scholarly journals THE EVOLUTION OF SELF-REGULATED TRANSPOSITION OF TRANSPOSABLE ELEMENTS

Genetics ◽  
1986 ◽  
Vol 112 (2) ◽  
pp. 359-383
Author(s):  
B Charlesworth ◽  
C H Langley
Keyword(s):  
Transposable Elements ◽  
High Frequency ◽  
Germ Line ◽  
Genetic Recombination ◽  
Somatic Cells ◽  
Selective Advantage ◽  
Selective Force ◽  
Cis Acting ◽  
Bacterial Plasmids ◽  
Regulatory Effects

ABSTRACT This paper examines the conditions under which self-regulated rates of transposition can evolve in populations of transposable elements infecting sexually reproducing hosts. Models of the evolution of both cis-acting regulation (transposition immunity) and trans-acting regulation (transposition repression) are analyzed. The potential selective advantage to regulation is assumed to be derived from the deleterious effects of mutations associated with the insertion of newly replicated elements. It is shown that both types of regulation can easily evolve in hosts with low rates of genetic recombination per generation, such as bacteria or bacterial plasmids. Conditions are much more restrictive in organisms with relatively free recombination. In haploids, the main selective force promoting regulation is the induction of lethal or sterile mutations by transposition; in diploids, a sufficiently high frequency of dominant lethal or sterile mutations associated with transpositions is required. Data from Drosophila and maize suggest that this requirement can sometimes be met. Coupling of regulatory effects across different families of elements would also aid the evolution of regulation. The selective advantages of restricting transposition to the germ line and of excising elements from somatic cells are discussed.

Identification of a cis-acting sequence required for germ line-specific splicing of the P element ORF2-ORF3 intron

1991 ◽  
Vol 11 (3) ◽  
pp. 1538-1546
Author(s):  
A C Chain ◽  
S Zollman ◽  
J C Tseng ◽  
F A Laski
Keyword(s):  
Drosophila Melanogaster ◽  
Splice Site ◽  
Germ Line ◽  
Somatic Cells ◽  
Regulatory Region ◽  
Systematic Search ◽  
P Element ◽  
Regulatory Sequence ◽  
Cis Acting ◽  
The Third

P element transposition in Drosophila melanogaster is limited to the germ line because the third intron (the ORF2-ORF3 intron) of the P element transcript is spliced only in germ line cells. We describe a systematic search for P element sequences that are required to regulate the splicing of the ORF2-ORF3 intron. We have identified three adjacent mutations that abolish the germ line specificity and allow splicing of this intron in all tissues. These mutations define a 20-base regulatory region located in the exon, 12 to 31 bases from the 5' splice site. Our data show that this cis-acting regulatory sequence is required to inhibit the splicing of the ORF2-ORF3 intron in somatic cells.

scholarly journals Identification of a cis-acting sequence required for germ line-specific splicing of the P element ORF2-ORF3 intron.

1991 ◽  
Vol 11 (3) ◽  
pp. 1538-1546 ◽  
Author(s):  
A C Chain ◽  
S Zollman ◽  
J C Tseng ◽  
F A Laski
Keyword(s):  
Drosophila Melanogaster ◽  
Splice Site ◽  
Germ Line ◽  
Somatic Cells ◽  
Regulatory Region ◽  
Systematic Search ◽  
P Element ◽  
Regulatory Sequence ◽  
Cis Acting ◽  
The Third

P element transposition in Drosophila melanogaster is limited to the germ line because the third intron (the ORF2-ORF3 intron) of the P element transcript is spliced only in germ line cells. We describe a systematic search for P element sequences that are required to regulate the splicing of the ORF2-ORF3 intron. We have identified three adjacent mutations that abolish the germ line specificity and allow splicing of this intron in all tissues. These mutations define a 20-base regulatory region located in the exon, 12 to 31 bases from the 5' splice site. Our data show that this cis-acting regulatory sequence is required to inhibit the splicing of the ORF2-ORF3 intron in somatic cells.

