Cadherin expression coincides with birth dating patterns in patchy compartments of the developing chicken telencephalon

Some gray matter regions of the vertebrate brain, e.g., the mammalian striatum, are organized into clusters of functionally similar neurons ("patches") that are surrounded by a gray matter matrix. A similar type of compartmentation recently has been found also in the avian telencephalon, based on two sorts of evidence. First, a birth dating study showed that, in some telencephalic areas, cells born at the same time form "isochronic" cell clusters, which differ in their birth dating pattern from their surrounding tissue. Second, patchy expression was found for different members of the cadherin family of adhesion molecules (R-cadherin, N-cadherin, and/or cadherin-7). The relation between these two findings has remained unclear. Here, we demonstrate a general spatial coincidence between the birth dating patterns and the heterogeneities in cadherin expression. This coincidence is found in areas of the avian ventral and lateral pallium (ventral hyperstriatum, neostriatum, and ectostriatum) and in a part of the archistriatum, which is of pallial origin. For example, in the neostriatum, a part of the ventral pallium, both the cadherin-7-positive patches and their R-cadherin-positive surroundings are born between embryonic day 5 and 7, but the cadherin-7-positive cells are born during a shorter time period than the R-cadherin-positive cells. We propose that the patchy gray matter architecture observed in the mammalian striatum and avian pallium are regulated by a common type of morphogenetic mechanism. This mechanism possibly involves the differential expression of adhesive factors, such as cadherins.