Neuraminic acid specific lectins as markers of early cortical plate neurons.

Early cortical plate and subplate cells in the developing neocortex of many animal species and humans contain one specific plasma protein, fetuin. Fetuin is heavily glycosylated and it is possible that due to the large amount of sugars, this molecule may play a part in cellular recognition during brain development. Cellular and extracellular carbohydrates in the developing brain of the sheep were studied histochemically using a battery of fluorescein-labelled lectins. Two neuraminic acid specific lectins, Sambucus nigra and Maackia amurensis, labelled consistently the fetuin-positive cells as demonstrated by double labelling with lectins and antifetuin antibodies. Brain sections from other species, known to contain fetuin-positive cells (fetal cow, postnatal tammar wallaby) showed a similar lectin staining pattern to that of the sheep fetus. Additionally, sections from species thought to contain fetuin in their developing brains that failed to cross-react with available antifetuin antibodies (postnatal Monodelphis, fetal cat) also demonstrated lectin-positive staining in the same neuronal cell population. Thus, neuraminic acid is a common and well conserved terminal carbohydrate in cortical plate and subplate neurons of the developing brain. Neuraminic-specific lectins are useful markers for these neurons in addition to the more traditional use of immunocytochemical methods in studies of formation of the neocortex.