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L Wieslander

Publications and source records attributed to L Wieslander.

At least 19 recordsLinked to original sources
PubMed1996

Demonstration of a dynamic, transcription-dependent organization of pre-mRNA splicing factors in polytene nuclei.

We describe the dynamic organization of pre-mRNA splicing factors in the intact polytene nuclei of the dipteran Chironomus tentans. The snRNPs and an SR non-snRNP splicing factor are present in excess, mainly distributed throughout the interchromatin. Approximately 10% of the U2 snRNP and an SR non-snRNP splicing factor are associated with the chromosomes, highly enriched in active gene loci where they are bound to RNA. We demonstrate that the splicing factors are specifically recruited to a defined gene upon induction of transcription during physiological conditions. Concomitantly, the splicing factors leave gene loci in which transcription is turned off. We also demonstrated that upon general transcription inhibition, the splicing factors redistribute from active gene loci to the interchromatin. Our findings demonstrate the dynamic intranuclear organization of splicing factors and a tight linkage between transcription and the intranuclear organization of the splicing machinery.

Animals↗
PubMed1996

The intranuclear site of excision of each intron in Balbiani ring 3 pre-mRNA is influenced by the time remaining to transcription termination and different excision efficiencies for the various introns.

The 10.9-kb Balbiani ring 3 (BR3) gene contains 38 constitutively excised introns. Both nascent and nucleoplasmic, released BR3 gene pre-mRNA can be isolated by microdissection of the polytene salivary gland nuclei in which the gene is transcribed. Here we analyze the order of intron excision in relation to transcription and to intranuclear transport. We demonstrate that the introns are excised with an overall 5' to 3' polarity that is established during transcription and maintained during transport. In contrast, we also show that individual introns are excised at very different rates and that neighboring introns are removed in a preferred order that is not necessarily 5' to 3'. Splicing factors are, in addition, shown to associate with the nascent BR3 pre-mRNA. Our data argue that functional spliceosomes assemble rapidly as introns appear in the pre-mRNA, but that intron-specific properties influence the kinetics of spliceosome assembly and/or function, resulting in cotranscriptional excision of some introns, preferentially those located in the 5' part of the pre-mRNA, and posttranscriptional excision of other introns, preferentially those located in the 3' part of the pre-mRNA.

Animals↗
PubMed1994

Splicing of Balbiani ring 1 gene pre-mRNA occurs simultaneously with transcription.

The 40 kb Balbiani ring 1 (BR1) gene is at a given moment transcribed by, on average, 120 RNA polymerases. Here we directly assay the excision of introns both in the nascent and in the released nucleoplasmic BR1 pre-mRNAs, isolated by microdissection. We show that intron 3, located 3 kb from the 5' end of the pre-mRNA, is excised simultaneous with transcription. Within 2.5 min of transcription time, 50% of the pre-mRNA molecules have lost the intron. Intron 4, located 600 bases from the polyadenylation site, is excised cotranscriptionally in 5%-10% of the molecules and after or during release to the nucleoplasm in the remaining molecules. Our results demonstrate that spliceosome assembly is a cotranscriptional process in vivo and that splicing may occur during transcription but also after completed transcription, depending on the position of the intron.

Animals↗
PubMed1994

Structure of the smallest salivary-gland secretory protein gene in Chironomus tentans.

The salivary gland secretion in the dipteran Chironomus tentans is composed of approximately 15 different secretory proteins. The most well known of the corresponding genes are the four closely related Balbiani ring (BR) genes, in which the main part of each approximately 40-kb gene is composed of tandemly arranged repetitive units. Six of the seven additional secretory protein genes described share structural similarities with the BR genes and are members of the same BR multigene family. Here we report the identification of a new secretory protein gene, the sp12 gene, encoding the smallest component of the C. tentans salivary gland secretion. The gene has a corresponding mRNA length of approximately 0.7 kb and codes for a protein with a calculated molecular weight of 7,619 Da. The sp12 gene was characterized in seven Chironomus species. Based on a comparison of the orthologous gene sequences, we conclude that the sp12 gene has a repetitive structure consisting of diverged 21-bp-long repeats. The repeat structure and the codon composition are similar to the so-called SR regions of the BR genes and the sp12 gene may represent a diverged member of the BR multigene family.

