DIFFERENTIAL LOCALIZATION OF CLASS-III BETA-TUBULIN ISOTYPE AND CALBINDIN-D(28K) DEFINES DISTINCT NEURONAL TYPES IN THE DEVELOPING HUMAN CEREBELLAR CORTEX

This immunohistochemical study compares the localization of the neuron al class III beta-tubulin isotype (betaIII) to that of calbindin-D28k in 40 human fetal and postnatal cerebella ranging from 12 weeks gestat ion to adulthood. In the external granule layer of the developing cere bellar cortex, betaIII staining was present in the premigratory (postm itotic) zone of horizontal neurons but was absent in ''epithelioid'' c ells of the subpial proliferative mitotic zone. In the molecular layer , intense betaIII staining was associated with parallel fibers, stella te/basket neurons and migrating fusiform granule neurons. BetaIII stai ning was also present in internal granule neurons. In contrast, betaII I was not detectable in fetal and neonatal Purkinje neurons and Golgi II neurons, but was evident in these neurons from juvenile and adult c erebella. Calbindin-D28k staining was present in Purkinje neurons also delineating their somatic spines (''pseudopodia''), lateralizing and apical dendrites (including dendritic spines), subpopulations of small to intermediate-sized Golgi II neurons in the internal granule layer (''synarmotic cells'' of Landau), large to medium-sized subcortical Go lgi II neurons and neurons of cerebellar roof nuclei, at various gesta tional stages and postnatally. It was absent in the external granule l ayer, parallel fibers, stellate/basket and internal granule neurons. V ariable degrees of betaIII and calbindin-D28k staining were detected i n subpopulations of immature neuroepithelial cells of the ventricular matrix at the roof of the fourth ventricle. Glial (including Bergmann glia) and mesenchymal cells were not stained for either antigenic dete rminants. The differential expression of calbindin-D28k and betaIII de fines distinct populations of neurons in the developing human cerebell ar cortex and supports the ontogenetic concept of Ramon y Cajal.