On the primary site of control in the spontaneous development of small-intestinal sucrase-isomaltase after birth

Dietary regulation of intestinal gene expression

We are becoming increasingly aware of inherited genetic abnormalities as causes of disease. However, alterations in gene expression can also contribute to other disease processes. Recently it has been suggested that our environment may alter such genes and thus be a direct influence on disease. Diet is a potent mechanism for altering the environment of cells of most organs, particularly the gastrointestinal tract. This review addresses the influence of nutritional factors on intestinal gene regulation. These influences include insulin, which is not a dietary component but responds to dietary changes, and butyrate, a short chain fatty acid produced by normal intestinal flora. Manipulation of diet may be a means of treating intestinal disorders. Nutritional treatment therefore is also discussed in the light of its effect on gene expression.

Sucrase-isomaltase gene expression in suckling rat intestine: hormonal, dietary, and growth factor control

The effect of hydrocortisone, sucrose, and epidermal growth factor (EGF), alone or in combination, was investigated on the precocious expression of sucrase activity and sucrase-isomaltase (SI) mRNA in normal and adrenalectomized (ADX) suckling rats. In normal rats, each regulatory factor administered separately from 12 to 13 days of age induced a parallel expression of sucrase activity and SI mRNA. A potentiation of both sucrase activity and SI mRNA was observed after administration of hydrocortisone plus sucrose. Only SI mRNA was potentiated after EGF-sucrose administration or EGF-hydrocortisone administration. However, the potentiation of the activity was obtained after a prolonged treatment period of 4 days. In adrenalectomized rats, sucrose and EGF were still able to induce precocious induction of SI mRNA and sucrase activity, but sucrase activity was lowered by 75% by sucrose and by 30% by EGF. The combined treatments gave results similar to those obtained in normal rats. The results obtained in ADX rats indicate that the effects of sucrose and EGF on the precocious expression of sucrase and the potentiation of SI mRNA are independent of endogenous glucocorticoids. The rate of [3H]thymidine incorporation into mucosal DNA of normal sucklings was similar after single or combined treatments. From this study, we conclude that the precocious induction of intestinal sucrase by various regulatory factors, alone or in combination, is primarily regulated at the level of mRNA and is independent of increases in cellular proliferation and circulating glucocorticoids.

Glucose-dependent insulinotropic peptide (GIP) gene expression in the rat salivary gland

Previous studies have indicated that following nutrient ingestion, GIP is released principally from the upper small intestine. In addition to its presence in the rat small intestine, GIP transcripts have also been localized to the submandibular salivary gland (SSG). The present studies were directed to further characterize expression of the GIP gene in the SSG. Pregnant rats were sacrificed at gestational days 18 and 20, followed by the removal of rat fetuses. The duodenum pancreas, and SSG were then excised from the fetuses, as well as from neonatal pups at ages 1, 3, 7, 10, 14, and 21 days. RNA was extracted and measured by Northern blot analysis using specific rat GIP probes. GIP transcripts were first detected in the duodenum in the 18-day fetus and reached maximum levels at birth. In contrast, GIP mRNA was not observed in the SSG until 10 days postnatally and was not detected at all in either the fetal or neonatal pancreas. In situ hybridization of the SSG using an 35S-labelled antisense GIP RNA probe demonstrated expression of the GIP gene to be limited to ductal cells, with no transcripts present in acini. In separate experiments, rats fasted overnight were given water or 10% glucose. While no changes were detected in water-fed rats following oral glucose ingestion, small, but significant increases in SSG GIP gene expression were detected at 60 and 240 min. The results of these initial studies suggest the possibility of a functional role for GIP in the rat salivary gland by the demonstration of GIP mRNA in the SSG by Northern analysis and in situ hybridization, as well as by an increase in SSG GIP gene expression following a glucose meal.

Morphological method for the diagnosis of human adult type hypolactasia

The primary adult type hypolactasia is the most common form of genetically determined disaccharidase deficiency. This study examined a large and homogeneous population of the south of Italy: surgical biopsy specimens of proximal jejunum from 178 adult subjects have been assayed for disaccharidase activities; the expression of lactase protein and lactase activity has also been investigated on tissue sections by immunomorphological and enzymohistochemical techniques. Histograms of lactase to sucrase ratio were found to provide a useful distribution of the lactase activity; a lactase to sucrase ratio of 0.17 was found to show discrimination between tissues with persistence of high lactase activity and tissues with adult type hypolactasia. In all 28 subjects with persistent high lactase activity, a uniform distribution of lactase protein and lactase activity in all villus enterocytes was detected, whereas in all 150 subjects with adult type hypolactasia a variable number of villus enterocytes failed to express the lactase. Moreover in hypolactasic samples the lactase activity on tissue sections was constantly detected later than in samples with persistent high lactase activity. The absolute correlation between the immunohistochemical and enzymohistochemical features and the assessment of lactase activity in intestinal homogenates suggests that the morphological criteria are an alternative method for the diagnosis of adult type hypolactasia in human biopsy specimens from proximal small jejunum.

