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PubMed2001

Gene expression studies on human primordial germ cells and preimplantation embryos.

Research on the regulation of gene expression in human germ cells and preimplantation embryos is restricted due to the scarcity of samples and the requirement for highly sensitive molecular techniques to investigate the few cells available. To overcome these difficulties, we have developed a reliable procedure capable of generating amplified cDNA preparations from single cells. Using this procedure, we prepared cDNA from primordial germ cells (PGCs) isolated from the gonads of fetuses at 10 weeks gestation and from preimplantation embryos at the 1-cell, 4-cell, 8-cell and blastocyst stages. Our cDNA preparations allow us to investigate the expression profile of an almost unlimited number of different genes in the same sample preparation. This is of great advantage for studies of a panel of genes in a particular family or functional group, or with related mechanisms of regulation, e.g., developmental genes, oncogenes, cell cycle-control genes and imprinted genes. We have used these cDNA preparations in conjunction with differential display to identify genes specifically expressed in PGCs and preimplantation embryos in a sex- and developmental stage-specific manner. Genes specifically expressed in PGCs, oocytes and embryos were further analysed for their expression in embryonal carcinoma cells and in their differentiated derivatives following treatment by retinoic acid. Our strategy will disclose genes essential for gametogenesis and embryonic development which may only be expressed at certain stages of their development. The germ cell- and embryo-specific cDNA molecules, cDNA libraries and microarrays are a valuable resource for other researchers in this field.

Blastocyst↗
PubMed2003

Isolation of human NURF: a regulator of Engrailed gene expression.

The modification of chromatin structure is an important regulatory mechanism for developmental gene expression. Differential expression of the mammalian ISWI genes, SNF2H and SNF2L, has suggested that they possess distinct developmental roles. Here we describe the purification and characterization of the first human SNF2L-containing complex. The subunit composition suggests that it represents the human ortholog of the Drosophila nucleosome-remodeling factor (NURF) complex. Human NURF (hNURF) is enriched in brain, and we demonstrate that it regulates human Engrailed, a homeodomain protein that regulates neuronal development in the mid-hindbrain. Furthermore, we show that hNURF potentiates neurite outgrowth in cell culture. Taken together, our data suggess a role for an ISWI complex in neuronal growth.

Adenosine Triphosphatases↗
PubMed2006

Casting a genetic light on the evolution of eyes.

Light has been exploited for information by organisms through the evolution of photoreceptors and, ultimately, eyes in animals. Only a handful of eye types exist because the physics of light constrains photodetection. In the past few years, genetic tools have revealed several parallel pathways through which light guides behavior and have provided insights into the convergent evolution of eyes. The gene encoding opsin (the primary phototransduction protein) and some developmental genes had very early origins and were recruited repeatedly during eye evolution. Eye lens proteins arose separately and make up a diverse group, many of which were co-opted from other functions. A major challenge now is understanding how newly discovered pathways for processing light evolved and how they collaborate with eyes to harvest information from light.

Animals↗
PubMed2004

Regulated gene expression of hyaluronan synthases during Xenopus laevis development.

Here reported is the developmental gene expression pattern of the three known vertebrate hyaluronan synthases (XHas1, XHas2 and XHas3) and a comparative analysis of their mRNAs spatio-temporal distribution during Xenopus laevis development. We found that while XHas2 shows a steady-state expression from gastrula to late tailbud stage, XHas1 is mainly present in the early phases of development while XHas3 is predominantly transcribed in tailbud embryos. XHas1, XHas2 and XHas3 show distinct tissue expression patterns. In particular, XHas1 is localized in ectodermal derivatives and in cranial neural crest cells, whereas XHas2 is mainly found in mesoderm-derived structures and in trunk neural crest cells. Moreover, the expression pattern of XHas2 overlaps that of MyoD in cells committed to a muscle fate. Unlike the other hyaluronan synthases, XHas3 mRNA distribution is very restricted. In particular, XHas3 is expressed in the otic vesicles and closely follows the inner ear development. In conclusion, XHas1, XHas2 and XHas3 mRNAs have distinct and never overlapping spatial expression domains, which would suggest that these three enzymes may play different roles during embryogenesis.

Animals↗
PubMed1991

Identification of a second human nm23 gene, nm23-H2.

