Role Of Retinoic Acid Signaling Research Articles

Intestinal epithelium intrinsic RARα signaling regulates gut barrier integrity via IL-18

Abstract Intestinal epithelium, overlying mucus layer and anti-microbial peptides together form a physico-chemical barrier crucial for homeostasis with the gut microbiota. Intestinal epithelial cells (IECs) are at the frontline of host-microbe interactions in the gut, yet how they modulate barrier function in response to dietary cues is poorly understood. Vitamin A and its key metabolite retinoic acid (RA), are crucial regulators of gut immune homeostasis. In this study, we employ a mouse model that expresses a dominant negative retinoic acid receptor exclusively in IECs (dnRARVillin-Cre) to establish a novel role for RA signaling in regulating the mucus barrier. The absence of RA signaling in colonic epithelium resulted in significant increase in mucus layer thickness indicating that RA regulates goblet cell function. Concomitant with this, we observed that in dnRARVillin-Cre mice there are more goblet cells and an enhanced spatial separation between host and the gut microbiota. Further, we showed that dnRARVillin-Cre mice have a diminished sensitivity to chemically induced colitis in comparison to wild-type mice. Quantitative RNA and protein analysis uncovered that gene transcription and protein activation and secretion of key pro-inflammatory cytokine IL-18 was severely impaired in epithelium of dnRARVillin-Cre mice. IL-18 has previously been shown to act as a negative regulator of goblet cell function in the intestinal epithelium. We now show that intestinal epithelium intrinsic RA signaling can modulate IL-18 levels to regulate the mucus barrier. Our results have thus disclosed a novel link between a diet derive metabolite and intestinal epithelial cell function that can be harnessed to modulate mucosal immunity.

The role of retinoic acid signaling in starfish metamorphosis

BackgroundAlthough retinoic acid (RA) signaling plays a crucial role in the body patterning of chordates, its function in non-chordate invertebrates, other than its mediation of environmental cues triggering metamorphosis in cnidarians, is largely unknown. We investigated the role of RA signaling in the metamorphosis of starfish (Echinodermata).ResultsWe found that exogenous RA treatment induced metamorphosis in starfish larvae. In contrast, inhibitors of RA synthesis and RA receptors suppressed metamorphosis triggered by attachment to a substrate. Gene expressions of the RA signaling component were detected in competent larvae.ConclusionsThis study provides insight into the ancestral function of RA signaling, which is conserved in the metamorphosis of cnidarians and starfish.

Role of Retinoic Acid Signaling in Epicardial‐Related Events During Late Heart Development

BackgroundDuring the final stages of heart development, the myocardium grows and becomes vascularized with the aid of paracrine factors and cell progenitors derived from the epicardium. Here, we study the involvement of retinoic acid (RA), a metabolite of vitamin A, in epicardial‐related developmental processes involving the formation of the coronary vasculature and the growth of the ventricular compact zone.MethodsTo explore the developmental consequences of altered RA signaling in late cardiogenic events, we employed a previously characterized model of embryonic RA excess based on mouse embryos deficient in the retinaldehyde reductase DHRS3. We also employed a complementary model based on embryonic RA deficiency generated by administering WIN 18,446, a bis(dichloroacetyl)diamine inhibitor of RA synthesis to pregnant dams. Using these two models we studied the formation of the coronary plexus and the formation and recruitment of epicardial‐derived mural cells by coronary vessels. We further explored the effect of altered RA in vitro by studying the epicardial epithelial‐to‐mesenchymal transition (EMT), and the formation, migration and differentiation of epicardial‐derived precursor cells (EPDCs).ResultsOur results demonstrated that both excess and deficiency of embryonic RA‐signaling led to a thin ventricular myocardium and aberrant coronary vessel formation and remodeling. In the case of both excess, or deficient RA‐signaling, the endothelial tubes did not become invested with epicardial‐derived vascular smooth muscle cells (VSMCs). In vitro assays of epicardial EMT combined with transcriptomic and proteomic analyses revealed that RA signaling not only affects the differentiation of EPDCs, but also controls the cytoskeletal reorganization and secretion of angiogenic and cardiotrophic factors by the epicardium.ConclusionWe report that RA signaling affects epicardial signaling and plays critical roles in the development of the myocardium and the coronary vasculature.Support or Funding InformationThis work was supported in part by the grant R01HD077260 (ARM, MAK) from the National Institutes of Health and by a Fulbright U.S. Scholar Award to ARM funded by the U.S. Department of State's Bureau of Educational and Cultural Affairs, the Commission for Educational Exchange between the United States of America and Brazil and CAPES, the Brazilian Federal Agency for Support and Evaluation of Graduate Education. Additional support to MAK was provided by the University of Maryland School of Pharmacy Mass Spectrometry Center (SOP1841‐IQB2014) and by startup funds to ARM from the Northern Ontario School of Medicine. Conflicts of interest: none.

