Porphobilinogen deaminase deficiency in mice causes a neuropathy resembling that of human hepatic porphyria.

Acute intermittent porphyria (AIP) is a human disease resulting from a dominantly inherited partial deficiency of the heme biosynthetic enzyme, porphobilinogen deaminase (PBGD). The frequency of the trait for AIP is 1/10,000 in most populations, but may be markedly higher (1/500) in psychiatric patients. The clinical expression of the disease is characterized by acute, life-threatening attacks of 'porphyric neuropathy' that include abdominal pain, motor and sensory neurological deficits and psychiatric symptoms. Attacks are frequently precipitated by drugs, alcohol and low caloric intake. Identical symptoms occur in other hepatic porphyrias. To study the pathogenesis of the neurologic symptoms of AIP we have generated Pbgd-deficient mice by gene targeting. These mice exhibit the typical biochemical characteristics of human AIP, notably, decreased hepatic Pbgd activity, increased delta-aminolevulinic acid synthase activity and massively increased urinary excretion of the heme precursor, delta-aminolevulinic acid after treatment with drugs such as phenobarbital. Behavioural tests reveal decreased motor function and histopathological findings include axonal neuropathy and neurologic muscle atrophy.

Intersections between blood cell development and leukemia genes.

Hematopoietic development is regulated in large part by transcription factors that control cell fate decisions and cellular differentiation. Several genes first discovered in the context of chromosomal translocations in leukemia also serve important functions in blood cell development. Gene-targeting experiments related to two of these factors, SCL/tal-1 and translocation-ets-leukemia (TEL), are reviewed here. SCL/tal-1, a T-cell basic helix-loop-helix oncoprotein, is required for the formation of all hematopoietic lineages. In addition, it is essential for angiogenesis in the yolk sac, indicating a dual function in blood and vessel development. TEL, an ets-related factor which is translocated to a variety of other genes in leukemias, is also required for proper angiogenesis in the yolk sac. Additional studies, however, demonstrate that TEL function is necessary for hematopoiesis to be established in the bone marrow microenvironment. These studies emphasize the intrinsic roles of leukemia-associated transcription factors in normal blood cell and vessel development.

A simplified method for determination of specific DNA or RNA copy number using quantitative PCR and an automatic DNA sequencer.

Quantification of specific RNA or DNA molecules that are present in minute amounts in biological samples has previously been performed using PCR in the presence of an internal standard. We have adapted this concept by introducing several modifications that facilitate the quantification of the products and obviate the need for radioisotopes. After amplification, individual products are separated on sequencing gels and directly quantified using a fluorescent automated DNA sequencer. We describe two applications of this approach: the quantitation of minute amounts of bcr-abl hybrid mRNA from malignant cells and the determination of gene copy number in cells stably transfected with a plasmid bearing a chloramphenicol acetyltransferase gene.

A qualitative and quantitative study on the enkephalinergic innervation of the pig gastrointestinal tract.

Enkephalins are involved in neural control of digestive functions such as motility, secretion, and absorption. To better understand their role in pigs, we analyzed the qualitative and quantitative distribution of enkephalin immunoreactivity (ENK-IR) in components of the intestinal wall from the esophagus to the anal sphincter. Immunohistochemical labelings were analyzed using conventional fluorescence and confocal microscopy. ENK-IR was compared with the synaptophysin immunoreactivity (SYN-IR). The results show that maximal ENK-IR levels in the entire digestive tract are reached in the myenteric plexuses and, to a lesser extent, in the external submucous plexus and the circular muscle layer. In the longitudinal muscle layer, ENK-IR was present in the esophagus, stomach, rectum, and anal sphincter, whereas it was absent from the duodenum to the distal colon. In the ENK-IR plexuses and muscle layers, more than 60% of the nerve fibers identified by SYN-IR expressed ENK-IR. No ENK-IR was observed in the internal submucous plexus and the mucosa; the latter was found to contain ENK-IR endocrine cells. These results strongly suggest that, in pigs, enkephalins play a major role in the regulatory mechanisms that underlie the neural control of digestive motility.

Constitutive and functional expression of cyclooxygenase 2 in the murine proximal colon.

