Characterizing an alternatively spliced NTRK2 isoform in development and cancer

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Project Summary/Abstract The link between developmental signaling and cancer initiation, maintenance and metastasis has long been known for several members of the Wnt, Hedgehog, and Notch pathways. The possibility remains that a developmentally-regulated splicing event may share similar features with these oncogenic pathways, driving normal development in an anatomically appropriate, temporally restricted context, and causing cancer when dysregulated. We have recently shown that a kinase-deficient NTRK2 neurotrophin receptor splice variant, TrkB.T1, predominates in glioma and amplifies several oncogenic signaling pathways. Our preliminary data suggest that TrkB.T1 is the predominate NTRK2 isoform expressed across multiple organs during embryonic development, is highly expressed in various cancer types in humans, and when over-expressed in combination with PTEN loss, causes a wide range of cancers in mice. The project proposed here seeks to characterize the role TrkB.T1 in development and cancer using a novel antibody and a novel mouse model to show that specific splice variants are oncogenic when overexpressed, postnatally, in the specific organs that expressed them during development. By perturbing cell-specific TrkB.T1 splice variant expression in mice, embryonically, and using single cell combinatorial indexing RNA-sequencing analysis to follow NTRK2 transcripts across embryonic and postnatal development, I aim to (1) link developmental mechanisms and splicing choices to cancer, (2) link a kinase deficient protein with increases in signaling, and (3) seek to discern whether trapping cells in a particular developmental state can lead to cancer. By further characterizing the mechanism by which TrkB.T1 functions, these projects have the potential to open new avenues for diagnostic and therapeutic targets for multiple cancer types. The experiments proposed here build upon my previous work in neurodevelopment, neurotrophin biology, and cancer and will help set the stage for my long-term career goals which center around employing a developmentally guided approach to studying neurotrophic contributions to tumor biology and uncovering developmental influences on oncogenesis.