A mouse organotypic tissue culture model for autosomal recessive congenital ichthyosis.

BACKGROUND: Autosomal recessive congenital ichthyoses (ARCIs) are keratinization disorders caused by impaired skin barrier function. Mutations in the genes encoding the lipoxygenases 12R-LOX and eLOX-3 are the second most common cause of ARCIs. In recent years, human skin equivalents recapitulating the ARCI phenotype have been established. OBJECTIVES: To develop a murine organotypic tissue culture model for ARCI. METHODS: Epidermal keratinocytes were isolated from newborn 12R-LOX-deficient mice and cocultivated with mouse dermal fibroblasts embedded in a scaffold of native collagen type I. RESULTS: With this experimental set-up the keratinocytes formed a well-organized multilayered stratified epithelium resembling skin architecture in vivo. All epidermal layers were present and the keratinocytes within showed the characteristic morphological features. Markers for differentiation and maturation indicated regular epidermal morphogenesis. The major components of epidermal structures were expressed, and were obviously processed and assembled properly. In contrast to their wild-type counterparts, 12R-LOX-deficient skin equivalents showed abnormal vesicular structures in the upper epidermal layers correlating with altered lipid composition and increased transepidermal water loss, comparable with 12R-LOX-deficient mice. CONCLUSIONS: The mouse skin equivalents faithfully recapitulate the 12R-LOX-deficient phenotype observed in vivo, classifying them as appropriate in vitro models to study molecular mechanisms involved in the development of ARCI and to evaluate novel therapeutic agents. In contrast to existing human three-dimensional skin models, the generation of these murine models is not constrained by a limited supply of material and does not depend on in vitro expansion and/or genetic manipulations that could result in inadvertent genotypic and phenotypic alterations.

Up-regulation of 12(S)-lipoxygenase induces a migratory phenotype in colorectal cancer cells.

12(S)-Lipoxygenase (LOX) and its product 12(S)-hydroxyeicosatetraenic (HETE) acid have been implicated in angiogenesis and tumour invasion in several tumour types while their role in colorectal cancer progression has not yet been studied. We have analysed 12(S)-LOX expression in colorectal tumours and found gene expression up-regulated in colorectal cancer specimens for which the pathology report described involvement of inflammation. Using cell line models exposed to 12(S)-HETE or over-expressing 12(S)-LOX malignant cell growth as well as tumour cell migration was found to be stimulated. Specifically, Caco2 and SW480 cells over-expressing 12(S)-LOX formed fewer colonies from sparse cultures, but migrated better in filter-migration assays. SW480 LOX cells also had higher anchorage-independent growth capacity and a higher tendency to metastasise in vivo. Knock-down or inhibition of 12(S)-LOX inhibited cell migration and anchorage-independent growth in both 12(S)-LOX transfectants and SW620 cells that express high endogenous levels of 12(S)-LOX. On the cell surface E-cadherin and integrin-ß1 expression were down-regulated in a 12(S)-LOX-dependent manner disturbing cell-cell interactions. The results demonstrate that 12(S)-LOX expression in inflammatory areas of colorectal tumours has the capacity to induce an invasive phenotype in colorectal cancer cells and could be targeted for therapy.

15-Lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor gamma.

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor gamma (PPARgamma) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), a product of 15-LOX-2 that binds to PPARgamma. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARgamma. After forced expression of wild-type PPARgamma, 15-(S)-HETE (1 microM) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARgamma reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 microM). Peroxisome proliferator-activated receptor gamma interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARgamma and orphan receptor RORalpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARgamma to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.

High velocity suspension flame spraying (HVSFS) of metal doped bioceramic coatings.

•Bioceramic coatings doped with metals for antibacterial effect.•Combination of suspension and precursor flame spraying.•Successful deposition of submicron metallic particles in bioceramic matrix.

Analysis of a variant Max sequence expressed in Xenopus laevis.

