Figure 1

The effect of cell mixing during development on the number of corneal epithelial stripes in an adult mosaic eye. The following sequence of events is proposed to occur in a mosaic eye comprising a mixture of blue (β-gal-positive) and yellow (β-gal-negative) cells. 1. During tissue morphogenesis the regions designated to become the corneal, limbal and conjunctival epithelia are determined. (The surface ectoderm is shown as a mosaic patchwork of pale blue and yellow cells. The translucent disk represents the cornea with the limbus at its perimeter.) 2. Some of the basal limbal epithelial cells are specified as LSCs (shown as blue and yellow stars). 3. Some (perhaps all) of the LSCs become activated and produce TACs that migrate centripetally (blue and yellow arrows). 4. The tissue is maintained by centripetal migration of LSC progeny forming striping patterns. Two alternative outcomes are highlighted in A-D and E-H. A-D: The two cell types (blue and yellow) mix extensively (non-coherent clonal growth). Therefore, each LSC is likely to be specified from a different coherent clone even where adjacent LSCs are the same colour (e.g. neighbouring yellow stars). E-H: If there is less mixing during morphogenesis (limited coherent clonal growth) some adjacent LSCs will probably arise from the same coherent clone of surface ectoderm cells and so some LSC coherent clones will comprise more than one specified LSC. In E-H the corrected stripe number will under-estimate the number of active LSCs.