Overexpression of DAZL, STRA8, and BOULE Genes and Treatment With BMP4 or Retinoic Acid Modulate the Expression of MSC Overexpressing Germ Cell Genes

In vitro gamete derivation from stem cells has potential applications in animal reproduction as an alternative method for the dissemination of elite animal genetics, production of transgenic animals, and conservation of endangered species. Mesenchymal stem cells (MSCs) may be suitable candidates for in vitro gamete derivation considering their differentiative capacity and their potential for cell therapy. Due to its relevance in gametogenesis, it has been reported that retinoic acid (RA) and bone morphogenetic protein (BMP) 4 are able to upregulate the expression of specific markers associated to the early stages of germ cell (GCs) differentiation in bovine fetal MSCs (bfMSCs). In the present study, we used polycistronic vectors containing combinations of GC genes DAZL, STRA8, and BOULE followed by exposure to BMP4 or RA to induce GC differentiation of bovine fetal adipose tissue-derived MSC (AT-MSCs). Cells samples at Day 14 were analyzed according to the expression of pluripotent genes NANOG and OCT4 and GC genes DAZL, STRA8, BOULE, PIWI, c-KIT, and FRAGILIS using Q-PCR. Fetal and adult testis and AT-MSCs samples were also analyzed for the expression of DAZL, STRA8, and NANOG using immunofluorescence. Increased gene expression levels in the adult testis and cell-specific distribution of DAZL, STRA8, and NANOG in the fetal testis suggest that these markers are important components of the regulatory network that control the in vivo differentiation of bovine GCs. Overexpression of DAZL and STRA8 in bi-cistronic and DAZL, STRA8, and BOULE in tri-cistronic vectors resulted in the upregulation of OCT4, NANOG, and PIWIL2 in bovine fetal AT-MSCs. While BMP4 repressed NANOG expression, this treatment increased DAZL and c-KIT and activated FRAGILIS expression in bovine fetal AT-MSCs. Treatment with RA for 14 days increased the expression of DAZL and FRAGILIS and maintained the mRNA levels of STRA8 in bovine fetal AT-MSCs transfected with bi-cistronic and tri-cistronic vectors. Moreover, RA treatment repressed the expression of OCT4 and NANOG in these cells. Thus, overexpression of DAZL, STRA8, and BOULE induced the upregulation of the pluripotent markers and PIWIL2 in transfected bovine fetal AT-MSCs. The partial activation of GC gene expression by BMP4 and RA suggests that both factors possess common targets but induce different gene expression effects during GC differentiation in overexpressing bovine fetal AT-MSCs.

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Serial analysis of gene expression (SAGE) during porcine embryo development

Reproduction Fertility and Development ◽

10.1071/rd03081 ◽

2004 ◽

Vol 16 (2) ◽

pp. 87 ◽

Cited By ~ 12

Author(s):

Le Ann Blomberg ◽

Kurt A. Zuelke

Keyword(s):

Gene Expression ◽

Functional Genomics ◽

Embryo Development ◽

Molecular Mechanisms ◽

Physiological Role ◽

Transgenic Animals ◽

Specific Gene ◽

Research Strategies

Functional genomics provides a powerful means for delving into the molecular mechanisms involved in pre-implantation development of porcine embryos. High rates of embryonic mortality (30%), following either natural mating or artificial insemination, emphasise the need to improve the efficiency of reproduction in the pig. The poor success rate of live offspring from in vitro-manipulated pig embryos also hampers efforts to generate transgenic animals for biotechnology applications. Previous analysis of differential gene expression has demonstrated stage-specific gene expression for in vivo-derived embryos and altered gene expression for in vitro-derived embryos. However, the methods used to date examine relatively few genes simultaneously and, thus, provide an incomplete glimpse of the physiological role of these genes during embryogenesis. The present review will focus on two aspects of applying functional genomics research strategies for analysing the expression of genes during elongation of pig embryos between gestational day (D) 11 and D12. First, we compare and contrast current methodologies that are being used for gene discovery and expression analysis during pig embryo development. Second, we establish a paradigm for applying serial analysis of gene expression as a functional genomics tool to obtain preliminary information essential for discovering the physiological mechanisms by which distinct embryonic phenotypes are derived.

