Evidence for endogenous proteases, mRNA level and insulin as multiple mechanisms of N-cadherin down-regulation during retinal development.
Our previous studies of the role of cell adhesion in retinal development have focused on the expression and function of N-cadherin, the predominant calcium-dependent intercellular adhesion protein of neural tissues. During the course of retinal development, N-cadherin expression undergoes significant qualitative and quantitative changes in its pattern of expression, most prominently a sharp down-regulation of expression throughout most of the retina. The present studies were directed at investigating the epigenetic mechanisms that could mediate this loss of N-cadherin from the retina. Using an in vitro intact retinal organ culture system, results were obtained which suggest that insulin enhances the down-regulation of N-cadherin expression in a protein-synthesis-dependent fashion. Furthermore, the metalloprotease inhibitor 1,10-phenanthroline inhibits the loss of N-cadherin from the retina. While N-cadherin is down-regulated in organ culture, other cell adhesion molecules, which are not down-regulated in vivo, are also not down-regulated in organ culture. The defined organ culture medium conditioned by the retina accumulates both a soluble 90 x 10(3) M(r) N-terminal fragment of N-cadherin as well as a number of secreted proteases. Both of these components are also shown to be present in vivo in the vitreous humor. Northern blot analysis indicates a single mRNA encoding N-cadherin in the retina and no evidence for a second message that could encode the 90 x 10(3) M(r) fragment. However, the amount of N-cadherin mRNA detectable on northern blots decreases during development. The results reported here suggest that the down-regulation of N-cadherin that occurs during retinal development is possibly mediated by multiple mechanisms, which include turnover at the cell surface mediated by endogenous proteolysis, reduced levels of N-cadherin mRNA and modulation by growth factors.
Roark
E F
EF
Department of Anatomy and Developmental Biology, Thomas Jefferson University, Philadelphia, PA 19107.
Paradies
N E
NE
Lagunowich
L A
LA
Grunwald
G B
GB
D000818:Animals; D015152:Blotting, Northern; D015820:Cadherins / Q000378:metabolism*; D002642:Chick Embryo; D015536:Down-Regulation / Q000502:physiology*; D004586:Electrophoresis; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism*; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000196:embryology* / Q000378:metabolism
D015820:Cadherins; D007328:Insulin; D012333:RNA, Messenger; D008666:Metalloendopeptidases