Reduced RNA and/or protein levels corresponding to the murine nm23-1 and human nm23-H1 complementary DNA clones have been correlated with high tumor metastatic potential in several rodent model systems and human breast carcinomas. We report the identification of a second human nm23 gene, designated nm23-H2. The pNM23-H2S complementary DNA clone predicted a Mr 17,000 protein 88% identical to nm23-H1. nm23-H2 also shared a significant homology with nucleoside diphosphate kinases and a Drosophila developmental gene. Southern blots containing BglII-restricted genomic DNA, which exhibited an allelic restriction fragment length polymorphism for nm23-H1, contained nonallelic bands upon rehybridization to the nm23-H2 probe. Thus, nm23-H1 and nm23-H2 are distinct genes. Northern blot hybridization of nm23-H1- and nm23-H2-specific probes to breast tumors and cell lines indicated that nm23-H1 expression was reduced in high metastatic potential tumor cells to a greater extent than nm23-H2. The data indicate the existence of a family of independently regulated nm23 genes.

Amino Acid Sequence↗
PubMed1994

Developmental decisions in Dictyostelium discoideum.

A few hours after the onset of starvation, amoebae of Dictyostelium discoideum start to form multicellular aggregates by chemotaxis to centers that emit periodic cyclic AMP signals. There are two major developmental decisions: first, the aggregates either construct fruiting bodies directly, in a process known as culmination, or they migrate for a period as "slugs." Second, the amoebae differentiate into either prestalk or prespore cells. These are at first randomly distributed within aggregates and then sort out from each other to form polarized structures with the prestalk cells at the apex, before eventually maturing into the stalk cells and spores of fruiting bodies. Developmental gene expression seems to be driven primarily by cyclic AMP signaling between cells, and this review summarizes what is known of the cyclic AMP-based signaling mechanism and of the signal transduction pathways leading from cell surface cyclic AMP receptors to gene expression. Current understanding of the factors controlling the two major developmental choices is emphasized. The weak base ammonia appears to play a key role in preventing culmination by inhibiting activation of cyclic AMP-dependent protein kinase, whereas the prestalk cell-inducing factor DIF-1 is central to the choice of cell differentiation pathway. The mode of action of DIF-1 and of ammonia in the developmental choices is discussed.

Ammonia↗
PubMed1992

A developmentally regulated chlamydial gene with apparent homology to eukaryotic histone H1.

We have developed a method for the isolation of genes whose expression is developmentally regulated from the murine strain of Chlamydia trachomatis. Here we describe the identification of two developmental stage-specific genes, one of which is predicted to encode a 26-kDa lysine- and alanine-rich protein that appears to be homologous to several eukaryotic histone H1 proteins. A substantial proportion of this homology relates to its distinctive amino acid composition. No sequence homology was observed between this protein and other bacterial "histone-like" chromosomal proteins, but homology does exist with two other recently described prokaryotic proteins. The protein is expressed late in chlamydial development, during the transition from reticulate bodies to elementary bodies. The basic nature of the protein predicts that it could bind DNA, and Southwestern blotting experiments confirm this finding. These properties are consistent with a role either in the regulation of late gene expression or in the compaction of the chlamydial genome.

Amino Acid Sequence↗
PubMed2006

Temporal and spatial delineation of mouse Otx2 functions by conditional self-knockout.

To identify the independent spatial and temporal activities of the essential developmental gene the Otx2, the germline mutation of which is lethal at embryonic day 8.5, we floxed one allele and substituted the other with an inducible CreER recombinase gene. This makes 'trans' self-knockout possible at any developmental stage. The transient action of tamoxifen pulses allows time-course mutation. We demonstrate efficient temporal knockout and demarcate spatio-temporal windows in which Otx2 controls the head, brain structures and body development.

Animals↗
PubMed1986

Sequence of the notch locus of Drosophila melanogaster: relationship of the encoded protein to mammalian clotting and growth factors.

The Notch locus is essential for proper differentiation of the ectoderm in Drosophila melanogaster. Notch corresponds to a 37-kilobase transcription unit that codes for a major 10.4-kilobase polyadenylated RNA. The DNA sequence of this transcription unit is presented, except for portions of the two largest intervening sequences. DNA sequences also were obtained from three Notch cDNA clones, allowing the 5' and 3' ends of the gene to be mapped, and the structures and locations of nine RNA coding regions to be determined. The major Notch transcript encodes a protein of 2,703 amino acids. The protein is probably associated with cell surfaces and carries an extracellular domain composed of 36 cysteine-rich repeating units, each of about 38 amino acids. The gene appears to have evolved by repeated tandem duplications of the DNA coding for the 38-amino-acid-long protein segments, followed by insertion of intervening sequences. These repeating protein segments are quite homologous to portions of mammalian clotting factors IX and X and to the product of the Caenorhabditis elegans developmental gene lin-12. They are also similar to mammalian growth hormones, typified by epidermal growth factor.

