(2) the expression of Foxc1 and Pitx2, which play crucial roles in anterior eye segment development; and (3) the growth of the ventral retina. We additionally show that RALDH1 and RALDH3 are the only enzymes that are required for RA synthesis in the eye region from E10.5 to E13.5, and that patterning of the dorsoventral axis of the retina does not require RA. Research articleDevelopment 4790 role in DV patterning Dräger et al., 2001;Peters and Cepko, 2002;Sakai et al., 2004).RALDH2, whose genetic ablation kills embryos at E9.5 (Niederreither et al., 1999;Mic et al., 2002), is required between E8.5 and E9.5 for optic cup formation and for setting up the correct expression of RALDH3 at later stages in the forming eye (Mic et al., 2004). RALDH1-null mice are viable and do not exhibit ocular defects, even though they lack RAdependent activity in the dorsal retina and in the corresponding axonal projections at E16.5 (Fan et al., 2003). RALDH3-null mice, which die at birth from respiratory distress due to choanal atresia, display only discrete ocular malformations, namely a retrolenticular membrane and a mild shortening of the ventral retina (Dupé et al., 2003). Furthermore, neither RALDH1-null nor RALDH3-null mice exhibit an altered DV patterning of the retina (Fan et al., 2003; Dupé et al., 2003). These observations raised the question as to whether the loss of RALDH1 or RALDH3 could be functionally compensated by RALDH3 or RALDH1, respectively, or by other RALDH proteins expressed in the eye region. To gain further insight into the roles of RA signaling pathways in the developing eye, we have analyzed the ocular phenotype of mutant mice (1) lacking both RALDH1 and RALDH3, and (2) lacking RAR␤ and RAR␥ selectively in the NCC-derived periocular mesenchyme (POM). We demonstrate that RA produced in the neural retina, the retinal pigmented epithelium and the corneal ectoderm by RALDH1 and RALDH3 acts in a paracrine manner to selectively control the expression of several genes in POM cells, whereas it is dispensable for the DV patterning of the retina. Materials and methods MiceAll mice, with a mixed C57BL/6ϫ129/Sv (50:50) genetic background, were housed in an animal facility licensed by the French Ministry of Agriculture , and all animal experiments were supervised by N.B.G. , who is qualified for experimenting with mice, in compliance with the European legislation on care and use of laboratory animals. The breeding diet (D03) contained 25000 UI of vitamin A per kg (UAR, Villemoisson sur Orge, France) and was provided ad libitum. Heterozygous mice were mated overnight, and animals with a vaginal plug at noon of the next day were considered as embryonic day (E) 0.5. Mice bearing loxP-flanked (floxed) RAR␤ (Rarb +/L2) and RAR␥ (Rarg +/L2) genes (Chapellier et al., 2002a; Chapellier, 2002b), as well as the Rare-hsp68-lacZ (Rossant et al., 1991), R26R (Soriano, 1999) and Wnt1-Cre (Danielian et al., 1998) transgenic mice were genotyped as described. Note that mutant fetuses lacking both RALDH1 and RALDH3 (hereafter designa...

In the adult mouse, single and compound null mutations in the genes for retinoic acid receptor beta and retinoid X receptors beta and gamma resulted in locomotor defects related to dysfunction of the mesolimbic dopamine signaling pathway. Expression of the D1 and D2 receptors for dopamine was reduced in the ventral striatum of mutant mice, and the response of double null mutant mice to cocaine, which affects dopamine signaling in the mesolimbic system, was blunted. Thus, retinoid receptors are involved in the regulation of brain functions, and retinoic acid signaling defects may contribute to pathologies such as Parkinson's disease and schizophrenia.

