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Germline unbalanced translocations arise from diverse mutational mechanisms including chromothripsis

ABSTRACT: Unbalanced translocations are a relatively common type of copy number variation and are a major contributor to neurodevelopmental disorders. We analyzed the breakpoints of 57 unique unbalanced translocations to investigate the mechanisms of how they form. 51 are simple unbalanced translocations between two different chromosome ends, and six rearrangements have more than three breakpoints involving two to five chromosomes. Sequencing 37 breakpoint junctions revealed that simple translocations have between zero and four basepairs (bp) of microhomology (n=26), short inserted sequences (n=8), or paralogous repeats (n=3) at the junctions, indicating that translocations do not arise primarily from non-allelic homologous recombination, but instead form most often via non-homologous end joining or microhomology-mediated break-induced replication. Three simple translocations fuse genes that are predicted to produce in-frame transcripts of SIRPG-WWOX, SMOC2-PROX1, and PIEZO2-MTA1, which may lead to gain of function. Three complex translocations have inversions, insertions, and multiple breakpoint junctions between only two chromosomes. Whole- genome sequencing and fluorescence in situ hybridization analysis of two de novo translocations revealed at least 18 and 33 breakpoints involving five different chromosomes. Breakpoint sequencing of one inherited translocation involving four chromosomes uncovered multiple breakpoints with inversions and insertions. All of these breakpoint junctions had zero to four bp of microhomology consistent with germline chromothripsis, and both de novo events occurred on paternal alleles. Breakpoint sequencing of our large collection of chromosome rearrangements offers a comprehensive analysis of the molecular mechanisms behind germline translocation formation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE68019 | GEO | 2015/04/22

SECONDARY ACCESSION(S): PRJNA281869

REPOSITORIES: GEO

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Project description:Somatic variants spontaneously appear during the vegetative multiplication of woody crops. The new white-berried grapevine cultivar Tempranillo Blanco (TB) originally appeared as a bud sport of the black skin-berried Tempranillo Tinto (TT) cultivar. To understand the origin of this variation, TT and TB genomes were sequenced. Structural variation and genetic segregation analyses uncovered that complex chromosome rearrangements consistent with chromothripsis, a catastrophic phenomenon recently described in human cancer, generated the variant genome of TB and the deletion of the color locus functional allele. Loss of heterozygosity and decreased copy number delimited alternating monosomic and disomic fragments in the distal arms of TB’s linkage groups 2 and 5. Hemizygous fragments collectively extended over 8.1 Mb and comprised 313 annotated genes. Clustered breakpoints for complex chromosome rearrangements disrupting linkage groups 2 and 5 were identified and junctions involved unbalanced inter- and intra-chromosome translocations and one unbalanced inversion. Signatures of blunt fusions or microhomology-mediated end joining mechanisms were detected at breakpoint junction flanks. Segregation distortion in TB-derived selfed progeny indicated linkage of rearrangements in a single copy of the affected chromosomes that was barely transmitted. Additionally to berry color loss, these dramatic changes have further viticultural consequences in TB associated to a decreased sexual fitness. Our findings show that chromothripsis spontaneously arise during mitotic multiplication of grapevine, evidencing that this phenomenon could contribute to clonal variation in woody crops and to the evolution of plant genomes. Grapevine GrapeGen GeneChips(R) were used for partial comparative genome hybridization between black-berried cultivars and their respective white-berried somatic variants. Differences in copy number were used to estimate chromosome deletions associated to the loss of berry color.

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Germline unbalanced translocations arise from diverse mutational mechanisms including chromothripsis

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