Yang Dong-Hua, Smith Elizabeth R, Roland Isabelle H, Sheng Zejuan, He Junqi, Martin W David, Hamilton Thomas C, Lambeth J David, Xu Xiang-Xi
Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Dev Biol. 2002 Nov 1;251(1):27-44. doi: 10.1006/dbio.2002.0810.
The signal transduction adapter protein Disabled-2 (Dab2) is one of the two mammalian orthologs of the Drosophila Disabled. The brain-specific Disabled-1 (Dab1) functions in positional organization of brain cells during development. Dab2 is widely distributed and is highly expressed in many epithelial cell types. The dab2 gene was interrupted by in-frame insertion of beta-galactosidase (LacZ) in embryonic stem cells and transgenic mice were produced. Dab2 expression was first observed in the primitive endoderm at E4.5, immediately following implantation. The homozygous Dab2-deficient mutant is embryonic lethal (earlier than E6.5) due to defective cell positioning and structure formation of the visceral endoderm. In E5.5 dab2 (-/-) conceptus, visceral endoderm-like cells are present in the deformed primitive egg cylinder; however, the visceral endoderm cells are not organized, the cells of the epiblast have not expanded, and the proamniotic cavity fails to form. Disorganization of the visceral endodermal layer is evident, as cells with positive visceral endoderm markers are scattered throughout the dab2 (-/-) conceptus. Only degenerated remains were observed at E6.5 for dab2 (-/-) embryos, and by E7.5, the defective embryos were completely reabsorbed. In blastocyst in vitro culture, initially cells with characteristics of endoderm, trophectoderm, and inner cell mass were observed in the outgrowth of the hatched dab2 (-/-) blastocysts. However, the dab2 (-/-) endodermal cells are much more dispersed and disorganized than those from wild-type blastocysts, the inner cell mass fails to expand, and the outgrowth degenerates by day 7. Thus, Dab2 is required for visceral endodermal cell organization during early mouse development. The absence of an organized visceral endoderm in Dab2-deficient conceptus leads to the growth failure of the inner cell mass. We suggest that Dab2 functions in a signal pathway to regulate endodermal cell organization using endocytosis of ligands from the blastocoel cavity as a positioning cue.
信号转导衔接蛋白Disabled-2（Dab2）是果蝇Disabled在哺乳动物中的两个直系同源物之一。脑特异性的Disabled-1（Dab1）在发育过程中参与脑细胞的位置组织。Dab2分布广泛，在许多上皮细胞类型中高表达。通过在胚胎干细胞中框内插入β-半乳糖苷酶（LacZ）中断dab2基因，并产生了转基因小鼠。Dab2表达首先在植入后E4.5的原始内胚层中观察到。纯合的Dab2缺陷型突变体由于内脏内胚层的细胞定位和结构形成缺陷而胚胎致死（早于E6.5）。在E5.5的dab2（-/-）胚胎中，变形的原始卵圆柱中存在内脏内胚层样细胞；然而，内脏内胚层细胞没有组织化，外胚层细胞没有扩张，羊膜腔未能形成。内脏内胚层层的紊乱很明显，因为具有阳性内脏内胚层标记的细胞散布在整个dab2（-/-）胚胎中。在E6.5时，dab2（-/-）胚胎仅观察到退化的残留物，到E7.5时，有缺陷的胚胎被完全吸收。在胚泡体外培养中，最初在孵化的dab2（-/-）胚泡的生长物中观察到具有内胚层、滋养外胚层和内细胞团特征的细胞。然而，dab2（-/-）内胚层细胞比野生型胚泡的内胚层细胞更加分散和无组织，内细胞团未能扩张，并且生长物在第7天退化。因此，在小鼠早期发育过程中，Dab2是内脏内胚层细胞组织所必需的。Dab2缺陷型胚胎中缺乏有组织的内脏内胚层会导致内细胞团生长失败。我们认为，Dab2在一个信号通路中发挥作用，利用来自囊胚腔的配体的内吞作用作为定位线索来调节内胚层细胞组织。
