Differential requirement for Dab2 in the development of embryonic and extra-embryonic tissues

Abstract

BackgroundDisabled-2 (Dab2) is an endocytic adaptor protein involved in clathrin-mediated endocytosis and cargo trafficking. Since its expression is lost in several cancer types, Dab2 has been suggested to be a tumor suppressor. In vitro studies indicate that Dab2 establishes epithelial cell polarity and organization by directing endocytic trafficking of membrane glycoproteins. Dab2 also modulates cellular signaling pathways by mediating the endocytosis and recycling of surface receptors and associated signaling components. Previously, two independent gene knockout studies have been reported, with some discrepancies in the observed embryonic phenotypes. To further clarify the in vivo roles of Dab2 in development and physiology, we designed a new floxed allele to delete dab2 gene.ResultsThe constitutive dab2 deleted embryos showed a spectrum in the degree of endoderm disorganization in E5.5 and no mutant embryos persisted at E9.5. However, the mice were grossly normal when dab2 deletion was restricted to the embryo proper and the gene was retained in extraembryonic tissues using Meox2-Cre and Sox2-Cre. Adult Dab2-deficient mice had a small but statistically significant increase in serum cholesterol levels.ConclusionThe study of the new dab2 mutant allele in embryos and embryoid bodies confirms a role for Dab2 in extraembryonic endoderm development and epithelial organization. Experimental results with embryoid bodies suggest that additional endocytic adaptors such as Arh and Numb could partially compensate for Dab2 loss. Conditional deletion indicates that Dab2 is dispensable for organ development, when the vast majority of the embryonic cells are dab2 null. However, Dab2 has a physiological role in the endocytosis of lipoproteins and cholesterol metabolism.

Endocytic adaptors Arh and Dab2 control homeostasis of circulatory cholesterol

“…The activity and ability of Dab2 to mediate LDLR endocytosis have been demonstrated in cultured cells (23). However, Dab2-deficient mice have only minor changes in serum cholesterol level (24), and the involvement of Dab2 in cholesterol metabolism in intact animals is uncertain.…”

“…Conventional dab2 gene deletion in mice results in early embryonic death (26)(27)(28). We generated a conditional knockout line and were able to produce Dab2-null mice to study their postnatal phenotypes (24). Here, we investigated the relative importance of Dab2, another endocytic adaptor capable of binding to LDLR (22), in LDLR-mediated clearance of circulating LDL and the regulation of cholesterol synthesis.…”

“…A line of dab2 floxed mice previously constructed by the lab was used throughout this study (24). Female dab2 (fl/fl) and male dab2 (+/df):Sox2-Cre mice were used as breeding pairs.…”

“…MEFs were isolated from E12.5 embryos generated from designated genotypes (24). Briefly, the head of dissected embryos was first removed and used for PCR genotyping, and the remainder was minced using a scalpel.…”

“…Dab2 conditional knockout mice (24) were bred into the arh knockout background as described in the strategy.…”