Differential expression of the members of the discoidin I multigene family during growth and development of Dictyostelium discoideum

Multiple regulatory genes control expression of a gene family during development of Dictyostelium discoideum

Mutant strains of Dictyostelium discoideum carrying dis mutations fail to transcribe specifically the family of developmentally regulated discoidin lectin genes during morphogenesis. The phenotypes of these mutants strongly suggested that the mutations reside in regulatory genes. Using these mutant strains, we showed that multiple regulatory genes are required for the expression of the lectin structural genes and that these regulatory genes (the dis+ alleles) act in trans to regulate this gene family. These regulatory genes fall into two complementation groups (disA and disB) and map to linkage groups II and III, respectively. A further regulatory locus was defined by the identification of an unlinked supressor gene, drsA (discoidin restoring), which is epistatic to disB, but not disA, and results in the restoration of lectin expression in cells carrying the disB mutation. Mutant cells carrying the drsA allele express the discoidin lectin gene family during growth and development, in contrast to wild-type cells which express it only during development. Therefore, the suppressor activity of the drsA allele appears to function by making the expression of the discoidin lectins constitutive and no longer strictly developmentally regulated. The data indicate that normal expression of the discoidin lectins is dependent on the sequential action of the disB+, drsA+, and disA+ gene products. Thus, we described an interacting network of regulatory genes which in turn controls the developmental expression of a family of genes during the morphogenesis of D. discoideum.

Analysis of gene expression in rapidly developing mutants of Dictyostelium discoideum

Developmentally regulated gene expression has been analyzed in the wild-type D. discoideum strain NC-4 and a series of temporally deranged mutants. The mutants include representatives from each class of rapid development mutation, Fr17(rdeA-) and HT506(rdeC-), and strain HIfm-1, which appears to be defective in the timing of events early in development. We have monitored four prespore-specific genes, three of which show coordinate expression in the wild type. The coordination is maintained in each of the mutant strains though the specific expression pattern varied from strain to strain. Likewise, a series of prestalk-specific genes have been analyzed. They also show coordinated expression in the wild type and in all of the mutants. The timing of expression, however, is different between the prestalk-specific and the prespore-specific with the overall pattern of expression being unique for each strain examined. These results confirm our previous suggestion that the major classes of prestalk- and prespore-specific genes are coordinately regulated and show that a great deal of tolerance is allowed in the timing of specific gene expression as it relates to terminal differentiation. In addition we have analyzed the expression of actin, discoidin I, and I42. These genes, or gene families, are preferentially expressed in either vegetatively growing cells or in cells during the early stages of development. As with the cell-type-specific genes, the pattern of expression of the three early gene classes is unique for each strain examined.

Developmental changes in the pattern of larval beta-globin gene expression in Xenopus laevis. Identification of two early larval beta-globin mRNA sequences

We have analysed beta-globin mRNA sequences in total RNA extracted from embryos and tadpoles of Xenopus laevis at different stages of development and we have identified the most abundantly transcribed beta-globin mRNA (beta T1). The entire nucleotide sequence of a cDNA clone corresponding to this mRNA is known. We have now identified the gene corresponding to this mRNA and we have determined the nucleotide sequences of its immediate 5'-flanking region. Using a DNA fragment from within the coding region of the cloned beta T1 cDNA we show, by primer extension analysis, that beta T1 mRNA is first detectable at stage 28-32 of development. This is the time at which the first presumptive erythropoietic tissue, the ventral blood island, becomes observable histologically. We show that two minor beta-globin genes, distinct from beta T1, are expressed during early stages of development, and that their expression ceases shortly after the beginning of the feeding stage. We term these two early larval genes beta E1 and beta E2. A third minor beta-globin gene is expressed during early development but, unlike beta E1 and beta E2, it is also expressed throughout subsequent larval development. We term this gene beta T2 and show that it corresponds to a gene previously termed beta LII. Finally, using a primer derived from the major adult beta-globin gene (beta 1), we have analysed the accumulation of the major adult beta-globin mRNA during larval development, and we show that this sequence does not accumulate to any significant level before metamorphosis.

