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

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Abstract
Background The class III β‐tubulin isotype (β 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 immunohistochemistry in the different cell types of the developing human adrenal medulla is described. Methods A mouse monoclonal antibody, TuJ1, was used to localize β 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, β III immuno‐reactivity was maximal in migrating sympathoadrenal neuroblasts/immature neurons through the end of the second trimester. Clusters of β 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 β III staining was observed in peripheral nerve bundles, sympathetic ganglia, and paraganglia at various developmental stages. In adrenal glands from 23 weeks of gestation on, and throughout adult life, all ganglion cells were β III immunoreactive. In contrast, not all chromaffin cells exhibited β III staining, but when present, the staining was finely granular. Sustentacular and satellite cells, adrenocortical cells and other mesenchymal elements were βIII‐negative. In sections of fetal and adult adrenal glands, S‐100 protein had a sustentacular localization. No GFAP staining was present in sustentacular cells from either fetal or adult adrenals. Conclusions In the developing human adrenal medulla, there is a peak of β III expression during the active wave of migration of sympathetic neuroblasts. In the mature medulla, β III is invariably present in adrenergic neurons. However, not all chromaffin‐like cells express β III, suggesting that the presence or absence of this protein identifies two subpopulations of chromaffin cells. Anat. Rec. 250:335–343, 1998.