Dufort D, Schwartz L, Harpal K, Rossant J
Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada, M5G 1X5.
Development. 1998 Aug;125(16):3015-25. doi: 10.1242/dev.125.16.3015.
During early embryogenesis, the transcription factor HNF3beta is expressed in visceral and definitive endoderm, node, notochord and floorplate. A targeted mutation in the HNF3&bgr ; gene results in the lack of a definitive node and notochord. Furthermore, lack of HNF3beta results in failure of proper primitive streak elongation. To address whether HNF3beta is required in visceral endoderm, we have used tetraploid embryo-ES cell aggregations to generate chimeric mouse embryos with wild-type visceral endoderm and homozygous mutant HNF3beta embryonic ectoderm or vice versa. Replacing the visceral endoderm of mutant HNF3beta embryos rescued proper primitive streak elongation and, conversely, mutant visceral endoderm imposed a severe embryonic-extraembryonic constriction on wild-type embryonic ectoderm. Restoration of normal streak morphogenesis was not sufficient to allow formation of the node and notochord in HNF3beta mutant embryos. Thus, our results demonstrate that HNF3beta has two separate roles in primitive streak formation. One is to act within the visceral endoderm to promote proper streak morphogenesis. The second is autonomous to the node and its precursors and involves specification of node and notochord cell fates. HNF3beta mutant embryos rescued for the embryonic-extraembryonic constriction developed further than mutant embryos, allowing examination of later roles for HNF3beta. We show that such mutant embryos lack foregut and midgut endoderm. In addition, left-right asymmetry is affected in the mutant embryos.
在胚胎发育早期，转录因子HNF3β在内脏和定形内胚层、原结、脊索和底板中表达。HNF3β基因的靶向突变导致原结和脊索缺失。此外，缺乏HNF3β会导致原条无法正常延伸。为了研究HNF3β在内脏内胚层中是否必需，我们利用四倍体胚胎-胚胎干细胞聚合法生成了具有野生型内脏内胚层和纯合突变型HNF3β胚胎外胚层的嵌合小鼠胚胎，反之亦然。替换突变型HNF3β胚胎的内脏内胚层可挽救原条的正常延伸，相反，突变型内脏内胚层会对野生型胚胎外胚层施加严重的胚胎-胚外收缩。恢复正常的原条形态发生不足以使HNF3β突变胚胎形成原结和脊索。因此，我们的结果表明，HNF3β在原条形成中有两个独立的作用。一是在内脏内胚层中起作用，促进原条的正常形态发生。二是对原结及其前体具有自主性，涉及原结和脊索细胞命运的特化。因胚胎-胚外收缩得到挽救的HNF3β突变胚胎比突变胚胎发育得更完善，从而能够研究HNF3β在后期的作用。我们发现，这类突变胚胎缺乏前肠和中肠内胚层。此外，突变胚胎的左右不对称性也受到影响。
