R- and B-cadherin expression defines subpopulations of glial cells involved in axonal guidance in the optic nerve head of the chicken

Glial cells play a crucial role in the organization and function of the ner vous system. Cell-cell adhesion receptors of the cadherin family have been shown to participate in distinct morphogenetic processes throughout the dev elopment of the CNS, but little is known about glial expression of cadherin s. Applying immunofluorescence and confocal laser scanning microscopy, we i nvestigated R- and B-cadherin expression in relation to the glial cell diff erentiation in the optic nerve head and pecten oculi of developing chicken. Throughout embryonic development, R- and B-cadherin were expressed in dist inct cell populations, which differentiated into distinct subtypes of glial cells. R-cadherin was located in the glia limitans perivascularis et super ficialis of the optic nerve and in cells bordering the optic nerve head, wh ere it comes in contact with the retina. B-cadherin was located in the glia limitans perivascularis et superficialis of the pecten oculi and in a subs et of cells at the retinal border. R-cadherin-expressing cells differentiat ed unequivocally into a glial fibrillary acidic protein (GFAP)-positive but glutamine synthetase (GS)-negative phenotype, whereas B-cadherin-expressin g glia developed into a GS-positive but GFAP-negative phenotype. In additio n, the B-cadherin-positive population developed into a highly pigmented cel l type, which was consistently associated with pecten-type capillaries. By contrast, the R-cadherin-positive glia remained unpigmented and surrounded normal brain-phenotype capillaries. These data suggest that glial cells, li ke neurons, may use the expression of different cadherins to segregate and differentiate into distinct subtypes, which goes hand in hand with their in volvement in special functions and morphogenetic processes. To address this issue, we selectively lysed both glial subtypes in developing embryos by m icroinjection of R- and B-cadherin antibodies with complement. First eviden ce is presented for R-cadherin-positive glial cells as crucial to the organ ization of the optic nerve and axonal guidance at its lateral margin. B-cad herin-positive cells are involved in the axonal guidance at the pecteneal m argin, avoiding the ingrowth of axons into the pecten. (C) 2000 Wiley-Liss, Inc.