Building the muscle pattern: Role of Retinoic acid signaling in extraocular muscle morphogenesis

Building the muscle pattern: Role of Retinoic acid signaling in extraocular muscle morphogenesis

Deficient retinoid-driven angiogenesis may contribute to failure of adult human lung regeneration in emphysema

BackgroundMolecular pathways that regulate alveolar development and adult repair represent potential therapeutic targets for emphysema. Signalling via retinoic acid (RA), derived from vitamin A, is required for mammalian alveologenesis, and...

Mechanisms of retinoic acid signaling during cardiogenesis.

Substantial experimental and epidemiological data have highlighted the interplay between nutritional and genetic factors in the development of congenital heart defects. Retinoic acid (RA), a derivative of vitamin A, plays a key role during vertebrate development including the formation of the heart. Retinoids bind to RA and retinoid X receptors (RARs and RXRs) which then regulate tissue-specific genes. Here, we will focus on the roles of RA signaling and receptors in gene regulation during cardiogenesis, and the consequence of deregulated retinoid signaling on heart formation and congenital heart defects.

Critical Roles of Retinoic Acid Signaling in Combating Acute Graft Versus Host Disease

Retinoic acid (RA), a metabolite of vitamin A, modulates a variety of aspects of the immune system, primarily because of its diverse effects on a wide range of immune cells. Initiation of RA-mediated transcription requires the binding of RA to heterodimeric nuclear receptors composed of RA receptors (RARα, β, and γ) and retinoid X receptors (RXRα, β, and γ). Although RA signaling is tolerogenic under steady state conditions, previous studies, including ours, have shown that RA can enhance pro-inflammatory responses in acute graft-versus-host disease (aGVHD) (Blood. 2013; 122(12): 2125). In that study, we demonstrated that donor T cells expressing a dominant negative RARα (DNRARα) markedly impaired GVHD lethality capacity. This paradoxical function in aGVHD was attributed to excessive RA production caused by the upregulation of RA-synthesizing enzymes, retinaldehyde dehydrogenases (RALDH), in hematopoietic and non-hematopoietic cells. In the current study, we investigated genetic and translational approaches to ablate RA synthesis and signaling as a means to treat aGVHD.The 4 isoforms of the RALDH enzyme are differentially expressed in a variety of cell types. RALDH-2 is the predominant isoform in dendritic cells (DCs), whereas RALDH-1 levels were found to be higher in intestinal epithelial cells (IECs) during aGVHD. We hypothesized that conditional deletion of either RALDH-2 in host CD11c+ DCs, or RALDH-1 in host IECs using a Cre-Lox system would diminish RA synthesis and reduce aGVHD. Consistent with this hypothesis, ablation of RA synthesis by RALDH-2 in host CD11c+ DCs significantly reduced aGVHD (Figure 1A; p <0.0001) in a fully MHC mismatched BALB/c (H-2d) into C57BL/6 (B6, H-2b) mouse model of aGVHD. However, deletion of RALDH-1 in IECs failed to attenuate aGVHD (not shown), which could be attributed to the existence of other isoforms in these cells. To circumvent the potential contribution of multiple RA synthesizing isoforms, we generated mice over expressing CYP26A1, a key RA catabolizing enzyme. Over expression of CYP26A1 in host hematopoietic cells using CYP26A1stop/stop-VAV-Cre recipients significantly mitigated aGVHD (p<0.005; not shown), providing novel insights into the tissue-specific role of RA signaling in aGVHD.We further explored RA signaling in aGVHD using a translational approach. IRX4204 is a novel and highly specific RXR agonist currently in clinical trials for autoimmune diseases, which can sequester RXR receptors and phenocopies the genetic approach using DNRARα T cells and allowing translation into the clinic. We discovered that IRX4204 can enhance in vitro CD4+CD25+Foxp3+ Regulatory T cell (iTreg) generation from naïve CD4+Foxp3- precursors (Figure 1B), suggesting it might increase Treg in vivo, and therefore be therapeutically useful for aGVHD prevention. To determine the effects of IRX4204 in aGVHD, we used two fully MHC mismatched mouse models: (B6 (H-2b) into BALB/c (H-2d) and BALB/c (H-2d) into B6 (H-2b). Recipients treated with IRX4204 had significantly prolonged survival time (Figure 1C&D), reduced weight loss, and better clinical scores compared to vehicle-treated mice. IRX4204 also significantly reduced donor T cell proliferation, effector differentiation and a 2-4 fold reduced production of pro-inflammatory cytokine (IFN-γ, TNF-α). Despite up-regulating gut-homing receptors on donor T cells, intestinal (and liver) GVHD pathology was reduced, which was associated with higher IEC integrity, assessed by po FITC-dextran serum levels. Compared to controls, IRX4204-treated recipients had a higher frequency of Treg in the spleen, mesenteric lymph nodes (p <0.0001) and colon (p <0.001). To determine whether IRX4204 mitigated aGVHD by promoting peripheral Treg (pTreg) generation, we utilized Treg-depleted donor T cells from either wild type (WT) or Scurfy (Sc) mice in our B6 into BALB/c GVHD model. Sc mice have a FoxP3 gene deletion and therefore cannot produce pTreg. Interestingly, IRX4204 attenuated aGVHD only in recipients that were given WT T cells, indicating that the generation of pTregs was critical for IRX4204-mediated aGVHD protection. Overall, these data lay a strong foundation for the development of novel drug based therapies for aGVHD and other inflammatory disorders by ablating RA synthesis and signaling. [Display omitted] [Display omitted] DisclosuresChandraratna:Io Pharmaceuticals: Other: Employed by Io Pharmaceuticals and is a board member, holding the titles of title of President and Chief Scientific Officer, and has ownership interest in Io Pharmaceuticals. .