Specific regulation of transcription of the discoidin gene family in Dictyostelium discoideum

Dictyostelium discoideum strains that carry the dis mutations fail to express the family of developmentally regulated discoidin lectin genes during morphogenesis. We show here that this absence of discoidin lectin expression is due to the failure to transcribe the discoidin genes. Furthermore, the dis mutations appear to affect only discoidin expression and not the expression of other proteins during development, as assessed by a two-dimensional gel analysis of pulse-labeled proteins and by the accumulation of developmentally regulated enzymes. The dis mutations appear to define trans-acting regulatory loci, the products of which act at the transcriptional level to control specifically the developmental expression of the discoidin gene family.

Specific regulation of transcription of the discoidin gene family in Dictyostelium discoideum

Dictyostelium discoideum strains that carry the dis mutations fail to express the family of developmentally regulated discoidin lectin genes during morphogenesis. We show here that this absence of discoidin lectin expression is due to the failure to transcribe the discoidin genes. Furthermore, the dis mutations appear to affect only discoidin expression and not the expression of other proteins during development, as assessed by a two-dimensional gel analysis of pulse-labeled proteins and by the accumulation of developmentally regulated enzymes. The dis mutations appear to define trans-acting regulatory loci, the products of which act at the transcriptional level to control specifically the developmental expression of the discoidin gene family.

Primary structure of human transferrin receptor deduced from the mRNA sequence

In vertebrates all iron is taken up via the carrier protein transferrin. The carrier first binds its receptor and the receptor-ligand complex is then internalized via coated pits. The transferrin receptor is a transmembrane glycoprotein (apparent molecular weight (MW) 180,000) composed of two disulphide-bonded sub-units (each of apparent MW 90,000) It contains three N-linked glycan units and is post-translationally modified with both phosphate and fatty acyl groups. Here we have determined the nucleotide sequence of the coding region of the human transferrin receptor mRNA and from this deduced the amino acid sequence of the protein. The receptor does not contain an N-terminal signal peptide but there is a membrane-spanning segment 62 amino acids from the N-terminus. It therefore has a somewhat unusual configuration with a small N-terminal cytoplasmic domain and a C-terminal extracellular domain of 672 amino acids.

Overproduction of discoidin I by a temperature-sensitive motility mutant of Dictyostelium discoideum

Dictyostelium discoideum MC2 is a temperature-sensitive motility mutant of AX3. Mutant cells are incapable of growth, phagocytosis, and migration under restrictive conditions (Kayman et al., J. Cell Biol. 92:705-711, 1982). We show here that at the restrictive temperature MC2 cells grown axenically or on bacteria synthesized excessive quantities of the lectin discoidin I. By two-dimensional gel electrophoresis and peptide mapping, the proteins overproduced by MC2 cells were indistinguishable from discoidin I synthesized at lower levels in AX3 cells. At least two of the three species of discoidin I were overproduced. This protein family constituted 9% of the total protein in cells that were incubated overnight at 27 degrees C in axenic medium. Although MC2 cells are defective in nutrient uptake under restrictive conditions, the overproduction of discoidin I did not appear to be part of a pleiotropic response to starvation. We propose that transcription of the coordinately regulated discoidin I genes is altered in mutant cells. This alteration may be related to the motility defects manifested by MC2.

Genomic instability and mobile genetic elements in regions surrounding two discoidin I genes of Dictyostelium discoideum

We have found that the genomic regions surrounding the linked discoidin I genes of various Dictyostelium discoideum strains have undergone rapid changes. Wild-type strain NC-4 has three complete discoidin I genes; its axenic derivative strain Ax-3L has duplicated a region starting approximately 1 kilobase upstream from the two linked genes and extending for at least 8 kilobases past the genes. A separately maintained stock, strain Ax-3K, does not have this duplication but has undergone a different rearrangement approximately 3 kilobases farther upstream. We show that there are repeat elements in these rapidly changing regions. At least two of these elements, Tdd-2 and Tdd-3, have characteristics associated with mobile genetic elements. The Tdd-3 element is found in different locations in related strains and causes a 9- to 10-base-pair duplication of the target site DNA. The Tdd-2 and Tdd-3 elements do not cross-hybridize, but they share a 22-base-pair homology near one end. At two separate sites, the Tdd-3 element has transposed into the Tdd-2 element, directly adjacent to the 22-base-pair homology. The Tdd-3 element may use this 22-base-pair region as a preferential site of insertion.