The retinoic acid (RA) signal, produced locally from vitamin A by retinaldehyde dehydrogenase (Raldh) and transduced by the nuclear receptors for retinoids (RA receptor and 9-cis-RA receptor), is indispensable for ontogenesis and homeostasis of numerous tissues. We demonstrate that Raldh3 knockout in mouse suppresses RA synthesis and causes malformations restricted to ocular and nasal regions, which are similar to those observed in vitamin A-deficient fetuses and͞or in retinoid receptor mutants. Raldh3 knockout notably causes choanal atresia (CA), which is responsible for respiratory distress and death of Raldh3-null mutants at birth. CA is due to persistence of nasal fins, whose rupture normally allows the communication between nasal and oral cavities. This malformation, which is similar to isolated congenital CA in humans and may result from impaired RA-controlled down-regulation of Fgf8 expression in nasal fins, can be prevented by a simple maternal treatment with RA.Harderian gland ͉ nasolacrimal duct ͉ development ͉ nuclear receptor ͉ llama

Retinoic acid (RA) is known to be required at various levels of eye patterning via Retinoic Acid Receptors (RAR); however the molecular and cellular mechanisms triggered by these nuclear receptors are still obscure. The genetic studies performed here enable us to present a new model to study RA action during eye development. By inactivating the three RARs, specifically in the periocular mesenchyme, we discriminate the individual contribution of each RAR during eye development and describe a new function for RARs during the formation of the optic nerve. We demonstrate that RARalpha is the only receptor that mediates RA signalling in the neurectoderm during ocular development. Surprisingly, and despite a sophisticated pattern of RA-activity in the developing retina, we observed that RA signalling is not autonomously required in this tissue for eye formation. We show that the action of RA during eye morphogenesis is occurring specifically in neural crest-derived periocular mesenchyme and is mediated by all three RARs. Furthermore, we point out that Pitx2, which encodes a homeodomain transcription factor, is a key RA-responsive gene in neural crest cells during eye development. Interestingly, we observed that RA is required in the neural crest cells for normal position of the extraocular muscle.

An algorithm is proposed based on these new phenotype-genotype correlations, to facilitate molecular analysis and genetic counselling for HPE.

Animal SWI2/SNF2 protein complexes containing either the brahma (BRM) or brahma-related gene 1 (BRG1) ATPase are involved in nucleosome remodelling and may control the accessibility of sequence-specific transcription factors to DNA. In vitro studies have indicated that BRM and BRG1 could regulate the expression of distinct sets of genes. However, as mice lacking BRM are viable and fertile, BRG1 might efficiently compensate for BRM loss. By contrast, as Brg1-null fibroblasts are viable but Brg1-null embryos die during the peri-implantation stage, BRG1 might exert cell-specific functions. To further investigate the in vivo role of BRG1, we selectively ablated Brg1 in keratinocytes of the forming mouse epidermis. We show that BRG1 is selectively required for epithelial-mesenchymal interactions in limb patterning, and during keratinocyte terminal differentiation, in which BRM can partially substitute for BRG1. By contrast, neither BRM nor BRG1 are essential for the proliferation and early differentiation of keratinocytes, which may require other ATP-dependent nucleosome-remodelling complexes. Finally, we demonstrate that cell-specific targeted somatic mutations can be created at various times during the development of mouse embryos cell-specifically expressing the tamoxifen-activatable Cre-ERT2 recombinase.

