The DNA-binding polycomb group protein pleiohomeotic mediates silencing of a Drosophila homeotic gene

Polycomb group (PcG) proteins repress homeotic genes in cells where these genes must remain inactive during development. This repression requires cis-acting silencers, also called PcG response elements. Currently, these silencers are ill-defined sequences and it is not known how PcG proteins associate with DNA. Here, we show that the Drosophila PcG protein Pleiohomeotic binds to specific sites in a silencer of the homeotic gene Ultrabithorax. In an Ultrabithorax reporter gene, point mutations in these Pleiohomeotic binding sites abolish PcG repression in vivo. Hence, DNA-bound Pleiohomeotic protein may function in the recruitment of other non-DNA-binding PcG proteins to homeotic gene silencers.

Characterization of human intestinal stromal cell lines: response to cytokines and interactions with epithelial cells

The maintenance of the physiological homeostasis of the gut mucosa characterized by continuous proliferation and differentiation processes results from epithelial-mesenchymal cell cross-talk. To set out stable and homogeneous models for the study of the (dys)regulation of various morphofunctional aspects, we established and characterized three clonal cell lines (C9, C11, and C20) derived from human duodenal mucosal connective tissue. We defined the expression of (i) cytoskeletal proteins; (ii) basement membrane molecules (laminins, collagen IV, nidogen) which have been shown formerly to be deposited at the epithelial/mesenchymal interface in situ by the mesenchymal compartment; and (iii) soluble factors, HGF, and TGFbeta1. The three cell lines display common but also specific proliferative responses to cytokines (IL1beta, IL2, IL8, TNFalpha, IFNgamma, TGFbeta1, and HGF). When cocultured with embryonic intestinal endoderms or with human colonic Caco2 or HT29 cancer cells, C9 versus C11 and C20 cell lines induced limited versus extensive growth of the associated epithelial cells. In addition C20 cells allowed spreading of HT29 cells with the formation of a basement membrane at the heterologous interface. Morphogenesis obtained by intracoelomic grafts of associations comprising the mesenchymal cell lines and intestinal endoderms was also different among those composed of C9 cells or of C11 or C20 cells. In conclusion, these data indicate that the mucosal connective tissue is heterogeneous and comprises several phenotypically different mesenchyme-derived cells whose equilibrium may be important in the gut homeostasis. These cells can now be used to define tissue-specific factors which may be involved in the physiopathology of the intestinal epithelium.

Optimum porphyrin accumulation in epithelial skin tumours and psoriatic lesions after topical application of delta-aminolaevulinic acid

Photodynamic therapy with topically applied delta-aminolaevulinic acid is used to treat skin tumours by employing endogenously formed porphyrins as photosensitizers. This study examines the time course of porphyrin metabolite formation after topical application of delta-aminolaevulinic acid. Porphyrin biosynthesis in human skin tumours (basal cell carcinoma, squamous cell carcinoma), in psoriatic lesions, and in normal skin was investigated. Skin areas were treated with delta-aminolaevulinic acid, and levels of total porphyrins, porphyrin metabolites and proteins were measured in samples excised after 1, 2, 4, 6, 9, 12 and 24 h. There was an increase in porphyrin biosynthesis in all tissues with maximum porphyrin levels in tumours between 2 and 6 h and in psoriatic lesions 6 h after treatment. The pattern of porphyrins showed no significant difference between normal and neoplastic skin, protoporphyrin being the predominant metabolite. The results suggest that optimum irradiation time for superficial epithelial skin tumours may be as soon as 2 h after application of delta-aminolaevulinic acid, whereas for treatment of psoriatic lesions an application time of 6 h is more suitable.

INTERMED--an assessment and classification system for case complexity. Results in patients with low back pain

STUDY DESIGN

Cross-sectional investigation and follow-up of patients with low back pain.

OBJECTIVES

To evaluate the capacity of the INTERMED--a biopsychosocial assessment and classification system for case complexity--to identify patients with a chronic, disabling course of low back pain and to predict treatment outcome.

