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PubMed2002

Evolutionary analyses of the small subunit of glutamate synthase: gene order conservation, gene fusions, and prokaryote-to-eukaryote lateral gene transfers.

Lateral gene transfer has been identified as an important mode of genome evolution within prokaryotes. Except for the special case of gene transfer from organelle genomes to the eukaryotic nucleus, only a few cases of lateral gene transfer involving eukaryotes have been described. Here we present phylogenetic and gene order analyses on the small subunit of glutamate synthase (encoded by gltD) and its homologues, including the large subunit of sulfide dehydrogenase (encoded by sudA). The scattered distribution of the sudA and sudB gene pair and the phylogenetic analysis strongly suggest that lateral gene transfer was involved in the propagation of the genes in the three domains of life. One of these transfers most likely occurred between a prokaryote and an ancestor of diplomonad protists. Furthermore, phylogenetic analyses indicate that the gene for the small subunit of glutamate synthase was transferred from a low-GC gram-positive bacterium to a common ancestor of animals, fungi, and plants. Interestingly, in both examples, the eukaryotes encode a single gene that corresponds to a conserved operon structure in prokaryotes. Our analyses, together with several recent publications, show that lateral gene transfers from prokaryotes to unicellular eukaryotes occur with appreciable frequency. In the case of the genes for sulfide dehydrogenase, the transfer affected only a limited group of eukaryotes--the diplomonads--while the transfer of the glutamate synthase gene probably happened earlier in evolution and affected a wider range of eukaryotes.

Amino Acid Sequence↗
PubMed2002

Gene expression profiling of isogenic cells with different TP53 gene dosage reveals numerous genes that are affected by TP53 dosage and identifies CSPG2 as a direct target of p53.

TP53 does not fully comply with the Knudson model [Knudson, A. G., Jr. (1971) Proc. Natl. Acad. Sci. USA 68, 820-823] in that a reduction of constitutional expression of p53 may be sufficient for tumor predisposition. This finding suggests a gene-dosage effect for p53 function. To determine whether TP53 gene dosage affects the transcriptional regulation of target genes, we performed oligonucleotide-array gene expression analysis by using human cells with wild-type p53 (p53 +/+), or with one (p53 +/-), or both (p53 -/-) TP53 alleles disrupted by homologous recombination. We identified 35 genes whose expression is significantly correlated to the dosage of TP53. These genes are involved in a variety of cellular processes including signal transduction, cell adhesion, and transcription regulation. Several of them are involved in neurogenesis and neural crest migration, developmental processes in which p53 is known to play a role. Motif search analysis revealed that of the genes highly expressed in p53 +/+ and +/- cells, several contain a putative p53 consensus binding site (bs), suggesting that they could be directly regulated by p53. Among those genes, we chose CSPG2 (which encodes versican) for further study because it contains a bona fide p53 bs in its first intron and its expression highly correlates with TP53 dosage. By using in vitro and in vivo assays, we showed CSPG2 to be directly transactivated by p53. In conclusion, we developed a strategy to demonstrate that many genes are affected by TP53 gene dosage for their expression. We report several candidate genes as potential downstream targets of p53 in nonstressed cells. Among them, CSPG2 is validated as being directly transactivated by p53. Our method provides a useful tool to elucidate additional mechanisms by which p53 exerts its functions.

Adenocarcinoma↗
PubMed1982

Translational control of bacteriophage f1 gene II and gene X proteins by gene V protein.

The gene II region of bacteriophage f1 DNA codes for two proteins, the 46 kd gene II protein and the 13 kd gene X protein, which results from an in-phase start at codon 300 of gene II. Using antigene II protein IgG, we show that the intracellular concentration of both proteins is controlled by the phage gene V protein. In wild-type f1-infected cells, the amount of gene II protein reaches a plateau of about 1500 molecules per cell at 20 min after infection, as measured by blot immunoassay. Similarly, the amount of gene X protein reaches a peak of about 500 molecules per cell around 10 min after infection. In contrast, when the gene V protein is inactive, both gene II and gene X proteins continue to accumulate at a high rate for at least 40 min after infection. This difference is caused by decreased synthesis of gene II and gene X proteins in the presence of gene V protein, which represses the translation of these two proteins.