Recent reports suggest that cyclo-oxygenase (COX)-2, an inducible COX isoform may be constitutively expressed in gastrointestinal tissues. This study has evaluated the expression and function of COX-2 in the tunica muscularis of the murine proximal colon. Cyclo-oxygenase-2-like (COX-2-LI) immunoreactivity was found in a subpopulation of neurones in the myenteric and submucosal ganglia and in interstitial cells of Cajal within the muscle layers (IC-IM). Reverse transcriptase polymerase chain reaction (RT-PCR) verified expression of COX-2 in colonic muscles, and quantitative PCR demonstrated that COX-1 transcriptional expression was greater than COX-2. To test the functional significance of COX-2 expression, the effects of a COX-2 inhibitor were compared with the effects of indomethacin (COX-1/COX-2 inhibitor) on circular muscle contractions. The experiments indicate that indomethacin and the specific COX-2 inhibitor, GR253035X, increased the amplitude of phasic contractions, suggesting production of inhibitory prostaglandins tonically dampen contractile activity. The effects of indomethacin were reduced when tested on phasic contractions of muscles from COX-2 knockout mice. GR253035X did not affect contractions in muscles of COX-2 knockout animals. These studies demonstrate constitutive expression of COX-2 in the tunica muscularis of the proximal colon. The COX-2 appears to contribute a significant amount of the prostaglandins that affect the contractile behaviour of colonic muscles.

Opioid peptide mRNA expression in the colon of the rat.

Since the discovery of opioid peptides, several immunohistochemical and radioimmunological studies have demonstrated their localization in the gastrointestinal tract without demonstrating the localization of their common precursor. The present study describes the distribution and the colocalization of proenkephalin and prodynorphin messenger RNAs (mRNAs) in the colon of rat by in situ hybridization. Proenkephalin and prodynorphin mRNAs were found in myenteric plexus, but not in the submucous plexus or in the mucosa. In myenteric plexus, the number of neurons expressing proenkephalin is 2.5 times greater than that of the neurons expressing only prodynorphin. Furthermore, double in situ hybridization histochemistry indicates that at least three groups of opioid neurons can be distinguished, those containing proenkephalin and prodynorphin mRNAs together, and those containing only proenkephalin mRNA or only prodynorphin mRNA.

Superparamagnetic iron oxide particles and positive enhancement for myocardial perfusion studies assessed by subsecond T1-weighted MRI.

Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 mumol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 +/- 23% vs. 74 +/- 22%, Mann-Whitney test alpha < 1%, n1 = 6, n2-n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the "no-reflow phenomenon."

Structure of the mouse H2A.X gene and physical linkage to the UPS locus on chromosome 9: assignment of the human H2A.X gene to 11q23 by sequence analysis.

The H2A.X gene was cloned from the C3H mouse strain, and its structure was determined. Sequence analysis revealed that this gene is situated in close proximity to the porphobilinogen deaminase (PBGD) gene in the opposite orientation. The synteny is conserved in human. This permits us to assign the H2A.X gene to chromosome 9 and 11q23 in mouse and human, respectively.

The deep muscular plexus of the pig duodenum: a histochemical and ultrastructural study with special reference to the interstitial cells.

The aim of the present study was to describe the deep muscular plexus of the pig duodenum and to characterize its cellular components. Numerous nerve varicosities have been detected in the deep muscular plexus using anti-synaptophysin antibodies. Nerve fibres were also detected here in the outer circular muscle layer, whereas no nerve fibres were observed in the inner circular muscle layer. In the deep muscular plexus, nerve fibres projected to interstitial cells which were characterized at the ultrastructural level. The interstitial cells were of two kinds: the interstitial fibroblastic-like cells (FLC) and the interstitial dense cells (IDC), both of which were interposed between nerve fibres and smooth muscle cells. The FLC were characterized by their elongated bipolar shape, the lack of basal lamina, a well-developed endoplasmic reticulum, a Golgi apparatus, and intermediate filaments. They were closely apposed to axon terminals containing small clear synaptic vesicles and/or dense-cored vesicles. They were frequently connected to each other and to smooth muscle cells of the inner and outer circular layer by desmosomes and more rarely by gap junctions. The IDC are myoid-like cells. They had a stellate appearance and were characterized by a dense cell body, numerous caveolae, and a discontinuous basal lamina. The IDC were always closely apposed to nerve fibres and were connected to smooth muscle cells by desmosomes and small gap junctions. The present results show the unique pattern of cellular organization of the deep muscular plexus of the pig small intestine. They suggest that the interstitial cells in the deep muscular plexus are involved in the integration and transmission of nervous inputs from myenteric neurons to the inner and outer circular muscle layers. The clear-cut distinction observed here between the two types of interstitial cells (fibroblastic and myoid-like) suggests that the interstitial cells of each type may also be involved in some other specific activity, which still remains to be determined.