Differential expression of the Xenopus laevis tadpole and adult beta-globin genes when injected into fertilized Xenopus laevis eggs

Xenopus laevis tadpole and adult beta-globin genes were injected into fertilized X. laevis eggs. Both injected genes replicated and were retained in the developing embryos with equal efficiency. Transcripts of the injected adult gene were detectable at gastrulation and reached a maximum level shortly thereafter. In contrast, transcripts of the injected tadpole gene were not detected until much later stages of development. The level of expression of both the injected genes was low compared with the level of expression of the chromosomal genes during erythropoiesis.

Cell-free biosynthesis of multiple preprosomatostatins: characterization by hybrid selection and amino-terminal sequencing

In vitro translation of mRNA isolated from islets of Langerhans results in the synthesis of three major preprosomatostatins of Mr 19 000, 18 000, and 16 000, each of which can be resolved into several isoelectric forms [Warren, T. G., & Shields, D. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 3729-3733]. Here we present further characterization of the somatostatin precursors by (i) hybrid selection translation of specific preprosomatostatin mRNAs, (ii) in vitro proteolytic processing of the nascent preprosomatostatins synthesized from hybrid-selected mRNAs, (iii) comparison of their tryptic peptides, and (iv) partial amino-terminal sequence analysis of the signal peptide regions. Hybrid selection experiments using specific cDNA clones demonstrated which preprosomatostatin species corresponded to previously characterized precursor cDNAs [Hobart, P., Crawford, R., Shen, L. P., Picket, R., & Rutter, W. J. (1980) Nature (London) 288, 137-141]; thus, the polypeptide encoded by plasmid pLaS1 corresponds to one form of the Mr 18 000 preprosomatostatins while one form of the Mr 16 000 preprosomatostatins is encoded by pLaS2. Analysis of the tryptic peptides demonstrated that the Mr 16 000 molecule possessed the mature hormone sequence at the carboxyl terminus, as had been shown for the Mr 19 000 and 18 000 precursors. Partial NH2-terminal sequence analysis (a) confirmed the data from hybrid selection and (b) demonstrated that the Mr 18 000 precursor contained a signal peptide manifesting amino acid heterogeneity at certain positions in the signal peptides of each preprosomatostatin. It is suggested that this heterogeneity might account, in part, for variants of the preprosomatostatin molecules.

Overproduction of discoidin I by a temperature-sensitive motility mutant of Dictyostelium discoideum

Dictyostelium discoideum MC2 is a temperature-sensitive motility mutant of AX3. Mutant cells are incapable of growth, phagocytosis, and migration under restrictive conditions (Kayman et al., J. Cell Biol. 92:705-711, 1982). We show here that at the restrictive temperature MC2 cells grown axenically or on bacteria synthesized excessive quantities of the lectin discoidin I. By two-dimensional gel electrophoresis and peptide mapping, the proteins overproduced by MC2 cells were indistinguishable from discoidin I synthesized at lower levels in AX3 cells. At least two of the three species of discoidin I were overproduced. This protein family constituted 9% of the total protein in cells that were incubated overnight at 27 degrees C in axenic medium. Although MC2 cells are defective in nutrient uptake under restrictive conditions, the overproduction of discoidin I did not appear to be part of a pleiotropic response to starvation. We propose that transcription of the coordinately regulated discoidin I genes is altered in mutant cells. This alteration may be related to the motility defects manifested by MC2.

Protein synthesis during development and differentiation in the cellular slime mould Dictyostelium discoideum

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Genomic instability and mobile genetic elements in regions surrounding two discoidin I genes of Dictyostelium discoideum

We have found that the genomic regions surrounding the linked discoidin I genes of various Dictyostelium discoideum strains have undergone rapid changes. Wild-type strain NC-4 has three complete discoidin I genes; its axenic derivative strain Ax-3L has duplicated a region starting approximately 1 kilobase upstream from the two linked genes and extending for at least 8 kilobases past the genes. A separately maintained stock, strain Ax-3K, does not have this duplication but has undergone a different rearrangement approximately 3 kilobases farther upstream. We show that there are repeat elements in these rapidly changing regions. At least two of these elements, Tdd-2 and Tdd-3, have characteristics associated with mobile genetic elements. The Tdd-3 element is found in different locations in related strains and causes a 9- to 10-base-pair duplication of the target site DNA. The Tdd-2 and Tdd-3 elements do not cross-hybridize, but they share a 22-base-pair homology near one end. At two separate sites, the Tdd-3 element has transposed into the Tdd-2 element, directly adjacent to the 22-base-pair homology. The Tdd-3 element may use this 22-base-pair region as a preferential site of insertion.

