The Drosophila melanogaster actin 5C gene uses two transcription initiation sites and three polyadenylation sites to express multiple mRNA species

Cloning and analysis of fs(1) Ya, a maternal effect gene required for the initiation of Drosophila embryogenesis

The maternal effect locus fs(1) Ya is required for the fusion of the apposed sperm and egg pronuclei (syngamy) following fertilization in Drosophila. It is tightly linked to another complementation group, fs(1) Yb, needed for both oogenesis and embryogenesis. We have isolated a set of overlapping cloned sequences in the 3B4-6 region of the X chromosome encompassing the fs(1) Ya-fs(1) Yb region. A single 2.4 kb maternal transcript is encoded within this region, and an 8.5 kb DNA fragment that contains this transcript complements both fs(1) Ya and fs(1) Yb mutations. Northern and in situ hybridization analyses show that the maternal transcript is only present in nurse cells and oocytes beginning in previtellogenic stages, and is evenly distributed in the cytoplasm of 0-2 h syncytial embryos. The transcript is not detected in later stages of embryonic development. This expression pattern correlates closely with the genetic and developmental characteristics expected of the fs(1) Ya gene product.

Vectors for Drosophila P-element-mediated transformation and tissue culture transfection

We describe nine P-element vectors that can be used to study gene regulation and function in Drosophila. These vectors were designed for use in germline transformation and cell culture transfection assays. One set consists of five P elements that can be used to study transcriptional regulatory sequences. These vectors contain several unique restriction sites for insertion of a foreign promoter upstream from either a cat or lacZ reporter gene. Two of the beta-galactosidase-coding vectors also require the insertion of a start codon for translation of the reporter enzyme and thus can be used to study translational regulatory sequences. The second set of P elements consists of four vectors that contain the Drosophila cytoplasmic actin 5C promoter and polyadenylation signals. Upon insertion of a foreign DNA segment, these vectors direct constitutive expression of the encoded RNA and protein.

Analysis of Sp1 in vivo reveals multiple transcriptional domains, including a novel glutamine-rich activation motif

We have adopted Drosophila tissue culture cells as a host system for studying the structure and function of mammalian transcription factors. These cells provide an Sp1-deficient background and have been used in a complementation assay to identify functional domains of human transcription factor Sp1. The SV40 early promoter, which contains six Sp1 binding sites (GC boxes), is induced up to 500-fold in Drosophila cells by the expression of Sp1, whereas promoters with fewer sites are activated less efficiently. Analysis of Sp1 mutants reveals multiple distinct regions outside of the DNA binding domain that are responsible for mediating transcriptional activation. The two most active domains, which appear to be functionally redundant with one another, consist of an unusual structure with a very low charge density, but a strikingly high glutamine content. A number of other sequence-specific transcription factors, such as the Drosophila zeste protein and several homeodomain proteins, contain glutamine-rich stretches, and we propose that these glutamine-rich domains represent a novel structural motif for transcriptional activation.

Transcriptional deviation of the rat insulin-like growth factor II gene initiated at three alternative leader-exons between neonatal tissues and ascites hepatomas

Insulin-like growth factor II (IGFII) is a mitogenic polypeptide, the mRNAs of which are present in multiple forms, despite derivation from a single gene. In the present study, we observed nearly full-length rat IGFII mRNA structures of major species with three alternative 5'-untranslated sequences and a common unusually-long 3'-untranslated region. These three 5' sequences (E1, E2 and E3) locate at different sites on the rat IGFII genome and are therefore independent leader-exons. Northern blotting using probes specific to E1, E2 and E3 sequences revealed major bands at 3.8 kilobases (kb), 4.6 kb and 3.6 kb in nucleotide length, respectively. The E1, E2 and E3 promoters were functional in all rat neonatal tissues examined and in the adult brain, and the relative level of mRNA species was fairly constant, although the bulk expression varied from tissue to tissue. Thus, the three mRNAs initiated from the single rat IGFII gene are co-ordinately regulated. However, this relative transcriptional constancy deviated variously in several lines of transplantable rat ascites hepatomas, thereby indicating that each mRNA level can also be regulated independently.