Characterization of hypersensitive sites, protein-binding motifs, and regulatory elements in both promoters of the mouse porphobilinogen deaminase gene.

Porphobilinogen deaminase, the third enzyme in the heme biosynthetic pathway, is encoded by a gene having two different promoters. Differential splicing of transcripts from the promoters yields two distinct mRNA species that are translated to give two isoforms of the protein. One isoform is ubiquitous, whereas the other is erythroid-specific. In this study, we have analyzed the gene regulatory elements that contribute to the tissue-specific promoter utilization of the mouse porphobilinogen deaminase gene. Six nuclear DNase I-hypersensitive sites were mapped in erythroid and nonerythroid cells, and four of these regions were further analyzed for in vitro nuclear protein-binding sites. The erythroid-specific promoter contains three erythroid nuclear factor GF-1-binding sites. The proximal GF-1-binding site, together with an adjacent duplicated CACCC motif, was sufficient to confer erythroid-specific expression in functional studies. Furthermore, as upstream gene sequences were shown to greatly increase promoter activity in erythroid cells, it suggests an upstream erythroid-specific enhancer may also be required for the up-regulation of the erythroid-specific promoter during erythropoiesis.

Functional analysis of DNase-I hypersensitive sites at the mouse porphobilinogen deaminase gene locus. Different requirements for position-independent expression from its two promoters.

Porphobilinogen deaminase (EC 4.3.1.8; PBG-D) is the third enzyme of the heme biosynthetic pathway. In both human and mouse, the gene encoding PBG-D possesses two promoters, lying in close proximity. We have previously reported the mapping of six nuclear DNase-I hypersensitive sites at the PBG-D locus which could contribute to the regulation of the gene. In the present study, and in order to define all the elements necessary for a high level of expression and an integration site independence, we studied the pattern and the level of expression of a cloned PBG-D gene following integration into a host genome. The longest construct that we tested (12.5 kilobases) contained sufficient regulatory elements to promote expression levels similar to that of the endogenous gene, both in transgenic mice and in transfected cells. The overall contribution of individual DNase-I hypersensitive sites to the expression of the gene was then studied using a series of mutants that were stably transfected into mouse erythroleukemia cells. Two regions seem to play a critical role in the erythroid-specific expression of the PBG-D gene: the proximal promoter and a region situated at -1000 relative to the initiation site. Study of individual clones of mouse erythroleukemia cells revealed that the erythroid-specific expression of the gene was submitted to position effects in the absence of the upstream region, although the housekeeping transcription is not sensitive to such effects. The tandem arrangement of the housekeeping and tissue-specific promoters of the PBG-D gene raises some questions about the functioning of these two overlapping transcriptional units in erythroid cells. Previous data have suggested that in erythroid cells most of the transcripts initiated at the upstream promoter stop downstream of the first ubiquitous exon, between the two promoters. Here, we show that the deletion of a constitutive DNase-I hypersensitive site that is located in the region of the elongation block results in opposite effects on the steady state levels of housekeeping and tissue-specific RNA. This finding is consistent with the hypothesis that this region promotes premature termination of the housekeeping transcripts therefore preventing promoter interference.

Overexpression of the ferritin H subunit in cultured erythroid cells changes the intracellular iron distribution.