Differential expression of the Xenopus laevis tadpole and adult beta-globin genes when injected into fertilized Xenopus laevis eggs

Xenopus laevis tadpole and adult beta-globin genes were injected into fertilized X. laevis eggs. Both injected genes replicated and were retained in the developing embryos with equal efficiency. Transcripts of the injected adult gene were detectable at gastrulation and reached a maximum level shortly thereafter. In contrast, transcripts of the injected tadpole gene were not detected until much later stages of development. The level of expression of both the injected genes was low compared with the level of expression of the chromosomal genes during erythropoiesis.

Conserved structural features are found upstream from the three co-ordinately regulated discoidin I genes of Dictyostelium discoideum

The discoidin I genes of Dictyostelium form a small, co-ordinately regulated multigene family. We have sequenced and compared the upstream regions of the DiscI-alpha, -beta and -gamma genes. For the most part the upstream regions of the three genes are non-homologous. The upstream sequences of the beta and gamma genes are exceedingly A + T-rich, while those of the alpha gene are less so. All three genes have a relatively G + C-rich region 20 to 40 base-pairs in length, found approximately 200 base-pairs 5' to the messenger RNA start site. This G + C-rich region 5' to the beta and gamma genes is flanked by short inverted repeats. Within this region, there is an 11 base-pair exact homology between the alpha and gamma genes, and a less perfect homology between these genes and the beta gene. The homology is flanked at a short distance by interspersed G and T residues. The gamma gene is greater than 90% A + T for greater than 800 base-pairs upstream. Further upstream there is a G + C-rich region that is also found inverted approximately 3.5 X 10(3) base-pairs away. The gamma and beta genes are tandemly linked, and the entire approximately 500 base-pair intergene region between the 3' end of the gamma gene and the 5' end of the beta gene is A + T-rich (approximately 90%) with the exception of the homology region 5' to the gamma gene. We demonstrate also the presence of a discoidin I pseudogene fragment having only 139 base-pairs of discoidin homology with greater than 8% mismatch. It is flanked upstream by five 39 base-pair G + C-rich repeats, and downstream by sequences that are extremely A + T-rich. We discuss the possible significance of the conserved G + C-rich structures on discoidin I gene expression.

Two nuclear DNA binding proteins of Dictyostelium discoideum with a high affinity for poly(dA)-poly(dT)

Intergenic regions of the Dictyostelium genome contain an extremely high proportion of AT base pairs. Those intergenic regions which have been subjected to nucleotide sequence analysis are predominantly composed of alternating runs of poly(dA) and poly(dT) and there is evidence to suggest that nucleosomes do not form on such sequences. We have identified two nuclear proteins, of molecular weight 70,000 and 74,000 daltons, which bind only to intergenic regions of a cloned Dictyostelium gene. Binding is specifically inhibited in the presence of synthetic poly(dA) - poly (dT) as competitor. These proteins may play some role in the chromosomal organization of intergenic regions in Dictyostelium discoideum.

Transcriptional activity of the human pseudogene psi alpha globin compared with alpha globin, its functional gene counterpart

Transcriptional analysis of the human pseudogene psi alpha globin has revealed the following features: (1) The promoter with a 23 bp deletion between the CCAAT and ATA boxes is functional both in vitro and in vivo, 3 fold and 10 fold less efficient, respectively, than alpha. (2) Both the psi alpha and alpha globin gene promoters are active in the absence of transcriptional enhancers, either a gene-encoded or viral enhancer. (3) The mutated poly(A) addition signal in psi alpha (AATGAA) appears to be completely nonfunctional. This result provides an explanation for the absence of psi alpha transcripts in human erythroid cells.

