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Genes expressed during conidiation in Neurospora crassa: molecular characterization of con-13.

Asexual development in Neurospora crassa proceeds through a series of discrete morphological stages that culminate in the production of dormant spores called conidia. Changes in the pattern of gene expression parallel the morphological transformations associated with conidiation. As a prerequisite to the analysis of developmental gene expression in N. crassa, several genes of unknown function that are preferentially expressed during conidiation were isolated [Berlin and Yanofsky, Mol. Cell. Biol. 5 (1985) 849-855]. The molecular structure and nucleotide sequence of one of these genes, designated con-13, is presented. The con-13 gene specifies a relatively rare 1.35-kb message which is first detected about 8 h following the induction of conidiation. Sequence analysis of both cDNA and genomic clones indicates that the con-13 gene consists of three exons divided by two small introns. It encodes a polypeptide of 340 amino acid residues (37.1 kDa). The Con-13 protein is weakly acidic and hydrophilic. A comparison of the regions upstream from the con-8, con-10, and con-13 genes revealed several short sequence motifs which may be important in developmental gene regulation.

Amino Acid Sequence↗

Introduction of a viral thymidine kinase gene and the human beta-globin gene into developmentally multipotential mouse teratocarcinoma cells.

Teratocarcinoma (TCC) stem cells provide unique prospects for the introduction of specific genes into mice, by virtue of their dual capacity for propagation in vitro and for normal differentiation in embryos. In this study, we have demonstrated that foreign genes amenable to selection in culture can be transferred into the stem cells and expressed. These cells maintain expression of the gene for long periods during differentiation in tumors in vivo in the absence of selective pressure. The cells also integrate an unlinked nonselectable gene at high frequency. Addition of the cloned herpes simplex virus (HSV) thymidine kinase (tk; ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) gene to cultures of tk(-)TCC cells yielded tk(+) colonies at a frequency of one colony per 4 mug of plasmid DNA. This transformation efficiency, although appreciably lower than for mouse L tk(-) cells, permits the isolation of many transformants. The HSV provenance of the transformed phenotype was verified by the characteristic electrophoretic mobility of the tk protein and by neutralization of the tk activity with specific antiserum. Moreover, blot hybridization tests revealed at least one intact copy of the viral tk gene integrated into the DNA of transformed cells. When injected into syngeneic mice, the cells formed solid tumors with various differentiating tissues. From blot hybridization comparisons with their cell lines of origin, seven of nine tumors examined had maintained the HSV tk gene without significant loss or rearrangement. Viral tk enzyme activity could also be demonstrated in at least some of the tumors. Cotransfer of the cloned human beta-globin gene along with the unlinked HSV tk gene was successful in 2 of 10 tk(+) transformants. Thus, defined genes can be stably introduced into TCC cells in culture and maintained in vivo in a form in which they are transcribed and translated to produce a functional protein.

Animals↗

Soybean seed lectin gene and flanking nonseed protein genes are developmentally regulated in transformed tobacco plants.

We introduced a 17.1-kilobase soybean DNA fragment containing the lectin gene and at least four nonseed protein genes into the tobacco genome. As in soybean plants, lectin mRNA is present in tobacco seeds, accumulates and decays during tobacco seed development, and is translated into a protein that accumulates prior to dormancy. Each soybean nonseed protein mRNA is present in tobacco leaves, roots, stems, and seeds at levels similar to that found in soybean plants. We conclude that a differentially expressed soybean gene cluster is correctly regulated in transformed tobacco plants and that sequences controlling their expression are recognized by regulatory factors present in tobacco cells.

Gene Expression Regulation↗

Highly efficient generation of signal transduction knockout mutants using a fungal strain deficient in the mammalian ku70 ortholog.