Amino Acid Sequence↗
PubMed1997

The MADS-box floral homeotic gene lineages predate the origin of seed plants: phylogenetic and molecular clock estimates.

Flower development in angiosperms is controlled in part by floral homeotic genes, many of which are members of the plant MADS-box regulatory gene family. The evolutionary history of these developmental genes was reconstructed using 74 loci from 15 dicot, three monocot, and one conifer species. Molecular clock estimates suggest that the different floral homeotic gene lineages began to diverge from one another about 450-500 mya, around the time of the origin of land plants themselves.

Arabidopsis↗
PubMed2006

Polycomb complexes and the propagation of the methylation mark at the Drosophila ubx gene.

Polycomb group proteins are transcriptional repressors that control many developmental genes. The Polycomb group protein Enhancer of Zeste has been shown in vitro to methylate specifically lysine 27 and lysine 9 of histone H3 but the role of this modification in Polycomb silencing is unknown. We show that H3 trimethylated at lysine 27 is found on the entire Ubx gene silenced by Polycomb. However, Enhancer of Zeste and other Polycomb group proteins stay primarily localized at their response elements, which appear to be the least methylated parts of the silenced gene. Our results suggest that, contrary to the prevailing view, the Polycomb group proteins and methyltransferase complexes are recruited to the Polycomb response elements independently of histone methylation and then loop over to scan the entire region, methylating all accessible nucleosomes. We propose that the Polycomb chromodomain is required for the looping mechanism that spreads methylation over a broad domain, which in turn is required for the stability of the Polycomb group protein complex. Both the spread of methylation from the Polycomb response elements, and the silencing effect can be blocked by the gypsy insulator.

Animals↗
PubMed1991

Microcycle conidiation and its genetic basis in Neurospora crassa.

Some wild isolates of Neurospora show microcycle conidiation in liquid culture under continuous agitation. Macroconidia from agar-grown mycelial cultures germinated in liquid and the germlings spontaneously produced conidia with no intervening mycelial phase. Three types of microcycle conidiation were seen among progeny of N. crassa Vickramam A x N. crassa a wild-type: (1) multinucleate blastoconidia produced by apical budding and septation, (2) multinucleate arthroconidia produced by holothallic septation and disarticulation of cells, and (3) uninucleate microconidia produced directly from conidiogenous cells of the germlings. Two genes were identified which control specific patterns of microcycle conidiogenesis. A single gene mcb in linkage group VR near al-3 (3.2% recombination) controls blastoconidiation. This gene is epistatic to gene mcm located in linkage group IIL, very near ro-7 (1.4%). mcm controls both microconidiation and arthroconidiation depending on temperature. Strains of genotype mcm produce microconidia almost exclusively at 18-22 degrees C, but arthroconidia with few or no microconidia at 30 degrees C. Because they result in rapid and synchronized conidiation in liquid culture, the two genes should be useful for studies of developmental gene regulation. mcm makes it possible to obtain large quantities of pure microconidia rapidly for experimentation.

Crossing Over, Genetic↗
PubMed1996

Genetic determination of coat color affects testicular steroidogenesis in the Mustela vison.

Coat color genes in mammals are known to be developmental genes with wide pleiotropic effects. The present study was undertaken to study testicular steroidogenesis in American Mink (Mustela vison) of various coat color phenotypes. No differences in testicular steroid levels were observed between fertile and infertile mink with the standard phenotype and genotype (BB jj MM PP). Mink with the opaline phenotype and genotype (bb mm pp), were found to have in their testes, 20-40% higher levels of progesterone, five times higher levels of 17-hydroxyprogesterone, and eight times higher levels of testosterone, than the corresponding values in other mink. No other differences were observed among the different types of mink. Since the genotype of the opaline mink differs from the other mink studied, only in their combination at the pastel (b) and moyle (m) loci, their bb mm genotype could be assumed to be responsible for the increase in testicular steroids.

17-alpha-Hydroxyprogesterone↗
PubMed2001

Gene imprinting in developmental toxicology: a possible interface between physiology and pathology.

Gene imprinting is an epigenetic mechanism for accomplishing persistent change in gene expression. In this brief paper, we explore the mechanisms for imprinting genes and present data showing that the synthetic estrogen, diethylstilbestrol (DES) can developmentally imprint genes by changing the pattern of DNA methylation. We further discuss the implications of this and other findings for non-mutagenic aspects of developmental toxicology, and suggest ways to use this concept in modifying in vitro screening for developmental toxicants.

Animals↗
PubMed2026

Mechanisms and functional implications of long-range enhancer-dependent gene regulation.

