RESUMO
Appropriate interactions between the epithelium and adjacent neural crest-derived mesenchyme are necessary for normal pharyngeal arch development. Disruption of pharyngeal arch development in humans underlies many of the craniofacial defects observed in the 22q11.2 deletion syndrome (del22q11), but the genes responsible remain unknown. Tbx1 is a T-box transcription factor that lies in the 22q11.2 locus. Tbx1 transcripts were found to be localized to the pharyngeal endoderm and the mesodermal core of the pharyngeal arches, but were not present in the neural crest-derived mesenchyme of the pharyngeal arches. Sonic hedgehog (Shh) is also expressed in the pharyngeal arches and is necessary for normal craniofacial development. We found that Tbx1 expression was dependent upon Shh signaling in mouse embryos, consistent with their overlapping expression in the pharyngeal arches. Furthermore, Shh was sufficient to induce Tbx1 expression when misexpressed in selected regions of chick embryos. These studies reveal a Shh-mediated pathway that regulates Tbx1 during pharyngeal arch development.
Assuntos
Síndrome de DiGeorge/genética , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Faringe/embriologia , Proteínas/fisiologia , Proteínas com Domínio T/genética , Transativadores , Sequência de Aminoácidos , Animais , Sequência de Bases , Embrião de Galinha , Deleção Cromossômica , Cromossomos Humanos Par 22 , Clonagem Molecular , Primers do DNA , DNA Complementar , Proteínas Hedgehog , Humanos , Hibridização In Situ , Camundongos , Dados de Sequência Molecular , RNA Mensageiro/genética , Homologia de Sequência de Aminoácidos , Proteínas com Domínio T/químicaRESUMO
dHAND is a basic helix-loop-helix (bHLH) transcription factor essential for cardiovascular development. Here we analyze its pattern of expression and functional role during chick limb development. dHAND expression was observed in the lateral plate mesoderm prior to emergence of the limb buds. Coincident with limb initiation, expression of dHAND became restricted to the posterior half of the limb bud. Experimental procedures that caused mirror-image duplications of the limb resulted in mirror-image duplications of the pattern of dHAND expression along the anterior-posterior axis. Retroviral overexpression of dHAND in the limb bud produced preaxial polydactyly, corresponding to mild polarizing activity at the anterior border. At the molecular level, misexpression of dHAND caused ectopic activation of members of the Sonic hedgehog (Shh) pathway, including Gli and Patched, in the anterior limb bud. A subset of infected embryos displayed ectopic anterior activation of Shh. Other factors implicated in anterior-posterior polarization of the bud such as the most 5' Hoxd genes and Bmp2 were also ectopically activated at the anterior border. Our results indicate a role for dHAND in the establishment of anterior-posterior polarization of the limb bud.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Sequências Hélice-Alça-Hélice , Botões de Extremidades/embriologia , Proteínas/metabolismo , Transdução de Sinais/fisiologia , Transativadores , Fatores de Transcrição/fisiologia , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos , Embrião de Galinha , Proteínas de Ligação a DNA/genética , Expressão Gênica , Proteínas Hedgehog , Polidactilia , Proteínas/genética , Fatores de Transcrição/genética , Proteínas de Peixe-ZebraRESUMO
Proper morphogenesis and positioning of internal organs requires delivery and interpretation of precise signals along the anterior-posterior, dorsal-ventral, and left-right axes. An elegant signaling cascade determines left- versus right-sided identity in visceral organs in a concordant fashion, resulting in a predictable left-right (LR) organ asymmetry in all vertebrates. The complex morphogenesis of the heart and its connections to the vasculature are particularly dependent upon coordinated LR signaling pathways. Disorganization of LR signals can result in myriad congenital heart defects that are a consequence of abnormal looping and remodeling of the primitive heart tube into a multi-chambered organ. A framework for understanding how LR asymmetric signals contribute to normal organogenesis has emerged and begins to explain the basis of many human diseases of LR asymmetry. Here we review the impact of LR signaling pathways on cardiac development and congenital heart disease.
Assuntos
Coração Fetal/crescimento & desenvolvimento , Regulação da Expressão Gênica no Desenvolvimento , Cardiopatias Congênitas/embriologia , Morfogênese/genética , Proteínas Nucleares , Anormalidades Múltiplas/embriologia , Anormalidades Múltiplas/genética , Animais , Padronização Corporal/genética , Embrião de Galinha , Coração Fetal/ultraestrutura , Proteínas Fetais/genética , Proteínas Fetais/fisiologia , Coração/embriologia , Cardiopatias Congênitas/genética , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/fisiologia , Humanos , Camundongos , Fatores de Transcrição Box Pareados , Situs Inversus/embriologia , Situs Inversus/genética , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologia , Vísceras/anormalidades , Xenopus laevis/embriologia , Peixe-Zebra/embriologia , Proteína Homeobox PITX2RESUMO
BACKGROUND: Human telomerase has an essential RNA component and is an ideal target for developing rules correlating oligonucleotide chemistry with disruption of biological function. Similarly, peptide nucleic acids (PNAs), DNA analogs that bind complementary sequences with high affinity, are outstanding candidates for inducing phenotypic changes through hybridization. RESULTS: We identify PNAs directed to nontemplate regions of the telomerase RNA that can overcome RNA secondary structure and inhibit telomerase by intercepting the RNA component prior to holoenzyme assembly. Relative potencies of inhibition delineate putative structural domains. We describe a novel protocol for introducing PNAs into eukaryotic cells and report efficient inhibition of cellular telomerase by PNAs. CONCLUSIONS: PNAs directed to nontemplate regions are a new class of telomerase inhibitor and may contribute to the development of novel antiproliferative agents. The dependence of inhibition by nontemplate-directed PNAs on target sequence suggests that PNAs have great potential for mapping nucleic acid structure and predictably regulating biological processes. Our simple method for introducing PNAs into cells will not only be useful for probing the complex biology surrounding telomere length maintenance but can be broadly applied for controlling gene expression and functional genomics.