A novel human homeobox gene distantly related to proboscipedia is expressed in lymphoid and pancreatic tissues.

A novel human homeobox gene, HB9, was isolated from a cDNA library prepared from in vitro stimulated human tonsil B lymphocytes and from a human genomic library. The HB9 gene is composed of 3 exons spread over 6 kilobases of DNA. An open reading frame of 1206 nucleotides is in frame with a diverged homeodomain. The predicted HB9 protein has a molecular mass of 41 kilodaltons and is enriched for alanine, glycine, and leucine. The HB9 homeodomain is most similar to that of the Drosophila melanogaster homeobox gene proboscipedia. Northern blot analysis of poly(A) RNA purified from the human B cell line RPMI 8226 and from activated T cells revealed a major mRNA transcript of 2.2 kilobases. Similar analysis of poly(A) RNA from a variety of adult tissues demonstrated HB9 transcripts in pancreas, small intestine, and colon. Reverse transcriptase-polymerase chain reaction was used to examine HB9 RNA transcripts in hematopoietic cell lines. HB9 RNA transcripts were most prevalent in several human B cell lines and K562 cells. In addition, transcripts were detected in RNA prepared from tonsil B cells and in situ hybridization studies localized them in the germinal center region of adult tonsil. These findings suggest the involvement of HB9 in regulating gene transcription in lymphoid and pancreatic tissues.