December 1, 2006;
Xenopus cadherin-6 regulates growth and epithelial development of the retina.
Cadherins are crucial for tissue
cohesion, separation of cell layers and cell migration during embryogenesis. To investigate the role of classical type II Xcadherin-6 (Xcad-6), we performed loss-of-function studies by morpholino oligonucleotide injections. This resulted in severe eye
defects which could be rescued with murine cadherin-6. In the absence of Xcadherin-6, morphological alterations and a decrease in cell proliferation were observed with eye
cup formation. Eye
field transplantations of Xcadherin-6 depleted donors yielded grafts that failed to form a proper neuroepithelium in a wildtype environment. At later developmental stages Xcadherin-6 deficient eyes
showed lamination defects in the outer neural retina
, a reduced thickness of the ganglion
cell layer (GCL) and a fragmented retina
). Thus, Xcadherin-6 is essential early in eye
development for structural organization and growth of the neuroepithelium before it differentiates into neural retina
[+] show captions
Fig. 3. Xcadherin-6 is expressed in the anterior neural plate but is not required in eye field formation or separation. (A) Gene expression of Xcadherin-6 in stage 13 embryos is restricted to the anterior neural plate (ANP), whereas in the residual embryonic mass no transcript was detected. Correct cutting of the ANP was verified by the presence of the ANP marker genes ET1 and Rx1. The control gene beta-actin was expressed in both parts of the embryo as well as in complete embryos. (B) Knockdown of Xcadherin-6 did not influence separation of the eye field as indicated by gene expression of Rx1 in the early eye field at stages 13 and 18. nis, not injected side; is, injected side. Scale bar: 100 μm.
Xenopus cdh6 expression in stage 18 neurula- anterior view. Image by Ruan et al., 2006
Fig. 8. Depletion of Xcadherin-6 disturbs lens development. (A) In situ hybridization of Xcadherin-6 depleted embryos demonstrates a reduction in the expression of the lens marker gene Pitx-3 on the injected side in stage 31 embryos. (C) Staining for β1-integrin shows the organization of lens fiber cells. On the injected side the cells are not properly arranged. nis, not injected side; is, injected side. Scale bars in (A, B): 50 μm, in (C): 10 μm.
Figure S2. In situ hybrididation showing Xcadherin-6 expression in the eye. (A) Ring-like expression domain of Xcadherin-6 at stage 31. (B) Transverse section of (A) yielding Xcadherin-6 transcripts in the outer layer of the optic cup. Arrows point to overlap with pigment cells. (C) Horshoe-like expression domain at stage 34. (D) Transverse section of (C), transcripts are restricted to the ciliary marginal zone. Scale bar: 100 μm.