SUMMARY OF BACKGROUND DATA

An impressive number of biologic and nonbiologic factors influencing the course of low back pain have been identified. However, the lack of a concise, comprehensive, reliable and validated classification system of this heterogeneous patient population hampers preventive and therapeutic progress.

METHODS

The INTERMED was used to assess patients with low back pain, who participated in a functional rehabilitation program (n = 50) and patients with low back pain who applied for disability compensation (n = 50). Patients of the rehabilitation program were observed to assess the effects of treatments.

RESULTS

The INTERMED distinguished between patients in different phases of disability and provided meaningful information about the biopsychosocial aspects of low back pain. In hierarchical cluster analysis two distinct clusters emerged that differed in the degree of case complexity and treatment outcomes.

CONCLUSIONS

This first application of the INTERMED indicates its potential utility as a classification system for patients with low back pain.

The thought translation device: a neurophysiological approach to communication in total motor paralysis

A thought translation device (TTD) for brain-computer communication is described. Three patients diagnosed with amyotrophic lateral sclerosis (ALS), with total motor paralysis, were trained for several months. In order to enable such patients to communicate without any motor activity, a technique was developed where subjects learn to control their slow cortical potentials (SCP) in a 2-s rhythm, producing either cortical negativity or positivity according to the task requirement. SCP differences between a baseline interval and an active control interval are transformed into vertical or horizontal cursor movements on a computer screen. Learning SCP self regulation followed an operant-conditioning paradigm with individualized shaping procedures. After prolonged training over more than 100 sessions, all patients achieved self-control, leading to a 70-80% accuracy for two patients. The learned cortical skill enabled the patients to select letters or words in a language-supporting program (LSP) developed for inter-personal communication. The results demonstrate that the fast and stable SCP self-control can be achieved with operant training and without mediation of any muscle activity. The acquired skill allows communication even in total locked-in states.

Intestinal epithelial-mesenchymal cell interactions

Intestinal morphogenesis, as well as maintenance of the stem cell population and of the steady state between cell proliferation and differentiation, results from controlled cell interactions. There is growing evidence that the mesenchymal cells control epithelial cell behavior via their own expression and induction in the epithelial cells of key regulatory genes. This heterologous cross talk involves basement membrane molecules and paracrine factors. New in vitro/in vivo cellular models allowed us to analyze various mesenchymal cell phenotypes and to show that they exhibit different inductive properties on epithelial cells and that their proliferation and metabolic properties are differentially modulated by cytokines. Finally the epithelial-mesenchymal unit is controlled by hormonal and exogenous factors.

Porphyria cutanea tarda

Porphyria cutanea tarda (PCT) is the most frequent form of porphyria. The underlying enzymatic defect in PCT is a reduced activity of the enzyme uroporphyrinogen decarboxylase (Uro-D). Four different types of Uro-D disturbances are known. Pseudoporphyrias such as porphyria cutanea uraemica or drug-induced PCT-like skin symptoms are distinguished from PCT. Porphyrinogens such as estrogens or alcohol, or other inducers of P450 isoenzymes provoke PCT. Polymorphisms of P450 isoenzymes, iron overload and infection with hepatitis C virus play an important role in the etiopathogenesis of disease manifestation. Dominant clinical symptoms are bullae, increased cutaneous vulnerability, hypertrichosis and elastosis. Biochemically, total porphyrin levels in urine are increased with a predominance of uroporphyrin and heptacarboxylic porphyrin. Isocoproporphyrin is demonstrable in feces. Best therapeutic strategies are the oral administration of chloroquine 125 mg twice a week and repetitive bloodlettings or the combination of both.

Congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is one of the rarest autosomal-recessive disorders of the porphyrin metabolism caused by the homozygous defect of uroporphyrinogen III cosynthase. High amounts of uroporphyrin I accumulate in all cells and tissues, reflected by an increased erythrocyte porphyrin concentration and excretion of high porphyrin amounts in urine and feces. Dermal deposits of uroporphyrin frequently induce a dramatic phototoxic oxygen-dependent skin damage with extensive ulcerations and mutilations. Splenomegaly and hemolytic anemia are typical internal symptoms. Skeletal changes such as osteolysis and calcifications are frequent. Up to date 130 cases of CEP have been published. Splenectomy and erythrocyte transfusions showed some beneficial effect. Bone marrow transplantation was performed in 3 patients and stem cell transplantation in 1. The best therapy is the avoidance of sunlight. We give a report on our latest cases of CEP.

Photodynamic diagnosis and therapy in dermatology

The topical application of delta-aminolevulinic acid (ALA) induces porphyrin formation in the skin, preferentially in tumor tissues. Irradiation of the porphyrin-enriched tumor tissue with Wood's light leads to emission of a brick-red fluorescence. This principle may be used as a diagnostic procedure which may be termed photodynamic diagnosis (PDD). In ALA-PDD, tumors and precancerous lesions of the skin reveal a homogeneous, intensive red fluorescence. Psoriatic lesions also show a strong but inhomogeneous porphyrin fluorescence. ALA-induced porphyrin fluorescence in preoperative planning is a valuable method to determine the peripheral borders of a given tumor. The histopathological extensions of the tumors correlate well with the borders detected by the tumor-specific fluorescence. The main indications of PDD are the delineation of clinically ill-defined skin tumors and the control of the efficacy of other tumor therapies. Photodynamic therapy (PDT) utilizes exogenously applied or endogenously formed photosensitizers and their activation by light to induce cell death via formation of singlet oxygen and other free radicals. PDT is highly efficient in the treatment of solar keratoses and superficial basal cell carcinomas. Initial squamous cell carcinomas also show good response to ALA-PDT. During the last decade, numerous studies on PDT for dermatologic diseases were published, the more important ones are reviewed here.

Activation of JNK and p38 but not ERK MAP kinases in human skin cells by 5-aminolevulinate-photodynamic therapy

5-Aminolevulinate (ALA) photodynamic therapy (PDT) is being used clinically for the treatment of skin cancers. ALA is applied as a precursor of porphyrins serving as endogenous photosensitizers. Irradiation of HaCaT cells preincubated with 1 mM ALA for 24 h with red light of 570-750 nm at a dose of 4.5 J/cm2 leads to a 6-fold elevation of cellular c-Jun N-terminal kinase activity; phosphorylation of p38 mitogen-activated protein kinase (MAPK) is enhanced to a similar extent. In contrast, neither activation nor increased phosphorylation of the extracellular stimulus-regulated kinase MAPKs is detected. p38 is also phosphorylated by ALA-PDT in the human melanoma cell lines Bro and SkMel-23, applying doses that lead to 80-95% cell death after 24 h. Hence, the effects of ALA-PDT on MAPKs are similar to stresses like UV irradiation or exposure to hydrogen peroxide with respect to activation of JNK and p38 MAPKs. They are different, however, in that extracellular stimulus-regulated kinase activity is not raised by ALA-PDT. Of the 830 pmol porphyrins/mg protein that were present at 24 h in HaCaT cells, 99 pmol/mg were intracellular. When extracellular porphyrins had been removed by washing, p38 responses were retained. Thus, intracellular porphyrins synthesized from ALA are sufficient to elicit activation of p38 on photosensitization.

