Alteration of c-myc chromatin structure by avian leukosis virus integration

The most common sites of integration of the leukosis virus (ALV) long terminal repeat (LTR) in bursal lymphomas and derivative cell lines correspond to a region encompassed by two major hypersensitive sites in the 5' flanking region of the pre-integration, unrearranged c-myc gene. After integration of the ALV LTR, the major hypersensitive site within the avian c-myc oncogene region is within the proviral LTR, and the major hypersensitive sites normally found in uninfected cells 5' to the first c-myc coding exon are no longer detectable.     

Translocation, breakage and truncated transcripts of c-myc oncogene in murine plasmacytomas

Comparative nucleotide sequence analysis of a rearranged c-myc gene in a murine plasmacytoma and c-myc cDNA from normal spleen reveals that chromosomal translocation in the plasmacytoma breaks the c-myc gene within the first exon or intron. In the plasmacytoma truncated c-myc RNAs initiate from newly exposed promoter sites. Nevertheless, the myc polypeptide produced in the plasmacytoma is probably the same as that from the intact c-myc gene because the exon lost by breakage and translocation is non-coding. The second and third exons of the mouse c-myc gene are substantially conserved in the v-myc gene of the avian retrovirus, MC29.     

Human N-myc is closely related in organization and nucleotide sequence to c-myc

N-myc, a cellular gene related to the c-myc proto-oncogene, was originally identified on the basis of its very frequent amplification and overexpression in a restricted set of tumours, most notably human neuroblastomas. That N-myc may have a causal role in the genesis of these tumours is suggested by the observation that in the rat embryo fibroblast co-transformation assay it has a transforming potential similar to that of c-myc. The apparent structural and functional homology of N-myc and c-myc suggests that they may be members of the same protooncogene family. However, despite these apparent similarities, expression of the two genes appears to be dramatically different with respect to tumour specificity, as well as tissue and developmental stage specificity. To further elucidate the common and unique aspects of N-myc and c-myc gene structure and function in normal and transformed cells, we have determined the organization of human N-myc and the nucleotide sequence of its messenger product, and we report here that N-myc and c-myc have a similar intron/exon structure and that their protein products share regions of significant homology.     

Identification of nuclear proteins encoded by viral and cellular myc oncogenes

The myelocytomatosis viruses are a family of replication-defective avian retroviruses that cause a variety of tumours in chickens and transform both fibroblasts and macrophages in culture through the activity of their oncogene v-myc. A closely related gene (c-myc) is found in vertebrate animals and is thought to be the progenitor of v-myc. Changes in the expression and perhaps the structure of c-myc have been implicated in the genesis of avian, murine and human tumours (for a review, see ref. 15). Elucidation of the mechanisms by which v-myc and c-myc might elicit tumorigenesis requires identification of the proteins encoded by these genes. To this end, we have expressed a portion of v-myc in a bacterial host and used the resulting protein to raise antisera that react with myc proteins. We report here that v-myc and c-myc encode closely related proteins with molecular weights (MWs) of approximately 58,000. Integration of retroviral DNA near or within c-myc in avian lymphomas apparently enhances expression of the gene. Here we have used cells from one such tumour to identify the protein encoded by c-myc and find that the coding domain for the gene is probably intact.     

Reciprocal chromosome translocation between c-myc and immunoglobulin gamma 2b genes

Specific chromosome translocations have been observed in transformed cell lines of both man and mouse and may be implicated in the origin or maintenance of malignancy. In mouse plasmacytomas, translocations have been identified that bring the immunoglobulin alpha heavy-chain gene (C alpha, normally located on chromosome 12) into proximity with c-myc (normally located on chromosome 15), c-myc being the mouse cellular homologue of the avian myelocytomatosis virus transforming gene (v-myc). Here we identify a DNA rearrangement in a mouse hybridoma that has brought c-myc close to C gamma 2b and show that this rearrangement occurred by reciprocal chromosome translocation, as recombinant clones were isolated from the same cell line in which a rearranged variable-region (VH) gene has been brought close to 5' c-myc sequences. The translocation has resulted in the net loss of 7 base pairs (bp) of chromosome 15 sequence as well as in the presence of an additional base of unknown provenance. This reciprocal translocation was analysed in DNA from a mouse hybridoma cell line but is shown to be characteristic of the X63Ag8 myeloma parent.     

