Expression of MAP1a and MAP1b in the ganglionic eminence and the interval capsule of the human fetal brain

The expression of microtubule-associated proteins 1a and 1b (MAP1a and 1b) were investigated in two transient structures, the ganglionic eminence (GE) being a prominent part of the telencephalic proliferative zone and the per ireticular nucleus (PR) within the internal capsule (IC). Anti-MAP1a immuno labels PR neurons from 18 weeks of gestation (wg) onwards, whereas anti-MAP 1b immunolabels long IC fibers between 18 and 22 wg. MAP1b is further prese nt in thalamic fibers that seem to terminate at the medial margin of the GE , in a moderate number of cells of the GE and its medial extension, the gan gliothalamic body (GTB). From 26 to 33 wg MAP1b is expressed in short fiber bundles of the IC, a few MAP1b-positive cells are seen in the GE. MAP1a ha s so far been described to appear in differentiated neurons and to be relat ed to late developmental events. However, the transient PR being involved i n axonal guidance as an intermediate target shows a precocious MAP1a-expres sion. The MAP1b-finding that thalamocortical fibers accumulate at the GE-ma rgin indicates that this region represents an intermediate target for these fibers. The short MAP1b fiber bundles found in the IC are in accordance wi th cell culture experiments showing that MAP1b is concentrated in distal pa rts of outgrowing axons. (C) 2000 Elsevier Science Ireland Ltd and the Japa n Neuroscience Society. All rights reserved.