Antibodies, Viral↗
PubMed1985

The fumarase genes of Escherichia coli: location of the fumB gene and discovery of a new gene (fumC).

The fumB gene of Escherichia coli, which complements the fumarase deficiency of a fumA mutant when present in multiple copies, has been located at 93.5 min in the E. coli linkage map and its product has been identified as a polypeptide of 61 kDal. Four overlapping ColE1-fumB+ plasmids representing a continuous segment of 23.3 kb of bacterial DNA have been isolated from the Clarke-Carbon E. coli gene bank and the location of the fumB gene relative to the restriction map and the adjacent mel operon has been defined. Hybridization studies have shown that the fumB gene is homologous to the fumA gene, which complements the fumA1 mutation in single and multi-copy situations, and encodes an analogous 61 kDal product formerly regarded as the E. coli fumarase. The hybridization studies also showed that the Bacillus subtilis fumarase gene (citG) is homologous to an independent gene, fumC (formerly g48), which lies adjacent to the fumA gene at 35.5 min in the E. coli linkage map. The N-terminal sequences of the citG and fumC products exhibit a 51% identity over 88 residues. It is possible that the fumC and citG genes are fumarase structural genes of E. coli and B. subtilis, and that the fumA gene may encode a differentially-regulated fumarase or be a positive regulator gene which is essential for the expression of fumC (but not citG). If so, the fumB gene may encode a related enzyme or activator that can replace the fumA function when amplified.

Autoradiography↗
PubMed1992

Molecular analysis of the avirulence gene avr9 of the fungal tomato pathogen Cladosporium fulvum fully supports the gene-for-gene hypothesis.

The interaction between the fungal pathogen Cladosporium fulvum and tomato is supposed to have a gene-for-gene basis. Races of C. fulvum which have 'overcome' the resistance gene Cf9 of tomato, lack the avirulence gene avr9 which encodes a race-specific peptide elicitor. Races avirulent on tomato genotypes carrying the resistance gene Cf9 produce the race-specific peptide elicitor, which induces the hypersensitive response (HR) on those genotypes. The causal relationship between the presence of a functional avr9 gene and avirulence on tomato genotype Cf9 was demonstrated by cloning of the avr9 gene and subsequent transformation of C. fulvum. A race virulent on tomato genotype Cf9 was shown to become avirulent by transformation with the cloned avr9 gene. These results clearly demonstrate that the avr9 gene is responsible for cultivar specificity on tomato genotype Cf9 and fully support the gene-for-gene hypothesis. The avr9 gene is the first fungal avirulence gene to be cloned.

Amino Acid Sequence↗
PubMed1988

Regulation of pS2 gene expression by affinity labeling and reversibly binding estrogens and antiestrogens: comparison of effects on the native gene and on pS2-chloramphenicol acetyltransferase fusion genes transfected into MCF-7 human breast cancer cells.