Distributive pairing in the grasshopper Chorthippus binotatus

Genome ◽  
1991 ◽  
Vol 34 (1) ◽  
pp. 139-143 ◽  
Author(s):  
M. D. Lopez-Leon ◽  
J. Cabrero ◽  
J. P. M. Camacho
Keyword(s):  
X Chromosome ◽  
High Frequency ◽  
Germ Line ◽  
Somatic Cells ◽  
Male Meiosis ◽  
Almost All ◽  
In Cells ◽  
Metaphase I

Six males of the grasshopper Chorthippus binotatus were mosaic for the presence of extra (E) chromosomes in the germ line, but lacked them in the somatic cells of gastric caeca. E chromosomes were very similar to the X chromosome in size and meiotic properties (heteropycnosis and autopairing). X and E chromosomes associated frequently at diplotene, but the associations never persisted until metaphase I, which indicated that they were not chiasmate. When one E was present, X and E univalents segregated preferentially to opposite poles. In cells with two E, they formed a bivalent in almost all cells, and decreased the frequency of X–E associations by 20%. These cells showed a high frequency of nondisjunction between the two E chromosomes, such that they segregated independently despite the high persistence of their association at metaphase I. These results are interpreted and discussed in the light of the distributive pairing model.Key words: distributive pairing, X chromosome, E chromosome, Chorthippus, male meiosis.

scholarly journals Sequence Variation and Haplotype Structure at the HumanHFELocus

Genetics ◽  
2002 ◽  
Vol 161 (4) ◽  
pp. 1609-1623 ◽  
Author(s):  
Christopher Toomajian ◽  
Martin Kreitman
Keyword(s):  
High Frequency ◽  
Nucleotide Diversity ◽  
Sequence Variation ◽  
Hla Class I ◽  
Selective Advantage ◽  
European Ancestry ◽  
Iron Regulation ◽  
Intragenic Recombination ◽  
Nucleotide Variability ◽  
Show Evidence

AbstractThe HFE locus encodes an HLA class-I-type protein important in iron regulation and segregates replacement mutations that give rise to the most common form of genetic hemochromatosis. The high frequency of one disease-associated mutation, C282Y, and the nature of this disease have led some to suggest a selective advantage for this mutation. To investigate the context in which this mutation arose and gain a better understanding of HFE genetic variation, we surveyed nucleotide variability in 11.2 kb encompassing the HFE locus and experimentally determined haplotypes. We fully resequenced 60 chromosomes of African, Asian, or European ancestry as well as one chimpanzee, revealing 41 variable sites and a nucleotide diversity of 0.08%. This indicates that linkage to the HLA region has not substantially increased the level of HFE variation. Although several haplotypes are shared between populations, one haplotype predominates in Asia but is nearly absent elsewhere, causing higher than average genetic differentiation among the three major populations. Our samples show evidence of intragenic recombination, so the scarcity of recombination events within the C282Y allele class is consistent with selection increasing the frequency of a young allele. Otherwise, the pattern of variability in this region does not clearly indicate the action of positive selection at this or linked loci.

The ethics of genome editing in the clinic: A dose of realism for healthcare leaders

2017 ◽  
Vol 30 (3) ◽  
pp. 159-163
Author(s):  
Tania Bubela ◽  
Yael Mansour ◽  
Dianne Nicol
Keyword(s):  
Genome Editing ◽  
Germ Line ◽  
Genetic Diseases ◽  
Somatic Cells ◽  
Clinical Translation ◽  
Preclinical Research ◽  
Societal Issues ◽  
Realistic Assessment ◽  
Healthcare Leaders

Genome editing technologies promise therapeutic advances for genetic diseases. We discuss the ethical and societal issues raised by these technologies, including their use in preclinical research, their potential to address mutations in somatic cells, and their potential to make germ line alterations that may be passed to subsequent generations. We call for a proportionate response from health leaders based on a realistic assessment of benefits, risks, and timelines for clinical translation.

