Class III β-Tubulin isotype (β III) in the adrenal medulla: I. Localization in the developing human adrenal medulla

Background: The class III b-tubulin isotype (b III) is present in neurons of the central and peripheral nervous systems at the earliest stages of morphological differentiation (Easter et al., J Neurosci 13:285-299, 1993; Katsetos et al., J Neuropathol Exp Neurol 52:655-666, 1993). The localization of this protein by immunohistochemis- try in the different cell types of the developing human adrenal medulla is described. Methods: A mouse monoclonal antibody, TuJ1, was used to localize b III in formalin-fixed, paraffin-embedded sections from 18 human fetal and adult adrenal glands. Tissue sections were also studied with rabbit antisera recognizing either S-100 protein or glial fibrillary acidic protein (GFAP). Results: In the developing human adrenal medulla, b III immuno- reactivity was maximal in migrating sympathoadrenal neuroblasts/ immature neurons through the end of the second trimester. Clusters of b III-positive migrating cells, focally forming Homer Wright rosettes, could be identified in a gradient of adrenocortical invasion, i.e., through the permanent cortex and within sinusoids of the fetal cortex en route to the medulla. Outside the adrenal gland, strong b III staining was observed in peripheral nerve bundles, sympathetic ganglia, and paraganglia at vari- ous developmental stages. In adrenal glands from 23 weeks of gestation on, and throughout adult life, all ganglion cells were b III immunoreac- tive. In contrast, not all chromaffin cells exhibited b III staining, but when present, the staining was finely granular. Sustentacular and satellite cells, adrenocortical cells and other mesenchymal elements were bIII-negative. In sections of fetal and adult adrenal glands, S-100 protein had a susten- tacular localization. No GFAP staining was present in sustentacular cells from either fetal or adult adrenals.