The RXRy (RXR, retinoid X receptor) gene was disrupted in the mouse. Homozygous mutant mice developed normally and were indistinguishable from their RXRy+/_ or wild-type littermates with respect to growth, fertility, viability, and apparent behavior in the animal facility. Moreover, RXRca-'/RXRy-/-and RXR8-/-/RXRy-/-mutant phenotypes were indistinguishable from those of RXRx1/-and RXRJ-/-mutants, respectively. Strikingly, RXRa+/'/RXRPj3'/RXR'y'/ triple mutants were viable.Thus, it appears that RXRy does not exert any essential function that cannot be performed by RXRxi or RXRi3, and one copy of RXRa is sufficient to perform most of the functions of the RXRs.(11-13). In contrast, RXRy transcripts appear to have a more restricted distribution. In the embryo, RXRy is mainly expressed in developing skeletal muscles where its expression persists throughout life. RXRy is also expressed in the heart (after birth), sensory epithelia of visual and auditory system, specific structures of the central nervous system, as well as tissues involved in thyroid hormone homeostasis (thyroid gland and thyrotrope cells in the pituitary; refs. 11, 12, 14, and 15). To investigate whether this restricted expression of RXR'y corresponds to specific functions in vivo, we have now produced RXRy knock-out mice and studied the effects of this mutation in single, as well as in compound, mutants for the other RXR isotypes.The retinoid X receptors RXRa, RXR3, and RXRy belong to the superfamily of nuclear receptors (for review see refs. 1-6). As they specifically bind 9-cis-retinoic acid, these receptors may be directly involved in the transduction of the retinoid signal. In vitro studies using cultured cells have shown that RXRs can act as homodimers or as heterodimeric partners of a number of nuclear receptors, including retinoic acid receptors (RARs), thyroid hormone receptors, the vitamin D3 receptor, peroxisomal proliferator-activated receptors, and a large number of orphan receptors (for review see refs. 3 and 5). Thus, RXRs may be key actors involved in the mediation of several hormonal signals.It is currently unclear whether all the molecular properties of RXRs characterized in vitro are relevant for their physiological functions in the animal. In particular, it is unknown under which conditions these receptors act as 9-cis-retinoic acid-dependent transcriptional regulators and whether all of the suggested heterodimeric combinations occur in vivo (3). The knock-outs of RXRa and RXR,B in the mouse have provided some insight into the physiological functions of these receptors. The ocular and cardiac malformations observed in RXRa'--fetuses (7,8) are similar to those found in the fetal vitamin A deficiency syndrome, thus suggesting an important function of RXRa in the transduction of a retinoid signal during development. An involvement of RXRs in retinoid signaling is further supported by studies of compound RXRa/ RAR mutants, which reveal defects that are either absent or less severe in the single mutants (7,9) (Fig. 1B), the 2.5...

We previously reported that mice lacking the RARgamma gene and one or both alleles of the RARbeta gene (i.e., RARbeta+/-/RARgamma-/- and RARbeta-/-/RARgamma-/- mutants) display a severe and fully penetrant interdigital webbing (soft tissue syndactyly), caused by the persistence of the fetal interdigital mesenchyme (Ghyselinck et al., 1997, Int. J. Dev. Biol. 41, 425-447). In the present study, these compound mutants were used to investigate the cellular and molecular mechanisms involved in retinoic acid (RA)-dependent formation of the interdigital necrotic zones (INZs). The mutant INZs show a marked decrease in the number of apoptotic cells accompanied by an increase of cell proliferation. This marked decrease was not paralleled by a reduction of the number of macrophages, indicating that the chemotactic cues which normally attract these cells into the INZs were not affected. The expression of a number of genes known to be involved in the establishment of the INZs, the patterning of the autopod, and/or the initiation of apoptosis was also unaffected. These genes included BMP-2, BMP-4, Msx-1, Msx-2, 5' members of Hox complexes, Bcl2, Bax, and p53. In contrast, the mutant INZs displayed a specific, graded, down-regulation of tissue transglutaminase (tTG) promoter activity and of stromelysin-3 expression upon the removal of one or both alleles of the RARbeta gene from the RARgamma null genetic background. As retinoic acid response elements are present in the promoter regions of both tTG and stromelysin-3 genes, we propose that RA might increase the amount of cell death in the INZs through a direct modulation of tTG expression and that it also contributes to the process of tissue remodeling, which accompanies cell death, through an up-regulation of stromelysin-3 expression in the INZs. Approximately 10% of the RARbeta-/- /RARgamma-/- mutants displayed a supernumerary preaxial digit on hindfeet, which is also a feature of the BMP-7 null phenotype (Dudley et al., 1995, Genes Dev. 9, 2795-2807; Luo et al., 1995, Genes Dev. 9, 2808-2820). BMP-7 was globally down-regulated at an early stage in the autopods of these RAR double null mutants, prior to the appearance of the digital rays. Therefore, RA may exert some of its effects on anteroposterior autopod patterning through controlling BMP-7 expression.