Developmental expression of the neural adhesion molecule F3 in the rat brain

We cloned a cDNA encoding rat F3 and analyzed the nucleotide sequences. The results have shown that rat F3 is comprised of 1021 amino acid residues. It shared 99% and 76% identities with mouse and chicken homologs, respectively, at the amino acid sequence level. During postnatal development of the rat brain, cells expressing F3 mRNA appeared in the cortex, hippocampus, superior and inferior colliculi, anterior olfactory nucleus, olfactory bulb and cerebellum, whereas little was observed at postnatal day 1 (P1). Extraordinarily high expression of F3 mRNA was observed in the cerebral cortical neurons of layer 5 at P7. The number of cells with high expression of F3 mRNA expanded to the entire region of the cerebral cortex at P14. The whole cerebrum displayed expression at P90 in which the cortex still showed the highest expression level, although the overall signals were weak in comparison with those at P14. In the hippocampal formation, F3-expressing granule cells of the dentate gyrus were restricted to the outer aspect, then expanded to the inner aspect during development. Finally the granule cells in the entire region of the dentate gyrus transcribed F3 mRNA. We discuss the significance of the expression pattern of F3 mRNA during development.