The possible roles of homeobox protein, Cdx-2 for the expression of LPH gene during postnatal development

Localized expression of genes related to carbohydrate and lipid absorption along the crypt-villus axis of rat jejunum

BACKGROUND

Enterocytes of the jejunum express several genes related to digestion/absorption of nutrients and ions when these cells rapidly differentiate from crypt to villus cells. However, it is unknown whether the distribution of extensive gene expression along the villus-crypt axis of the jejunum is altered during differentiation.

METHODS

We investigated the changes in jejunal gene expression during differentiation from crypt to villus cells in rats using DNA microarray analysis on cryostat sections of the villus-crypt columns.

RESULTS

During differentiation, the expression of many genes related to cell growth rapidly decreased, while expression of genes related to digestion and absorption of nutrients and ions increased. Expression of a subset of genes related to the digestion and absorption of starch and sucrose was highest at the middle of the villi, whereas expression of genes related to dietary fat absorption was highest at the top of the villi. Several transcriptional factors such as Pdx1, Foxa2 and Thra were expressed in the crypt, whereas Klf15 was highly expressed during the crypt-villus transition. Expression of Klf4 and Pparg was highest at the top of the villi.

CONCLUSIONS

Subsets of genes related to the digestion and absorption of starch/sucrose and dietary fat as well as their transcriptional factors/co-factors are expressed in the specific locations along the crypt-villus axis.

GENERAL SIGNIFICANCE

The jejunum may absorb nutrients effectively by simultaneously expressing subsets of genes along the villus-crypt axis.

Higher expression of jejunal LPH gene in rats fed the high-carbohydrate/low-fat diet compared with those fed the low-carbohydrate/high-fat diet is associated with in vitro binding of Cdx-2 in nuclear proteins to its promoter regions

It has been previously demonstrated that the expression of lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) genes are higher in rats fed a high-carbohydrate/low-fat (HCT) diet than in those fed a low-carbohydrate/high-fat (LCT) diet. In the present study, using a nuclear run-on assay we clearly show that higher expression of LPH and SI genes in jejunum of rats fed the HCT diet compared with those fed a LCT diet was regulated at the transcription levels. DNase I foot printing analysis of the 5' flanking region of the rat LPH gene demonstrated that by incubating the jejunal nuclear extract the protected region was conserved as the same sequence as the homeodomain protein-binding element designated as CE-LPH1. UV-cross linking and electromobility shift assay in vitro clearly showed that Cdx-2 was including proteins bound to CE-LPH1. Moreover, in vitro binding of Cdx-2 to CE-LPH1 as well as SIF1, a cis-element identified as the binding element of Cdx-2 on the SI gene, in jejunal nuclear extracts of rats fed a HCT diet were greater than those fed a LCT diet. These results suggest that in vitro binding of Cdx-2 to CE-LPH1 as well as SIF1 in jejunal nuclear extracts is associated with the higher expression of the LPH and SI genes in rats fed the HCT diet compared with those fed a LCT diet.

Fatty acids in component of milk enhance the expression of the cAMP-response-element-binding-protein-binding protein (CBP)/p300 gene in developing rats

Fatty acids in milk are thought to play an important role in intestinal maturation and gene expression in the rat small intestine during the suckling-weaning period. In the present study, we determined the jejunal mRNA level of the cAMP-response-element-binding-protein-binding protein (CBP)/p300, which is one of the chromatin remodelling factors and regulates histone acetylation, during the postnatal period in rats. The mRNA level of CBP/p300 was high during the suckling and middle of the weaning period (day 5 to 20) and then declined sharply to a low level at the end of the weaning period and after weaning. In situ hybridisation also showed that CBP/p300 mRNA levels in the villus as well as the basal membrane clearly decreased after weaning. Rat pups at age 17 d, weaned to a high-fat diet, showed higher levels of CBP/p300 mRNA than those weaned to a low-fat diet. Oral administration of caprylic acid, oleic acid and linoleic acid, which are major fatty acid components in milk, induced jejunal CBP/p300 gene expression. The present results suggest that fatty acids in components of milk enhance expression of the CBP/p300 genes in the small intestine.

Triiodothyronine (T3) and fructose coordinately enhance expression of the GLUT5 gene in the small intestine of rats during weaning period

Jejunal GLUT5 is elevated with triiodothyronine (T(3)) during weaning of rats. A perfusion of fructose into the small intestine of T(3)-injected rats at 21 d induced expression of the GLUT5 gene, but one into that of vehicle-injected rats did not. These results suggest that T(3) and fructose coordinately enhance jejunal expression of the GLUT5 gene in rats during weaning period.