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BRCA2 is a clinically actionable gene implicated in breast and ovarian cancer predisposition that has become a high priority target for improving the classification of variants of unknown significance (VUS). Among all BRCA2 VUS, those causing partial/leaky splicing defects are the most challenging to classify because the minimal level of full-length (FL) transcripts required for normal function remains to be established. Here, we explored BRCA2 exon 3 ( BRCA2 e3) as a model for calibrating variant-induced spliceogenicity and estimating thresholds for BRCA2 haploinsufficiency. In silico predictions, minigene splicing assays, patients' RNA analyses, a mouse embryonic stem cell (mESC) complementation assay and retrieval of patient-related information were combined to determine the minimal requirement of FL BRCA2 transcripts. Of 100 BRCA2 e3 variants tested in the minigene assay, 64 were found to be spliceogenic, causing mild to severe RNA defects. Splicing defects were also confirmed in patients' RNA when available. Analysis of a neutral leaky variant (c.231T>G) showed that a reduction of approximately 60% of FL BRCA2 transcripts from a mutant allele does not cause any increase in cancer risk. Moreover, data obtained from mESCs suggest that variants causing a decline in FL BRCA2 with approximately 30% of wild-type are not pathogenic, given that mESCs are fully viable and resistant to DNA-damaging agents in those conditions. In contrast, mESCs producing lower relative amounts of FL BRCA2 exhibited either null or hypomorphic phenotypes. Overall, our findings are likely to have broader implications on the interpretation of BRCA2 variants affecting the splicing pattern of other essential exons. SIGNIFICANCE: These findings demonstrate that BRCA2 tumor suppressor function tolerates substantial reduction in full-length transcripts, helping to determine the pathogenicity of BRCA2 leaky splicing variants, some of which may not increase cancer risk., (©2020 American Association for Cancer Research.)

von Hippel-Lindau (VHL) disease is a multisystem inherited cancer syndrome characterized by the development of highly vascular tumors including hemangioblastomas of the retina and central nervous system, pheochromocytomas, and clear cell renal carcinoma, which result from somatic inactivation of the wild-type VHL allele in cells harboring a germ-line VHL mutation. Homozygous inactivation of the VHL gene in mice resulted in embryonic lethality. To produce a mouse model that closely mimics human VHL disease and avoids embryonic lethality, we used Cre/lox site-specific recombination technology. We generated mice carrying conditional VHL alleles and a cre transgene under the control of the human beta-actin promoter, which directs cre expression in a mosaic pattern in multiple organs. VHL(f/d)/Cre mice developed multiple, hepatic hemangiomas that led to premature death, as well as angiectasis and angiogenesis in multiple organs. Interestingly, testes of male VHL(f/d)/Cre mice were unusually small with severely reduced sperm count resulting in infertility. Loss of pVHL function in this VHL conditional knockout mouse model results in an extensive abnormal vascular phenotype in multiple mouse organs, which will provide a useful animal model for testing potential antiangiogenic therapies for VHL disease treatment. Importantly, the phenotypic defects in sperm development observed in these mice support a novel role for VHL in spermatogenesis. This VHL conditional knockout mouse model will provide an in vivo system for studying the functional requirement of the VHL gene in reproductive biology.