Mosaic regulation of lactase in human adult-type hypolactasia

BACKGROUND/AIMS

We have previously shown that in the proximal-jejunum of hypolactasic humans, just a few villus enterocytes express lactase protein and activity. In the present study, we compared the distribution of lactase messenger RNA (mRNA), protein, and activity in villus enterocytes in tissues obtained from subjects with persistent high lactase activity and those with hypolactasia.

METHODS

Immunohistochemical and enzymohistochemical staining was performed on closely adjacent sections of human proximal jejunum from 5 individuals with persistent high lactase activity and 32 with hypolactasia. In all the persistent and in 9 hypolactasic samples, in situ hybridization was also performed using a digoxygenin-labeled RNA probe.

RESULTS

In persistent tissues, lactase mRNA, protein, and activity were present in all villus enterocytes. In hypolactasic tissues, lactase mRNA was detected only in some villus enterocytes; some of them also expressed protein and activity, whereas others did not. In 8 of these hypolactasic samples, a variable number of villus enterocytes with lactase mRNA and protein did not express lactase activity.

CONCLUSIONS

Various types of enterocytes are present even on a single villus from individuals with adult-type hypolactasia. These results show that different mechanisms control lactase expression in enterocytes on the same villus.

Two intestinal specific nuclear factors binding to the lactase-phlorizin hydrolase and sucrase-isomaltase promoters are functionally related oligomeric molecules

Lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are enterocyte-specific gene products. The identification of regulatory cis-elements in the promoter of these two genes has enabled us to carry out comparative studies of the corresponding intestinal-specific nuclear factors (NF-LPH1 and SIF1-BP). Electrophoretic mobility shift assays demonstrated that the two nuclear factors compete for binding on the same cis-elements. The molecular size of the DNA binding polypeptide is estimated to be approximately 50 kDa for both factors. In the native form the factors are found as 250 kDa oligomeric complexes. Based on these results NF-LPH1 and SIF1-BP are suggested to be either identical or closely related molecules.

Surface staining on the villus of lactase protein and lactase activity in adult-type hypolactasia

BACKGROUND

We have shown in previous studies the presence of a patchy pattern of lactase protein expression in the proximal jejunum of hypolactasic humans, adult rabbits, and rats. The present study investigated the mechanisms underlying the heterogeneous expression of lactase on the villus.

METHODS

Proximal jejunal tissue from 18 adult humans and 12 adult rabbits was examined using enzymocytochemical and surface-staining techniques for lactase protein and activity.

RESULTS

In the proximal jejunum of hypolactasic humans and adult rabbits, lactase activity is patchily distributed on the villus enterocytes. In humans, the patches of lactase-positive enterocytes are randomly distributed on the villus, whereas in rabbits, vertical, continuous sheets of positive enterocytes arise from the base of the villus.

CONCLUSIONS

The presence of enterocytes without lactase activity is one of the mechanisms causing adult-type hypolactasia in the proximal jejunum of humans and mammals. The patchy pattern of lactase in rabbits suggests a clonal origin with heterogeneity of the cells arising from the crypts. In hypolactasic humans, the enterocyte heterogeneity occurs as a consequence of mechanisms that do not have a clonal origin.

Patchy expression of lactase protein in adult rabbit and rat intestine

Enzymatic and immunohistological analyses of lactase were performed at different stages of development and within different regions of the small intestine of the rabbit and rat. As previously reported, there seems to be a sharp decline of lactase activity on weaning but variable and higher levels of activity are seen in adult animals. Two monoclonal antibodies to rat lactase were available to study the protein in rats. Four monoclonal antibodies to human lactase were shown to cross-react with rabbit lactase and used for the rabbit studies. Immunohistological analysis of small intestine of adult rabbits and rats showed residual lactase protein within the enterocytes throughout the small intestine. In the middle of the small intestine (lower jejunum, upper ileum), uniform staining of the brush border was observed. In the proximal and distal regions, a patchy pattern of staining was observed. This pattern, which resembles that observed in adult hypolactasic humans, indicates an underlying heterogeneity of enterocyte differentiation.

