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Retinoic acid (RA) is an active metabolite of vitamin A that is essential for embryonic development, and homeostasis of adult tissues. RA is a ligand for the nuclear retinoic acid receptor, and RA-mediated signaling is critical for regulation of cell proliferation, differentiation and apoptosis. There is a spatio-temporal distribution of RA in the developing embryo such that some tissues are rich in RA, while others are devoid. This patterned distribution of RA is tightly controlled through the coordinated expression of RA-synthesizing (retinaldehyde dehydrogenase) and RA-catabolizing (CYP26) enzymes. In this thesis, I describe the cloning of a mouse gene encoding one of the CYP26 proteins, Cyp26b1. Cyp26b1 was shown to be highly expressed in the embryo, with transcripts localized to the hindbrain, limb buds and branchial arches. We also used homologous recombination to generate a line of transgenic mice with a loss-of-function deletion in Cyp26b1. These mice die shortly after birth with severe malformations affecting the limbs, craniofacial structures and epidermis; phenotypes that are all reminiscent of RA teratogenesis. We present an extensive characterization of the craniofacial and epidermal abnormalities in Cyp26b1-/- animals, and examine several molecular pathways that may be deregulated. CYP26B1 null embryos exhibit a truncated mandible, lack numerous facial bones, and show reduced ossification of the calvaria. Molecular analysis of Cyp26b1-/- embryos indicates hindbrain and branchial arch patterning is largely unaffected in early to mid-gestational mutants. However, there appear to be some subtle abnormalities in neural crest cell migration, which may contribute to the development of some of the observed phenotypes. CYP26B1 null mutants also lack hair follicles, which appears to be due to a downregulation of -catenin mediated signaling. Thus, in addition to cloning and characterizing the expression of murine Cyp26b1, we have demonstrated in vivo, that regulation of RA distribution by CYP26B1 is essential for morphogenesis of the epidermis and craniofacial structures. / Thesis (Ph.D, Pathology & Molecular Medicine) -- Queen's University, 2007-09-28 13:49:35.17

Previous studies showed haploinsufficiency of RAI1 is the main cause of Smith-Magenis syndrome (SMS). SMS is a developmental neurobehavioral syndrome characterized by intellectual disability, congenital anomalies, obesity, neurobehavioral abnormalities, and disrupted circadian sleep-wake pattern. SMS is caused by deletion or mutation of chromosomal region 17p11.2 that includes RAI1. Studies in the Elsea lab have shown that RAI1 is a dosage-sensitive gene. Haploinsufficiency of RAI1 leads to dysregulation of CLOCK, NR1D2, POMC, and BDNF, which are responsible for circadian rhythm, metabolism, and cognitive development. Based on the data from Elsea’s recent study on zebrafish, rai1 gene expression in zebrafish is regulated by retinoic acid. Treatment with retinoic acid increases the expression of rai1. In this study, we focused on the effect of retinoic acid on human RAI1 expression. We found the expression of RAI1 was enhanced by the treatment with retinoic acid. The different concentrations of the retinoic acid affect the levels of increase in expression, but we found little evidence that RAI1 expression was affected by the length of treatment time. In this study, we were unable to find consistency in the pattern of changes in the expression level in respect to the different treatment concentrations. We identified nine strong retinoic acid response element (RARE) candidate sites upstream of the start codon in human RAI1. Since there are possible RARE sites present in the upstream sequence of RAI1, it is more likely that RAI1 is regulated by retinoic acid. However, further experimental evidence will be needed to confirm those sites selected in silico are able to bind RAR/RXR heterodimers, to prove the selected sites are real RARE sites and were not identified by chance.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 123-159).

Thesis (Ph. D.)--Cornell University, May, 2007. / Vita. Includes bibliographical references (leaves 144-163).

All-trans retinoic acid (RA), as a ligand for retinoic acid receptors (RAR) and retinoid X receptors (RXR), modulates their transcriptional activity. The AF-1 and AF-2 domains mediate the transcriptional activity. The ligand dependent activation of the AF-2 domain by RA is well understood to involve chromosome decompaction in the presence of ligand with the aid of coactivators. The mechanism of the ligand independent action of the AF-1 domain is less clear. The AF-1 domain of RARs may be regulated by interacting proteins such as HACE1. In vitro and in vivo studies in our lab have shown that HACE1 interacts with RARα1, - β1, -β2, -β3, and -γ1 at the variable AF-1 domain. Transactivation studies have shown that HACE1 represses RA dependent transcriptional activity of RARγ1, but not RARβ3 and RARα1. Our original hypothesis proposed that HACE1 represses RAR transcriptional activity by inhibiting RA-dependent degradation of RARs. Current data confirms previous observations that the half life of RARβ3 is shortened in the presence of RA, compared to a vehicle control. Protein stability assays show that HACE1 does not have an effect on degradation of RARβ3 and RARγ1; however, it increases the ligand independent degradation of RARα1.This data suggests the A/B domain of RARγ1 recruits HACE1 for binding which results in transcriptional repression. Also, in a separate mechanism, the A/B domain of RARα1 binds to HACE1 which then accelerates its degradation in a ligand independent manner. The mechanisms behind these novel roles of HACE1 will need to be studied further and may help in understanding the method of AF-1 transcactivation function. / Microbiology and Immunology

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Development is a dynamic process characterized by critical periods in which organ systems are sensitive to changes in the surrounding environment. In the current study, critical windows of embryonic growth and kidney development were assessed in the embryonic chicken. All‐trans retinoic acid (tRA) influences not only organogenesis and cell proliferation, but also targets metanephric kidney nephrogenesis. Embryonic chickens were given a single injection of tRA on embryonic day 8. tRA decreased embryo, kidney, and heart mass from day 16 to day 18. However, mass specific kidney and heart masses showed no differences. Whole blood, plasma, and allantoic fluid osmolality were altered in tRA treated embryos from day 16 to day 18. In addition, hematocrit, red blood cell count, and hemoglobin concentration were altered in tRA treated embryos. The results suggest that although nephrogenesis was not affected by tRA, the developing osmoregulatory system was altered in tRA treated embryos.