Research in our laboratory focuses on the identification and characterization of human rare disease genes, their mutations, variants and patho-mechanisms that underlie several Mendelian diseases, using classical genetics and molecular genetics, functional genomics and mechanism-based biology approaches, including mouse and fly models. Diseases include hereditary cancer syndromes (Li-Fraumeni Syndrome and its variants, LFS/LFL) and neuromuscular disorders (myotonic dystrophies, DM). Another focus has been the molecular characterization of sporadic cancers that are part of the LFS tumor spectrum (sarcomas, brain, leukemia, lung, head and neck) by genome-wide approaches to identify genomic, epigenomic and transcriptomic changes underlying tumor initiation, progression and metastasis. A common underlying theme of our research is the application of state-of-the-art omics methodologies towards both discovery and translational goals.
Hereditary Cancer Predisposition
Li-Fraumeni syndrome (LFS) is a genetically heterogeneous, rare
inherited cancer syndrome. Most cases are due to mutations in the
tumor suppressor gene TP53 (p53). In collaboration with Dr. Strong,
we previously mapped a novel LFS/LFL predisposition locus to
chromosome 1q23. We recently identified a novel mutated tumor
suppressor gene in multiple non-p53 LFS/LFL families, which we are now
investigating functionally for its molecular and cellular roles in
tumorigenesis. LFS predisposition and/or modifier genes may also be
functionally important in other tumor types lacking a clear genetic
In both p53 and non-p53 LFS, there is additional evidence for risk modifiers and factors in addition to the inherited susceptibility. We investigated various putative modifier alleles in TP53, including MDM2 and MDM4, two negative regulators of p53. To dissect the complex genetic and epigenetic events underlying LFS tumorigenesis, we are using integrated approaches combining genomic and epigenomic profiling in tumors of human LFS patients.
We have used similar comparative genomics approaches to deconstruct tumors of genetically engineered LFS mouse models generated by Dr. Lozano. To determine the cooperativity between mutant p53 and these novel variant genes in vivo, we are generating suitable LFS mouse models carrying mutations in multiple genes.
The molecular characterization and classification of sporadic cancers (sarcomas, brain, leukemia, lung, head and neck) through genomics methodologies to identify genomic, epigenomic and transcriptomic changes underlying tumor initiation, progression and metastasis has been another focus.
Myotonic Dystrophies (DM)
Myotonic dystrophy, the most common adult neuromuscular disorder, is caused by mutant (CTG)DM1 or (CCTG)DM2 repeat expansion mutations that when transcribed cause disease. It is still unclear how exactly these mutant (CUG)DM1/(CCUG)DM2 RNAs mediate their disease-causing effects at the molecular and cellular level.
My lab confirmed that the causative mutation in phenotypically diverse patients with proximal myotonic myopathy/dystrophy of different European origins was the (CCTG)DM2 expansion that segregates on a single shared haplotype common to almost all DM2 patients, indicating an ancestral founder effect.
We showed that, similar to DM1, DM2 also has a pre-mutation allele
pool from which mutant alleles are derived, and proposed an
evolutionary model for the origin of the DM2 mutation. Contrary to the
original paradigm that the resident gene of the (CCTG)DM2 mutation
plays no role in the disease, we showed that the expansion causes
abnormal expression of ZNF9 at both the RNA and protein levels. As the
underlying mechanisms leading to a reduction to half of normal levels,
we identified impaired pre-mRNA splicing of intron 1 in mutant ZNF9
Using global splice variant profiling on the largest patient sample set to date, including other inherited dystrophies, we showed that most expression and splicing changes in DM1 and DM2 were shared with other muscular dystrophies lacking repeat expansion mutations, providing no evidence for a widespread DM-specific spliceopathy. Thus, missplicing may not be the only driving patho-mechanism and may be compensatory, even in DM. To further dissect the pathophysiology and mechanisms underlying DM2, we are using functional genomics and molecular genetics approaches. Recent efforts have focused on the generation of different and complementing models, including transgenic, knock-in and knock-out mouse models and transgenic fly models.
Muscle pathologies of three different DM2 mouse models. (A,B) A transgenic model expressing (CCTG)121 in intron 1 of the human skeletal actin (HSA) transgene. (C, D) A knock-in mouse model expressing (CCTG)189 in intron 1 of the homologous Cnbp gene. (E, F) A Cnbp knockout model. The three different models were designed to be complementary and allow the study of different aspects of the DM2 pathophysiology, including toxic (CCUG)DM2 gain-of-function outside and within the context of the CNBP gene carrying the (CCTG)DM2 expansion, as well as loss-of function of the resident gene.
Myotonia in the three different DM2 mouse models.
DM2 transgenic fly model expressing (CCTG)106 in the eye. Expression of toxic (CCUG)106 causes disorganized eyes and retinal degeneration. The phenotype can be completely or partially rescued by the concomitant expression of human MBNL1 gene or the fly apoptosis inhibitor p35, respectively.