P-Cadherin is necessary for retinal stem cell behavior in vitro, but not in vivo

- Retinal stem cells are rare pigmented cells in the pigmented ciliary epithelium that express P-Cadherin.
- P-Cadherin is required for the initiation of sphere formation in vitro.
- Both P- and N-Cadherin are required for the formation of the retinal stem cell spheres in vitro.
- P-Cadherin is not required for retinal stem cell maintenance in vivo, and may be compensated for by other adhesion mechanisms.

Adult retinal stem cells (RSCs) are rare quiescent cells within the ciliary epithelium of the eye, which is made up of non-pigmented N-Cadherin+ ve inner and pigmented P-Cadherin+ ve outer cell layers. Through FACs and single cell analyses, we have shown that RSCs arise from single cells from within the pigmented CE and express P-Cadherin. However, whether the expression of P-Cadherin is required for maintenance of the stem cell in vivo or in the formation of the clonal stem cell spheres in vitro is not known. Using cadherin functional blocking antibody experiments and a P-Cadherin −/− mouse to test whether the RSC population is affected by the loss of P-Cadherin expression, our experiments demonstrate that the RSCs reside in the pigmented CE layer and express P-Cadherin, which is important to the formation of adherent sphere colonies in vitro, however P-Cadherin is not required for maintenance of RSCs in vivo.