Max is a small helix-loop-helix protein which forms heterodimers with members of the Myc protein family. Myc/Max heterodimers exhibit sequence-specific DNA binding with much greater affinity than Myc homodimers. The Xenopus laevis homologue of Max, XMax, is shorter than the equivalent mammalian protein. This difference results from the deletion of a 24 amino acid sequence located near the C-terminus of the protein. Xenopus max transcripts undergo alternative splicing. In addition to the 27 base alternatively spliced sequence (exon A) previously detected in mice and humans, some Xmax transcripts also contain an 81 base sequence (exon B) at a second site within the coding sequence. Although exon B insertion alters part of the leucine zipper protein/protein interaction domain, the resulting XMax protein retains the ability to form stable heterodimers with both c-Myc and N-Myc. Xmax mRNA is present at approximately constant levels during early development. This contrasts with the rapidly changing levels of c-myc and N-myc mRNA in the embryo and has implications for regulation of gene expression during differentiation. All four alternatively spliced forms of Xmax mRNA are present during development and in all adult tissue examined.

cDNA cloning of a 8-lipoxygenase and a novel epidermis-type lipoxygenase from phorbol ester-treated mouse skin.

Using a combination of PCR cloning and conventional screening procedures, we isolated from phorbol ester-treated mouse epidermis two full length cDNA clones encoding novel lipoxygenases. One of the cDNAs turned out to be identical to the recently cloned 8-lipoxygenase [Jisaka et al., J. Biol. Chem. 272 (1997) 24 410-24 416], the open reading frame of the second one corresponded to a protein of 701 amino acids with a calculated molecular mass of 80.6 kDa. The amino acid sequence showed 50.8% identity to human 15-lipoxygenase 2, approximately 40% to 5-lipoxygenase and 35% to 12- and 15-lipoxygenases. A unique structural feature is the insertion of 31 amino acid residues in the amino-terminal part of the molecule. Based on these data, we conclude that this epidermis-derived cDNA encodes a novel lipoxygenase isoform termed provisionally epidermis-type lipoxygenase 2 (e-LOX 2).

Efficient expression of cloned complementary DNAs for secretory proteins after injection into Xenopus oocytes.

Cloned complementary DNAs encoding chicken ovalbumin, chicken prelysozyme and calf preprochymosin, prochymosin and chymosin were inserted downstream from various viral promoters in modified recombinant "shuttle" vectors. Microinjection of the ovalbumin, prelysozyme and preprochymosin constructs into the nuclei of Xenopus laevis oocytes resulted in the synthesis, segregation in membranes and secretion into the extracellular medium of ovalbumin, lysozyme and prochymosin, respectively. Judging from molecular weight estimations, lysozyme and prochymosin were correctly proteolytically processed while ovalbumin, which lacks a cleavable signal sequence, was glycosylated. Injection of the DNA construct encoding prochymosin without its signal sequence resulted in synthesis of prochymosin protein that was localized exclusively in the oocyte cytoplasm. No immunospecific protein was detected after injection of the DNA encoding mature chymosin. In terms of protein expression in oocytes, the Herpes simplex thymidine kinase (TK) promoter was up to sevenfold more effective than the simian virus 40 (SV40) early promoter, and equally as effective as the Moloney murine sarcoma virus long terminal repeat element. Where tested, protein expression in oocytes was much reduced if DNA sequences encoding the SV40 small t intron and its flanking sequences were present in the constructs. S1 nuclease mapping of transcripts produced after injection of DNAs containing the TK promoter indicated that the majority of transcripts initiated at, or within, two bases of the known "cap" site. However, minor transcripts initiating upstream from this site were observed and one (or more) of these transcripts was responsible for the synthesis of an ovalbumin polypeptide containing a 51 amino acid N-terminal extension. This extended protein remained in the oocyte cytosol. When ovalbumin cDNA was inserted into the vectors with opposite polarity to the viral promoter, expression in oocytes resulted in the predominant synthesis and secretion of a variant ovalbumin with a 21 amino acid N-terminal extension, although some full-length ovalbumin was also synthesized and secreted. S1 mapping revealed the presence, in these oocytes, of transcripts of predicted polarity initiating 118 bases upstream from the wild type ovalbumin initiator ATG, at a previously unreported SV40 "promoter". No protein synthesis was detected after the injection of these reverse-orientation constructs into baby hamster kidney (BHK-21) cells.