Application of Impermeable Barriers Combined with Candidate Factor Soaked Beads to Study Inductive Signals in the Chick.

The chick embryo provides a superb vertebrate model that can be used to dissect developmental questions in a direct way. Its accessibility and robustness following surgical intervention are key experimental strengths. Mica plates were the first barriers used to prevent chick limb bud initiation1. Protocols that use aluminum foil as an impermeable barrier to wing bud or leg bud induction and or initiation are described. We combine this technique with bead placement lateral to the barrier to exogenously supply candidate endogenous factors that have been blocked by the barrier. The results are analyzed using in situ hybridization of subsequent gene expression. Our main focus is on the role of retinoic acid signaling in the induction and later initiation of the chick embryo fore and hindlimb. We use BMS 493 (an inverse agonist of retinoic acid receptors (RAR)) soaked beads implanted in the lateral plate mesoderm (LPM) to mimic the effect of a barrier placed between the somites (a source of retinoic acid (RA)) and the LPM from which limb buds grow. Modified versions of these protocols could also be used to address other questions on the origin and timing of inductive cues. Provided the region of the chick embryo is accessible at the relevant developmental stage, a barrier could be placed between the two tissues and consequent changes in development studied. Examples may be found in the developing brain, axis extension and in organ development, such as liver or kidney induction.