Nucleotide sequence of cloned cDNA of human c-myc oncogene

Like other transforming genes of retroviruses, the v-myc gene of the avian virus, MC29, has a homologue in the genome of normal eukaryotic cells. The human cellular homologue, c-myc, located on human chromosome 8, region q24 leads to qter (refs 1, 2), is translocated into the immunoglobulin heavy-chain locus on human chromosome 14 (ref. 3) in Burkitt's lymphoma, suggesting that c-myc has a primary role in transformation of some human haematopoietic cells. In addition, c-myc is amplified in the human promyelocytic leukaemia cell line, HL60 (refs 6, 7) which also contains high levels of c-myc mRNA. Recently, Colby et al. reported the nucleotide sequence of the human c-myc DNA isolated from a genomic recombinant DNA library derived from human fetal liver. This 4,053-base pair (bp) sequence includes two exons and one intron of the myc gene, and the authors have suggested the existence of a human c-myc mRNA of 2,291 nucleotides that has a coding capacity for a protein of molecular weight (Mr) 48,812. We have approached the problem of accurately defining the characteristics of the human c-myc mRNA and c-myc protein by determining the sequence of the c-myc cDNA isolated from a cDNA library prepared from mRNA of a clone of the K562 human leukaemic cell line. K562 cells are known to contain c-myc mRNA which is similar in size to the c-myc mRNA of other human cell types. We report here the sequence of 2,121 nucleotides of a human c-myc mRNA and demonstrate that its 5' noncoding sequence does not correspond to the sequence of the reported genomic human sequence. However, our data confirm that the intact human c-myc mRNA can encode a 48,812-Mr protein with a sequence identical to that reported by Colby et al.     

Mutations analysis of STK_(11) gene in Chinese families with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disease that is characterized by multiple gastrointestinal hamartomatous polyps and melanin spots on lips and buccal mucosa at young age[1,2]. Previous studies have demonstrated that PJS predisposes carriers to cancers of gastrointestinal tract, uterus, ovary, testis, breast and other extragastrointestinal organs[3—5]. The STK11 gene, encoding a serine/threonine kinase at chro-mosome 19p13.3, was identified in 1998 as the main causativ…     

Mutations analysis of STK11 ene in Chinese families with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominantly inherited disease characterized by multiple gastrointestinal hamartomatous polyps and melanin spots on lips and buccal mucosa, with an increased risk for various cancers. ThePJS gene, a potential tumour suppressor gene, encoding a serine/ threonie kinase (STK11), was mapped to chromosome 19p13.3. To investigate the mutations of STK11 gene in Chinese with PJS, we analyzed its coding sequence in fifteen patientsand twenty unaffected members of six families, including three multigenerational families with PJS and three sporadic families with PJS, by PCR, PCR-DHPLC and DNA sequencing techniques. Ten point mutations were found in the six families, including five missense mutations, one acceptor-splice site mutation, a nonsense mutation and three silent mutations. Our data showed that five missense mutations occurrd at codon 123 (CAG to CAT) in exon 2, codon 161 (ATT to AGT) in exon 4,codon 194 (GAC to GAG) in exon 4, codon 245 (CTC to TTC) in exon 5 and codon 354 (TTC to TTG) in exon 8. One kind of nonsense mutation was detected at codon 37(CAG to TAG) in exon 1. Furthermore, we found an intronic mutation at a splice-acceptor site: a one base substitution from AG to AA in intron 4. These mutations were not detected in 20 normal DNA samples. In three sporadic families, only in one patient, we detected a missense mutation in exon 5. In addition, we found three silent mutations, which may cause polymorphisms of STK11 gene in introns 1(+36), 3(-51) and 5(+27). These results indicated that the point mutation in STK11 might be involved in PJS pathogenesis. Mutation frequency is higher in the families suffering PJS in three or more generations than that of the sporadic cases.     

Differential expression of myc family genes during murine development

The myc family of cellular oncogenes contains three known members. The N-myc and c-myc genes have 5'-noncoding exons, strikingly homologous coding regions, and display similar oncogenic potential in an in vitro transformation assay. The L-myc gene is less well characterized, but shows homology to N-myc and c-myc (ref. 6; also see below). c-myc is expressed in most dividing cells, and deregulated expression of this gene has been implicated in the development of many classes of tumours. In contrast, expression of N-myc has been found only in a restricted set of tumours, most of which show neural characteristics; these include human neuroblastoma, retinoblastoma and small cell lung carcinoma (SCLC). L-myc expression has so far been found only in SCLC. Activated N-myc and L-myc expression has been implicated in oncogenesis; for example, although N-myc expression has been found in all neuroblastomas tested, activated (greatly increased) N-myc expression, resulting from gene amplification, is correlated with progression of the tumour. We now report that high-level expression of N- and L-myc is very restricted with respect to tissue and stage in the developing mouse, while that of c-myc is more generalized. Furthermore, we demonstrate that N-myc is not simply a neuroectoderm-specific gene; both N- and L-myc seem to be involved in the early stages of multiple differentiation pathways. Our findings suggest that differential myc gene expression has a role in mammalian development and that the normal expression patterns of these genes generally predict the types of tumours in which they are expressed or activated.     