Targeted gene replacement via homologous recombination is a routinely used approach to elucidate the function of unknown genes. Integration of exogenous DNA in the genomic DNA requires the action of double-strand repair mechanisms. The filamentous ascomycete Sordaria macrospora is a model system for studying fruiting body development in fungi. In contrast to the budding yeast Saccharomyces cerevisiae, but similar to many filamentous fungi, plants and animals, transformed DNA is ectopically integrated into the genome of S. macrospora. Most probably this occurs by non-homologous end joining (NHEJ), a mechanism that involves the binding of the Ku heterodimer (Ku70/Ku80) at the ends of a DNA double-strand break (DSB). Phylogenetic analysis of Ku70 orthologs of fungal, plant, and animal origin reveals that the Ku70 protein is well conserved among eukaryotes. To improve gene targeting efficiency in S. macrospora, we identified and deleted the S. macrospora ku70 gene. No impairment of the Deltaku70 mutant in vegetative or fruiting body nor ascospore development was observed making this strain an ideal recipient for gene targeting of developmental genes. As a case study, the S. macrospora Deltaku70 strain was used for targeted deletion of the pheromone gene ppg2 and the pheromone receptor gene pre2. PCR generated deletion constructs containing 1000 bp of homologous flanking sequence resulted in a drastically increased gene targeting efficiency. As a consequence, almost all transformants generated carried a disrupted target gene.

Amino Acid Sequence↗

Production of a mutation in mouse En-2 gene by homologous recombination in embryonic stem cells.

A full understanding of the function of genes that control developmental events can be obtained only by a combination of molecular and mutational analysis. One putative developmental gene is the mouse engrailed-like gene En-2, which was isolated by virtue of its extensive homology to Drosophila engrailed, which contributes to the control of segmentation in the developing insect. Our hybridization analysis in situ has revealed that expression of En-2 is restricted to a specific domain of the developing central nervous system from 8 days of development on, indicating a role for the gene in establishing spatial domains in the brain. Unfortunately no En-2 mutations are available to elucidate further its function in development. To this end, we report here the isolation of three pluripotent embryonic stem cell lines in which one copy of the homoeobox-containing gene, En-2, has been altered by homologous recombination.

Animals↗

Evolutionary conservation pattern of zinc-finger domains of Drosophila segmentation genes.

A number of genes of the developmental gene hierarchy in Drosophila encode transcription factors containing Cys2His2 zinc finger domains as DNA-binding motifs. To learn more about the evolution of these genes, it is necessary to clone the homologs, or more correctly the orthologs, from different species. Using PCR, we were able to obtain apparently orthologous fragments of hunchback (hb), Krüppel (Kr), and snail (sna) from a variety of arthropods and partly also from other animal phyla. Sequence alignments of these fragments show that the amino acid differences can normally not be correlated with the evolutionary distances of the respective species. This is due to an apparent saturation of potential replacements within the finger domains, which is also evident from the frequent occurrence of convergent replacements. Another recurrent feature of these alignments is that those amino acids that are directly involved in determining the DNA-binding specificity of the fingers are most conserved. Using in vitro bandshift experiments we can indeed show that the binding specificity of a hunchback finger fragment from different species is not changed. This implies that there is a high selective pressure to maintain the regulatory target elements of these genes during evolution.

Amino Acid Sequence↗

A genomewide survey of developmentally relevant genes in Ciona intestinalis. VI. Genes for Wnt, TGFbeta, Hedgehog and JAK/STAT signaling pathways.

Cell-cell interactions play important roles in a variety of developmental processes, and therefore molecules involved in the signaling pathways have been studied extensively. Recently, the draft genome sequence of the basal chordate, Ciona intestinalis, was determined. Here we annotated genes for the signaling pathways of Wnt, transforming growth factor beta (TGFbeta), Hedgehog, and JAK/STAT in the genome of Ciona intestinalis. The Ciona genome contains ten wnt genes, six frizzled genes, four sFRP genes, ten TGFbeta family member genes, five TGFbeta-receptor genes, and five Smad genes; most of the genes were found with less redundancy than in vertebrate genomes. The other genes in the signaling pathways are present as a single copy in the Ciona genome. In addition, all of the identified genes for the signaling pathway, except for a few genes, have EST evidence, and their cDNAs are available from the Ciona intestinalis gene collection. Therefore, Ciona intestinalis may provide an experimental system for exploring the basic genetic cascade associated with the signaling pathways in chordates.

