Organisation and maturation of the human thalamus as revealed by CD15

The distribution of the CD15 antigen (CD15, 3-fucosyl-N-acetyl-lactosamine, Lewis x) has been studied immunohistochemically in the fetal human thalamus. Its changing patterns could be related to three successive, but overlapping, periods primarily due to its association with radial glial cells, neuropil, and neural cell bodies, respectively. From 9 weeks of gestation (wg), a subset of CD15-positive radial glial cells distinguished the neuroepithelium of the ventral thalamus, a characteristic also seen in the developing mouse. Distal processes of the radial glial cells converged at the root of the forebrain choroid tenia, which was also CD15 positive. From 13 wg until approximately 20 wg, CD15-positive neuropil labeling marked the differentiation areas of prospective nuclei within the dorsal thalamus and progressively outlined their territories in a time sequence, which appeared specific for each nucleus. CD15 labeling of differentiating nuclei of the ventral, medial, anterior, and intralaminar thalamic divisions showed a transient topographic relationship with restricted areas of the ventricular wall. After 26 wg, CD15 immunoreactivity was observed in subpopulations of glial cells and neurons. Transient CD15 immunoreactivity was also found in delimited compartments within the subventricular region. The time of CD15 expression, its location, and cellular association suggest that CD15 is involved in segmentation of diencephalon, in the specification of differentiating nuclear areas and initial processes regarding the formation of intercellular contacts and cellular maturation.