RESUMO
The signals that regulate peripheral blood vessel formation during development are still under investigation. The hormone leptin promotes blood vessel formation, adipose tissue establishment and expansion, tumor growth, and wound healing, but the underlying mechanisms for these actions are currently unknown. We investigated whether leptin promotes angiogenesis in the developing tail fin using embryonic transgenic xflk-1:GFP Xenopus laevis, which express a green fluorescent protein on vascular endothelial cells to mark blood vessels. We found that leptin protein is expressed in endothelial cells of developing blood vessels and that leptin treatment via injection increased phosphorylated STAT3 signaling, which is indicative of leptin activation of its receptor, in blood vessels of the larval tail fin. Leptin administration via media increased vessel length, branching, and reconnection with the cardinal vein, while decreased leptin signaling via immunoneutralization had an opposing effect on vessel development. We also observed disorganization of major vessels and microvessels of the tail fin and muscle when leptin signaling was decreased. Reduced leptin signaling lowered mRNA expression of cenpk, gpx1, and mmp9, markers for cell proliferation, antioxidation, and extracellular matrix remodeling/cell migration, respectively, in the developing tail, providing insight into three possible mechanisms underlying leptin's promotion of angiogenesis. Together these results illustrate that leptin levels are correlated with embryonic angiogenesis and that leptin coordinates multiple aspects of blood vessel growth and development, showing that leptin is an important morphogen during embryonic development.
Assuntos
Larva , Leptina , Neovascularização Fisiológica , Transdução de Sinais , Cauda , Xenopus laevis , Animais , Leptina/metabolismo , Cauda/irrigação sanguínea , Cauda/embriologia , Xenopus laevis/embriologia , Xenopus laevis/metabolismo , Larva/metabolismo , Vasos Sanguíneos/embriologia , Vasos Sanguíneos/metabolismo , Proteínas de Xenopus/metabolismo , Proteínas de Xenopus/genética , Animais Geneticamente Modificados , Fator de Transcrição STAT3/metabolismo , Embrião não Mamífero/metabolismo , Proteínas de Fluorescência Verde/metabolismo , Regulação da Expressão Gênica no DesenvolvimentoRESUMO
The loss of the tail is among the most notable anatomical changes to have occurred along the evolutionary lineage leading to humans and to the 'anthropomorphous apes'1-3, with a proposed role in contributing to human bipedalism4-6. Yet, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown. Here we present evidence that an individual insertion of an Alu element in the genome of the hominoid ancestor may have contributed to tail-loss evolution. We demonstrate that this Alu element-inserted into an intron of the TBXT gene7-9-pairs with a neighbouring ancestral Alu element encoded in the reverse genomic orientation and leads to a hominoid-specific alternative splicing event. To study the effect of this splicing event, we generated multiple mouse models that express both full-length and exon-skipped isoforms of Tbxt, mimicking the expression pattern of its hominoid orthologue TBXT. Mice expressing both Tbxt isoforms exhibit a complete absence of the tail or a shortened tail depending on the relative abundance of Tbxt isoforms expressed at the embryonic tail bud. These results support the notion that the exon-skipped transcript is sufficient to induce a tail-loss phenotype. Moreover, mice expressing the exon-skipped Tbxt isoform develop neural tube defects, a condition that affects approximately 1 in 1,000 neonates in humans10. Thus, tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects, which continue to affect human health today.
Assuntos
Processamento Alternativo , Evolução Molecular , Hominidae , Proteínas com Domínio T , Cauda , Animais , Humanos , Camundongos , Processamento Alternativo/genética , Elementos Alu/genética , Modelos Animais de Doenças , Genoma/genética , Hominidae/anatomia & histologia , Hominidae/genética , Íntrons/genética , Defeitos do Tubo Neural/genética , Defeitos do Tubo Neural/metabolismo , Fenótipo , Isoformas de Proteínas/deficiência , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Proteínas com Domínio T/deficiência , Proteínas com Domínio T/genética , Proteínas com Domínio T/metabolismo , Cauda/anatomia & histologia , Cauda/embriologia , Éxons/genéticaRESUMO
A observaçäo da cauda de girinos totalmente desenvolvidos e no envolver de sua regressäo, ao microscópio eletrônico, permitiu constatar fibras musculares estriadas esqueletícas íntegras e fibroblastos bem desenvolvidos quando a cauda atingia o seu maior comprimento. No entanto, durante sua regressäo notamos nas fibras musculares ruptura e desorganizaçäo das miofibrilas, além de grandes gotículas de lipídios e mitocôndrias alteradas, indicando degeneraçäo celular. Durante esta última fase observamos entre as fibras musculares grande concentraçäo de macrófagos com miofibrilas no citoplasma e fibroblastos contendo no seu interior vesículas com fibrilas colágenas.