Animals↗

Identification of a set of genes with developmentally down-regulated expression in the mouse brain.

Using a subtraction cloning approach, we have isolated a set of cDNA clones from mouse neural precursor cells whose respective mRNA levels are down-regulated during the development of mouse brain. Single stranded DNA prepared from neuronal precursor cell cDNA library in lambda Zap vector was subtracted with poly (A)+ RNA prepared from postnatal and adult mouse brain to obtain several clones which show developmental down-regulation of expression. Their patterns of expression indicate that these genes may play important roles during the embryonic development and differentiation of central nervous system.

Aging↗

A gene for Crouzon craniofacial dysostosis maps to the long arm of chromosome 10.

Crouzon craniofacial dysostosis (CFD) is an autosomal dominant craniofacial disorder characterized by premature craniosynostosis, shallow orbits and hypoplastic maxilla. To map the gene responsible, we have used a mapping strategy of testing for linkage to known developmental genes. Analysis of a large kindred established linkage between CFD and three loci (D10S190, D10S209 and D10S216) that span a 13 cM region on chromosome 10q. A maximum pairwise lod score of 4.42 (theta = 0) at D10S190 was obtained and the addition of a second kindred produced a combined pairwise lod score of 5.32 (theta = 0) at the same locus. The developmental gene, PAX2, located within this region, is an attractive candidate gene.

Chromosome Mapping↗

Evolution of yellow gene regulation and pigmentation in Drosophila.

BACKGROUND: Changes in developmental gene expression are central to phenotypic evolution, but the genetic mechanisms underlying these changes are not well understood. Interspecific differences in gene expression can arise from evolutionary changes in cis-regulatory DNA and/or in the expression of trans-acting regulatory proteins, but few case studies have distinguished between these mechanisms. Here, we compare the regulation of the yellow gene, which is required for melanization, among distantly related Drosophila species with different pigment patterns and determine the phenotypic effects of divergent Yellow expression. RESULTS: Yellow expression has diverged among D. melanogaster, D. subobscura, and D. virilis and, in all cases, correlates with the distribution of black melanin. Species-specific Yellow expression patterns were retained in D. melanogaster transformants carrying the D. subobscura and D. virilis yellow genes, indicating that sequence evolution within the yellow gene underlies the divergence of Yellow expression. Evolutionary changes in the activity of orthologous cis-regulatory elements are responsible for differences in abdominal Yellow expression; however, cis-regulatory element evolution is not the sole cause of divergent Yellow expression patterns. Transformation of the D. melanogaster yellow gene into D. virilis altered its expression pattern, indicating that trans-acting factors that regulate the D. melanogaster yellow gene have also diverged between these two species. Finally, we found that the phenotypic effects of evolutionary changes in Yellow expression depend on epistatic interactions with other genes. CONCLUSIONS: Evolutionary changes in Yellow expression correlate with divergent melanin patterns and are a result of evolution in both cis- and trans-regulation. These changes were likely necessary for the divergence of pigmentation, but evolutionary changes in other genes were also required.

Animals↗

Developmentally regulated gene expression of the small heat shock protein Hsp27 in zebrafish embryos.

Mammalian small heat shock proteins including Hsp27 and alpha-B crystallin are constitutively expressed in various adult and embryonic tissues including skeletal and cardiac muscle. However, the function of these proteins during embryonic development is not understood, and information on their expression during the earliest stages of development is limited. We have recently demonstrated constitutive and stress inducible expression of a homologue of human Hsp27 in adult zebrafish, an important experimental model of vertebrate developmental processes. Here, we assessed the temporospatial dynamics of zebrafish Hsp27 (hsp27) and alpha-B crystallin (cryab) gene expression using reverse-transcriptase PCR (RT-PCR) and hsp27 expression by in situ hybridization. Our results reveal that initial upregulation of hsp27 expression occurs during early gastrulation. Expression of hsp27 is detected transiently in developing myotomes, lens and brain, and more persistently in developing heart. The constitutive expression level of hsp27 in embryos at some stages of development is considerably greater than that observed in unstressed adult tissues. Expression of hsp27 was also observed in all tissues examined in embryos recovering from heat stress. The pattern of expression observed for hsp27 overlaps partially, but not completely, with that reported for other heat shock proteins.