Metazoan development relies on the coordinated establishment of diverse gene regulatory programs that drive the formation of specific cell types, tissues and organs. The temporal and spatial control of gene expression is achieved through the concerted activity of multiple classes of cis-regulatory elements encoded in the genome. Among these, enhancers enable the establishment of specific and precise gene expression patterns and control gene expression over long linear distances, a property often referred to as distance-independent regulatory activity. However, enhancer activity is, in fact, inversely correlated with linear genomic distance, and target gene expression and transcriptional precision decrease with increasing enhancer-promoter linear distances. Here, we highlight emerging insights into multiple mechanisms that enable enhancers to precisely and robustly activate gene expression across large genomic distances. Finally, we provide a more speculative perspective on the potential advantages that long-range regulation might confer during the establishment of developmental gene expression programs.

Enhancer Elements, Genetic↗
PubMedDate not supplied

Association of histone H1(0) with a gene repressed during liver development.

Histone H1(0) has a number of unusual properties that set it apart from other H1 subtypes (for review see ref. 1). For example, H1(0) synthesis is not strictly coupled to DNA synthesis, it is absent from the embryonic liver of mice (but present shortly after birth) and its synthesis is hormone-dependent in some of the glands of adult rodents. All the H1 subtypes differ in their DNA binding properties, and H1(0) has been shown to be preferentially associated with nuclease-resistant chromatin. These features suggest that the H1(0) may have a role in developmental gene control. To investigate this further, we have fractionated the H1(0)-containing nucleosomes of chromatin from adult mouse liver. We report here that the gene for alpha-fetoprotein, which is expressed in embryonic tissue but repressed soon after birth, is preferentially associated with the H1(0)-containing nucleosomes. The related gene for albumin, which is expressed in both embryonic and adult tissues, is absent from the H1(0)-containing nucleosome fraction. These results support a role for histone H1(0) in the control of gene expression.

Albumins↗
PubMed2005

Changes in the extracellular proteome caused by the absence of the bldA gene product, a developmentally significant tRNA, reveal a new target for the pleiotropic regulator AdpA in Streptomyces coelicolor.

The extracellular proteome of Streptomyces coelicolor grown in a liquid medium was analyzed by using two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization-time of flight peptide mass fingerprint analysis. Culture supernatants became protein rich only after rapid growth had been completed, supporting the idea that protein secretion is largely a stationary phase phenomenon. Out of about 600 protein spots observed, 72 were characterized. The products of 47 genes were identified, with only 11 examples predicted to be secreted proteins. Mutation in bldA, previously known to impair the stationary phase processes of antibiotic production and morphological differentiation, also induced changes in the extracellular proteome, revealing even greater pleiotropy in the bldA phenotype than previously known. Four proteins increased in abundance in the bldA mutant, while the products of 11 genes, including four secreted proteins, were severely down-regulated. Although bldA encodes the only tRNA capable of efficiently translating the rare UUA (leucine) codon, none of the latter group of genes contains an in-frame TTA. SCO0762, a serine-protease inhibitor belonging to the Streptomyces subtilisin inhibitor family implicated in differentiation in other streptomycetes, was completely absent from the bldA mutant. This dependence was shown to be mediated via the TTA-containing regulatory gene adpA, also known as bldH, a developmental gene that is responsible for the effects of bldA on differentiation. Mutation of the SCO0762 gene abolished detectable trypsin-protease inhibitory activity but did not result in any obvious morphological defects.

Amino Acid Sequence↗
PubMed1991

Forespore-specific transcription of a gene in the signal transduction pathway that governs Pro-sigma K processing in Bacillus subtilis.

We present studies on the regulation of a developmental gene (spoIVB) whose product is required at a late stage of morphogenesis during the process of sporulation in Bacillus subtilis. Earlier work implicated the spoIVB gene product in a signal-transduction pathway that governs the conversion of pro-sigma K to the mature and active form of the mother cell sigma factor, sigma K, in response to a signal generated within the forespore chamber of the sporangium. We now show that (1) spoIVB is induced at the engulfment stage of sporulation, (2) this transcription is restricted to the forespore, and (3) spoIVB is under the direct control of the forespore sigma factor sigma G. The discovery that spoIVB is a forespore-expressed gene suggests that the spoIVB gene product, or a developmental event under its control, triggers the processing of pro-sigma K and thereby mediates the coupling of sigma K-directed gene expression in the mother cell to sigma G-directed gene expression in the forespore. We also show that spoIVB transcription is partially dependent on the action of the mother cell regulatory gene spoIIID, a finding that suggests that the transcription of certain forespore-expressed genes is influenced by events in the mother cell.

Bacillus subtilis↗