We have examined the effects of reversibly and irreversibly binding estrogenic and antiestrogenic ligands for the estrogen receptor on pS2 RNA accumulation in MCF-7 human breast cancer cells and on pS2-chloramphenicol acetyl transferase (CAT) fusion gene expression in transfected MCF-7 cells. In MCF-7 cells grown in the absence of estrogens, the reversibly binding estrogen, estradiol, and the affinity labeling estrogen, ketononestrol aziridine, KNA, evoked a 13-fold increase in pS2 RNA level. The reversibly binding antiestrogen trans-hydroxytamoxifen and the affinity labeling antiestrogens tamoxifen aziridine or desmethylnafoxidine aziridine behaved as partial agonists/antagonists. In thymidine kinase-chloramphenicol acetyltransferase (tk-CAT) fusion genes containing a 1000 base pair fragment of the pS2 5'-flanking region encompassing the estrogen responsive element of the gene [pS2 (-1100/-90) tk-CAT], estradiol and ketononestrol aziridine evoked a marked stimulation of CAT activity and, in transfected cells grown in both the presence or absence of the weak estrogen phenol red, the antiestrogens behaved as partial agonists/antagonists. This pS2 5'-flanking region displayed both estrogen-dependent and estrogen-independent enhancer activity as monitored by stimulation of CAT activity. Hormonal regulation of the transfected pS2 fusion gene was similar to that observed in the native pS2 gene of MCF-7 cells; however, antiestrogens, while still partial agonists-antagonists, were relatively more agonistic on the transfected fusion gene than on the native gene. One antiestrogen (ICI 164,384) that behaved as a pure estrogen antagonist on the native gene was a partial agonist-antagonist of pS2 gene expression in the plasmid. This study illustrates that the hormonal regulation of the pS2 gene, as characterized by the agonist-antagonist balance of estrogens and antiestrogens, is influenced by the DNA context of the pS2 estrogen responsive element. Also, the fact that estrogens and antiestrogens that form covalent bonds with the estrogen receptor modulate activity of the native pS2 gene and the pS2-tk-CAT fusion gene in a manner similar to that of their reversibly binding counterparts suggests that it may be possible to use these irreversibly binding ligands to follow the interaction of hormone-receptor complexes with regions regulating estrogenic stimulation of the pS2 gene.

Affinity Labels↗
PubMed1991

Structure of the murine fifth complement component (C5) gene. A large, highly interrupted gene with a variant donor splice site and organizational homology with the third and fourth complement component genes.

To understand fifth complement component (C5) gene regulation, splicing, and C5 protein deficiency at the molecular level, the organization of the murine C5 gene was determined. The C5 structural gene is present as a single copy in the mouse genome as demonstrated by Southern blot analysis. Accordingly, three cosmid clones were isolated from a genomic library that was prepared from mouse strain B10.D2/nSnJ. These clones overlapped and contained the structural gene encoding the complete C5 alpha-chain and 90% of the beta-chain. The 5'-flanking region of the C5 gene was obtained from a clone isolated from a genomic lambda-MOPC-41 library. Unique restriction fragments were prepared from the genomic clones and subcloned, and the exons were sequenced. All introns were sized by sequencing or Southern analysis. The C5 structural gene was found to be a highly interrupted gene of approximately 78 kilobases containing 42 exons and 41 introns. The exons ranged in length from 58 to 247 base pairs, with an average length of 131 base pairs. The introns ranged in size from 100 base pairs to 4 kilobases with an average length of 1.5 kilobases. The C5 alpha-chain was encoded by 49 kilobases containing 26 exons; the beta-chain was encoded by 29 kilobases containing 16 exons. The C5a coding sequence was split between two exons. All intron/exon junctions followed the normal consensus rule except at intron 35 in which the 5'-donor GT was substituted by GC. The 2-base-pair gene deletion and HindIII and PvuII restriction fragment length polymorphisms associated with murine C5 deficiency were localized to exon 7, exon 16, and intron 20, respectively. Comparison of the intron-exon junctions of the murine C5, human C3, and mouse C4 genes indicated that these genes are nearly identical in structural organization. However, the rat alpha 2-macroglobulin gene showed only moderate genomic organizational similarity to the murine C5 gene. A major and a minor transcriptional initiation site in the C5 gene were identified by primer extensions and confirmed by RNase protection assays. Sequence analysis of the 5'-flanking region (760 base pairs) revealed a TATA-like and CAAT box upstream of the major transcriptional initiation site at positions -274 and -303, respectively, suggesting an atypical promoter. The 5'-flanking region also contained sequences identical with several cis-acting motifs known to bind the liver-specific nuclear protein LF-A1 and the nuclear protein NF-kappa B.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Down syndrome--a gene dosage disease caused by trisomy of genes within a small segment of the long arm of chromosome 21, exemplified by the study of effects from the superoxide-dismutase type 1 (SOD-1) gene.