The levels of lactase and of sucrase-isomaltase along the rabbit small intestine are regulated both at the mRNA level and post-translationally

We determined along the small intestine of young and adult rabbits the activities of lactase (LPH) and sucrase (SI), the levels of their cognate mRNAs, and examined the in vitro biosynthesis of LPH and pro-SI. Lactase activity is low in the proximal 1/3 of the intestine, whereas the mRNA levels are high. However, the rates of biosynthesis of the LPH forms correlated well with the steady-state levels of LPH mRNA in all segments, indicating that factor(s) acting post-translationally produce a decline in brush border LPH in the proximal small intestine. These factor(s) are not involved in the processing of pro-LPH to mature LPH, since the relative amounts of the various forms of LPH are almost the same along the small intestine. Unexpectedly, we find that also for SI the ratio of activity to mRNA is low in proximal intestine. The biosynthesis of pro-SI correlates with the steady-state levels of its mRNA. Hence, the steady-state levels of LPH and SI along the small intestine are regulated both by mRNA levels and by posttranslational factor(s).

Clonal analysis of sucrase-isomaltase expression in the human colon adenocarcinoma Caco-2 cells

To investigate the biosynthetic basis for the mosaic expression of brush border enzymes in confluent Caco-2 cells, a human colon carcinoma cell line exhibiting characteristics of adult small intestinal enterocytes, we have obtained a series of clones differing markedly in their growth rates, amounts of transforming growth factor-alpha/epidermal growth factor-like activity released into the culture medium, and sucrase-isomaltase (SI) activity. Other intestinal markers (aminopeptidase N, dipeptidylpeptidase IV, lactase, alkaline phosphatase and 'crypt cell antigen') displayed a much more limited variability in expression, suggesting that the Caco-2 cell clones we have obtained did not differ in their overall ability to differentiate. Immunofluorescence staining, metabolic labelling with radioactive methionine and hybridization analysis of SI mRNA abundance were used to investigate SI synthesis and its regulation in clones endowed with low, intermediate or high sucrase activity. The results obtained have demonstrated heterogeneous SI expression, even in clonal cell lines, and a negative correlation between SI expression and growth factor concentrations in the culture medium, suggesting an autocrine regulation of cell proliferation and differentiation in confluent Caco-2 cells. Pulse-chase experiments using the two clones endowed with the lowest and highest levels of SI activity, followed by immunoprecipitation of labelled SI with epitope-specific antibodies and SDS/PAGE analysis, suggested that both transcriptional and post-translational mechanisms play a role in the regulation of SI expression in intestinal cells.

Cortisone and thyroxine modulate intestinal lactase and sucrase mRNA levels and activities in the suckling rat

Glucocorticoids and thyroxine modulate postnatal intestinal sucrase and lactase activities. Whether changes in enzyme activity are accompanied by changes in enzyme mRNA levels were determined in day 6 rats given thyroxine, cortisone, or thyroxine plus cortisone and killed 3 days later. Cortisone induced precocious expression of jejunal sucrase activity which was enhanced when cortisone plus thyroxine was administered; sucrase mRNA changed in parallel. Jejunal lactase activity was unaffected by thyroxine and was increased after cortisone, but not after thyroxine plus cortisone. Jejunal lactase mRNA levels increased equally after cortisone or after cortisone plus thyroxine. Thus, cortisone induces coordinated increases in sucrase and lactase activities and in corresponding mRNA levels. Thyroxine only enhances cortisone induced sucrase expression and antagonizes cortisone by depressing lactase activity post-translationally.

Developmental control over vitamin-D-induced calbindin gene expression during early differentiation of chicken jejunal enterocytes

In situ hybridization and immunocytochemical techniques have been used to examine the distribution of vitamin-D-induced calbindin mRNA and calbindin protein in enterocytes lining the crypts and villi of chicken small intestine. Basal villus enterocytes contained approximately twice as much calbindin but over three times as much calbindin mRNA compared to values found in basal crypt and upper villus enterocytes, all values being measured 2 days after vitamin D injection into D-deficient chickens. Virtually no calbindin mRNA was detected in tissues taken from control D-deficient birds. Direct proportionality found between calbindin mRNA and calbindin content in enterocytes of basal crypt, mid and upper villus suggests pre-translational control over calbindin synthesis. The implications of possible inefficient translation of calbindin mRNA in basal villus enterocytes are discussed. Present methods of analysis provide a novel way to study mechanisms controlling gene expression throughout the whole process of enterocyte differentiation.