Expression of c-myc changes during differentiation of mouse erythroleukaemia cells

The transforming gene of avian myelocytomatosis virus MC29, v-myc, causes a variety of malignancies in chickens. A cellular homologue, c-myc, has been implicated in B-cell malignancies in mice and humans but is also expressed in many normal cell types and may be important in the control of normal cell proliferation. c-myc is highly conserved in vertebrates. We have been investigating the relationship between c-myc expression and the terminal differentiation of cultured mouse erythroleukaemia (MEL) cells. We find that the level of c-myc messenger RNA shows a rapid biphasic change in MEL cells induced to differentiate by dimethyl sulphoxide or hypoxanthine. The changes occur during the first few hours of the differentiation programme and require active protein synthesis. These data suggest that changes in c-myc expression may be important in the irreversible commitment of MEL cells to terminal erythroid differentiation.     

Primary structure and genomic organization of the histidine-rich protein of the malaria parasite Plasmodium lophurae

The nucleotide sequence of a complete genomic clone for the histidine-rich protein of Plasmodium lophurae has been determined. The deduced amino acid sequence of the mature protein shows numerous tandemly repeated units preceded by a signal and a pro peptide. The gene is interrupted by an intron with a separate exon coding for the signal peptide. The signal peptide-encoding exon detects multiple cross-hybridizing sequences in the parasite genome.     

山羊INHA和INHBA基因的cDNA克隆、序列分析及组织表达研究

分别提取处于同一发情周期的5只低繁藏山羊和5只高繁金堂黑山羊的卵巢、垂体的总RNA,并通过RT-PCR技术对INHA、INHBA基因cDNA进行克隆、序列分析,以Real-time PCR技术对其进行组织表达研究.结果表明:藏山羊和金堂黑山羊INHA基因编码区均长1083bp,编码360个氨基酸,两品种基因编码区有7处碱基不同,并导致3处氨基酸的差异;INHBA基因编码区均长1278bp,编码425个氨基酸,两品种基因编码区有4处碱基不同,并导致1处氨基酸的差异.藏山羊INHA基因编码区核苷酸序列与金堂黑山羊、绵羊、牛、野猪、小鼠、褐家鼠、人的同源性分别为:99.4%、98.9%、95.8%、88.6%、81.0%、79.5%和84.8%;藏山羊INHBA基因编码区核苷酸序列与金堂黑山羊、绵羊、牛、野猪、小鼠、褐家鼠、人的同源性分别为:99.7%、99.4%、98.1%、91.7%、88.0%、88.5%和91.2%.INHA和INHBA基因mRNA在两个山羊品种的卵巢、垂体中均有表达,但两品种间无显著性差异(P0.05).说明INHA和INHBA基因在动物进化中比较保守,与山羊多羔性状的相关性有待进一步研究.     

The c-myc coding DNA sequences of cyprinids （Teleostei： Cypriniformes）： Implications for phylogeny

The family Cyprinidae is one of the largest fish families in the world, which is widely distributed in East Asian, with obvious difference in characteristic size among species. The phylogeneUc analysis of cyprinid taxa based on the functionally important genes can help to understand the speciation and functional divergence of the Cyprinidae. The c-myc gene is an important gene regulating individual growth. In the present study, the sequence variations of the cyprinid c-myc gene and their phylogenetic significance were analyzed. The 41 complete sequences of the c-myc gene were obtained from cyprinids and outgroups through PCR amplification and clone. The coding DNA sequences of the c-myc gene were used to infer molecular phylogenetic relationships within the Cyprinidae. Myxocyprinus asiaticus （Catostomidae）, Misgurnus anguillicaudatus （CobiUdae） and Hemimyzon sinensis （Homalopteridae） were assigned to the outgroup taxa. Phylogenetic analyses using maximum parsimony （MP）, maximum likelihood （ML）, and Bayesian retrieved similar topology. Within the Cyprinidae, Leuciscini and Barbini formed the monophyletic lineage respectively with high nodal supports. Leuciscini comprises Xenocyprinae, CuItrinae, East Asian species of Leuciscinae and Danioninae, Gobioninae and Acheilognathinae, and Barbini contains Schizothoracinae, Barbinae, Cyprininae and Labeoninae. Danio rerio, D. myersi and Rasbora trilineata were supposed to separate from Leuciscinae and Barbini and to form another lineage. The positions of some Danioninae species were still unresolved. Analyses of both amino acid variation with parsimony information and two high variation regions indicated that there is no correlation between variations of single amino acid or high variation regions and characteristic size of cyprinids. In addition, the species with smaller size were usually found to be basal within clades in the tree, which might be the results of the adaptation to the primitive ecology and survival pressure.