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182 In Vitro Derivation of Male Germ Cells from Bovine Bone Marrow-Derived Mesenchymal Stem Cells

Reproduction Fertility and Development ◽

10.1071/rdv30n1ab182 ◽

2018 ◽

Vol 30 (1) ◽

pp. 231

Author(s):

J. Cortez ◽

J. Bahamonde ◽

J. Palomino ◽

M. De los Reyes ◽

C. Torres ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Mesenchymal Stem Cells ◽

Germ Cell ◽

Mrna Expression ◽

Male Germ Cell ◽

Bovine Bone ◽

Mrna Levels ◽

Germ Cell Differentiation

During the last few years, the in vitro derivation of germ cell lineages from stem cells has emerged as an exciting new strategy for obtaining mature gametes. In vitro gamete derivation technology has potential applications as an alternative method for dissemination of elite animal genetics, production of transgenic animals, and conservation of endangered species. Germ cell differentiation and gametogenesis is a complex process and potential of different stem cell donors (i.e. SSC, ESC, iPSC) for in vitro male germ cell derivation has been inconsistent. Mesenchymal stem cells (MSC) may be suitable candidates for in vitro gamete derivation considering their (1) plasticity that is not limited to mesodermal derivatives, (2) availability of abundant tissues sources for isolation, (3) high proliferative potential, (4) simple and inexpensive isolation, and (5) high potential for cell therapy, including autologous or allogenic transplantation. The present study aimed to induce differentiation of MSC isolated from bone marrow derived from bovine male fetuses (bfMSC) into the germ cell lineage using an in vitro approach based on the exogenous effect of retinoic acid (RA) and bone morphogenetic protein 4 (BMP4). Differentiation media consisted in control media (DMEM with high glucose plus 10% fetal bovine serum, 100 IU mL−1 penicillin, 100 μg mL−1 streptomycin, and 0.25 μg mL−1amphotericin B) supplemented with RA (0.01, 0.1, or 1 µM) or BMP4 (10, 50, or 100 ng mL−1). Cell samples were obtained from differentiating and control bfMSC cultures and analysed for expression of housekeeping genes β-ACTIN and GAPDH, pluripotent genes OCT4 and NANOG, germ cell genes FRAGILLIS, STELLA, and VASA, male germ cell genes DAZL, PIWIl2, and STRA8, and meiotic biomarker SCP3 by quantitative-PCR (Q-PCR). OCT4, NANOG, and DAZL were immunodetected in undifferentiated and differentiated bfMSC using flow-cytometry analysis. The mRNA expression of DAZL was activated by RA or BMP4 supplementation, although no differences (P > 0.05) were detected among different concentrations. DAZL and NANOG mRNA levels increased (P < 0.05) from Day 7 to Day 21 during supplementation of RA (0.1 μM). In comparison, DAZL mRNA levels increased (P < 0.05) at Day 14 during supplementation of BMP4 (100 ng). OCT4 and SCP3 mRNA levels were not affected by RA or BMP4 treatments. Transcripts of FRAGILLIS, STELLA, VASA, PIWIl2, and STRA8 were not detected in control or differentiated bfMSC. Higher (P < 0.05) percentages of undifferentiated bfMSC were positive for NANOG (80.6%) and OCT4 (83.4%). DAZL- and NANOG-positive cells were 2.1% and 2.9%, and 95.9% and 97.8% at Days 0 and 21 of RA treatment, respectively. Data indicated that expression of germ cell biomarker DAZL in bfMSC is activated and increased after in vitro supplementation of RA and BMP4. Moreover, NANOG mRNA levels were regulated by RA treatment. Similar levels of SCP3 mRNA expression suggest that differentiated bfMSC were not induced into meiosis. Thus, exposure of bfMSC to RA or BMP4 under in vitro conditions might induce an early stage of premeiotic germinal differentiation.

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A Retinoid-Resistant Acute Promyelocytic Leukemia Subclone Expresses a Dominant Negative PML-RARα Mutation

Blood ◽

10.1182/blood.v89.12.4282 ◽

1997 ◽

Vol 89 (12) ◽

pp. 4282-4289 ◽

Cited By ~ 135

Author(s):

Wenlin Shao ◽

Laura Benedetti ◽

William W. Lamph ◽

Clara Nervi ◽

Wilson H. Miller

Keyword(s):

Gene Expression ◽

Retinoic Acid ◽

Ligand Binding ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Regulation Of Gene Expression ◽