Animals↗

Cross-species microarray hybridization to identify developmentally regulated genes in the filamentous fungus Sordaria macrospora.

The filamentous fungus Sordaria macrospora forms complex three-dimensional fruiting bodies that protect the developing ascospores and ensure their proper discharge. Several regulatory genes essential for fruiting body development were previously isolated by complementation of the sterile mutants pro1, pro11 and pro22. To establish the genetic relationships between these genes and to identify downstream targets, we have conducted cross-species microarray hybridizations using cDNA arrays derived from the closely related fungus Neurospora crassa and RNA probes prepared from wild-type S. macrospora and the three developmental mutants. Of the 1,420 genes which gave a signal with the probes from all the strains used, 172 (12%) were regulated differently in at least one of the three mutants compared to the wild type, and 17 (1.2%) were regulated differently in all three mutant strains. Microarray data were verified by Northern analysis or quantitative real time PCR. Among the genes that are up- or down-regulated in the mutant strains are genes encoding the pheromone precursors, enzymes involved in melanin biosynthesis and a lectin-like protein. Analysis of gene expression in double mutants revealed a complex network of interaction between the pro gene products.

Blotting, Northern↗

Discovery of genes expressed in Hydra embryogenesis.

Hydra's remarkable capacity to regenerate, to proliferate asexually by budding, and to form a pattern de novo from aggregates allows studying complex cellular and molecular processes typical for embryonic development. The underlying assumption is that patterning in adult hydra tissue relies on factors and genes which are active also during early embryogenesis. Previously, we reported that in Hydra the timing of expression of conserved regulatory genes, known to be involved in adult patterning, differs greatly in adults and embryos (Fröbius, A.C., Genikhovich, G., Kürn, U., Anton-Erxleben, F. and Bosch, T.C.G., 2003. Expression of developmental genes during early embryogenesis of Hydra. Dev. Genes Evol. 213, 445-455). Here, we describe an unbiased screening strategy to identify genes that are relevant to Hydra vulgaris embryogenesis. The approach yielded two sets of differentially expressed genes: one set was expressed exclusively or nearly exclusively in the embryos, while the second set was upregulated in embryos in comparison to adult polyps. Many of the genes identified in hydra embryos had no matches in the database. Among the conserved genes upregulated in embryos is the Hydra orthologue of Embryonic Ectoderm Development (HyEED). The expression pattern of HyEED in developing embryos suggests that interstitial stem cells in Hydra originate in the endoderm. Importantly, the observations uncover previously unknown differences in genes expressed by embryos and polyps and indicate that not only the timing of expression of developmental genes but also the genetic context is different in Hydra embryos compared to adults.

Animals↗

Protection of Xenopus laevis embryos against alcohol-induced delayed gut maturation and growth retardation by peroxiredoxin 5 and catalase.

Accumulated evidence indicates that maternal alcohol consumption causes fetal enteric damage and growth retardation. In this study, we investigated the underlying molecular mechanisms in a Xenopus model of fetal alcohol exposure. We established a condition of transient alcohol exposure that produces tadpoles with delayed gut maturation and decreased body length. We then investigated the roles of reactive oxygen species (ROS) and reactive nitrogen species (RNS) by microinjecting plasmids expressing catalase and peroxiredoxin 5 (PRDX5) into two-cell stage embryos. Finally, the effects of these enzymes on the expression of key gut developmental genes were determined by animal cap explant assay. We showed that exposure of Xenopus embryos to 0.5% alcohol from stage 13 to stage 22 produced tadpoles with delayed gut maturation, reduced growth, and down-regulation in several gut developmental genes, with VegT, Pax6 and Sox17 most vulnerable. We further demonstrated that microinjection of catalase attenuated alcohol-induced ROS production and restored the expression of VegT and Pax6, but protected the embryos from delayed gut development and retarded growth only partially. By contrast, microinjection of PRDX5 reduced both ROS and RNS production, and prevented the gut and growth defects, and restored VegT, Pax6 and Sox17 gene expression. A positive correlation was found between delayed gut maturation and reduced body length. These results indicate the crucial roles of both the ROS-Pax6 and RNS-Sox17 signaling axes in alcohol-induced fetal gut defects and growth retardation. In addition, they suggest strongly a cause-and-effect relationship between alcohol-induced delayed gut maturation and growth retardation.