Application of Impermeable Barriers Combined with Candidate Factor Soaked Beads to Study Inductive Signals in the Chick

The chick embryo provides a superb vertebrate model that can be used to dissect developmental questions in a direct way. Its accessibility and robustness following surgical intervention are key experimental strengths. Mica plates were the first barriers used to prevent chick limb bud initiation1. Protocols that use aluminum foil as an impermeable barrier to wing bud or leg bud induction and or initiation are described. We combine this technique with bead placement lateral to the barrier to exogenously supply candidate endogenous factors that have been blocked by the barrier. The results are analyzed using in situ hybridization of subsequent gene expression. Our main focus is on the role of retinoic acid signaling in the induction and later initiation of the chick embryo fore and hindlimb. We use BMS 493 (an inverse agonist of retinoic acid receptors (RAR)) soaked beads implanted in the lateral plate mesoderm (LPM) to mimic the effect of a barrier placed between the somites (a source of retinoic acid (RA)) and the LPM from which limb buds grow. Modified versions of these protocols could also be used to address other questions on the origin and timing of inductive cues. Provided the region of the chick embryo is accessible at the relevant developmental stage, a barrier could be placed between the two tissues and consequent changes in development studied. Examples may be found in the developing brain, axis extension and in organ development, such as liver or kidney induction.

Transcriptomics of Environmental Enrichment Reveals a Role for Retinoic Acid Signaling in Addiction.

There exists much variability in susceptibility/resilience to addiction in humans. The environmental enrichment paradigm is a rat model of resilience to addiction-like behavior, and understanding the molecular mechanisms underlying this protective phenotype may lead to novel targets for pharmacotherapeutics to treat cocaine addiction. We investigated the differential regulation of transcript levels using RNA sequencing of the rat nucleus accumbens after environmental enrichment/isolation and cocaine/saline self-administration. Ingenuity Pathways Analysis and Gene Set Enrichment Analysis of 14,309 transcripts demonstrated that many biofunctions and pathways were differentially regulated. New functional pathways were also identified for cocaine modulation (e.g., Rho GTPase signaling) and environmental enrichment (e.g., signaling of EIF2, mTOR, ephrin). However, one novel pathway stood out above the others, the retinoic acid (RA) signaling pathway. The RA signaling pathway was identified as one likely mediator of the protective enrichment addiction phenotype, an interesting result given that nine RA signaling-related genes are expressed selectively and at high levels in the nucleus accumbens shell (NAcSh). Subsequent knockdown of Cyp26b1 (an RA degradation enzyme) in the NAcSh of rats confirmed this role by increasing cocaine self-administration as well as cocaine seeking. These results provide a comprehensive account of enrichment effects on the transcriptome and identify RA signaling as a contributing factor for cocaine addiction.

Regulation of IgA Class Switch Recombination in Immunoglobulin A Nephropathy: Retinoic Acid Signaling and BATF

Background: Immunoglobulin (Ig) A nephropathy (IgAN) is the finding of immune deposits predominantly containing polymeric IgA in the glomerular mesangium on renal biopsy. Increasing evidence suggested that retinoic acid (RA) signaling selectively induces IgA isotype switching and basic leucine zipper transcription factor, ATF-like (BATF) controls the global regulators of class switch recombination (CSR) in lymphocytes. Great effort has been paid to identify whether impaired immune regulation along the ‘mucosa-bone marrow (BM) axis' play an important role in the pathogenesis of IgAN. Methods: The aim of the study was to investigate the expression of all-trans-RA (ATRA) and BATF, and to identify their impact on IgA CSR in IgAN patients and rat animal models. Blood samples and tonsillar tissue specimens were obtained from 22 patients with IgAN and 24 patients with chronic tonsillitis as control. Results: Immunohistochemical, RT-PCR and western blotting examination revealed that RA signaling and BATF productions are activated in IgAN patients compared with controls. Lipopolysaccharide and α-hemolytic streptococcus stimulation upregulated RA receptor (RAR) and BATF expression, promote IgA CSR and ATRA productions in tonsil mononuclear cells. RAR alpha (RARα) or BATF siRNA decreases IgA expression. We also built IgAN rat models and found that RARα, BATF and activation-induced cytidine deaminase were upregulated in the peripheral blood, spleen and BM. With ATRA (500 μg/kg body weight) treatment for 8 weeks, IgA deposition on glomeruli and mesangial cells proliferation increased. It also revealed that ATRA activated BATF and IgA CSR in vivo. Conclusion: These data point toward the role of RA signaling together with BATF in IgA CSR of IgAN, and the data also support the notion that mucosal immunization with neoantigen results in impaired mucosal and systemic IgA responses.

Retinoic Acid Specifically Enhances Embryonic Stem Cell Metastate Marked by Zscan4.