Promyelocytic Leukemia ◽

Dominant Negative

Abstract The unique t(15; 17) of acute promyelocytic leukemia (APL) fuses the PML gene with the retinoic acid receptor α (RARα) gene. Although retinoic acid (RA) inhibits cell growth and induces differentiation in human APL cells, resistance to RA develops both in vitro and in patients. We have developed RA-resistant subclones of the human APL cell line, NB4, whose nuclear extracts display altered RA binding. In the RA-resistant subclone, R4, we find an absence of ligand binding of PML-RARα associated with a point mutation changing a leucine to proline in the ligand-binding domain of the fusion PML-RARα protein. In contrast to mutations in RARα found in retinoid-resistant HL60 cells, in this NB4 subclone, the coexpressed RARα remains wild-type. In vitro expression of a cloned PML-RARα with the observed mutation in R4 confirms that this amino acid change causes the loss of ligand binding, but the mutant PML-RARα protein retains the ability to heterodimerize with RXRα and thus to bind to retinoid response elements (RAREs). This leads to a dominant negative block of transcription from RAREs that is dose-dependent and not relieved by RA. An unrearranged RARα engineered with this mutation also lost ligand binding and inhibited transcription in a dominant negative manner. We then found that the mutant PML-RARα selectively alters regulation of gene expression in the R4 cell line. R4 cells have lost retinoid-regulation of RXRα and RARβ and the RA-induced loss of PML-RARα protein seen in NB4 cells, but retain retinoid-induction of CD18 and CD38. Thus, the R4 cell line provides data supporting the presence of an RARα-mediated pathway that is independent from gene expression induced or repressed by PML-RARα. The high level of retinoid resistance in vitro and in vivo of cells from some relapsed APL patients suggests similar molecular changes may occur clinically.

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LYL1, Class II Basic Helix-Loop-Helix Transcription Factor, Induces the Differentiation of Common Marmoset Embryonic Stem Cells to Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v118.21.2348.2348 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2348-2348

Author(s):

Hirotaka Kawano ◽

Tomotoshi Marumoto ◽

Michiyo Okada ◽

Tomoko Inoue ◽

Takenobu Nii ◽

...

Keyword(s):

Gene Expression ◽

Stem Cells ◽

Lymphoblastic Leukemia ◽

Embryonic Stem ◽

Common Marmoset ◽

Hematopoietic Stem ◽

Helix Loop Helix ◽

Cd34 Cells

Abstract Abstract 2348 Since the successful establishment of human embryonic stem cells (ESCs) in 1998, transplantation of functional cells differentiated from ESCs to the specific impaired organ has been expected to cure its defective function [Thomson JA et al., Science 282:1145–47, 1998]. For the establishment of the regenerative medicine using ESCs, the preclinical studies utilizing animal model systems including non-human primates are essential. We have demonstrated that non-human primate of common marmoset (CM) is a suitable experimental animal for the preclinical studies of hematopoietic stem cells (HSCs) therapy [Hibino H et al., Blood 93:2839–48, 1999]. Since then we have continuously investigated the in vitro and in vivo differentiation of CM ESCs to hematopoietic cells by the exogenous hematopoietic gene transfer. In earlier study, we showed that the induction of CD34+ cells having a blood colony forming capacity from CM ESCs is promoted by lentiviral transduction of TAL1 cDNA [Kurita R et al., Stem Cells 24:2014-22,2006]. However those CD34+ cells did not have a bone marrow reconstituting ability in irradiated NOG (NOD/Shi-scid/IL-2Rγnull) mice, suggesting that transduction of TAL1 gene is not enough to induce functional HSCs which have self-renewal capability and multipotency. Thus we tried to find other hematopoietic genes being able to promote hematopoietic differetiation more efficiently than TAL1. We selected 6 genes (LYL1, HOXB4, BMI1, GATA2, c-MYB and LMO2) as candidates for factors that induce the differentiation from ESCs to HSCs, based on the comparison of gene expression level between human ESCs and HSCs by Digital Differential Display from the Uni-Gene database at the NCBI web site (http://www.ncbi.nlm.nih.gov/UniGene/). Then, we transduced the respective candidate gene in CM ESCs (Cj11), and performed embryoid body (EB) formation assay to induce their differentiation to HSCs for 9 days. We found that lentiviral transduction of LYL1, a basic helix-loop-helix transcription factor, in EBs derived from Cj11, one of CM ESC lines, markedly increased the number of cells positive for CD34, a marker for hematopoietic stem/progenitors. The lymphoblastic leukemia 1 (LYL1) was originally identified as the factor of a chromosomal translocation, resulting in T cell acute lymphoblastic leukemia [Mellentin JD et al., Cell 58:77-83.1989]. These class II bHLH transcription factors regulate gene expression by binding to target gene sequences as heterodimers with E-proteins, in association with Gata1 and Gata2 [Goldfarb AN et al., Blood 85:465-71.1995][Hofmann T et al., Oncogene 13:617-24.1996][Hsu HL et al., Proc Natl Acad Sci USA 91:5947-51.1994]. The Lyl1-deficient mice display the reduction of B cells and impaired long-term hematopoietic reconstitution capacity [Capron C et al., Blood 107:4678-4686. 2006]. And, overexpression of Lyl1 in mouse bone marrow cells induced the increase of HSCs, HPCs and lymphocytes in vitro and in vivo [Lukov GL et al., Leuk Res 35:405-12. 2011]. These information indicate that LYL1 plays important roles in hematopoietic differentiation in primate animals including human and common marmoset. To examine whether overexpression of LYL1 in EBs can promote hematopoietic differentiation in vitro we performed colony-forming unit (CFU) assay, and found that LYL1-overexpressing EBs showed the formation of multi-lineage blood cells consisting of erythroid cells, granulocytes and macrophages. Next, we analyzed gene expression level by RT-PCR, and found that the transduction of LYL1 induced the expression of various hematopoietic genes. These results suggested that the overexpression of LYL1 can promote the differentiation of CM ESCs to HSCs in vitro. Furthermore we found that the combined overexpression of TAL1 and LYL1 could enhance the differentiation of CD34+ cells from CM ESCs than the respective overexrpession of TAL1 or LYL1. Collectively, our novel technology to differentiate hematopoietic cells from ESCs by the transduction of specific transcription factors is novel, and might be applicable to expand human hematopoietic stem/progenitor cells in vitro for future regenerative medicine to cure human hematopoietic cell dyscrasias. Disclosures: No relevant conflicts of interest to declare.

