Wolfe Adam D, Downs Karen M
Department of Pediatrics, Division of Pediatric Hematology, Oncology & Bone Marrow Transplant, University of Wisconsin-Madison School of Medicine and Public Health, 1111 Highland Avenue, 4105 WIMR, Madison, WI 53705, United States.
Department of Cell and Regenerative Biology, University of Wisconsin-Madison School of Medicine and Public Health, 1300 University Avenue, Madison, WI 53706, United States.
Gene Expr Patterns. 2014 May;15(1):8-20. doi: 10.1016/j.gep.2014.02.002. Epub 2014 Mar 12.
Mixl1 is thought to play important roles in formation of mesoderm and endoderm. Previously, Mixl1 expression was reported in the posterior primitive streak and allantois, but the precise spatiotemporal whereabouts of Mixl1 protein throughout gastrulation have not been elucidated. To localize Mixl1 protein, immunohistochemistry was carried out at 2-4 h intervals on mouse gastrulae between primitive streak and 16-somite pair (s) stages (E6.5-9.5). Mixl1 localized to the entire primitive streak early in gastrulation. However, by headfold stages (E7.75-8.0), Mixl1 diminished within the mid-streak but remained concentrated at either end of the streak, and localized throughout midline posterior visceral endoderm. At the streak's anterior end, Mixl1 was confined to the posterior crown cells of Hensen's node, which contribute to dorsal hindgut endoderm, and the posterior notochord. In the posterior streak, Mixl1 localized to the Allantoic Core Domain (ACD), which is the source of most of the allantois and contributes to the posterior embryonic-extraembryonic interface. In addition, Mix1 co-localized with the early hematopoietic marker, Runx1, in the allantois and visceral yolk sac blood islands. During hindgut invagination (4-16s, ~E8.5-9.5), Mixl1 localized to the hindgut lip, becoming concentrated within the midline anastomosis of the splanchnopleure, which appears to create the ventral component of the hindgut and omphalomesenteric artery. Surrounding the distal hindgut, Mixl1 identified midline cells within tailbud mesoderm. Mixl1 was also found in the posterior notochord. These findings provide a critical systematic, and tissue-level understanding of embryonic Mixl1 localization, and support its role in regulation of crucial posterior axial mesendodermal stem cell niches during embryogenesis.
Mixl1被认为在中胚层和内胚层的形成中发挥重要作用。此前，Mixl1的表达曾在原条后部和尿囊中有报道，但在整个原肠胚形成过程中Mixl1蛋白精确的时空分布尚未阐明。为了定位Mixl1蛋白，在小鼠原肠胚从原条期到16体节对期（约E6.5 - 9.5）每隔2 - 4小时进行免疫组织化学分析。在原肠胚形成早期，Mixl1定位于整个原条。然而，到头褶期（约E7.75 - 8.0），Mixl1在原条中部减少，但仍集中在原条两端，并定位于中线后部的脏壁内胚层。在原条前端，Mixl1局限于亨氏结的后部冠状细胞，这些细胞形成背侧后肠内胚层以及后部脊索。在原条后部，Mixl1定位于尿囊核心区域（ACD），该区域是大部分尿囊的来源，并形成胚胎 - 胚外界面的后部。此外，Mix1在尿囊和脏壁卵黄囊血岛中与早期造血标志物Runx1共定位。在后肠内陷期间（4 - 16体节，约E8.5 - 9.5），Mixl1定位于后肠唇，集中在内脏层中胚层的中线吻合处，此处似乎形成了后肠和卵黄肠动脉的腹侧部分。在远端后肠周围，Mixl1识别出尾芽中胚层内的中线细胞。Mixl1也存在于后部脊索中。这些发现为胚胎Mixl1定位提供了关键的系统和组织水平的理解，并支持其在胚胎发育过程中对关键的后部轴向中内胚层干细胞龛的调节作用。