Amino Acid Sequence↗
PubMed1993

A repetitive secretory protein gene of a novel type in Chironomus tentans is specifically expressed in the salivary glands and exhibits extensive length polymorphism.

The secretion from the salivary glands in the dipteran Chironomus tentans has previously been shown to contain secretory proteins encoded by a set of related genes belonging to the Balbiani ring multigene family. Here we describe the characterization of a gene for an additional secretory protein of a novel type. This sp240/420 gene is built from virtually identical 477-base pair repeats organized in tandem. The gene exhibits extensive length polymorphism since allelic length variants with from 12 to 22 repeats were recorded. Antibodies have been raised against the gene product, and it is shown also that the protein varies in size between 240 and 420 kDa. The protein is rich in serine and threonine residues (30%) and has N-linked carbohydrate chains, presumably on each repeat. Despite careful preparation of the gland lumen proteins, the sp240/420 protein was found to form protein ladders of regularly degraded protein, suggesting that this degradation occurs naturally in the salivary glands. Although all previously characterized salivary gland secretory protein genes in C. tentans belong to the same multigene family, the sp240/420 gene appears to represent a novel, unrelated type of repetitive gene. The chromosomal location of the gene was mapped and was found to reside in region 17 on chromosome I.

Amino Acid Sequence↗
PubMed1993

Two secretory protein genes in Chironomus tentans have arisen by gene duplication and exhibit different developmental expression patterns.

The salivary gland cells in the dipteran Chironomus tentans produce approximately 15 different secretory proteins, with relative molecular masses ranging between 1 x 10(4) and 1 x 10(6). Together these proteins form two types of extra corporal tubes, a larval protective housing and feeding tube or a pupation tube. The developmental change in tube formation is accompanied by a switch in production from one combination of secretory proteins to another. Here we characterize two genes, the sp38-40.A and B genes, which encode secretory proteins with relative molecular masses of 38,000 to 40,000. The two genes are located 346 base-pairs apart in the same orientation and have presumably arisen by gene duplication as the result of an illegitimate recombination event. Both genes contain two regions with cysteine codons, surrounded by regions with short repeats coding for proline and charged amino acid residues. The two genes and alleles of the genes differ in their number of repeats. This structure resembles the structure of the Balbiani ring (BR) genes, which encode the four largest salivary gland secretory proteins. The sp38-40.A and B genes are therefore likely to belong to a BR multigene family containing all or most of the 15 salivary gland secretory protein genes. The expression of the sp38-40.A and B genes are different: the A gene is expressed throughout the larval fourth instar but considerably less in the prepupal stage, while the B gene shows the opposite expression pattern. The developmental regulation of the expression of the two genes has therefore diverged after the gene duplication event.

Amino Acid Sequence↗
PubMed1993

A new member of the balbiani ring multigene family in the dipteran Chironomus tentans consists of a single-copy version of a unit repeated in other gene family members.

The known Balbiani ring (BR) multigene family members in the dipteran Chironomus tentans encode salivary gland secretory proteins in the size range between 38 and 1,000 kDa. The proteins interact to form protein fibers used by the aquatic larvae to spin feeding and protective larval tubes or pupation tubes. Here, we describe a new BR multigene family member, the sp17 gene, which codes for an 89-amino-acid-long protein with a relative mobility of 17k. The gene has a high content of charged amino acid residues and consists of two structurally different halves. Five regularly spaced cysteine codons are present in the 5' half while the 3' half contains five proline codons. These two different halves exhibit similarities to the C and SR regions, respectively, which form the tandemly repeated units in the about 40-kb-long BR genes and which also, in different versions, are the building blocks of all genes in the BR multigene family. In this multigene family, encoding interacting structural proteins, the long BR genes with their 125-150 tandemly arranged repeat units as well as the short sp17 gene with its single-copy version of such a repeat unit, have therefore evolved from a common ancestor.

Amino Acid Sequence↗
PubMed1993

Long-term effect of treatment with the headgear-Herbst appliance in the early mixed dentition. Stability or relapse?