To test the hypothesis that variations in H- and L-subunit composition in the ferritin shell affect intracellular iron metabolism, we established stable transfectants of mouse erythroleukemia cells overexpressing the H-ferritin subunit. Analyses were performed on individual clones of transfected cells induced to differentiate with hexamethylenbisacetamide (HMBA). The results showed that there was a reduction in the amount of hemoglobin produced, in inverse relationship with the level of H-subunit overexpression. Incorporation of [2-14C]glycine into heme was reduced by 20% t0 30% in the clones overexpressing H-ferritin subunit compared with control clone. However, the reduction in hemoglobin production was not reversed by addition of heme precursors (delta-aminolevulinic acid or iron) or by hemin itself. A reduced accumulation of beta-globin mRNA was also observed, which could account for the impaired hemoglobin synthesis. Furthermore, synthesis of the endogenous L-ferritin subunit was greatly repressed. Gel retardation assays performed on cytoplasmic extracts of transfected cells using an iron-responsive element (IRE) as a probe revealed that in overexpressing cells, the iron-regulatory protein (IRP) had a conformation with a high RNA-binding affinity, thus leading to translational repression of the endogenous L-ferritin synthesis. These data suggest that an increased formation of H-rich isoferritins leads to a rapid chelation of the regulatory iron pool. While the mechanism underlying the reduction in beta-globin mRNA remains to be elucidated, this study provides direct evidence for the role of IRP-mediated regulation of ferritin expression in erythroid cell metabolism.

The T cell leukemia oncoprotein SCL/tal-1 is essential for development of all hematopoietic lineages.

The T cell leukemia oncoprotein SCL/tal-1, a basic-helix-loop-helix transcription factor, is required for production of embryonic red blood cells in the mouse yolk sac. To define roles in other lineages, we studied the hematopoietic potential of homozygous mutant SCL/tal-1 -/- embryonic stem cells upon in vitro differentiation and in vivo in chimeric mice. Here we show that in the absence of SCL/tal-1, hematopoiesis, Including the generation of red cells, myeloid cells, megakaryocytes, mast cells, and both T and B lymphoid cells, is undetectable. These findings suggest that SCL/tal-1 functions very early in hematopoietic development, either in specification of ventral mesoderm to a blood cell fate, or in formation or maintenance of immature progenitors.

Specification of hematopoietic and vascular development by the bHLH transcription factor SCL without direct DNA binding.

Transcription factors, such as those of the basic-helix-loop-helix (bHLH) and homeodomain classes, are primary regulators of cell fate decisions and differentiation. It is considered axiomatic that they control their respective developmental programs via direct binding to cognate DNA sequences in critical targets genes. Here we test this widely held paradigm by in vivo functional assay of the leukemia oncoprotein SCL, a bHLH factor that resembles myogenic and neurogenic proteins and is essential for both hematopoietic and vascular development in vertebrates. Contrary to all expectation, we find that SCL variants unable to bind DNA rescue hematopoiesis from gene-targeted SCL(-)(/)(-) embryonic stem cells and complement hematopoietic and vascular deficits in the zebrafish mutant cloche. Our findings establish DNA-binding-independent functions of SCL critical for transcriptional specification, and should encourage reassessment of presumed requirements for direct DNA binding by other transcription factors during initiation of developmental programs.

Distribution of heme oxygenase 2 in nerves and c-kit(+) interstitial cells in human stomach.

Different populations of interstitial cells (ICs) may serve as gut pacemakers or as intermediaries between enteric nerves and smooth muscle cells. However, very little is known about the substances that ICs might use to communicate with other cells and no data are available in humans. Because carbon monoxide (CO) is emerging as a putative mediator in the regulation of gastrointestinal motility, this study examined the presence of heme oxygenase (HO2), the constitutive form of the enzyme for CO production, in human stomach with particular attention to ICs. The distribution of HO2 in nerves and ICs in human antrum was studied using specific antibodies. The immunostaining was observed using confocal laser scanning microscopy. HO2 immunoreactivity was found in myenteric neurons and nerve fibers supplying the circular muscle layer and in intramuscular c-kit(+) ICs, but not in c-kit(+) ICs surrounding the myenteric ganglia. The presence of HO2 in different cell types suggests that CO may serve as an intercellular messenger between myenteric neurons and ICs and between ICs and smooth muscle cells in human stomach.

