Molecular cloning and characterization of a human brain-specific gene implicated in neuronal differentiation

A 2.5 kb human cDNA clone containing a CAG trinucleotide repeat, designated HB20, was isolated from a human fetal brain library. Northern analysis on multi-tissue blots and various cell lines confirmed that HB20 is specifically expressed in the brain. Its expression is low in two glioma cells, moderate in a neuron precursor cell, NT2, but absent in lymphoma, cervical carcinoma, or colonic carcinoma cells. Significant increase of HB20 mRNA was shown along with retinoic acid-induced terminal differentiation of NT2 cells into neuron cells, hNT. Homology comparison of the predicted HB20 amino acid sequence with the current database revealed that it belongs to a newly recognized protein family composed of nucleosome assembly proteins and SET proto-oncogene, which has been shown to interact specifically with B-type cyclins involved in the control of cell proliferation. Together with the detection of nuclear localization signals and apparent nuclear distribution of expressed protein, HB20 is likely to be a brain-specific nuclear protein, functioning in the process of neuronal differentiation.