Changes in the rate of laminin and entactin synthesis in F9 embryonal carcinoma cells treated with retinoic acid and cyclic amp

The synthesis of laminin A and B chains, and of entactin, has been measured in murine F9 embryonal carcinoma cells differentiating in response to retinoic acid and cyclic AMP. Undifferentiated cells synthesis low levels of laminin, amounting to approximately 0.02% of the [35S]methionine incorporated into cytoplasmic protein during a 15-min pulse. After 6 days induction, laminin synthesis has increased 15- to 20-fold. Undifferentiated F9 cells synthesise more intracellular laminin B2 chains (Mr 225,000) than B1 chains (Mr 225,000), but the excess B2 chains are apparently not assembled into the secreted laminin molecule. Indirect immunofluorescence shows faint cytoplasmic staining and short fibrils of laminin between the undifferentiated F9 cells.

Replication and expression of Xenopus laevis globin genes injected into fertilized Xenopus eggs

Cloned Xenopus adult alpha 1- and beta 1-globin genes were injected into fertilized Xenopus eggs, and the eggs were allowed to develop into swimming tadpoles. The injected DNA replicated during early Xenopus development but did not become methylated de novo. When DNA was modified with Hpa II methylase before injection, methylation was maintained during replication. Although the Xenopus adult globin genes are not normally expressed until metamorphosis, both the unmethylated and in vitro methylated adult alpha- and beta-globin genes were transcribed at low levels, but from the correct promoters, during early development.

Regulation of dictyostelium discoideum mRNAs specific for prespore or prestalk cells

Prespore and prestalk cells in Dictyostelium discoideum aggregates can be separated by density gradient centrifugation. Using poly(A+) RNA from the fractionated cells to probe a cDNA library of mRNAs from postaggregation cells, we were able to identify six cDNA clones representing RNAs enriched in prespore or prestalk cells. Remarkably, transcripts of six of seven cDNA clones, previously selected to encode mRNAs present in postaggregating cells but low or absent in growing cells, also are enriched in RNA from either prestalk or prespore cells. By hybridization of cDNA probes to nitrocellulose blots of formaldehyde RNA gels, these 13 mRNA species have been examined with respect to cell type specificity, temporal pattern of accumulation, and affect of disaggregation and cAMP on accumulation. Aggregation-stage mRNAs tend to fit into three different classes. All prespore mRNAs are similar in all aspects of their regulation, while prestalk mRNAs fall into two co-regulated classes. All mRNAs that are present at significant levels during growth and differentiation are found in both cell types at comparable levels. Our results indicate that there is coordinate control of expression of genes specific for the two principal cell types.

On the evolution of multigene families

Multigene families are classified into three groups: small families as exemplified by hemoglobin genes of mammals; middlesize multigene families, by genes of mammalian histocompatibility antigens; and large multigene families, by variable region genes of immunoglobulins. Facts and theories on these evolving multigene families are reviewed, with special reference to the population genetics of their concerted evolution. It is shown that multigene families are evolving under continued occurrence of unequal (but homologous) crossing-over and gene conversion, and that mechanisms for maintaining genetic variability are totally different from the conventional models of population genetics. Thus, in view of widespread occurrence of multigene families in genomes of higher organisms, the evolutionary theory based mainly on change of gene frequency at each locus would appear to need considerable revision.

Cell-type-specific actin mRNA populations in dictyostelium discoideum

We have analyzed actin mRNA sequences present in the terminal stages of the development of Dictyostelium discoideum. Four different actin mRNA sequences were detected in migrating pseudoplasmodia. Nucleotide sequence analysis of primer-extension products derived from the four mRNA sequences showed that they each encoded an actin protein with the same eight N-terminal amino acids and that they did not derive from transcription of any previously characterized actin gene. Preculmination pseudoplasmodia of Dictyostelium contain two distinct populations of committed cells, termed prespore and prestalk cells. We show that prestalk cells contain all four of the actin mRNA sequences found in pseudoplasmodia, while prespore cells contain only three of the sequences, and mature spores contain only two. Thus there is a differential loss of actin mRNA sequences during spore-cell differentiation in Dictyostelium.