In this investigation of the long-term effect of mandibular protrusive function in children with severe Class II malocclusions, a group of children age 8 years 8 months were initially treated for 5 months with a headgear-Herbst appliance followed by a 3- to 5-year period of activator retention. The patients were studied out of retention at the mean age of 17 years 4 months and compared with an untreated control group. Part of the sagittal correction relapsed. As compared with the control group, the average 3.9 mm protrusive effect of treatment on the mandible decreased to a nonsignificant 1.5 mm out of retention. The significant 2.0 mm therapeutic increase of the condylion-gnathion distance decreased to 1.3 mm and was not significantly different from control values at age 17 years 4 months. However, the 1.5 mm posterior effect of treatment on the maxilla continued to increase during activator retention and the difference compared with the control group was 2.3 mm postretention. This effect on the maxilla partly compensated the relapse tendency observed in the mandible so that 3.8 mm of the 5.4 mm posttreatment sagittal improvement still remained out of retention. Because of the sample size and individual variability, the results should be interpreted cautiously, but the findings indicate that maxillary sutural remodeling might be more receptive long-term to orthopedic treatment than the mandibular condylar growth process.

Case-Control Studies↗
PubMed1992

Balbiani ring 1 gene in Chironomus tentans. Sequence organization and dynamics of a coding minisatellite.

Balbiani ring (BR) genes in diptera encode large secretory proteins and are classical model systems for studies of gene expression. In Chironomus tentans, four closely related BR genes, BR 1, BR 2.1, BR 2.2 and BR 6 form a gene family. The BR genes have been partially characterized and are known to contain long arrays of tandemly arranged repeat units with an hierarchical repeat organization. Here, we report the sequence organization of the complete transcribed part of the BR 1 gene in C. tentans. The gene contains five exons and four introns. Three of the introns are located at the 5' end and the fourth at the 3' end of the gene. Exon 4 is approximately 35,000 bases long and is built completely from tandemly organized repeats. We show that this long repeat block contains two types of related repeat units, beta and gamma. Each type forms a large uninterrupted array, a 5' beta array and a 3' gamma array with a sharp border between them. In the hierarchical repeat structure in each repeat array, all repeats are virtually identical at one level of repetition, but shown differences at the next level. The whole repeat block in the BR 1 gene fluctuates in size between different alleles, but not by more than 10%. In contrast, within the block, the beta and gamma arrays vary in length between 8000 and 29,000 bases in an inverse fashion, together keeping the overall length requirement. We propose that the length of exon 4 is conserved by selection of cross-over products of a given length, and that the internal hierarchical sequence organization in the BR 1 gene is a consequence of the combined action of several different sequence turnover mechanisms, all dependent on the unequal pairing of homologous sequences at different, competing levels of repetition.

Amino Acid Sequence↗
PubMed1992

Sequence organization of the Balbiani ring 2.1 gene in Chironomus tentans.

Balbiani rings are giant chromosomal puffs, containing related genes that provide unique possibilities for in vivo analysis of gene expression at the chromatin and ribonucleoprotein levels. Here, the 5' end of the Balbiani ring 2.1 gene in the dipteran Chironomus tentans has been isolated and the sequence organization of the entire Balbiani ring gene is presented. The gene contains five exons, one being extremely small, only 6 base pairs, and one being extremely large, approximately 30 kilobase pairs. Three introns are located at the 5' end and a fourth one is located at the 3' end. The central 30-kilobase-pair exon is entirely built from tandemly organized repeats. All repeats are virtually identical except for a few variant repeats at both ends of the repeat array. The number of repeats may vary between alleles and the length of the gene therefore changes between 30 and 35 kilobase pairs.

Amino Acid Sequence↗
PubMed1992

Secretory proteins of Chironomus salivary glands: structural motifs and assembly characteristics of a novel biopolymer.