Segregation of mutant ovalbumins and ovalbumin-globin fusion proteins in Xenopus oocytes. Identification of an ovalbumin signal sequence.

The intramolecular signals for chicken ovalbumin secretion were examined by producing mutant proteins in Xenopus oocytes. An ovalbumin complementary DNA clone was manipulated in vitro, and constructs containing altered protein-coding sequences and either the simian virus 40 (SV40) early promoter or Herpes simplex thymidine kinase promoter, were microinjected into Xenopus laevis oocytes. The removal of the eight extreme N-terminal amino acids of ovalbumin had no effect on the segregation of ovalbumin with oocyte membranes nor on its secretion. A protein lacking amino acids 2 to 21 was sequestered in the endoplasmic reticulum but remained strongly associated with the oocyte membranes rather than being secreted. Removal of amino acids 231 to 279, a region previously reported to have membrane-insertion function, resulted in a protein that also entered the endoplasmic reticulum but was not secreted. Hybrid proteins containing at their N terminus amino acids 9 to 41 or 22 to 41 of ovalbumin fused to the complete chimpanzee alpha-globin polypeptide were also sequestered by oocyte membranes. We conclude that the ovalbumin "signal" sequence is internally located within amino acids 22 to 41, and we speculate that amino acids 9 to 21 could be important for the completion of ovalbumin translocation through membranes.

Gdf16, a novel member of the growth/differentiation factor subgroup of the TGF-beta superfamily, is expressed in the hindbrain and epibranchial placodes.

We have isolated and characterized the developmental expression of Xenopus gdf16, a novel member of the growth/differentiation factor (gdf) gene family. The gdf16 gene encodes a pre-proprotein of 413 amino acids and a mature peptide of 122 amino acids. Gdf16 is most closely related to the zebrafish genes dynamo and radar, but exhibits a completely different expression pattern. Gene expression is detected at early tailbud (stage 25) in the first two epibranchial placodes and in a hindbrain-specific domain. As development proceeds, the gene is expressed in all the epibranchial placodes, the hindbrain, and the diencephalon.

The XHex homeobox gene is expressed during development of the vascular endothelium: overexpression leads to an increase in vascular endothelial cell number.

The Hex/Prh homeobox gene is expressed in a subset of adult blood cell types and may play a role in the differentiation of the myeloid and B-cell lineages. In a search for homeobox genes involved in cardiovascular development, we have independently isolated a Xenopus laevis cDNA which appears to be the amphibian orthologue of Hex/Prh. Based on high sequence similarity in a number of regions, particularly the critical homeobox, we have named this gene XHex. This developmentally regulated gene is first expressed in the dorsal endomesoderm of the gastrula stage embryo. This tissue goes on to contribute to the structures of the embryonic liver and XHex continues to be expressed in the liver throughout development. From the tailbud stage, XHex is expressed in vascular endothelial cells throughout the developing vascular network. Vascular expression of XHex is transient and commences slightly after expression of the receptor tyrosine kinase gene, flk-1, which is known to be essential for vascular development. This observation raises the possibility that XHex is one of the transcription factors that responds to the VEGF/Flk-1 signal transduction pathway leading to differentiation of vascular endothelial cells. XHex is unique amongst homeobox genes in displaying expression in the endothelial layer throughout the developing vasculature. Overexpression of XHex sequences in the frog embryo causes disruption to developing vascular structures and an increase in the number of vascular endothelial cells, suggesting a possible role in regulation of cell proliferation.