Pluripotency confers Embryonic Stem Cells (ESCs) the ability to differentiate in ectoderm, endoderm, and mesoderm derivatives, producing the majority of cell types. Although the majority of ESCs divide without losing pluripotency, it has become evident that ESCs culture consists of multiple cell populations with different degrees of potency that are spontaneously induced in regular ESC culture conditions. Zscan4, a key pluripotency factor, marks ESC subpopulation that is referred to as high-level of pluripotency metastate. Here, we report that in ESC cultures treated with retinoic acid (RA), Zscan4 ESCs metastate is strongly enhanced. In particular, we found that induction of Zscan4 metastate is mediated via RA receptors (RAR-alpha, RAR-beta, and RAR-gamma), and it is dependent on phosphoinositide-3-kinase (PI3K) signaling. Remarkably, Zscan4 metastate induced by RA lacks canonical pluripotency genes Oct3/4 and Nanog but retained both self-renewal and pluripotency capabilities. Finally we demonstrated that the conditional ablation of Zscan4 subpopulation is dispensable for both endoderm and mesoderm but is required for ectoderm lineage. In conclusion, our research provides new insights about the role of RA signaling during ESCs high pluripotency metastate fluctuation.

Inhibition of Axl Kinase Reverses the Mesenchymal Phenotype in Leukemic Cells through the Disruption of Retinoic Acid Signaling

Mesenchymal stem cells (MSCs) contribute to the regeneration of mesenchymal tissues, and are essential in providing support for the growth and differentiation of primitive hemopoietic cells within the bone marrow microenvironment. It is becoming increasingly clear that the tumor microenvironment plays a very important role in tumor progression and drug resistance, and the selection of cancer cells possessing the mesenchymal phenotype leads to drug resistance in many different tumor types. We have been exploring the role of the protein Axl in promoting the mesenchymal phenotype in both myeloid and lymphoid malignancies, and the role of Axl in promoting drug resistance in these malignancies. The signaling downstream of Axl that leads to the acquisition of the mesenchymal phenotype has not been well elucidated. Following results from a genetic screen using a zebrafish model, we have discovered a role for retinoic acid (RA) signaling which is regulated by Axl and controls the mesenchymal phenotype in leukemic cells. In addition, recent reports have shown an interaction between a retinoic acid regulated gene, RARRES1, and Axl, leading our group to seek to understand the role of retinoic acid signaling in the control of AXL. We hypothesized that treatment with our AXL inhibitor, TP-0903, would disrupt RA signaling and lead to a reversal of the mesenchymal phenotype in leukemia cells. Following TP-0903 treatment, we interrogated changes in mRNA expression using RT-PCR, protein expression using standard immunoblotting, and endogenous RA levels using a competitive ELISA. We also assessed the effect of TP-0903 on tumor growth in an in vivo model, assessing efficacy of TP-0903 in an MV4-11 xenograft mouse model. One of the genes that we detected being dramatically changed by treatment with TP-0903 was the RA metabolizing protein CYP26A1, suggesting that Axl inhibition indeed leads to changes in RA metabolism. We observed a strong induction of CYP26 mRNA expression following RA treatment in MV4-11 leukemia cells which was also observed in treatment with our AXL inhibitor, TP-0903, at levels as low as 100 nM. We also assessed TP-0903 activity in additional cell lines (HL60, A549, and H1650), and with an alternative AXL inhibitor, R428. Importantly, TP-0903 treatment correlated with increased CYP26 expression and reduced levels of endogenous RA. In vivo, TP-0903 strongly inhibited xenograft tumor volumes by up to 100% with multiple dose levels and treatment schedules. CYP26 expression in fixed tissues correlated well with mRNA levels observed in xenograft tumors following treatment. Taken together, our observations support our hypothesis that inhibition of AXL kinase by TP-0903 can disrupt RA metabolism by inducing CYP26 expression and this disruption of RA metabolism leads to reversal of the mesenchymal phenotype in leukemic cells. DisclosuresSoh:Tolero Pharmaceuticals: Employment. Bahr:Tolero Pharmaceuticals: Employment. Bearss:Tolero Pharmaceuticals: Employment. Kim:Tolero Pharmaceuticals: Employment. Peterson:Tolero Pharmaceuticals: Employment. Whatcott:Tolero Pharmaceuticals: Employment. Siddiqui-Jain:Tolero Pharmaceuticals: Employment. Bearss:Tolero Pharmaceuticals: Employment. Warner:Tolero Pharmaceuticals: Employment.