Identification of genes involved in replication and movement of peanut clump virus

The genome of peanut clump pecluvirus (PCV) consists of two messenger RNA components which contain, respectively, three and five open reading frames (ORFs). Inoculation of transcripts from full-length cDNA clones derived from the PCV RNAs showed that RNA-1 is able to replicate in the absence of RNA-2 in protoplasts, but both RNAs are necessary for plant infection. To investigate the role of different gene products in viral RNA replication and movement, transcripts from mutant cDNA clones were inoculated to protoplasts and to Chenopodium quinoa or Nicotiana benthamiana plants, and progeny RNA was detected by Northern blot analysis. The protein P15, encoded by the third ORF of RNA-1, is essential for efficient replication of the viral genome. The three proteins, P51, P14, and P17, of the triple gene block contained in RNA-2 are involved in localized movement of the viral genome, whereas the coat protein (P23) is also required for vascular movement. Insertion of the beta-glucuronidase reporter gene (GUS) in place of the P23 or P39 genes (the first and the second genes of RNA-2) allows visualization of the virus infection in inoculated leaves. Although the presence of the GUS gene resulted in a lower accumulation of progeny RNA and, despite instability of the construct in planta, histochemical detection of PCV multiplication was more sensitive than Northern blot detection.

Preferential relative porphyrin enrichment in solar keratoses upon topical application of delta-aminolevulinic acid methylester

Topically applied delta-aminolevulinic acid is used efficiently for the treatment of solar keratoses by photodynamic therapy. Recent animal studies suggest that porphyrin sensitization of epithelial tissue is improved by using esters rather than free delta-aminolevulinic acid. The present study examines porphyrin metabolite formation after topical application of delta-aminolevulinic acid or delta-amino-levulinic acid methylester in human solar keratoses versus adjacent normal skin. Level of total porphyrins, porphyrin metabolites and protein were measured in skin samples excised after 1 and 6 h. Higher levels of porphyrins were observed in solar keratoses than in normal skin with both substances. Maximum porphyrin levels were present in solar keratoses treated with delta-aminolevulinic acid for 6 h. However, the ratio of porphyrins in solar keratoses versus adjacent normal skin was higher with delta-aminolevulinic acid methylester. The pattern of porphyrins showed no significant difference between normal and afflicted skin, protoporphyrin being predominant. The results suggest that application of free delta-aminolevulinic acid may be more effective in sensitizing solar keratoses. However, treatment with delta-aminolevulinic acid methylester leads to a preferential enrichment of porphyrins within lesional skin.

Intraoperative detection of malignant gliomas by 5-aminolevulinic acid-induced porphyrin fluorescence

OBJECTIVE

Survival after surgery and radiotherapy for the treatment of malignant gliomas is linked to the completeness of tumor removal. Therefore, methods that permit intraoperative identification of residual tumor tissue may be of benefit. In a preliminary investigation, we have studied the value of fluorescent porphyrins that accumulate in malignant tissue after administration of a precursor (5-aminolevulinic acid) for labeling of malignant gliomas in nine patients.

METHODS

Three hours before the induction of anesthesia, 10 mg 5-aminolevulinic acid/kg body weight was administered orally. Intraoperatively, red porphyrin fluorescence was observed with a 455-nm long-pass filter after excitation with violet-blue (375-440 nm) xenon light and was verified by analysis of fluorescence spectra. Fluorescing and nonfluorescing samples taken from the tumor perimeters were examined histologically or used to study the photobleaching of porphyrins by excitation light and white light from the operating microscope. Plasma and erythrocyte porphyrin levels were determined by fluorescence photometry.

RESULTS

Normal brain tissue revealed no porphyrin fluorescence, whereas tumor tissue was distinguished by bright red fluorescence. For a total of 89 tissue biopsies, sensitivity was 85% and specificity was 100% for the detection of malignant tissue. For seven of nine patients, visible porphyrin fluorescence led to further resection of the tumor. Under operating light conditions, fluorescence decayed to 36% in 25 minutes for violet-blue light and in 87 minutes for white light. Plasma and erythrocyte porphyrin contents increased slightly, without exceeding normal levels.

CONCLUSION

Our observations suggest that 5-aminolevulinic acid-induced porphyrin fluorescence may label malignant gliomas safely and accurately enough to enhance the completeness of tumor removal.