Developmental expression of the Xenopus Nkx2-1 and Nkx2-4 genes.

The homeodomain transcription factor Nkx2-1 (TTF-1) plays an essential role in the development of the thyroid, lung and ventral forebrain. We report the cloning and developmental expression patterns of two Xenopus NK-2 genes, Nkx2-1 and Nkx2-4, that are closely related to Nkx2-1. These genes show readily distinguishable expression patterns during development. Similar to its orthologues in chicken and mouse, the Xenopus Nkx2-1 gene is expressed in the developing thyroid, lung, and ventral forebrain. In contrast, expression of Nkx2-4 is specifically localized to the ventral diencephalon.

Transient cardiac expression of the tinman-family homeobox gene, XNkx2-10.

In Drosophila, the tinman homeobox gene is absolutely required for heart development. In the vertebrates, a small family of tinman-related genes, the cardiac NK-2 genes, appear to play a similar role in the formation of the vertebrate heart. However, targeted gene ablation of one of these genes, Nkx2-5, results in defects in only the late stages of cardiac development suggesting the presence of a rescuing gene function early in development. Here, we report the characterization of a novel tinman-related gene, XNkx2-10, which is expressed during early heart development in Xenopus. Using in vitro assays, we show that XNkx2-10 is capable of transactivating expression from promoters previously shown to be activated by other tinman-related genes, including Nkx2-5. Furthermore, Xenopus Nkx2-10 can synergize with the GATA-4 and SRF transcription factors to activate reporter gene expression.

The RNA-binding protein gene, hermes, is expressed at high levels in the developing heart.

In a screen for novel sequences expressed during embryonic heart development we have isolated a gene which encodes a putative RNA-binding protein. This protein is a member of one of the largest families of RNA-binding proteins, the RRM (RNA Recognition Motif) family. The gene has been named hermes (for HEart, RRM Expressed Sequence). The hermes protein is 197-amino acids long and contains a single RRM domain. In situ hybridization analysis indicates that hermes is expressed at highest levels in the myocardium of the heart and to a lesser extent in the ganglion layer of the retina, the pronephros and epiphysis. Expression of hermes in each of these tissues begins at approximately the time of differentiation and is maintained throughout development. Analysis of the RNA expression of the hermes orthologues from chicken and mouse reveals that, like Xenopus, the most prominent tissue of expression is the developing heart. The sequence and expression pattern of hermes suggests a role in post-transcriptional regulation of heart development.

Two neural-cell adhesion molecule (NCAM)-encoding genes in Xenopus laevis are expressed during development and in adult tissues.

Expression of genes encoding neural-cell adhesion molecules (NCAM) is regulated to a large extent at the level of alternative splicing. Xenopus laevis contains two functional copies of the NCAM gene and comparison of the amino acid sequences of NCAM proteins derived from both genes shows that they differ at approximately 8% of positions. Differential expression of these proteins during development or in adult tissues could provide an additional level of regulation above that obtained by alternative splicing. PCR analysis however, shows that both NCAM genes are expressed at similar levels throughout embryonic development and in all adult tissues examined.

pXeX, a vector for efficient expression of cloned sequences in Xenopus embryos.

We describe the construction of pXeX, a plasmid vector that efficiently expresses cloned sequences in Xenopus embryos. This plasmid contains the transcription regulatory regions from the Xenopus laevis elongation factor-1 alpha-encoding gene (EF-1 alpha). Expression of cloned sequences commences in blastula-stage embryos, coincident with transcriptional activation of the embryonic genome, and transcripts may persist until the tadpole stage of development.

Remarkable sequence conservation of transcripts encoding amphibian and mammalian homologues of quaking, a KH domain RNA-binding protein.

