RESUMO
The ultimate goal of in vitro embryo culture systems is to perfectly mimic the condition of oocyte maturation, fertilization and embryo development. These systems are far more complex than standard in vitro cell culture because of the various environments through which the gametes and embryos pass during in vivo development. Improvement of the medium and other culture conditions has allowed for full development of a percentage of the fertilized oocytes but the great majority of bovine zygotes stop developing within a few cell cycles after initiating cleavage. This developmental block arises in the bovine embryo at the eight-cell-stage and is likely correlated with the cytoplasmic quality of the oocyte. Oocytes harbor all mRNAs and proteins needed to reach the fourth or fifth cell cycle, however, embryos that fail to transcribe their own genome fail to further develop. In this article, we review some of the advances in developmental block knowledge and describe a possible role of active embryo transcription that drives incompetent embryos to block and death.
Assuntos
Bovinos/embriologia , Desenvolvimento Embrionário e Fetal/genética , Regulação da Expressão Gênica , Animais , Técnicas de Cultura , Citoplasma/química , Embrião de Mamíferos/química , Embrião de Mamíferos/metabolismo , Genes , RNA Mensageiro/análise , Transcrição GênicaRESUMO
The blood supply of the Papillary Muscle (PM) of the left ventricle, cranial (PM) and caudal (PM), in Hereford cattle was studied. The results obtained from the dissection of 50 hearts injected with neoprene latex, indicated that the cranial PM is supplied by collateral of the Ramus descendens paraconalis in all cases, alone or together with vessels from the Ramus circumflexus of the Arteria coronaria sinistra. The caudal PM is supplied from arteries coming mainly from the Ramus circumflexus of the A. coronaria sinistra, and also from the Ramus descendens subsinuosus and Ramus descendens paraconalis. When present, the A. diagonalis supplies the cranial PM and in some cases the caudal PM too. Thus this vessel can be termed "artery of the papillary muscle".
Assuntos
Bovinos/anatomia & histologia , Vasos Coronários/anatomia & histologia , Músculos Papilares/anatomia & histologia , Animais , Ventrículos do Coração/anatomia & histologiaRESUMO
The objective of this study was to compare enzymatic and mechanical methods, at distinct fetal ages, on isolation of different developmental stages of preantral follicles from bovine ovaries. Fetal ovaries were obtained from pregnant cattle at 150 to 270 d of gestation, and 135,521 preantral follicles at different stages of development were studied. The dissociation of ovaries with a mechanical procedure resulted in an average of 938.16 prenatral follicles. In contrast, 3,715.56 follicles were obtained when enzymatic digestion was used (P = 0.0001). Histological evaluation confirmed follicular stages and demonstrated that both mechanical and mechanical-enzymatic procedure did not affect the cellular integrity of the follicles. Granulosa cell-oocyte complexes surrounded by a basal membrane, were considered preantral follicles in this study. The ratio of different stages of isolated preantral follicles was significantly (P = 0.0001) correlated to fetal age. The earliest fetal age at which tertiary follicles were identified was at 210 d of gestation. The results confirm previous observation that follicular development and atresia are initiated during fetal development. These data provide information on methodologies to isolate intact bovine preantral follicles for investigating the control and regulation of follicular development and the growth of preantral follicles in vitro.
Assuntos
Desenvolvimento Embrionário e Fetal , Folículo Ovariano/embriologia , Ovário/citologia , Ovário/embriologia , Animais , Bovinos , Separação Celular/métodos , Feminino , Feto , Idade Gestacional , Folículo Ovariano/citologia , GravidezRESUMO
A ramificaçäo e a disposiçäo das artérias e veias placentárias foram estudadas em 20 vacas da raça Nelore. Uma anastomose entre as duas artérias do funículo umbilical aparece em 75 por cento dos casos (70 por cento única e 5 por cento dupla). Os tipos de distribuiçäo vásculo-cotiledonário foram baseados nos arranjos das artérias e veias nas suas relaçöes com os cotilédones. Um cotilédone suprido por uma única artéria é drenado por múltiplas veias e, em poucos casos, as artérias e veias suprem e drenam respectivamente cotilédones dos cornos uterinos gestante e näo gestante