Modulated expression of human homeobox genes in differentiating intestinal cells

Identification and comparative analysis of human colonocyte short-chain fatty acid response genes

Short-chain fatty acids (SCFAs) butyrate, propionate, and acetate produced during fiber fermentation promote colonic differentiation and can reverse or suppress neoplastic progression. We sought to identify candidate genes responsible for SCFA activity on colonocytes and to compare the relative activities of independent SCFAs. cDNA was generated from polyA+ mRNA isolated from control Caco-2 cells and cells treated with equimolar butyrate, propionate, and acetate. GeneCalling, a restriction-based differential RNA expression platform linked to a DNA sequence database lookup, was applied. A total of 30,000 individual genetic sequences were analyzed for differential expression among the three SCFAs. Differentially expressed peaks corresponding to cancer-related genes were isolated, sequenced, and cross-referenced to the GenBank human database. Gene identities were independently confirmed by oligonucleotide poisoning. More than 1000 gene fragments were identified as being substantially modulated in expression by butyrate. Butyrate tended to have the most pronounced effects and acetate the least. Five fragments selected for further study were fully sequenced and proved 100% homologous with human sequences for clusterin, amyloid precursor-like protein 2, and caudal homeobox 2 protein, not previously known to be modulated by SCFAs. In each case, a similar order of potency for the three SCFAs studied was observed. The common SCFAs appear to exert different effects. This study suggests the diversity of the SCFA response at the molecular level and facilitates identifying genes important in the biologic activity of dietary fiber.

Expression of homeobox genes, including an insulin promoting factor, in the murine yolk sac at the time of hematopoietic initiation

The visceral yolk sac (YS), a simple bilayer structure formed during gastrulation, supplies blood cells and intestine- and liver-like functions to support embryonic growth. To better understand gene regulation in extraembryonic tissues, we examined the early murine YS for expression of the homeobox family of developmental transcription regulators. We identified a subset of known homeobox sequences (Hox 1l, b1, a9, c9, a7, b7, b8, a10, cdx-1, and PDX-1), as well as two novel homeodomains consisting of a fourth labial class Hox genes and one that matches the Antennapedia class on the amino acid level. The two most frequently isolated YS Hox genes, a9 and c9, are initially expressed only in the YS (E.5) and subsequently expressed in both the embryo and YS (E8.5). Another of the identified genes, PDX-1, is involved in pancreatic development and insulin regulation. Whereas the4 rodent YS is known to produce insulin from mid to late gestation, YS insulin expression had not been examined earlier in development . We detected insulin mRNA in the YS at both E7.5 and E8.5, prior to expression in the embryo proper or formation of the pancreas. However, other pancreatic products, such as glucagon, somatostatin, and carboxypeptidase A, are not expressed in the YS. In situ analysis indicates insulin is produced in YS mesothelial cells and endoderm cells, but not in blood cells. We hypothesize the early expression of insulin in the YS is required for the expansion of insulin responsive cells including primitive erythroblasts.

Lineage-restricted expression of homeobox-containing genes in human hematopoietic cell lines

We investigated the role of homeobox-containing genes in human hematopoiesis because homeobox genes (i) control cell fate in the Drosophila embryo, (ii) are expressed in specific patterns in human embryos, and (iii) appear to function as transcription factors that control cell phenotype in other mammalian organs. Using four homeobox probes from the HOX2 locus and a previously undescribed homeobox cDNA (PL1), we screened mRNAs from 18 human leukemic cell lines representing erythroid, myeloid, and T- and B-cell lineages. Complex patterns of lineage-restricted expression are observed: some are restricted to a single lineage, while others are expressed in multiple lineages. No single homeobox gene is expressed in all types of hematopoietic cells, but each cell type exhibits homeobox gene expression. HOX2.2 and -2.3 homeobox-containing cDNAs were cloned from an erythroleukemia cell (HEL) cDNA library, while the homeobox cDNA PL1 was isolated from a monocytic cell (U-937) library. Differentiation of HEL and K-562 cells with various inducers results in modulation of specific homeobox transcripts. In addition, HOX2.2 is expressed in normal bone marrow cells. We have demonstrated (i) lineage-restricted expression of five homeobox genes in erythroid and monocytic cell lines; (ii) expression of additional homeobox genes in other cell lineages (HL-60 and lymphoid cells); (iii) expression of one homeobox gene in normal marrow cells; and (iv) modulation of expression during differentiation. These data suggest that these genes play a role in human hematopoietic development and lineage commitment.