Mosaic pattern of lactase expression by villous enterocytes in human adult-type hypolactasia

Immunohistological analysis of the expression of lactase protein in adults with hypolactasia has been carried out using monoclonal antibodies. Eight different antibodies that recognize at least three distinct epitopes on the lactase protein each gave the same result. Strong brush border staining was observed in all the lactase-persistent adults. No staining at all was detected in 9 of the hypolactasic subjects. In the remaining 12 individuals a mosaic pattern of expression was observed: small patches of enterocytes stained strongly, whereas the surrounding areas showed no staining at all. Sucrase-isomaltase, in contrast, showed no such mosaicism in these or in any of the other individuals. The mosaicism observed in the 12 hypolactasic individuals suggests that the differentiation of the columnar cells along the villus is not homogeneous. Furthermore, the existence of two patterns of expression of the lactase protein in the lactase-deficient individuals (i.e., absence of protein and mosaicism), if characteristic of the entire length of the intestine of the individuals tested, would suggest the existence of two phenotypes of adult-type hypolactasia in the population studied.

Lactase expression is controlled differently in the jejunum and ileum during development in rats

This study shows the distribution of the messenger RNA for lactase-phlorizin hydrolase during postnatal development and along the longitudinal axis of the rat small intestine. At birth, this messenger RNA was present along the whole length of small intestine, and its concentration remained elevated during the suckling period despite the concomitant decrease in enzyme activity. At weaning, the amount of lactase messenger RNA dropped specifically in the distal ileum. This decrease in lactase messenger RNA was initiated at the ileocecal junction, progressed gradually towards the jejunum, and followed the decrease in lactase activity several days later. Starvation and refeeding were also found to cause modifications of lactase activity and messenger RNA expression that were prominent in the distal part of small intestine. These data support that posttranscriptional and pretranslational levels of regulation are required to define the spatial and temporal expression of lactase in the rat small intestine.

Reversibility of spermine-induced intestinal maturation in the rat

In the present investigation, the reversibility of spermine-induced precocious intestinal maturation was studied. Neonatal rats received either saline or spermine (4 mumol, twice daily) solution orally on the 11th and 12th postnatal day. They were killed on the 13th, 14th, 15th, 16th, and 17th postnatal days. After the small bowel was removed, it was either divided into three equal parts or prepared for electrophoretic analysis. Histological examination, protein content measurement, and disaccharidase activity estimation were performed on each part of the intestine. Spermine administration was shown to induce structural and mucosal enzyme changes characteristic of postnatal maturation. This phenomenon, which was generally clearly observed in 13- and 14-day-old rats, then became less apparent in 15- and 16-day-old animals. Differences were noted according to the segment of intestine or the biochemical parameter analyzed. When rats were 17 days old, no significant differences generally existed between control and spermine-treated rats. If the 140- to 150-kDa proteins, isolated by electrophoresis, are assumed to represent the subunits of the sucrase-isomaltase complex, the results obtained indicate that spermine induces a modification of the concentration of this complex. When compared to values obtained in adult rats, the concentration of the complex was approximately three times higher in spermine-treated 13-day-old rats, while no differences were found in spermine-treated 14-day-old rats. Further, similar concentrations were found in control and spermine-treated rats with an age of 17 days. These results suggest that spermine-induced precocious intestinal maturation is reversible when spermine treatment is stopped.

Detection and characterization of sucrase-isomaltase in adult human colon and in colonic polyps

A panel of monoclonal antibodies specific for sucrase-isomaltase, but differing in their ability to stain the proliferative crypt cells in human jejunum, was used to investigate expression of this enzyme in adult human colon and colonic tumors. Immunofluorescence staining on cryostat sections demonstrated the presence of sucrase-isomaltase in the apical region of normal colonic crypt cells but not on surface epithelium. Colonic sucrase-isomaltase was purified by immunoprecipitation with selected monoclonal antibodies and identified predominantly as high-mannose and complex glycosylated single-chain precursors endowed with relatively low levels of enzyme activities. Most polyps examined (10/16) were also found to express significant amounts of sucrase-isomaltase. In contrast, only 3 of 45 adenocarcinomas were positive by immunofluorescence staining; no correlation was found between enzyme expression and tumor classification either by "Dukes" stage or degree of histological differentiation. These results demonstrate that colonic crypt cells and some benign tumor cells synthesize and express at their cell surface a form of sucrase-isomaltase immunologically distinct from that present in the brush borders of small intestinal villose cells.