Salivary glands of Chironomus synthesize a family of at least ten secretory proteins that can be grouped into three size classes: the large (about 1000 kDa), intermediate (100- to 200 kDa), and small (less than 100 kDa). After synthesis, secretory proteins undergo a dramatic transformation to form a novel biopolymer. Secretory proteins accumulate in the central lumen of the gland, forming dissociable complexes that appear as a network of smooth fibrils and multistranded beaded fibers. When secretory protein complexes are extruded through the secretory duct, the fibers become oriented in parallel arrays; when these parallel arrays of fibers emerge from the mouth of larvae they are an insoluble, silk-like thread. Regulation of secretory protein-coding gene expression determines which secretory proteins are synthesized, thus, the composition of silk threads. At least two types of threads are produced: larval silk is used to construct tubes for protective housing and assist with feeding; prepupal silk is used to construct tubes for larval/pupal ecdysis (pupation). Variations in composition presumably contribute to different mechanical properties of larval and prepupal silk threads. Since the macroscopic physical properties of polymerized silk most likely reflect the microscopic structure and interaction of secretory proteins, it becomes important to learn the principles which govern secretory protein assembly at the molecular level. Which secretory proteins interact and what are the sites used for intraportein and protein-protein interactions during the assembly of this biopolymer? All eight secretory proteins characterized thus far contain tandemly repeated peptide sequences (ranging from 14-90 amino acids in length) and/or a periodic distribution of Cys residues. These motifs appear to be unique; no other biopolymer has either the repeated peptide sequences or composite structure of chironomid silk threads. The evolutionary conservation of motifs within repeats and among different secretory proteins suggests that the sequences and three-dimensional structures of the motifs may be important for assembly of secretory proteins into complexes, oriented fibers, and silk threads. Further study of secretory protein assembly will bring us closer to understanding how this silk assembles in vivo. By learning principles that nature employs to construct such a novel composite biopolymer, it may become feasible to design and produce new classes of fibers or biomolecular materials with distinctive properties that are currently unavailable.

Amino Acid Sequence↗
PubMed1992

Conserved and variable repeat structures in the Balbiani ring gene family in Chironomus tentans.

The four Balbiani ring (BR) genes, BR1, BR2.1, BR2.2, and BR6 in the midge Chironomus tentans constitute a gene family encoding secretory proteins with molecular weights of approximately 10(6) daltons. The major part of each gene is known to consist of tandemly organized composite repeat units resulting in a hierarchic repeat arrangement. Here, we present the sequence organization of the 5' part of the BR2.2 and BR6 genes and describe the entire transcribed part of the two genes. As the BR1 and BR2.1 genes were also fully characterized recently, this allows the comparison of all genes in the BR gene family. All four genes share the same exon-intron structure and have evolved by gene duplications starting from a common ancestor, having the same overall organization as the BR genes of today. The genes encode proteins that have an approximately 10,000-amino acid residue extended central domain, flanked by a highly charged, approximately 200-residue amino-terminal domain and a globular 110-residue carboxy-terminal domain. Exons 1-3 and the beginning of exon 4 encode the amino-terminal domain, which throughout contains many regions built from short repeats. These repeats are often degenerate as to repeat unit and sequence and are present in different numbers between the genes. In several instances these repeat structures, however, are conserved at the protein level where they form positively or negatively charged regions. Each BR gene has a 26-38-kb-long exon 4, which consists of an array of 125-150 repeat units and encodes the central domain. The number of repeat units appears to be largely preserved by selection and all repeat units in the array are very efficiently homogenized. Occasionally variant repeats have been introduced, presumably from another BR gene by gene conversion, and spread within the array. Introns 1-3 at the 5' end of the genes have diverged extensively in sequence and length between the genes. In contrast, intron 4 at the 3' end is virtually identical between three of the four genes, suggesting that gene conversion homogenizes the 3' ends of the genes, but not the 5' ends.

Amino Acid Sequence↗
PubMed1990

[Methods of studying genes and gene function].

In several fields, such as immunology, biochemistry, and structural biology, but particularly in molecular genetics, modern methods enable genes and their protein products to be analysed and described. The tools are now available to study any physiological process or disease at the molecular level. As a result, genetic diseases and viral infections can be better identified and understood. Basic cellular and physiological mechanisms are beginning to be elucidated, the disturbance of which is a factor involved in cancerogenesis, for instance, or the development of hypercholesterolaemia. The article is intended as a brief review of current methods of studying genes and their function. The isolation and characterisation of genes by means of recombinant DNA technology, the identification of defective genes, and the analysis of gene function, both in vitro and in vivo are presented.

Chromosome Mapping↗