The mouse porphobilinogen deaminase gene. Structural organization, sequence, and transcriptional analysis.

The porphobilinogen deaminase gene encodes the third enzyme of the heme biosynthetic pathway. This gene is expressed in a tissue-specific manner and gives rise to two isoenzymatic forms encoded by mRNA species differing in their 5' extremity. Recent studies in human demonstrated that the tissue-specific expression of the porphobilinogen deaminase gene is determined in erythropoietic cells, by the utilization of a specific promoter situated 3' to the housekeeping promoter used in other cell types. This results, through differential splicing, in the mutually exclusive presence of either exon 1 or exon 2 in mature mRNAs. Here, we report the cloning and sequencing of the porphobilinogen deaminase gene from mouse. The overall organization of the mouse gene is similar to that of the human one. In the housekeeping promoter, only a short stretch of homology is found including two potential Sp1 binding sites; in contrast, more extensive similarity appears in the erythroid-specific promoter including two motifs also found in globin gene, a CACCC box, and a recently described Ery F1 consensus binding sequence. We derived a set of single-stranded probes corresponding to different parts of the mouse gene to carry out a detailed analysis of the transcriptional unit in various cell types, using a run-on transcription assay on isolated nuclei. In liver cells, the first (non-erythropoietic) exon is more actively transcribed than parts of the gene situated downstream, suggesting that the elongation of transcripts is blocked within the 5' part of the first intron. In erythropoietic cells, the downstream promoter becomes activated; surprisingly, the initiation of transcription is also enhanced from the upstream (housekeeping) promoter and most of the transcripts initiated at the housekeeping promoter stop downstream of the first exon, between the two promoters.

Ultrastructural study of relationships between c-kit immunoreactive interstitial cells and other cellular elements in the human colon.

C-kit immunocytochemistry was performed on ultrathin sections of human distal colon. Our attention was focused on relationships between c-kit immunoreactive interstitial cells (c-kit ICs) and muscular cells and nervous elements located in the external muscular layers of the colonic wall. C-kit ICs established membrane apposition with both nerve fibers and smooth muscle cells of, respectively, the longitudinal and circular muscle layers, the myenteric area, and the extremus submucosus plexus. C-kit ICs also surrounded the external submucosus plexus and established membrane appositions with nerve elements located inside the myenteric ganglia. These membrane appositions were observed either at the level of the c-kit IC bodies or at that of their cytoplasmic processes. In some cases, membrane appositions were observed concomitantly between the c-kit ICs, nerve fibers, and smooth muscle cells. In all the regions studied, the c-kit ICs were also found to be located in the close vicinity of blood vessels and to have established close contacts with non-immunoreactive fibroblast-like cells. The results of the present study shed essential light on the relationships of c-kit ICs with the neighboring muscle cells and nerve elements, and confirm that the intercalated c-kit ICs well fit with the so-called "interstitial cells of Cajal".

Basic fibroblast growth factor positively regulates hematopoietic development.

Recently identified BLast Colony Forming Cells (BL-CFCs) from in vitro differentiated embryonic stem (ES) cells represent the common progenitor of hematopoietic and endothelial cells, the hemangioblast. Access to this initial cell population committed to the hematopoietic lineage provides a unique opportunity to characterize hematopoietic commitment events. Here, we show that BL-CFC expresses the receptor tyrosine kinase, Flk1, and thus we took advantage of the BL-CFC assay, as well as fluorescent activated cell sorter (FACS) analysis for Flk1(+) cells to determine quantitatively if mesoderm-inducing factors promote hematopoietic lineage development. Moreover, we have analyzed ES lines carrying targeted mutations for fibroblast growth factor receptor-1 (fgfr1), a receptor for basic fibroblast growth factor (bFGF), as well as scl, a transcription factor, for their potential to generate BL-CFCs and Flk1(+) cells, to further define events leading to hemangioblast development. Our data suggest that bFGF-mediated signaling is critical for the proliferation of the hemangioblast and that cells expressing both Flk1 and SCL may represent the hemangioblast.