Limits...
Complex germline and somatic mutation processes at a haploid human minisatellite shown by single-molecule analysis.

Shanks ME, May CA, Dubrova YE, Balaresque P, Rosser ZH, Adams SM, Jobling MA - Mutat. Res. (2008)

Bottom Line: Sperm DNA showed significantly more length mutants than blood DNA, with mutants in both tissues involving small-scale (1-3 repeat units in a 77 repeat progenitor allele) increases or decreases in repeat block lengths, with no gain or loss bias.Isometric mutations altering structure but not length were found in both tissues, and involved either the apparent shift of a boundary between repeat unit blocks (a 'boundary switch') or the conversion of a repeat within a block to a different repeat type ('modular structure' mutant).There was a significant excess of boundary switch mutants and deficit of modular structure mutants in sperm.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Leicester, Leicester, UK.

ABSTRACT
Mutation at most human minisatellites is driven by complex interallelic processes that give rise to a high degree of length polymorphism and internal structural variation. MSY1, the only highly variable minisatellite on the non-recombining region of the Y chromosome, is constitutively haploid and therefore precluded from interallelic interactions, yet maintains high diversity in both length and structure. To investigate the basis of its mutation processes, an unbiased structural analysis of >500 single-molecule MSY1 PCR products from matched sperm and blood samples from a single donor was undertaken. The overall mutation frequencies in sperm and blood DNAs were not significantly different, at 2.68% and 1.88%, respectively. Sperm DNA showed significantly more length mutants than blood DNA, with mutants in both tissues involving small-scale (1-3 repeat units in a 77 repeat progenitor allele) increases or decreases in repeat block lengths, with no gain or loss bias. Isometric mutations altering structure but not length were found in both tissues, and involved either the apparent shift of a boundary between repeat unit blocks (a 'boundary switch') or the conversion of a repeat within a block to a different repeat type ('modular structure' mutant). There was a significant excess of boundary switch mutants and deficit of modular structure mutants in sperm. A comparison of mutant structures with phylogenetically matched alleles in population samples showed that alleles with structures resembling the blood mutants were unlikely to arise in populations. Mutation seems likely to involve gene conversion via synthesis-dependent strand annealing, and the blood-sperm differences may reflect more relaxed constraint on sister chromatid alignment in blood.

Show MeSH

Related in: MedlinePlus

Structures of mutant alleles. At the top is shown the progenitor structure, with circles corresponding to repeat units (see Fig. 1), and a simplified structure to the right. (a) Mutants identified in sperm DNA. Showing length mutants, boundary switch mutants, and the single example of a boundary switch mutant. Large open arrows to the right indicate gains or losses of repeats with respect to the progenitor. (b) Mutants identified in blood DNA. Showing length mutants, and multiple modular structural mutants; note the absence of boundary switch mutants.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2599865&req=5

fig3: Structures of mutant alleles. At the top is shown the progenitor structure, with circles corresponding to repeat units (see Fig. 1), and a simplified structure to the right. (a) Mutants identified in sperm DNA. Showing length mutants, boundary switch mutants, and the single example of a boundary switch mutant. Large open arrows to the right indicate gains or losses of repeats with respect to the progenitor. (b) Mutants identified in blood DNA. Showing length mutants, and multiple modular structural mutants; note the absence of boundary switch mutants.

Mentions: Initial experiments sought to identify length mutants. From the 24 sperm DNA experiments 597 molecules were amplified using nested PCR and a total of 9 mutants observed as PCR products larger or smaller than the progenitor allele (Fig. 2(a)). This corresponds to a mutation frequency to new-length alleles of 1.51% (9/597 amplifiable molecules). There was no preference for gain or loss of repeats, with four mutants representing gains, and five losses (Fig. 3(a)). All mutants were within three repeats of the original progenitor size.


Complex germline and somatic mutation processes at a haploid human minisatellite shown by single-molecule analysis.

Shanks ME, May CA, Dubrova YE, Balaresque P, Rosser ZH, Adams SM, Jobling MA - Mutat. Res. (2008)

Structures of mutant alleles. At the top is shown the progenitor structure, with circles corresponding to repeat units (see Fig. 1), and a simplified structure to the right. (a) Mutants identified in sperm DNA. Showing length mutants, boundary switch mutants, and the single example of a boundary switch mutant. Large open arrows to the right indicate gains or losses of repeats with respect to the progenitor. (b) Mutants identified in blood DNA. Showing length mutants, and multiple modular structural mutants; note the absence of boundary switch mutants.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2599865&req=5

fig3: Structures of mutant alleles. At the top is shown the progenitor structure, with circles corresponding to repeat units (see Fig. 1), and a simplified structure to the right. (a) Mutants identified in sperm DNA. Showing length mutants, boundary switch mutants, and the single example of a boundary switch mutant. Large open arrows to the right indicate gains or losses of repeats with respect to the progenitor. (b) Mutants identified in blood DNA. Showing length mutants, and multiple modular structural mutants; note the absence of boundary switch mutants.
Mentions: Initial experiments sought to identify length mutants. From the 24 sperm DNA experiments 597 molecules were amplified using nested PCR and a total of 9 mutants observed as PCR products larger or smaller than the progenitor allele (Fig. 2(a)). This corresponds to a mutation frequency to new-length alleles of 1.51% (9/597 amplifiable molecules). There was no preference for gain or loss of repeats, with four mutants representing gains, and five losses (Fig. 3(a)). All mutants were within three repeats of the original progenitor size.

Bottom Line: Sperm DNA showed significantly more length mutants than blood DNA, with mutants in both tissues involving small-scale (1-3 repeat units in a 77 repeat progenitor allele) increases or decreases in repeat block lengths, with no gain or loss bias.Isometric mutations altering structure but not length were found in both tissues, and involved either the apparent shift of a boundary between repeat unit blocks (a 'boundary switch') or the conversion of a repeat within a block to a different repeat type ('modular structure' mutant).There was a significant excess of boundary switch mutants and deficit of modular structure mutants in sperm.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Leicester, Leicester, UK.

ABSTRACT
Mutation at most human minisatellites is driven by complex interallelic processes that give rise to a high degree of length polymorphism and internal structural variation. MSY1, the only highly variable minisatellite on the non-recombining region of the Y chromosome, is constitutively haploid and therefore precluded from interallelic interactions, yet maintains high diversity in both length and structure. To investigate the basis of its mutation processes, an unbiased structural analysis of >500 single-molecule MSY1 PCR products from matched sperm and blood samples from a single donor was undertaken. The overall mutation frequencies in sperm and blood DNAs were not significantly different, at 2.68% and 1.88%, respectively. Sperm DNA showed significantly more length mutants than blood DNA, with mutants in both tissues involving small-scale (1-3 repeat units in a 77 repeat progenitor allele) increases or decreases in repeat block lengths, with no gain or loss bias. Isometric mutations altering structure but not length were found in both tissues, and involved either the apparent shift of a boundary between repeat unit blocks (a 'boundary switch') or the conversion of a repeat within a block to a different repeat type ('modular structure' mutant). There was a significant excess of boundary switch mutants and deficit of modular structure mutants in sperm. A comparison of mutant structures with phylogenetically matched alleles in population samples showed that alleles with structures resembling the blood mutants were unlikely to arise in populations. Mutation seems likely to involve gene conversion via synthesis-dependent strand annealing, and the blood-sperm differences may reflect more relaxed constraint on sister chromatid alignment in blood.

Show MeSH
Related in: MedlinePlus