Mutations in the mouse quaking locus can result in two different types of developmental phenotypes: (1) a deficiency of myelin in the central nervous system that is accompanied by a characteristic tremor, or (2) embryonic lethality around day 9 of gestation. A quaking candidate gene (qkI) that encodes a KH motif protein has recently been identified. We have isolated and characterized cDNAs encoding the Xenopus quaking homologue (Xqua) and also assembled an almost complete human quaking sequence from expressed sequence tags. Sequence comparisons show that the amphibian and mammalian quaking transcripts exhibit striking conservation, both within the coding region and, unexpectedly, in the 3' UTR. Two Xqua transcripts 5 kb and 5.5 kb in length are differentially expressed in the Xenopus embryo, with the 5 kb transcript being detected as early as the gastrula stage of development. Using an in vitro assay, we have demonstrated RNA-binding activity for quaking protein encoded by the 5 kb transcript. Overall, the high sequence conservation of quaking sequences suggests an important conserved function in vertebrate development, probably in the regulation of RNA metabolism.

Murine 12(R)-lipoxygenase: functional expression, genomic structure and chromosomal localization.

A cDNA, recently cloned (by Krieg et al. (1998)) from mouse skin, was shown to encode a 12(R)-lipoxygenase. When expressed in HEK cells, the recombinant protein converted methyl arachidonate into the corresponding 12-HETE ester which was shown to be the R-enantiomer by chiral phase chromatography. Neither arachidonic acid nor linoleic acid were substrates for the recombinant protein. The structure of the 12(R)-lipoxygenase gene is unique among all animal lipoxygenases in that it is divided into 15 exons and 14 introns spanning approximately 12.5 kb. By interspecific backcross analysis, the 12(R)-lipoxygenase gene was localized to the central region of mouse chromosome 11.

Murine epidermal lipoxygenase (Aloxe) encodes a 12-lipoxygenase isoform.

Using a combination of conventional screening procedures and polymerase chain reaction cloning, we have isolated a cDNA encoding an epidermis-type 12-lipoxygenase (e12-lipoxygenase) from mouse epidermis. The open reading frame corresponds to a protein of 662 amino acids and was found to be 99.8% identical to the ORF of an epidermal lipoxygenase gene Aloxe, described recently [Van Dijk et al. (1995) Biochim. Biophys. Acta 1259, 4-8]. When expressed in human embryonic kidney cells the recombinant protein could be shown to synthesize 12(S)-HETE from arachidonic acid. By fluorescence in situ hybridization the e12-lipoxygenase gene was localized to chromosome band 11 B1-B3.

Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins.

The development of an efficient expression system for insulin-like growth factor-I (IGF-I) in Escherichia coli as a fusion protein is described. The fusion protein consists of an N-terminal extension made up of the first 46 amino acids of methionyl porcine GH ([Met1]-pGH) followed by the dipeptide Val-Asn. The latter two residues provide a unique hydroxylamine-sensitive link between [Met1]-pGH(1-46) and the N-terminal Gly of IGF-I. Downstream processing of the fusion proteins involved isolation of inclusion bodies, cleavage at the Asn-Gly bond, refolding of the reduced IGF-I peptide and purification to homogeneity. This expression system was also used to produce two variants of IGF-I in which Glu3 was substituted by either Gly or Arg to give [Gly3]-IGF-I and [Arg3]-IGF-I respectively. Production of milligram quantities of IGF-I peptide was readily achieved. The purity of the IGF-I, [Gly3]-IGF-I and [Arg3]-IGF-I was established by high-performance liquid chromatography and N-terminal sequence analysis. [Gly3]-IGF-I and [Arg3]-IGF-I were more potent than IGF-I in biological assays measuring stimulation of protein synthesis and DNA synthesis or inhibition of protein breakdown in rat L6 myoblasts. Both analogues bound very poorly to bovine IGF-binding protein-2 and slightly less well than IGF-I to the type-1 receptor on rat L6 myoblasts. We conclude that reduced binding to IGF-binding proteins rather than increased receptor binding is the likely explanation for the greater biological potency of the analogues compared with IGF-I.