Human aldolase A gene. Structural organization and tissue-specific expression by multiple promoters and alternate mRNA processing

The complete nucleotide sequence of the human aldolase A isoenzyme gene is reported. The cloned gene sequence, spanning 7530 bp, includes twelve exons and occurs as a single copy per haploid human genome. The structural organization of the gene is quite complex: eight exons containing the coding sequence are common to all mRNAs extracted from human and other mammalian sources; four additional exons are present in the 5' untranslated region, of these one is contained in the ubiquitous type of mRNA, the second is in the muscle-specific type of mRNA and the third and fourth are in a minor species of mRNA found in human liver tissue. Furthermore, the determined sequence includes 1000 nucleotides upstream from the first exon (exon I) in the 5' flanking region, and 400 nucleotides, which include the polyadenylation signal, downstream from the termination codon. S1-nuclease-protection analysis of the 5' end of mRNA extracted from human cultured fibroblasts, muscle and hepatoma cell lines indicates the existence of four different transcription-initiation sites. The latter are also supported by the presence of conventional sequences for eukaryotic promoters. Therefore, the four promoters on the same gene generate different tissue-specific transcripts, which share the translated sequence, but each has a unique 5' untranslated region as a result of differential mRNA processing. The nucleotide homology at the coding region and the intron-exon organization of the three human and mammalian aldolase A, B and C genes confirm that they arose from a common ancestral gene, and that aldolase B diverged first.

Expression of the three unlinked isocoding actin genes of Physarum polycephalum

The actin gene family in Physarum polycephalum contains four unlinked loci: ardA, ardB, ardC, and ardD. The ardA locus is complex and probably contains two genes which we designated ardA2-7 and ardA2-17. cDNA clones corresponding to the ardB and ardC loci were isolated. Nucleic acid sequencing showed that these two cDNAs coded for the only abundant form of Physarum actin, which is 96% homologous to human gamma-cytoplasmic actin. The ardA2-17 gene also codes for this same actin protein (Nader et al., Gene 48, 133-144, 1986). The coding regions of ardB and ardC differ by 15 nucleotides. A comparison of the ardB and ardC sequences with ardA2-17 showed 73 and 77 nucleotide substitutions, respectively, in the coding regions. The noncoding regions of these three sequences were not homologous to each other or to the noncoding regions of actin genes from other organisms. Southern genomic hybridizations indicated that the ardA2-7 and ardD genes have weak sequence similarities to the three isocoding actin genes and thus form a different subclass of the family. Northern hybridizations showed that the ardB and ardC transcripts varied in abundance but were present in all the developmental stages. No ardA2-17 transcripts were seen. The relative abundance of the ardB and ardC transcripts was measured in amoebae and plasmodia by S1 nuclease protection and dot hybridization assays. A ratio of approximately 3:1 for ardC versus ardB was found for both stages. P. polycephalum is the first organism shown to contain three unlinked isocoding actin genes, of which at least two are expressed.

Transcriptional activity at the 3' end of the actin gene at 5C on the X chromosome of Drosophila melanogaster

Polyribosomal poly(A)+ RNA from stage-specific embryos of Drosophila melanogaster was analyzed by Northern hybridizations to determine the transcription at the 5C actin gene (act5C) and to establish whether these mRNAs are used in translation. A 3' end probe, which contains 30 nucleotides of the actin coding sequence as well as 3'-end-adjacent sequence, hybridizes in addition to the act5C transcript to a smaller transcript 450 nucleotides long. Hybridizations with the 3' end strand-specific probes show that this transcript has the same orientation as the actin gene. This transcript is temporally coexpressed with the act5C gene over most of the developmental stages examined. S1 nuclease mapping and primer extension experiments place its 5' end about 20 nucleotides upstream from the actin translation termination signal. Furthermore, the transcript appears to translate in an in vitro translation system into a protein of 7.4 kDa, as expected from the size of the open reading frame. The data suggest, but do not prove, that the 3'-end-transcribed but untranslated region of act5C may be involved in actin gene expression.

Temporal pattern of alcohol dehydrogenase gene transcription reproduced by Drosophila stage-specific embryonic extracts

Regulation of transcription during development has been analysed in vitro using extracts derived from Drosophila embryos. Transcription of mutant templates reveals cis-control regions of the alcohol dehydrogenase promoter responsible for temporal regulation. The activity of a trans-acting protein correlates with the profile of alcohol dehydrogenase expression during embryogenesis.

