The lactase phlorizin hydrolase (LCT) gene maps to pig chromosome 15q13

Single-nucleotide polymorphisms and activity analysis of the promoter and enhancer of the pig lactase gene

Lactose intolerance in northern Europeans is strongly associated with a single-nucleotide polymorphism (SNP) located 14 kb upstream of the human lactase gene: -13,910 C/T. We examined whether SNPs in the 5' flanking region of the pig lactase gene are similar to those in the human gene and whether these polymorphisms play a functional role in regulating pig lactase gene expression. The 5' flanking region of the lactase gene from several different breeds of pigs was cloned and analyzed for gene regulatory activity of a luciferase reporter gene. One SNP was found in the enhancer region (-797 G/A) and two were found in the promoter region (-308G/C and -301 A/G). The promoter C-308,G-301(Pro-CG) strongly promotes the expression of the lactase gene, but the promoter G-308,A-301(Pro-GA) does not. The enhancer A-797(Enh-A) genotype for Pro-GA can significantly enhance promoter activity, but has an inhibitory effect on Pro-CG. The Enhancer G-797(Enh-G) has a significant inhibitory effect on both promoters. In conclusion, the order of effectiveness on the pig lactase gene is Enh-A+Pro-GA>Enh-A/G+Pro-CG>Enh-G+Pro-GA.

Transcriptional regulation of pig lactase-phlorizin hydrolase: involvement of HNF-1 and FREACs

BACKGROUND & AIMS

One-kilobase sequence of the upstream fragment of the pig lactase-phlorizin hydrolase gene has been shown to control small intestinal-specific expression and postweaning decline of lactase-phlorizin hydrolase in transgenic mice. The aim of this study was to identify the regulatory DNA elements and transcription factors controlling lactase-phlorizin hydrolase expression.

METHODS

The activity of different lactase-phlorizin hydrolase promoter fragments was investigated by transfection experiments using Caco-2 cells. Electrophoretic mobility shift assays and supershift analyses were used to characterize the interaction between intestinal transcription factors and the identified regulatory elements.

RESULTS

Functional analysis revealed three previously undescribed regulatory regions in the lactase-phlorizin hydrolase promoter: a putative enhancer between -894 and -798 binding hepatocyte nuclear factor (HNF)-1 at position -894 to -880; a repressor-binding element between -278 to -264 to which an HNF-3-like factor is able to bind; and an element between -178 to -164 that binds an activating transcription factor.

CONCLUSIONS

Identification of three new regulatory regions and HNF-1 and HNF-3-like transcription factor as players in the regulation of lactase-phlorizin hydrolase gene transcription has an impact on the understanding of the molecular mechanisms behind age-dependent, tissue-specific, differentiation-dependent, and regional regulation of expression in the intestine.

Chromosomal localization of homeobox genes and associated markers on porcine chromosomes 3, 5, 12, 15, 16 and 18: comparative mapping study with human and mouse

Four homeobox genes that belong to the four homeobox gene clusters known in mammals have been regionally assigned to four distinct porcine chromosomes in conserved regions between human and pig. HOXA11, HOXB6, HOXC8, and HOXD4 genes were mapped by radioactive in situ hybridization to porcine Chromosomes (Chrs) 18q21-24 (with a secondary signal in 16q14-21), 12p11-12, 5p11-12, and 15q22-23 respectively. Besides, we have also revealed the presence of a porcine homeobox (pig Hbx24) which, although showing DNA sequence homology with a mouse gene of HOXB cluster, was located on porcine Chr 3 (3p14-13) outside the Hox clusters. To support the identity of the homeobox gene clusters analyzed and in the light of the high sequence similarity among homeobox genes, we also localized markers known to be mapped near each Hox cluster in human. In this way, four genes were also mapped in pig: GAPD (5q12-21), GAD1 (15q21-22), INHBA (18q24), and IGFBP3 (18q24). Mapping of HOXA11, INHBA, and IGFBP3 on pig Chr 18 constitutes the first assignments of genes on this small chromosome. These new localizations extend the information on the conservation of four human chromosomal regions in the pig genome.

The PiGMaP consortium linkage map of the pig (Sus scrofa)

A linkage map of the porcine genome has been developed by segregation analysis of 239 genetic markers. Eighty-one of these markers correspond to known genes. Linkage groups have been assigned to all 18 autosomes plus the X Chromosome (Chr). As 69 of the markers on the linkage map have also been mapped physically (by others), there is significant integration of linkage and physical map data. Six informative markers failed to show linkage to these maps. As in other species, the genetic map of the heterogametic sex (male) was significantly shorter (approximately 16.5 Morgans) than the genetic map of the homogametic sex (female) (approximately 21.5 Morgans). The sex-averaged genetic map of the pig was estimated to be approximately 18 Morgans in length. Mapping information for 61 Type I loci (genes) enhances the contribution of the pig gene map to comparative gene mapping. Because the linkage map incorporates both highly polymorphic Type II loci, predominantly microsatellites, and Type I loci, it will be useful both for large experiments to map quantitative trait loci and for the subsequent isolation of trait genes following a comparative and candidate gene approach.