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Tropism of liver epithelial cells toward hepatocellular carcinoma in vitro and in vivo with altering gene expression of cancer stem cells

The American Journal of Surgery ◽

10.1016/j.amjsurg.2017.11.041 ◽

2018 ◽

Vol 215 (4) ◽

pp. 735-743

Author(s):

Kuo-Shyang Jeng ◽

Chi-Juei Jeng ◽

Wen-Juei Jeng ◽

I-Shyan Sheen ◽

Shih-Yun Li ◽

...

Keyword(s):

Gene Expression ◽

Hepatocellular Carcinoma ◽

Stem Cells ◽

Epithelial Cells ◽

Cancer Stem Cells ◽

Liver Epithelial Cells

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Human and murine amniotic fluid c-Kit+Lin− cells display hematopoietic activity

Blood ◽

10.1182/blood-2008-10-182105 ◽

2009 ◽

Vol 113 (17) ◽

pp. 3953-3960 ◽

Cited By ~ 100

Author(s):

Andrea Ditadi ◽

Paolo de Coppi ◽

Olivier Picone ◽

Laetitia Gautreau ◽

Rim Smati ◽

...

Keyword(s):

Gene Expression ◽

Stem Cells ◽

Amniotic Fluid ◽

Expression Analysis ◽

Gene Expression Analysis ◽

Lymphoid Cells ◽

Immunocompromised Hosts ◽

Hematopoietic Activity

Abstract We have isolated c-Kit+Lin− cells from both human and murine amniotic fluid (AF) and investigated their hematopoietic potential. In vitro, the c-Kit+Lin− population in both species displayed a multilineage hematopoietic potential, as demonstrated by the generation of erythroid, myeloid, and lymphoid cells. In vivo, cells belonging to all 3 hematopoietic lineages were found after primary and secondary transplantation of murine c-Kit+Lin− cells into immunocompromised hosts, thus demonstrating the ability of these cells to self-renew. Gene expression analysis of c-Kit+ cells isolated from murine AF confirmed these results. The presence of cells with similar characteristics in the surrounding amnion indicates the possible origin of AF c-Kit+Lin− cells. This is the first report showing that cells isolated from the AF do have hematopoietic potential; our results support the idea that AF may be a new source of stem cells for therapeutic applications.