Photodynamic therapy in dermatology

Photodynamic therapy (PDT) uses exogenously administered or endogenously formed photosensitizers activated by light to induce cell death via formation of singlet oxygen and other free radicals. Photodynamic therapy is increasingly used for the treatment of skin cancers and other indications. The efficacy of PDT depends on the structure of the photosensitizer, the administration modality, the light source, and the treatment procedure. We reviewed the most recent clinical and experimental developments in PDT research related to dermatology. The substrate under most intense investigation in PDT research is delta-aminolevulinic acid (ALA). Photodynamic therapy with topically applied ALA has been shown to be highly efficient in the treatment of cutaneous neoplasms by using intralesionally formed porphyrins as photosensitizers. For solar keratoses, best response rates have been described. delta-Aminolevulinic-PDT is also efficient in the treatment of superficial basal cell and squamous cell carcinomas. In addition, the fluorescence of ALA-induced porphyrins under a Wood light is highly selective in neoplastic cutaneous tissue and offers a useful technique in detecting and delineating skin tumors with ill-defined borders.

Carbon dioxide laser treatment of extramammary Paget's disease guided by photodynamic diagnosis

Extramammary Paget's disease (EPD) is a rare malignancy occurring mainly in apocrine gland-bearing regions. Surgical excision is the treatment of choice. This may be very difficult or even impossible if the disease is widespread or located in a critical anatomical site. We report on the successful treatment of a 71-year-old man with EPD in the suprapubic region with CO2 laser guided by photodynamic diagnosis.

Influence of indoles (melatonin, serotonin and tryptophan) on the porphyrin metabolism in vitro

We examined the influence of melatonin, serotonin and tryptophan on the basal and delta-aminolevulinic acid (ALA)-induced porphyrin content in HaCaT, SKMel-23 and HepG2 cells. ALA-preincubated and ALA-free cells were fed with medium containing 1 mM melatonin, serotonin or tryptophan. After 24 h the porphyrin content in the cells and in the culture medium was measured. In the three cell lines the inbucation with 1 mM ALA over 24 h increased the porphyrin concentration in all cell lines in different degrees: HepG2 > SKMel-23 > HaCaT cells. In HepG2 cells, neither melatonin, serotonin nor tryptophan influenced ALA-induced porphyrin concentrations significantly, but all three indoles depressed the porphyrin levels in SKMel-23 and HaCaT cells. The indoles may decrease the ALA uptake in HaCat or SKMel-23 cells. Another mechanism could be the inhibition of enzymes converting ALA into porphyrins.

Successful surgery of multiple recurrent basal cell carcinomas guided by photodynamic diagnosis

We describe a 56-year-old Caucasian man with history of multiple regressed basal cell carcinomas. During the last 20 years approximately 200 histologically proven basal cell carcinomas preferentially localized on the face were surgically treated. Several large skin grafts were necessary to cover the extensive tissue defects on the face and scalp. Although all excised tissues were histologically proven to be basal cell carcinomas with tumor-free margins, new tumors developed in proximity to the skin graft margins. The dissemination of the new tumors made it difficult to perform additional invasive operation procedures without influencing the cosmetic result. Thus, we used photodynamic diagnosis to improve detection and demarcation of the neoplastic tissues. This procedure facilitated surgical planning and enabled primary in toto excisions. Surgical trauma and a number of interventions were thus minimized with the consequence of improved cosmetic and functional results.

5-aminolaevulinic-acid-induced formation of different porphyrins and their photomodifications

The relative amounts of 5-aminolaevulinic acid (ALA)-induced hydrophobic and hydrophilic porphyrins produced in normal mouse tissue and solid Ehrlich ascites carcinoma in mice were investigated as a function of added glucose, light irradiation and restricted blood flow to the tumour. Protoporphyrin IX (PpIX) is the predominant porphyrin produced from exogenous ALA in tissues that have viable mitochondria. However, under special conditions which seem to be connected with a reduced viability of the mitochondria, the formation of water-soluble porphyrins can be observed in vivo. Fluorescence maxima of the water-soluble porphyrins are located in the region between 615 and 625 nm. Irradiation can further lead to the formation of PpIX photoproduct(s), showing a fluorescence emission band at 676 nm. The photobleaching of PpIX in normal tissue and tumour tissue is different under restricted blood flow. ALA-induced PpIX can be observed in the normal blood stream, and can be linked to a slower photobleaching than in tissue with restricted blood flow.