Down syndrome (DS), the most common postnatally viable human autosomal chromosomal abnormality is caused by trisomy for chromosome 21. The mechanism whereby the supernumerary chromosome 21 contributes to the pathology of DS remains elusive. There are, however, several evidences that DS is a gene dosage disease. This means that overproduction of certain proteins, encoded by normal genes on the extra chromosome, distorts the delicate balance of some biochemical pathways that are important for proper development and function of the organs affected in DS. It has been shown that only the distal segment of the long arm of chromosome 21 is involved in the pathogenesis of DS. Great efforts to define this "DS specific" segment are made today, with the aim to find the "DS responsible" genes. It is suggested that as few as 10-20 genes might be responsible for the DS phenotype. We will report from a world-wide collaboration study and especially the result from one single patient. It is a woman with a characteristic phenotype of DS, but with microscopically normal karyotype. She had a sister with DS, who is dead. The parents were related, why an autosomal recessive disorder is suspected. Autoradiograms of quantitative Southern blots of DNAs from the patient and her parents were analyzed after hybridization with unique DNA sequences regionally mapped on chromosome 21. The patient seems to have three alleles at the VTNR-polymorphism in the Col6A1 gene, one copy from the father and two copies from the mother. The Col6A1 gene is mapped at the very distal segment of the long arm of chromosome 21 (21q22.3). She has only two alleles of all loci analyzed proximal to Col6A1. This might indicate that she has trisomy only for the very distal part of band 21q22.3. It is, however, not enough to find the genes within the "DS specific" segment. The metabolic gene dosage effects from these genes must be evaluated. Although several genes have been mapped on chromosome 21, not one single feature of DS has been proved to be an effect of any single gene. As an example of the difficulties to assign features of DS to chromosome 21 specific genes the gene dosage effects of the superoxide dismutase type I (SOD-1) will be presented.

Adult↗
PubMed1985

Complete nucleotide sequence of a functional HLA-DP beta gene and the region between the DP beta 1 and DP alpha 1 genes: comparison of the 5' ends of HLA class II genes.

The complete nucleotide sequence of an HLA-DP beta 1 gene and part of the adjacent DP alpha 1 gene, up to and including the signal sequence exon, were determined. The sequence of the DP beta 1 gene identified it as the DPw4 allele. The six exons of the DP beta 1 gene spanned over 11,000 bp of sequence. The arrangement of the gene was broadly analogous to genes of other class II beta chains. The beta 1 exon was flanked by introns of over 4 kb. Comparisons with published sequences of cDNA clones indicated that an alternative splice junction, at the 3' end of the gene, is used in at least one allele. Variation in choice of splice junction indicates an additional mechanism for allelic variation in class II genes. The sequence also indicated that the DP beta 1 and DP alpha 1 genes are separated by only 2 kb at their 5' ends. Comparison of the 5' ends of the DP alpha 1 and beta 1 genes with other class II sequences, including the DZ alpha gene, showed conservation of several blocks of sequences thought to be involved in control of expression. Some areas of the introns were partially conserved in the DQ beta gene, and several other intron sequences were homologous to sequences found in other unrelated genes.

Alleles↗
PubMed1987

Complementation of nitrogen-regulatory (ntr-like) mutations in Rhodobacter capsulatus by an Escherichia coli gene: cloning and sequencing of the gene and characterization of the gene product.