Loss of MT1-MMP causes cell senescence and nuclear defects which can be reversed by retinoic acid.

MT1-MMP (MMP14) is a collagenolytic enzyme located at the cell surface and implicated in extracellular matrix (ECM) remodeling. Mmp14(-/-) mice present dwarfism, bone abnormalities, and premature death. We demonstrate herein that the loss of MT1-MMP also causes cardiac defects and severe metabolic changes, and alters the cytoskeleton and the nuclear lamina structure. Moreover, the absence of MT1-MMP induces a senescent phenotype characterized by up-regulation of p16(INK4a) and p21(CIP1/WAF) (1), increased activity of senescence-associated β-galactosidase, generation of a senescence-associated secretory phenotype, and somatotroph axis alterations. Consistent with the role of retinoic acid signaling in nuclear lamina stabilization, treatment of Mmp14(-/-) mice with all-trans retinoic acid reversed the nuclear lamina alterations, partially rescued the cell senescence phenotypes, ameliorated the pathological defects in bone, skin, and heart, and extended their life span. These results demonstrate that nuclear architecture and cell senescence can be modulated by a membrane protease, in a process involving the ECM as a key regulator of nuclear stiffness under cell stress conditions.

Sex specific retinoic acid signaling is required for the initiation of urogenital sinus bud development.

The mammalian urogenital sinus (UGS) develops in a sex specific manner, giving rise to the prostate in the male and the sinus vagina in the embryonic female. Androgens, produced by the embryonic testis, have been shown to be crucial to this process. In this study we show that retinoic acid signaling is required for the initial stages of bud development from the male UGS. Enzymes involved in retinoic acid synthesis are expressed in the UGS mesenchyme in a sex specific manner and addition of ligand to female tissue is able to induce prostate-like bud formation in the absence of androgens, albeit at reduced potency. Functional studies in mouse organ cultures that faithfully reproduce the initiation of prostate development indicate that one of the roles of retinoic acid signaling in the male is to inhibit the expression of Inhba, which encodes the βA subunit of Activin, in the UGS mesenchyme. Through in vivo genetic analysis and culture studies we show that inhibition of Activin signaling in the female UGS leads to a similar phenotype to that of retinoic acid treatment, namely bud formation in the absence of androgens. Our data also reveals that both androgens and retinoic acid have extra independent roles to that of repressing Activin signaling in the development of the prostate during fetal stages. This study identifies a novel role for retinoic acid as a mesenchymal factor that acts together with androgens to determine the position and initiation of bud development in the male UGS epithelia.

Roles of retinoic acid signaling in normal and abnormal development of the palate and tongue

Palatogenesis involves various developmental events such as growth, elevation, elongation and fusion of opposing palatal shelves. Extrinsic factors such as mouth opening and subsequent tongue withdrawal are also needed for the horizontal elevation of palate shelves. Failure of any of these steps can lead to cleft palate, one of the most common birth defects in humans. It has been shown that retinoic acid (RA) plays important roles during palate development, but excess RA causes cleft palate in fetuses of both rodents and humans. Thus, the coordinated regulation of retinoid metabolism is essential for normal palatogenesis. The endogenous RA level is determined by the balance of RA-synthesizing (retinaldehyde dehydrogenases: RALDHs) and RA-degrading enzymes (CYP26s). Cyp26b1 is a key player in normal palatogenesis. In this review, we discuss recent progress in the study of the pathogenesis of RA-induced cleft palate, with special reference to the regulation of endogenous RA levels by RA-degrading enzymes.