Green light is effective and less painful than red light in photodynamic therapy of facial solar keratoses

Photodynamic therapy (PDT) with topically applied delta-aminolevulinic acid (ALA) is increasingly employed to treat patients with multiple solar keratoses and superficial skin tumors. For these indications, ALA-PDT has been shown to be highly efficient. Treatment of multiple or extended lesions, however, is substantially hampered by the fact that ALA-PDT is associated with burning pain during the irradiation procedure. The standard irradiation devices commonly used for ALA-PDT emit red light around 630 nm. In the present half-side comparison study we have observed that ALA-PDT employing a green light irradiation device (543-548 nm) is equally effective, as compared with standard red light ALA-PDT. In contrast to red light ALA-PDT, however, green light ALA-PDT caused only little tingling and burning but no pain. These observations indicate that green light ALA-PDT is superior to standard ALA-PDT, because it is associated with less unwanted side effects.

Photodynamic therapy with 5-aminolaevulinic acid-induced porphyrins of an amelanotic melanoma in vivo

Of particular interest for photodynamic therapy (PDT) are the endogenously formed and photodynamically active porphyrins produced following topical or systemic application of 65-aminolaevulinic acid (ALA), a haem precursor. Having determined the pharmacokinetics and wavelength dependence of PDT with ALA-induced porphyrins, we analysed the porphyrin metabolites in tumour and surrounding skin. The therapeutic efficacy of PDT using ALA-induced porphyrins was investigated. Amelanotic melanomas (A-Mel-3) were implanted subcutaneously in the back of Syrian golden hamsters (body weight (b.w.), 70-80 g). After 5-7 days, tumours with a volume of approximately 150 mm3 were used for PDT (n = 36). ALA (500 mg kg-1 b.w., pH 6.5) was injected intravenously 45, 90, 150 and 300 min before light irradiation (635 nm, 100 mW cm-2, 100 J cm-2). Tumours with light irradiation only served as controls. The tumour volume was measured after PDT for 28 days. The total porphyrin content was determined in the tumours, the surrounding skin and erythrocytes prior to and 45, 90, 180, 240, 300 and 480 min and 24 h following intravenous injection of ALA (500 mg kg-1 b.w.; n = 32). Porphyrin metabolites were separated by high pressure liquid chromatography (HPLC). Tumour growth was significantly delayed when PDT with ALA was performed 45, 90 or 150 min following intravenous administration. At that time, protoporphyrin (1.8 +/- 0.4 nmol g-1), coproporphyrin (2.2 +/- 0.5 nmol g-1) and uroporphyrin (1.7 +/- 1.4 nmol g-1) were the main metabolites in the tumour tissue. Erythrocytes also contained significant amounts of porphyrins (11.8 +/- 1.3 nmol g-1). The tumour and surrounding skin exhibited a different pattern of porphyrin metabolites. Unexpectedly, a single treatment of PDT with ALA-induced porphyrin resulted in only one complete remission out of six amelanotic melanomas when the final therapeutic outcome was assessed after 28 days. The therapeutic efficacy of PDT with ALA-induced porphyrins can be positively correlated with the fluorescence kinetics previously determined. The analysis of the porphyrin metabolites in amelanotic melanoma by HPLC indicates that the porphyrin accumulation is not due to a decreased activity of ferrochelatase. Moreover, the photodynamic effects may not be mediated solely by porphyrins localized in the tumour parenchyma, but also by significant amounts of porphyrins in the microvasculature. PDT with this endogenous photosensitizer failed to induce complete emission of the treated tumours despite irradiation at the time of maximum porphyrin concentration using the optimum therapeutic wavelength. Thus PDT with ALA-induced porphyrins is less effective in our model relative to that observed for the exogenous photosensitizer Photofrin or synthetic porphycenes after a single treatment.