In vivo genetic engineering by R' plasmid formation was used to isolate an Escherichia coli gene that restored the Ntr+ phenotype to Ntr- mutants of the photosynthetic bacterium Rhodobacter capsulatus (formerly Rhodopseudomonas capsulata; J. F. Imhoff, H. G. Trüper, and N. Pfenning, Int. J. Syst. Bacteriol. 34:340-343, 1984). Nucleotide sequencing of the gene revealed no homology to the ntr genes of Klebsiella pneumoniae. Furthermore, hybridization experiments between the cloned gene and different F' plasmids indicated that the gene is located between 34 and 39 min on the E. coli genetic map and is therefore unlinked to the known ntr genes. The molecular weight of the gene product, deduced from the nucleotide sequence, was 30,563. After the gene was cloned in an expression vector, the gene product was purified. It was shown to have a pI of 5.8 and to behave as a dimer during gel filtration and on sucrose density gradients. Antibodies raised against the purified protein revealed the presence of this protein in R. capsulatus strains containing the E. coli gene, but not in other strains. Moreover, elimination of the plasmid carrying the E. coli gene from complemented strains resulted in the loss of the Ntr+ phenotype. Complementation of the R. capsulatus mutations by the E. coli gene therefore occurs in trans and results from the synthesis of a functional gene product.

Amino Acids↗
PubMed2001

Genes for intermediate filament proteins and the draft sequence of the human genome: novel keratin genes and a surprisingly high number of pseudogenes related to keratin genes 8 and 18.

We screened the draft sequence of the human genome for genes that encode intermediate filament (IF) proteins in general, and keratins in particular. The draft covers nearly all previously established IF genes including the recent cDNA and gene additions, such as pancreatic keratin 23, synemin and the novel muscle protein syncoilin. In the draft, seven novel type II keratins were identified, presumably expressed in the hair follicle/epidermal appendages. In summary, 65 IF genes were detected, placing IF among the 100 largest gene families in humans. All functional keratin genes map to the two known keratin clusters on chromosomes 12 (type II plus keratin 18) and 17 (type I), whereas other IF genes are not clustered. Of the 208 keratin-related DNA sequences, only 49 reflect true keratin genes, whereas the majority describe inactive gene fragments and processed pseudogenes. Surprisingly, nearly 90% of these inactive genes relate specifically to the genes of keratins 8 and 18. Other keratin genes, as well as those that encode non-keratin IF proteins, lack either gene fragments/pseudogenes or have only a few derivatives. As parasitic derivatives of mature mRNAs, the processed pseudogenes of keratins 8 and 18 have invaded most chromosomes, often at several positions. We describe the limits of our analysis and discuss the striking unevenness of pseudogene derivation in the IF multigene family. Finally, we propose to extend the nomenclature of Moll and colleagues to any novel keratin.

Amino Acid Sequence↗
PubMed1998

From genes to gene medicines: recent advances in nonviral gene delivery.

Over the last decade, research in somatic gene therapy has focused on selected approaches to deliver therapeutic genes to cells both ex vivo and in vivo. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, nonviral gene medicines are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Nonviral technologies consist of plasmid-based expression systems containing a gene encoding a therapeutic protein and synthetic gene delivery systems. In addition to the therapeutic gene, plasmid-based expression systems contain other genetic sequences to control the in vivo production and secretion of a protein. They may include elements that prolong extrachromosomal gene expression, cell-specific promoters and, optionally, gene switches for enabling drug-regulated gene therapy. Unique gene delivery systems will be required depending upon the biology and (patho)physiology of the target tissue. This review provides a critical view of gene therapy with a major focus on advanced nonviral technologies to control the in vivo location and function of administered genes.

Clinical Trials as Topic↗
PubMed1997

Bombyxin F1 gene: structure and expression of a new bombyxin family gene that forms a pair with bombyxin B10 gene.

Bombyxin F1 gene, a new bombyxin family gene, has been identified. The F1 gene forms a pair with bombyxin B10 gene with an opposite transcriptional orientation and the gene pair F1/B10 is located between bombyxin gene pairs B9/C1 and A7/B7 in a bombyxin gene cluster. The nucleotide sequence of the F1 gene and its deduced amino acid sequence deviate moderately from those characterized previously for the family-A, family-B, family-C, family-D, and family-E bombyxin genes; the bombyxin F1 gene and preprobombyxin F1 share no more than 62% and 53% sequence identities with other bombyxin members, respectively. Harr-plot analysis indicated that the spacer of the F1/B10 gene pair has low sequence similarity with that of other bombyxin gene pairs characterized. The bombyxin F1 mRNA in Bombyx mori brain was shown to locate in four pairs of medial neurosecretory cells, which also produce other bombyxin family mRNAs. Genomic Southern hybridization indicated that the Bombyx haploid genome contains a single copy of the family-F bombyxin gene.