Insertion and excision of Caenorhabditis elegans transposable element Tc1

1988 ◽  
Vol 8 (2) ◽  
pp. 737-746
Author(s):  
D Eide ◽  
P Anderson
Keyword(s):  
Amino Acid ◽  
Caenorhabditis Elegans ◽  
Transposable Element ◽  
Dna Sequences ◽  
Germ Line ◽  
Consensus Sequence ◽  
Somatic Cells ◽  
Chain Gene ◽  
Imprecise Excision ◽  
Insertion Sites

The transposable element Tc1 is responsible for most spontaneous mutations that occur in Caenorhabditis elegans variety Bergerac. We investigated the genetic and molecular properties of Tc1 transposition and excision. We show that Tc1 insertion into the unc-54 myosin heavy-chain gene was strongly site specific. The DNA sequences of independent Tc1 insertion sites were similar to each other, and we present a consensus sequence for Tc1 insertion that describes these similarities. We show that Tc1 excision was usually imprecise. Tc1 excision was imprecise in both germ line and somatic cells. Imprecise excision generated novel unc-54 alleles that had amino acid substitutions, amino acid insertions, and, in certain cases, probably altered mRNA splicing. The DNA sequences remaining after Tc1 somatic excision were the same as those remaining after germ line excision, but the frequency of somatic excision was at least 1,000-fold higher than that of germ line excision. The genetic properties of Tc1 excision, combined with the DNA sequences of the resulting unc-54 alleles, demonstrated that excision was dependent on Tc1 transposition functions in both germ line and somatic cells. Somatic excision was not regulated in the same strain-specific manner as germ-line excision was. In a genetic background where Tc1 transposition and excision in the germ line was not detectable, Tc1 excision in the soma still occurred at high frequency.

High-frequency germ line gene conversion in transgenic mice

1992 ◽  
Vol 12 (6) ◽  
pp. 2545-2552
Author(s):  
J R Murti ◽  
M Bumbulis ◽  
J C Schimenti
Keyword(s):  
Gene Conversion ◽  
Dna Sequences ◽  
High Frequency ◽  
Germ Line ◽  
Gene Families ◽  
Histochemical Staining ◽  
Evolutionary Significance ◽  
Evolutionary Divergence ◽  
Lacz Gene ◽  
Male Gametes

Gene conversion is the nonreciprocal transfer of genetic information between two related genes or DNA sequences. It can influence the evolution of gene families, having the capacity to generate both diversity and homogeneity. The potential evolutionary significance of this process is directly related to its frequency in the germ line. While measurement of meiotic inter- and intrachromosomal gene conversion frequency is routine in fungal systems, it has hitherto been impractical in mammals. We have designed a system for identifying and quantitating germ line gene conversion in mice by analyzing transgenic male gametes for a contrived recombination event. Spermatids which undergo the designed intrachromosomal gene conversion produce functional beta-galactosidase (encoded by the lacZ gene), which is visualized by histochemical staining. We observed a high incidence of lacZ-positive spermatids (approximately 2%), which were produced by a combination of meiotic and mitotic conversion events. These results demonstrate that gene conversion in mice is an active recombinational process leading to nonparental gametic haplotypes. This high frequency of intrachromosomal gene conversion seems incompatible with the evolutionary divergence of newly duplicated genes. Hence, a process may exist to uncouple gene pairs from frequent conversion-mediated homogenization.

Recombination hot spot in the human beta-globin gene cluster: meiotic recombination of human DNA fragments in Saccharomyces cerevisiae

1985 ◽  
Vol 5 (8) ◽  
pp. 2029-2038
Author(s):  
D Treco ◽  
B Thomas ◽  
N Arnheim
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Meiotic Recombination ◽  
High Frequency ◽  
Genetic Recombination ◽  
Hot Spot ◽  
Globin Gene ◽  
Beta Globin ◽  
Beta Globin Gene ◽  
Human Dna ◽  
Yeast Meiosis

We describe a novel system for the analysis of sequence-specific meiotic recombination in Saccharomyces cerevisiae. A comparison of three adjacent restriction fragments from the human beta-globin locus revealed that one of them, previously hypothesized to contain a relative hot spot for genetic recombination, engages in reciprocal exchange during yeast meiosis significantly more frequently than either of the other two fragments. Removal of the longest of four potential Z-DNA-forming regions from this fragment does not affect the high frequency of genetic recombination.

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