Ex vivo application of delta-aminolevulinic acid induces high and specific porphyrin levels in human skin tumors: possible basis for selective photodynamic therapy

In photodynamic therapy with topically applied delta-aminolevulinic acid porphyrins are acting as photosensitizers. The profile of porphyrin metabolites in normal or in neoplastic skin after administration of delta-aminolevulinic acid has not been determined in detail yet. Thus, to study porphyrin biosynthesis in human skin an organ culture model was developed. Explant pieces of normal skin, keratoacanthoma, and basal cell carcinoma were incubated with 1 mM delta-aminolevulinic acid for 36 h. Levels of delta-aminolevulinic acid, porphyrins and porphyrin metabolites were measured in tissues and supernatants. After incubation with delta-aminolevulinic acid, higher porphyrin levels were demonstrated in tumors as compared to normal skin. In supernatants, most of formed porphyrins, preferentially highly carboxylated porphyrin metabolites, were measured. The pattern of synthesized porphyrins differed between normal and neoplastic skin explants. In tissues of basal cell carcinomas protoporphyrin was preferentially shown and tissues of keratoacanthomas were characterized by a predominance of coproporphyrin as compared to normal skin. The results show that explant cultures offer an easy approach to examine the porphyrin biosynthesis of various tissues. The tumor-specific delta-aminolevulinic acid metabolism indicates additional porphyrin metabolites such as coproporphyrin apart from protoporphyrin as effective photosensitizers and may offer a novel approach to tumor-selective photodynamic damage.

Changing intestinal connective tissue interactions alters homeobox gene expression in epithelial cells

In segmented organs, homeobox genes are involved in axial patterning and cell identity. Much less is known about their role in non-segmented endoderm derivatives such as the digestive epithelium. Using a xenograft model of fetal intestinal anlagen implanted under the skin of nude mice, we have investigated whether the expression of five homeobox genes (HoxA-4, HoxA-9, HoxC-8, Cdx-1 and Cdx-2) is modified when intestinal epithelium undergoes normal development or displays heterodifferentiation in association with heterotopic mesenchyme. In homotypic associations of fetal endoderm and mesenchyme that recapitulate normal development, the overall pattern of homeobox gene expression was maintained: HoxA-9 and HoxC-8 were the highest in the colon and ileum, respectively, and HoxA-4 was expressed all along the intestine; Cdx-1 and Cdx-2 exhibited an increasing gradient of expression from small intestine to colon. Yet, grafting per se caused a faint upregulation of HoxA-9 and HoxC-8 in small intestinal regions in which these genes are not normally expressed, while the endoderm-mesenchyme dissociation-association step provoked a decay of Cdx-1 in the colon. In heterotopic associations of colonic endoderm with small intestinal mesenchyme, the colonic epithelium exhibited heterodifferentiation to a small intestinal-like phenotype. In this case, we observed a decay of HoxA-9 expression and an upregulation of HoxC-8. Additionally, heterodifferentiation of the colonic epithelium was accompanied by a downregulation of Cdx-1 and Cdx-2 to a level similar to that found in the normal small intestine. To demonstrate that mesenchyme-derived cells can influence Cdx-1 and Cdx-2 expression in the bowel epithelium, fetal jejunal endoderm was associated with intestinal fibroblastic cell lines that either support small intestinal-like or colonic-like morphogenesis. A lower expression of both homeobox genes was shown in grafts presenting the small intestinal phenotype than in those showing glandular colonic-like differentiation. Taken together, these results suggest that homeobox genes participate in the control of the positional information and/or cell differentiation in the intestinal epithelium. They also indicate that the level of Cdx-1 and Cdx-2 homeobox gene expression is influenced by epithelial-mesenchymal cell interactions in the intestinal mucosa.