Animals↗

Visualization of gene expression in living adult Drosophila.

To identify genes involved in the patterning of adult structures, Gal4-UAS (upstream activating site) technology was used to visualize patterns of gene expression directly in living flies. A large number of Gal4 insertion lines were generated and their expression patterns were studied. In addition to identifying several characterized developmental genes, the approach revealed previously unsuspected genetic subdivisions of the thorax, which may control the disposition of pattern elements. The boundary between two of these domains coincides with localized expression of the signaling molecule wingless.

Animals↗

Genetic research in embryology.

Based on findings on the molecular mechanisms of differentiation in drosophila, developmental genes have been identified in mammals similar to those in drosophila. Moreover, sequence similarities between drosophila developmental genes and mammalian growth factors provide evidence for common ancestors of such genes and suggest a complex link between growth and differentiation. As numerous oncogenes display their action as growth factors and are expressed during embryogenesis, differentiation and oncogenesis seem to be two sides of the same coin. Therefore, the aim of molecular embryology is twofold; elucidating differentiation processes and disclosing oncogenesis by studying the physiological function of oncogenes during development. Recent progress in molecular genetic technology now allows gene function to be studied by modification or disruption of genes. Models of clinical diseases have already evolved from such work and it is anticipated that progress in molecular embryology will further stimulate work on the diagnosis and therapy of genetic diseases as well as clinical oncology.

Animals↗

Murine Pkd1 is a developmentally regulated gene from morula to adulthood: role in tissue condensation and patterning.

PKD1 is the most common genetically mutated gene involved in autosomal dominant polycystic kidney disease (ADPKD). Our previous studies have shown that the pathogenesis of human and murine polycystic kidney disease (PKD) involves failure to switch out of a renal developmental program, suggesting a role for PKD1 in development. To investigate this hypothesis, we have cloned a portion of the murine Pkd1 gene and characterized the fetal to adult tissue expression pattern of Pkd1. We chose to clone the transmembrane region of Pkd1, a region prone to mutations in ADPKD. The transmembrane coding region (2.6 kb) has 80.3% nucleotide homology with human PKD1 and 85.3% amino acid similarity. The cloned murine Pkd1 fragment closely resembles that of human PKD1 with respect to both genomic size and exon/intron position. We have demonstrated that this Pkd1 region is not conserved in lower organisms and is mammalian specific. A detailed expression analysis of Pkd1 revealed expression as early as the morula stage and in ES cells with differential expression levels in various tissues/organs throughout development. Highest expression levels were observed in the early condensing mesenchyme of primitive mesoderm and ectoderm. Pkd1 was also expressed at high levels in developing neural tube, neural crest derivatives, prechondrogenic tissue, metanephros, bladder, salivary glands, lung, and blood vessels with lower expression levels in other organs and tissues. Specific spatial and temporal patterns of Pkd1 expression were demonstrated in individual organs, such as lung, kidney, brain, indicating it is highly developmentally regulated. Particularly high levels persisted in mature derivatives of neural tube, neural crest, chondrogenic tissue, metanephros, and lung. In summary, our data suggest that Pkd1 has at least two cellular functions, one a basic function involved in early tissue condensation processes, and the other a mammalian-specific function, that evolved with tissue patterning and tubulogenesis in metanephric and pulmonary development.

Animals↗