PRC1 coordinates timing of sexual differentiation of female primordial germ cells

In mammals, sex differentiation of primordial germ cells (PGCs) is determined by extrinsic cues from the environment. In mouse female PGCs, expression of stimulated by retinoic acid gene 8 (Stra8) and meiosis are induced in response to retinoic acid provided from the mesonephroi. Given the widespread role of retinoic acid signalling during development, the molecular mechanisms that enable PGCs to express Stra8 and enter meiosis in a timely manner are unknown. Here we identify gene-dosage-dependent roles in PGC development for Ring1 and Rnf2, two central components of the Polycomb repressive complex 1 (PRC1). Both paralogues are essential for PGC development between days 10.5 and 11.5 of gestation. Rnf2 is subsequently required in female PGCs to maintain high levels of Oct4 (also known as Pou5f1) and Nanog expression, and to prevent premature induction of meiotic gene expression and entry into meiotic prophase. Chemical inhibition of retinoic acid signalling partially suppresses precocious Oct4 downregulation and Stra8 activation in Rnf2-deficient female PGCs. Chromatin immunoprecipitation analyses show that Stra8 is a direct target of PRC1 and PRC2 in PGCs. These data demonstrate the importance of PRC1 gene dosage in PGC development and in coordinating the timing of sex differentiation of female PGCs by antagonizing extrinsic retinoic acid signalling.

ALDH1A3 Mutations Cause Recessive Anophthalmia and Microphthalmia

Anophthalmia and microphthalmia (A/M) are early-eye-development anomalies resulting in absent or small ocular globes, respectively. A/M anomalies occur in syndromic or nonsyndromic forms. They are genetically heterogeneous, some mutations in some genes being responsible for both anophthalmia and microphthalmia. Using a combination of homozygosity mapping, exome sequencing, and Sanger sequencing, we identified homozygosity for one splice-site and two missense mutations in the gene encoding the A3 isoform of the aldehyde dehydrogenase 1 (ALDH1A3) in three consanguineous families segregating A/M with occasional orbital cystic, neurological, and cardiac anomalies. ALDH1A3 is a key enzyme in the formation of a retinoic acid gradient along the dorso-ventral axis during early eye development. Transitory expression of mutant ALDH1A3 open reading frames showed that both missense mutations reduce the accumulation of the enzyme, potentially leading to altered retinoic acid synthesis. Although the role of retinoic acid signaling in eye development is well established, our findings provide genetic evidence of a direct link between retinoic-acid-synthesis dysfunction and early-eye-development anomalies in humans.

Retinoic acid signalling in gastrointestinal parasite infections: lessons from mouse models

SummaryRetinoic acid or vitamin A is important for an extensive range of biological processes, including immunomodulatory functions, however, its role in gastrointestinal parasite infections is not yet clear. Despite this, parasite infected individuals are often supplemented with vitamin A, given the co-localised prevalence of parasitic infections and vitamin deficiencies. Therefore, it is important to understand the impact of this vitamin on the immune responses to gastrointestinal parasites. Here, we review data regarding the role of retinoic acid signalling in mouse models of intestinal nematode infection, with a view to understanding better the practice of giving vitamin A supplements to worm-infected people.

Median facial clefts in Xenopus laevis: Roles of retinoic acid signaling and homeobox genes

The upper lip and primary palate form an essential separation between the brain, nasal structures and the oral cavity. Surprisingly little is known about the development of these structures, despite the fact that abnormalities can result in various forms of orofacial clefts. We have uncovered that retinoic acid is a critical regulator of upper lip and primary palate development in Xenopus laevis. Retinoic acid synthesis enzyme, RALDH2, and retinoic acid receptor gamma (RARγ) are expressed in complementary and partially overlapping regions of the orofacial prominences that fate mapping revealed contribute to the upper lip and primary palate. Decreased RALDH2 and RARγ result in a median cleft in the upper lip and primary palate. To further understand how retinoic acid regulates upper lip and palate morphogenesis we searched for genes downregulated in response to RARγ inhibition in orofacial tissue, and uncovered homeobox genes lhx8 and msx2. These genes are both expressed in overlapping domains with RARγ, and together their loss of function also results in a median cleft in the upper lip and primary palate. Inhibition of RARγ and decreased Lhx8/Msx2 function result in decreased cell proliferation and failure of dorsal anterior cartilages to form. These results suggest a model whereby retinoic acid signaling regulates Lhx8 and Msx2, which together direct the tissue growth and differentiation necessary for the upper lip and primary palate morphogenesis. This work has the potential to better understand the complex nature of the upper lip and primary palate development which will lead to important insights into the etiology of human orofacial clefts.