Abstract
Disabled-2 (Dab2), one of two mammalian orthologs comprising the Drosophila Disabled gene, is widely expressed throughout adult murine tissues as well as during embryogenesis. Two transgenic murine lines were generated. First, Dab2-GFP reporter mice conveyed the ocular expression of Dab2 in the cornea, limbus, iris, and ciliary body. A conditional knockout mouse line was also generated, where loss of Dab2 manifested multiple biological abnormalities, one of which was the abnormal opacification of the cornea. The corneal opacification phenotype was hallmarked by ipsilateral corneal vascularization, iridocorneal attachment, high intraocular pressure, and elevated inflammatory cytokine levels. The prevalence of normal eyes within these genetically identical mice indicates that other factors ultimately involved in determining the phenotypic outcomes but suggests Dab2 as an important determinant.
As Dab2 is also essential for the organization of the primitive endoderm epithelium during embryonic development, we investigated the dynamics underlying the spontaneous aggregation and organization of mouse embryonic stem (ES) cells in a cell culture model within the context of cells possessing differential adhesive affinity. In aggregates of wild-type (WT) and E-cadherin-deficient ES cells, cell assemblies exhibited an initial and expected sorting pattern with the more adhesive WT cells engulfed by less adhesive E-cadherin-deficient ES cells, conforming to the pattern predicted by Malcolm Steinberg. However, in further study of more mature cell aggregates, the initial sorting pattern reversed with the WT ES cells forming an outer shell layer enveloping E-cadherin-deficient cells. While resembling an endoderm, these WT cells were not differentiated but still formed a polarized, highly adhesive outer layer, marked by a contiguous actin cap across the apical surface of multiple adjacent cells. These findings suggest that the force of differential adhesive affinity can be overcome by subtle polarity generated by undifferentiated, bilateral ligation of adhesive cells.