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Retinoic acid activates interferon regulatory factor-1 gene expression in myeloid cells

Blood ◽

10.1182/blood.v88.1.114.bloodjournal881114 ◽

1996 ◽

Vol 88 (1) ◽

pp. 114-123 ◽

Cited By ~ 4

Author(s):

S Matikainen ◽

T Ronni ◽

M Hurme ◽

R Pine ◽

I Julkunen

Keyword(s):

Gene Expression ◽

Retinoic Acid ◽

Growth Inhibition ◽

Molecular Mechanisms ◽

Gene Activation ◽

Oligoadenylate Synthetase ◽

Nb4 Cells ◽

Drug Of Choice

All-trans-retinoic acid (ATRA) is the drug of choice in the treatment of acute promyelocytic leukemia (APL). ATRA induces both in vitro and in vivo differentiation of APL cells into mature granulocytes. However, the molecular mechanisms involved in ATRA-dependent growth inhibition and cellular differentiation are not presently understood. The NB4 cell line, which is derived from the bone marrow of a patient with APL during relapse, can be used as a model system to study the growth and differentiation of APL cells. Because interferon (IFN) regulatory factors (IRF-1 and IRF-2) and other IFN-inducible gene products regulate cell growth, we analyzed the effects of ATRA on the expression of these genes. We show that ATRA directly activates IRF-1 gene expression, followed by activation of IRF-2 and 2′–5′ oligoadenylate synthetase (OAS) gene expression with slower kinetics. In addition to NB4 cells, ATRA also activated IRF-1 gene expression in HL-60, U937, and THP-1 cells, which all respond to ATRA by growth inhibition. A more than additive increase in IRF-1 gene expression was seen with ATRA and IFN-gamma in NB4 cells. ATRA did not activate nuclear factor kappa B or signal transducer and activator of transcription (STAT) activation pathways, suggesting that an alternate mechanism is involved in IRF-1 gene activation. The ATRA-induced expression of IRF-1, an activator of transcription and repressor of transformation, may be one of the molecular mechanisms of ATRA-induced growth inhibition, and the basis for the synergistic actions of ATRA and IFNs in myeloid leukemia cells.

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Hairless is a nuclear receptor corepressor essential for skin function

Nuclear Receptor Signaling ◽

10.1621/nrs.07010 ◽

2009 ◽

Vol 7 (1) ◽

pp. nrs.07010 ◽

Cited By ~ 19

Author(s):

Catherine C. Thompson

Keyword(s):

Gene Expression ◽

Stem Cells ◽

Nuclear Receptors ◽

Chromatin Remodeling ◽

Transcriptional Repression ◽

Critical Role ◽

Epithelial Stem Cells ◽

Skin Function

The activity of nuclear receptors is modulated by numerous coregulatory factors. Corepressors can either mediate the ability of nuclear receptors to repress transcription, or can inhibit transactivation by nuclear receptors. As we learn more about the mechanisms of transcriptional repression, the importance of repression by nuclear receptors in development and disease has become clear. The protein encoded by the mammalian Hairless (Hr) gene was shown to be a corepressor by virtue of its functional similarity to the well-established corepressors N-CoR and SMRT. Mutation of the Hr gene results in congenital hair loss in both mice and men. Investigation of Hairless function both in vitro and in mouse models in vivo has revealed a critical role in maintaining skin and hair by regulating the differentiation of epithelial stem cells, as well as a putative role in regulating gene expression via chromatin remodeling.

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6 GENE EXPRESSION ANALYSIS OF IN VIVO- AND IN VITRO-MATURED PORCINE METAPHASE II OOCYTES

Reproduction Fertility and Development ◽

10.1071/rdv26n1ab6 ◽

2014 ◽

Vol 26 (1) ◽

pp. 117 ◽

Cited By ~ 2

Author(s):

L. Cox ◽

G. Saunders ◽

J. Stevens ◽

S. C. Isom

Keyword(s):

