EXPRESSION OF MULTIPLE CADHERINS AND CATENINS IN THE CHICK OPTIC TECTUM

Cadherins form a large family of hemophilic cell adhesion molecules th at are involved in numerous aspects of neural development. The best-st udied neural cadherin, N-cadherin, is concentrated at synapses made by retinal axons in the chick optic tectum and is required for the arbor ization of retinal axons in their target (retinorecipient) laminae. By analogy, other cadherins might mediate arborization or synaptogenesis in other tectal laminae. Here we consider which cadherins are express ed in tectum, which cells express them, and how their expression is re gulated. First, using N-cadherin as a model, we show that synaptic inp ut regulates both cadherin gene expression and the subcellular distrib ution of cadherin protein. Second, we demonstrate that N-, R-, and T-c adherin are each expressed in distinct laminar patterns during retinot ectal synaptogenesis and that N- and R- are enriched in nonoverlapping synaptic subsets. Third, we show that over 20 cadherin superfamily ge nes are expressed in the tectum during the time that synapses are form ing and that many of them are expressed in restricted groups of cells. Finally, we report that both beta-catenin and gamma-catenin (plakoglo bin), cytoplasmic proteins required for cadherin signaling, are enrich ed at synapses and associated with N-cadherin. However, beta- and gamm a-catenins are differentially distributed and regulated, and form mutu ally exclusive complexes. This result suggests that cadherin-based spe cificity involves multiple cadherin-dependent signaling pathways as we ll as multiple cadherins.