Brush border membrane sucrase-isomaltase, maltase-glucoamylase and trehalase in mammals. Comparative development, effects of glucocorticoids, molecular mechanisms, and phylogenetic implications

1. Trehalase, sucrase-isomaltase and maltase-glucoamylase are three integral glycoproteins of the brush border membranes of the enterocytes. On the basis of a comparative study on alpha-glycosidase activities (sucrase, isomaltase, maltase, glucoamylase and trehalase) associated to these glycoproteins during neonatal development, mammals could be basically divided into three groups. 2. In rodents and rabbit alpha-glycosidase activities are low or undetectable during the suckling period and increase to adult levels during the weaning period. In cat, dog and the primates examined, alpha-glycosidase activities are well or fully developed at birth. 3. In ruminants and pinnipedia alpha-glycosidases are low or absent throughout life. 4. During the suckling period of rat, mouse and rabbit, glucocorticoids trigger a premature and dramatic increase of all alpha-glycosidases. 5. On the contrary, alpha-glycosidases development during the weaning period appears to be independent of glucocorticoids. Neither hypophysectomy nor adrenalectomy prevent the development of alpha-glycosidases; only the rate of increase is reduced. 6. Transplantations of intestinal isografts either in adult or suckling animal, have shown that (1) no systemic factor inhibits the expression of alpha-glycosidase, (2) alpha-glycosidases induction is neither triggered by luminal alimentary substances, nor by hormones, (3) alpha-glycosidase development is controlled by an intrinsic ontogenic program. 7. The use of an antiglucocorticoid failed to inhibit the spontaneous development of alpha-glycosidase activities. 8. The increase of maltase and sucrase activities triggered by glucocorticoids is associated with an increase of the concentration of two glycoproteins in the microvillous membrane: sucrase-isomaltase and maltase-glucoamylase. 9. After administration of glucocorticoids the increase of maltase, sucrase and trehalase is strongly inhibited by actinomycin-D and the increase of sucrase activity is associated with a parallel increase of sucrase-isomaltase mRNA. Transcription is most likely the primary site of control of alpha-glycosidase biosynthesis. 10. In the crypt cells, alpha-glycosidases biosynthesis appears to be triggered by a receptor-mediated glucocorticoid interaction. 11. The enterocytes synthesize more alpha-glycosidase molecules as they travel to the tip of the villi. 12. The simultaneous, biosynthesis of sucrase-isomaltase and maltase-glucoamylase triggered by glucocorticoids, as well as their simultaneous normal development suggest that they may be subjected to related control mechanisms. 13. It is suggested that sucrase-isomaltase and maltase-glucoamylase might have arisen by several cycles of partial gene duplication of an ancestor gene coding for a single site maltase-isomaltase; subsequent mutation would have transformed isomaltase into sucrase or glucoamylase.

The biosynthesis of intestinal sucrase-isomaltase in human embryo is most likely controlled at the level of transcription

Although sucrase-isomaltase appears in the small intestine at quite different stages of development in man as compared with most mammals, we find that in human embryo also the appearance of sucrase-isomaltase mRNA closely parallels that of sucrase and isomaltase activities, as we have previously found to be the case in baby rabbits. Also, in the proximal-distal gradient of human embryonic intestine (proximal small intestine greater than distal small intestine greater than colon) the levels of these enzyme activities and those of the corresponding mRNA correlate closely. Finally, glucocorticosteroid treatment of a human colon carcinoma cell line (Caco-2) in vitro or of baby rabbits in vivo leads to a parallel increase of both sucrase and isomaltase activities and of sucrase-isomaltase mRNA. We conclude that in man also, in spite of the different timing in development, the biosynthesis of sucrase-isomaltase is most likely to be controlled at the level of transcription or perhaps of the mRNA stability.

Modulated expression of human homeobox genes in differentiating intestinal cells

Homeobox genes (Hox genes) control segmentation and segment specificity in Drosophila. Hox genes have been detected in several species from insects to vertebrates. Differential and stage-related expression has been observed in human embryonic tissues as well. We have investigated whether the cell line Caco-2 and human adult intestine express Hox genes. Caco-2 is a cell line derived from a human colon carcinoma and exhibits a spontaneous enterocytic differentiation after cellular confluency in vitro. At 7, 14 and 21 days after seeding we have found that Hox-2.3 and one Hox-3 gene hybridize to poly(A)+RNA in a stage-related fashion. Moreover, the 21 days pattern of hybridization resembles that one observed in adult small intestine. The Caco-2 cell line provides a model system that allows a detailed analysis of cellular factors controlling transcription and stability of Hox gene products.