Amino Acid Sequence↗
PubMed1990

Evidence for segmental gene conversion between a cognate hsp 70 gene and the temperature-sensitively transcribed hsp70 genes of Trypanosoma brucei.

The protozoan parasite Trypanosoma brucei expresses several heat shock proteins of 70 kDa (hsp70). We show that, from 5' to 3', a diverged cognate hsp70 gene (gene 1) is separated by about 6 kb of DNA from a cluster of five identical hsp70 genes (genes 2-6). The hsp70 cognate gene has a predicted open reading frame of 676 amino-acids. The steady-state mRNA levels of gene 1 are unaffected by temperature shifts up to 42 degrees C. Hsps of diverse organisms share several fully conserved amino acid domains in the N-terminal region of the hsp70 proteins. These conserved amino acid domains are also observed in the T. brucei hsp70 genes 1-6. However they are, in contrast to the heat shock genes of other eukaryotes, encoded by nucleotide sequence blocks that are identical in all six hsp70 genes. These conserved domains, located in the 5' coding region, range in size from several to hundreds of nucleotides and are separated by highly diverged nucleotide sequences. The nucleotide sequence conservation between hsp70 gene 1 and hsp70 genes 2-6 indicates that selective sequence homogenization, presumably through gene conversion, maintained the amino acid sequence conservation.

Amino Acid Sequence↗
PubMed1997

Aminoglycoside 2'-N-acetyltransferase genes are universally present in mycobacteria: characterization of the aac(2')-Ic gene from Mycobacterium tuberculosis and the aac(2')-Id gene from Mycobacterium smegmatis.

The genus Mycobacterium comprises clinically important pathogens such as M. tuberculosis, which has reemerged as a major cause of morbidity and mortality world-wide especially with the emergence of multidrug-resistant strains. The use of fast-growing species such as Mycobacterium smegmatis has allowed important advances to be made in the field of mycobacterial genetics and in the study of the mechanisms of resistance in mycobacteria. The isolation of an aminoglycoside-resistance gene from Mycobacterium fortuitum has recently been described. The aac(2')-Ib gene is chromosomally encoded and is present in all isolates of M. fortuitum. The presence of this gene in other mycobacterial species is studied here and genes homologous to that of M. fortuitum have been found in all mycobacterial species studied. In this report, the cloning of the aac(2')-Ic gene from M. tuberculosis H37Rv and the aac(2')-Id gene from M. smegmatis mc(2)155 is described. Southern blot hybridizations have shown that both genes are present in all strains of this species studied to date. In addition, the putative aac(2')-Ie gene has been located in a recent release of the Mycobacterium leprae genome. The expression of the aac(2')-Ic and aac(2')-Id genes has been studied in M. smegmatis and only aac(2')-Id is correlated with aminoglycoside resistance. In order to elucidate the role of the aminoglycoside 2'-N-acetyltransferase genes in mycobacteria and to determine whether they are silent resistance genes or whether they have a secondary role in mycobacterial metabolism, the aac(2')-Id gene from M. smegmatis has been disrupted in the chromosome of M. smegmatis mc(2)155. The disruptant shows an increase in aminoglycoside susceptibility along with a slight increase in the susceptibility to lysozyme.

Acetyltransferases↗
PubMed1989

Early rearrangements of genes encoding murine immunoglobulin kappa chains, unlike genes encoding heavy chains, use variable gene segments dispersed throughout the locus.

