title: BRCA2 minor transcript lacking exons 4-7 supports viability in mice and may account for survival of humans with a pathogenic biallelic mutation.
abstract: The breast cancer gene, BRCA2, is essential for viability, yet patients with Fanconi anemia-D1 subtype are born alive with biallelic mutations in this gene. The hypomorphic nature of the mutations is believed to support viability, but this is not always apparent. One such mutation is IVS7+2T>G, which causes premature protein truncation due to skipping of exon 7. We previously identified a transcript lacking exons 4-7, which restores the open-reading frame, encodes a DNA repair proficient protein and is expressed in IVS7+2T>G carriers. However, because the exons 4-7 encoded region contains several residues required for normal cell-cycle regulation and cytokinesis, this transcript's ability to support viability can be argued. To address this, we generated a Brca2 knock-in mouse model lacking exons 4-7 and demonstrated that these exons are dispensable for viability as well as tumor-free survival. This study provides the first in vivo evidence of the functional significance of a minor transcript of BRCA2 that can play a major role in the survival of humans who are homozygous for a clearly pathogenic mutation. Our results highlight the importance of assessing protein function restoration by premature truncating codon bypass by alternative splicing when evaluating the functional significance of variants such as nonsense and frame-shift mutations that are assumed to be clearly pathogenic. Our findings will impact not only the assessment of variants that map to this region, but also influence counseling paradigms and treatment options for such mutation carriers.
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research.
authors.forename: Eswary
authors.initials: E
authors.lastname: Thirthagiri
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research, Basic Sciences Program.
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Klarmann
authors.affiliation: Laboratory of Protein Dynamics and Signaling.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Shukla
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research, Basic Sciences Program.
authors.forename: Eileen
authors.initials: E
authors.lastname: Southon
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research.
authors.forename: Kajal
authors.initials: K
authors.lastname: Biswas
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research, Basic Sciences Program.
authors.forename: Betty K
authors.initials: BK
authors.lastname: Martin
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research.
authors.forename: Susan Lynn
authors.initials: SL
authors.lastname: North
authors.affiliation: Optical Microscopy and Analysis Laboratory and.
authors.forename: Valentin
authors.initials: V
authors.lastname: Magidson
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research.
authors.forename: Sandra
authors.initials: S
authors.lastname: Burkett
authors.affiliation: Pathology/Histotechnology Laboratory, Leidos Biomedical Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA.
authors.forename: Diana C
authors.initials: DC
authors.lastname: Haines
authors.affiliation: Frederick CCR Flow Cytometry Core Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Noer
authors.affiliation: Frederick CCR Flow Cytometry Core Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA.
authors.forename: Roberta
authors.initials: R
authors.lastname: Matthai
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research.
authors.forename: Lino
authors.initials: L
authors.lastname: Tessarollo
authors.affiliation: Laboratory of Protein Dynamics and Signaling.
authors.forename: Jadranka
authors.initials: J
authors.lastname: Loncarek
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research, Basic Sciences Program, sharans@mail.nih.gov kellerjo@mail.nih.gov.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Keller
authors.affiliation: Mouse Cancer Genetics Program, Center for Cancer Research, sharans@mail.nih.gov kellerjo@mail.nih.gov.
authors.forename: Shyam K
authors.initials: SK
authors.lastname: Sharan
mesh_terms: D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D024682:BRCA2 Protein / Q000235:genetics*; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D005091:Exons / Q000235:genetics; D005199:Fanconi Anemia / Q000235:genetics* / Q000473:pathology; D055879:Gene Knock-In Techniques; D020022:Genetic Predisposition to Disease; D018095:Germ-Line Mutation; D006801:Humans; D051379:Mice; D009154:Mutation; D010375:Pedigree; D022821:RNA Splice Sites
chemical_list: D024682:BRCA2 Protein; D022821:RNA Splice Sites