Hydra: what does it take to build a "simple" animal?

Developmental processes in multicellular animals depend on an array of signal transduction pathways. Studies of model organisms have identified a number of such pathways and dissected them in detail. However, these model organisms are all bilaterians. Investigations of the roles of signal transduction pathways in the early-diverging metazoan Hydra have revealed that a number of the well-known developmental signaling pathways were already in place in the last common ancestor of Hydra and bilaterians. In addition to these shared pathways, it appears that developmental processes in Hydra make use of pathways involving a variety of peptides. Such pathways have not yet been identified as developmental regulators in more recently diverged animals. In this review I will summarize work to date on developmental signaling pathways in Hydra and discuss the future directions in which such work will need to proceed to realize the potential that lies in this simple animal.

Antioxidant vitamin levels in term and preterm infants and their relation to maternal vitamin status

BACKGROUND

Lipid peroxidation plays a vital role in the pathogenesis of many neonatal complications. Preterm babies are especially predisposed to lung diseases and retinopathy, probably due to a deficiency in their antioxidant systems. Vitamins E, A, and C are part of the natural antioxidant defense systems. We aimed to determine the levels of vitamins E, A, and C in maternal and cord blood plasma of term and preterm infants and to investigate the relationships between these levels.

METHODS

In the present study we determined vitamin E, A, and C levels in the umbilical cord blood of term (n = 30) and preterm (n = 22) infants and their mothers by HPLC. Blood samples were taken during delivery.

RESULTS

Levels of lipid soluble antioxidant vitamin E and A in cord blood were lower than maternal values (p <0.01, p <0.05, respectively). Conversely, the level of water-soluble vitamin C was higher in cord blood than in maternal level (p <0.05). Significantly higher levels of vitamins E, A, and C were found in term babies as compared with those born preterm (p <0.05).

CONCLUSIONS

There was a positive correlation between maternal and cord blood levels of vitamins E and A (r = 0.775, r = 0.725, respectively). In conclusion, preterm babies have fewer lipid-soluble antioxidant vitamins in their serum compared to term infants. Therefore, it is possible to postulate that preterm infants are more susceptible to oxidative stress.

Expression of a retinol dehydrogenase (hRoDH-4), a member of the retinol/steroid dehydrogenase family implicated in retinoic acid biosynthesis, in normal and neoplastic endometria

OBJECTIVE

Retinoic acid plays an essential role in epithelial differentiation, and retinoid homeostasis is disrupted in cancers of epithelial origin. The goal of this study was to determine whether hRoDH-4, an enzyme that can catalyze the first and rate-limiting step in retinoic acid biosynthesis, is expressed in normal endometrium and, if so, whether its expression is altered in endometrial cancer.

STUDY DESIGN

Proliferative, secretory, hyperplastic, and neoplastic endometria were examined by immunocytochemistry for hRoDH-4 protein and by reverse transcriptase-polymerase chain reaction for the hRoDH-4 transcript.

RESULTS

In proliferative and secretory glandular epithelia, immunoreactive hRoDH-4 was uniformly present. In endometrial cancers, hRoDH-4 immunoreactivity was markedly reduced in many neoplastic epithelial cells. Expression of hRoDH-4 in normal and neoplastic endometrium was confirmed by findings on reverse transcriptase-polymerase chain reaction.

CONCLUSION

These findings are consistent with the hypothesis that altered expression of enzymes essential for in situ retinoic acid biosynthesis is an important phenotypic change associated with the development of endometrial cancer.

Manipulating the sulfur amino acid content of the early diet and its implications for long-term health