Gene Expression ◽

Rna Degradation ◽

Functional Gene ◽

Gene Set Enrichment Analysis ◽

Developmental Competence ◽

Mrna Levels ◽

Multiple Testing Correction ◽

Metaphase Ii Oocytes

In vitro-matured (IVM) oocytes lack the same developmental competence as oocytes that are matured in vivo (IVV), yet no compelling explanation for this discrepancy has been provided at the molecular level. The aim of this study was to quantify and compare mRNA levels in IVM and IVV oocytes for genes from a wide variety of functional gene categories, including RNA degradation, pluripotency, epigenome modification, oocyte-specific, and apoptosis. Quantitative real-time PCR (qPCR) was used to evaluate the relative gene expression levels of 70 genes in each of 33 individual IVM oocytes from 4 different collection days and 29 individual IVV oocytes from 4 different donor animals. The qPCR data were analysed using ANOVA and significance was assigned at P < 0.05. After a multiple testing correction was applied, relative transcript abundances for 32 of the 70 genes tested were found to be significantly different (q < 0.05) between the IVM and IVV oocytes. Of these significantly different genes, 23 were higher in the IVM oocytes and only 9 were higher in the IVV oocytes. The 32 significantly differentially expressed genes were then evaluated in relation to their corresponding functional gene categories. Of particular interest, transcripts for 7/14 RNA degradation-related genes (CNOT3, DCP1A, DDX6, LSM1, PABPN1, PABPN1L, PARN) and 3/9 oocyte specific genes (BMP15, YBX2, H1FOO) were significantly more abundant in the IVM oocytes. In contrast, transcripts for 4/8 epigenetic related transcripts (ASH2l, DNMT1, EHMT2, EZH2), 2/2 apoptosis related genes (BCL2, XIAP), and 1/4 pluripotency factors (LIN28) were significantly more abundant in the IVV oocytes. Gene set enrichment analysis confirmed that, within the context of this experimental design, RNA degradation and chromatin remodelling pathways are significantly perturbed in IVM oocytes. We conclude that in vitro maturation has profound effects on transcript populations of metaphase-II oocytes, with most transcripts being higher in IVM oocytes. We expect that this data will lead to a better understanding of how we can improve the quality of oocytes that are matured in vitro as well as provide information to help to identify markers that could be indicative of oocyte quality.

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Exogenous retinoic acid rapidly induces anterior ectopic expression of murine Hox-2 genes in vivo

Development ◽

10.1242/dev.116.2.357 ◽

1992 ◽

Vol 116 (2) ◽

pp. 357-368 ◽

Cited By ~ 47

Author(s):

R.A. Conlon ◽

J. Rossant

Keyword(s):

Gene Expression ◽

Retinoic Acid ◽

Ectopic Expression ◽

Teratogenic Effects ◽

Altered Expression ◽

Early Embryos ◽

Specific Manner ◽

Maternal Administration

Exogenous retinoic acid (RA) has teratogenic effects on vertebrate embryos and alters Hox-C gene expression in vivo and in vitro. We wish to examine whether RA has a role in the normal regulation of Hox-C genes, and whether altered Hox-C gene expression in response to RA leads to abnormal morphology. The expression of 3′ Hox-2 genes (Hox-2.9, Hox-2.8, Hox-2.6 and Hox-2.1) and a 5′ gene (Hox-2.5) were examined by whole-mount in situ hybridization on embryos 4 hours after maternal administration of teratogenic doses of RA on embryonic day 7 to 9. The expression of the 3′ Hox-2 genes was found to be ectopically induced in anterior regions in a stage-specific manner. The Hox-2.9 and Hox-2.8 genes were induced anteriorly in the neurectoderm in response to RA on day 7 but not at later stages. Expression of Hox-2.6 and Hox-2.1 was ectopically induced anteriorly in neurectoderm in response to RA on day 8. Hox-2.1 remained responsive on day 9, whereas Hox-2.6 was no longer responsive at this stage. The expression of the 5′ gene Hox-2.5 was not detectably altered at any of these stages by RA treatments. We also examined the response of other genes whose expression is spatially regulated in early embryos. The expression of En-2 and Wnt-7b was not detectably altered by RA, whereas RAR beta expression was induced anteriorly by RA on day 7 and 8. Krox-20 expression was reduced in a stage- and region-specific manner by RA. The ectopic anterior expression of Hox-2.8 and Hox-2.9 induced by RA on day 7 was persistent to day 8, as was the altered expression of Krox-20. The altered pattern of expression of these genes in response to RA treatment on day 7 may be indicative of a transformation of anterior hindbrain to posterior hindbrain, specifically, a transformation of rhombomeres 1 to 3 towards rhombomere 4 identity with an anterior expansion of rhombomere 5. The ectopic expression of the 3′ Hox-2 genes in response to RA is consistent with a role for these genes in mediating the teratogenic effects of RA; the rapid response of the Hox-C genes to RA is consistent with a role for endogenous RA in refining 3′ Hox-C gene expression boundaries early in development.

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