Immunoglobulin heavy-chain variable region (TH) gene segments located closest to the joining (JH) gene segments are preferentially rearranged during ontogeny, indicating that chromosomal position influences the frequency of rearrangement. In addition, certain VH gene segments are repeatedly rearranged, suggesting that the DNA sequence or structure surrounding these segments may increase the probability of rearrangement. To determine whether there is similar based rearrangement of kappa variable (V kappa) gene segments, 25 rearrangements were sequenced from murine fetal and neonatal B-cell hybridomas and from subclones of a pre-B cell line that rearranged V kappa genes during in vitro culture. Four gene segments were isolated twice and one gene segment was isolated three times, suggesting that the process that targets individual variable gene segments for repeated rearrangement operates on both the VH and V kappa loci. Based on a current map of the V kappa locus, the rearranged gene segments belong to nine families that are dispersed throughout the locus. Thus, in these cell types, V kappa rearrangements use germ-line gene segments located across the entire locus, whereas the corresponding VH rearrangements use gene segments proximal to the JH gene segments. Heterogeneity of V kappa rearrangements would add diversity to the biased pool of VH rearrangements, producing a broad repertoire of antibodies early in development.

Amino Acid Sequence↗
PubMed2003

Crystallin genes: specialization by changes in gene regulation may precede gene duplication.

The crystallins account for 80-90% of the water-soluble proteins of the transparent lens. These diverse proteins are responsible for the optical properties of the lens and have been recruited from metabolic enzymes and stress proteins. They often differ among species (i.e. are taxon-specific) and may be expressed outside of the lens where they have non-refractive roles (a situation we call gene sharing). Crystallin recruitment has occurred by changes in gene regulation resulting in high lens expression. Duck lactate dehydrogenase/epsilon-crystallin and alpha-enolase/tau-crystallin are each encoded in single-copy genes, consistent with these enzymes acquiring a crystallin role, without loss of their nonlens metabolic function, by a change in gene regulation in the absence of gene duplication. The small heat shock protein/alpha-crystallins and avian argininosuccinate lyase/delta-crystallins were also recruited by a change in gene regulation leading to high lens expression, except this was followed by a gene duplication with further lens specialization of the alphaA and the delta1 (in chickens) crystallin genes. Cephalopod (squid and octopus) S-crystallins were recruited from glutathione S-transferase apparently after duplication of the original gene encoding the enzyme, although this remains uncertain. We speculate that one of the new genes (glutathione S-transferase/S11-crystallin) specialized for lens expression by a change in gene regulation and subsequently duplicated many times to form the lens-specialized, multiple S-crystallins that lack enzymatic activity. That similar transcription factors (e.g. Pax-6, retinoic acid receptors, maf, Sox, AP-1, CREB) regulate different crystallin genes suggest that common features of lens-specific expression have played a pivotal role for recruiting the diverse, multifunctional proteins as crystallins.

Animals↗
PubMed2000

The tkNeo gene, but not the pgkPuro gene, can influence the ability of the beta-globin LCR to enhance and confer position-independent expression onto the beta-globin gene.

Whether drug-selectable genes can influence expression of the beta-globin gene linked to its LCR was assessed here. With the tkNeo gene placed in cis and used to select transfected cells, the beta-globin gene was expressed fourfold lower when it was positioned upstream of the LCR rather than downstream. This difference did not occur when the pgkPuro gene replaced tkNeo. Moreover, the beta-globin gene situated upstream of the LCR was transcribed without position effects when it was cotransfected with a pgkPuro-containing plasmid, whereas cotransfection with a tkNeo plasmid gave measurable position effects. Previous results from transfected cells selected via a linked tkNeo gene suggested that the 3' end of the beta-globin gene has no impact on LCR-enhanced expression. Here, removal of the 3' end of the beta-globin gene resulted in lower and much more variable expression in both transgenic mice and cells cotransfected with pgkPuro. Together, the results suggest that tkNeo, but not pgkPuro, can strongly influence expression of the beta-globin gene linked to its LCR. The findings could partly explain why data on beta-globin gene regulation obtained from transfected cells have often not agreed with those obtained using transgenic mice. Hence, one must be careful in choosing a drug-selectable gene for cell transfection studies.

Animals↗