Epidemiological studies of human populations show that poor growth in utero predisposes an individual to the later development of type 2 (non-insulin-dependent) diabetes mellitus and hypertension in adulthood. This phenomenon is not confined to man; feeding pregnant rats diets moderately deficient in protein has a similar effect, programming the adult blood pressure and glucose metabolism of the offspring. A restriction in the amino acid supply was thought to cause poor fetal growth. However, recent experiments have shown that this is not the case and instead have implicated the metabolism of the S-containing amino acids. Many semi-synthetic experimental diets contain an imbalance in S-containing amino acids, forcing the animal to synthesise a sizeable part of its cysteine requirement from methionine. Unfortunately, when the diet is low in protein, the oxidation of amino acids is reduced, perturbing methionine metabolism and increasing levels of homocysteine. It is this interaction between protein content and composition of the diet which influences neonatal viability and may also determine the long-term health of the offspring. An excess of homocysteine is known to affect levels of two of the main mediators of cellular methylation reactions, S-adenosyl methionine and methylene tetrahydrofolate. S-adenosyl methionine is the methyl donor for the methylation of newly-synthesised DNA, regulating chromatin assembly and gene expression. The balance between S-adenosyl methionine and the methylated derivatives of folic acid may be critical for the development of differentiating cells and the long-term regulation of gene expression.

The gamma -secretase-cleaved C-terminal fragment of amyloid precursor protein mediates signaling to the nucleus

Sequential processing of the amyloid precursor protein (APP) by beta- and gamma-secretases generates the Abeta peptide, a major constituent of the senile plaques observed in Alzheimer's disease. The cleavage by gamma-secretase also results in the cytoplasmic release of a 59- or 57-residue-long C-terminal fragment (Cgamma). This processing resembles regulated intramembrane proteolysis of transmembrane proteins such as Notch, where the released cytoplasmic fragments enter the nucleus and modulate gene expression. Here, we examined whether the analogous Cgamma fragments of APP also exert effects in the nucleus. We find that ectopically expressed Cgamma is present both in the cytoplasm and in the nucleus. Interestingly, expression of Cgamma59 causes disappearance of PAT1, a protein that interacts with the APP cytoplasmic domain, from the nucleus and induces its proteosomal degradation. Treatment of cells with lactacystin prevents PAT1 degradation and retains its nuclear localization. By contrast, Cgamma57, a minor product of gamma-cleavage, is only marginally effective in PAT1 degradation. Furthermore, Cgamma59 but not Cgamma57 potently represses retinoic acid-responsive gene expression. Thus, our studies provide the evidence that, as predicted by the regulated intramembrane proteolysis mechanism, Cgamma seems to function in the nucleus.

Molecular characterization of a mouse short chain dehydrogenase/reductase active with all-trans-retinol in intact cells, mRDH1

Metabolic activation of retinol (vitamin A) via sequential actions of retinol and retinal dehydrogenases produces the active metabolite all-trans-retinoic acid. This work reports cDNA cloning, enzymatic characterization, function in a reconstituted path of all-trans-retinoic acid biosynthesis in cell culture, and mRNA expression patterns in adult tissues and embryos of a mouse retinol dehydrogenase, RDH1. RDH1 represents a new member of the short chain dehydrogenase/reductase superfamily that differs from other mouse RDH in relative activity with all-trans and cis-retinols. RDH1 has a multifunctional catalytic nature, as do other short chain dehydrogenase/reductases. In addition to retinol dehydrogenase activity, RDH1 has strong 3alpha-hydroxy and weak 17beta-hydroxy steroid dehydrogenase activities. RDH1 has widespread and intense mRNA expression in tissues of embryonic and adult mice. The mouse embryo expresses RDH1 as early as 7.0 days post-coitus, and expression is especially intense within the neural tube, gut, and neural crest at embryo day 10.5. Cells cotransfected with RDH1 and any one of three retinal dehydrogenase isozymes synthesize all-trans-retinoic acid from retinol, demonstrating that RDH1contributes to a path of all-trans-retinoic acid biosynthesis in intact cells. These characteristics are consistent with RDH1 functioning in a path of all-trans-retinoic acid biosynthesis starting early during embryogenesis.

Cytochrome P450s: coupling development and environment

There is growing evidence that some members of the cytochrome P450 superfamily could be involved in the regulation of basic developmental processes such as pattern formation, morphogenesis, cell differentiation and growth. This development calls attention to the myriad small molecules metabolized by cytochrome P450s, some of which might function as the morphogens proposed by the Local Source-Dispersed Sink hypothesis. This new information also suggests a mechanism for the developmental toxicity of drugs and environmental pollutants: such compounds could interfere with normal development by altering the spatial and temporal expression patterns of cytochrome P450s required for normal development.