Transcription from each of the Drosophila act5C leader exons is driven by a separate functional promoter

The Drosophila act5C gene has two leader exons at which transcription initiation occurs. In this way two classes of transcripts that are different with respect to the 5'-untranslated sequences are synthesized. Both are present in Drosophila Kc cell mRNA. To define the sequences necessary for transcription from each start point and to determine if each is driven by a separate promoter, 5'-flanking regions from the act5C gene were inserted upstream from the bacterial chloramphenicol acetyltransferase gene and tested for promoter activity by transient assays in Drosophila Kc cells. We show that both leader exons are preceded by separate, functional, promoters. The exon 1 proximal promoter contains at least two regions important for optimal expression. One is at more than 1.9 kb upstream from the exon 1 cap site while the other lies between 1.2 and 0.09 kb of the cap site. The promoter elements necessary for transcription from exon 2 are within 450 bp upstream from its cap site. The data suggest that, in some constructions, transcription initiation at exon 1 inhibits transcription initiation at exon 2. There is a sequence of dyad symmetry which is present upstream from both exon 1 and exon 2 of the form CC(A-rich)6GG. The same sequences are found upstream from many mammalian and chicken actin genes and of the human and mouse c-fos genes, where they are believed to be transcription regulatory sequences.

Nucleotide sequence and structural analysis of the zeste locus of Drosophila melanogaster

The zeste locus plays a central role in transvection phenomena, where the synaptic pairing of chromosomes carrying genes with which zeste interacts influences the expression of these genes. To explore the possible functions of the zeste gene product in this process, we have determined the DNA sequences both of a fragment of Drosophila genomic DNA capable of rescuing mutant zeste phenotypes, and of a near full-length cDNA clone derived from the 2.4-kb zeste mRNA. These data show that the zeste gene is interrupted by two small introns, and suggest that the majority of zeste sequences are contained within an intron of another transcriptional unit of opposite polarity. A large region of the predicted zeste product is comprised almost exclusively of glutamine and alanine residues. A domain near the N terminus of this protein, which is sufficient for site-specific DNA binding, is highly charged, as is the C-terminal region of the protein. A breakpoint of the rearrangement In (1)e(bx), which is associated with a za-like phenotype, is found within sequences encoding the zeste product, and would produce a truncated protein. The neomorphic mutation zv77h is correlated with a 300-bp deletion of sequences determining the untranslated 5' leader of the zeste messenger, but may also remove the initiating ATG codon, resulting in a zeste protein with an altered N terminus.

Developmental switches of sericin mRNA splicing in individual cells of Bombyx mori silkgland

Four mRNA of 10.5, 9.0, 4.0, and 2.8 kb are made from the sericin Ser1 gene by alternative maturation of a unique mRNA precursor. By means of RNA blots and in situ hybridization, we investigated variations in the distribution of these mRNA during the last larval instar in different territories of the middle silkgland. Taken together, the results from these two techniques show that 150 out of the 266 cells of this region of the organ express the Ser1 gene, but accumulate distinct mature mRNA species. Of these 150 cells 42 are specialized in a processing pathway resulting in the production of the 2.8-kb Ser1 mRNA throughout the larval instar. The 108 others perform successively three distinct splicing pathways leading to a development-dependent accumulation of, respectively, the 4.0-, the 10.5-, and the 9.0-kb mRNA. This suggests the occurrence of two switches in the splicing capacities of these cells during the fifth instar. The middle silkgland cells also express another sericin gene (Ser2) which encodes two mRNA of 5.4 and 3.1 kb, also arising by differential splicing. At the beginning of development, all the middle silkgland cells express this gene but, as development proceeds, expression becomes restricted to only the anterior cells. The biological consequence of this topological and temporal regulation of the mode of expression of these two genes is the sequential secretion and layering of the different sericins around the silk thread.

Genomic blot hybridization as a tool of phylogenetic analysis: evolutionary divergence in the genus Drosophila

Comparative, quantitative Southern analysis of genomic DNA, using single-copy sequence probes, potentially is valuable for phylogenetic analysis. We have examined 27 Drosophila species, belonging to two subgenera, seven species groups, and ten subgroups, using a variety of cloned and characterized probes: twelve cloned sequences from D. melanogaster, two from D. pseudoobscura, and two from D. grimshawi. The data are generally congruent with accepted phylogenetic relationships in Drosophila, and confirm or clarify some previously uncertain relationships. The potential and limitations of the method are discussed.