Abstract
How and why do processes and molecular players that were once an integral part of normal neurodevelopment go awry in pathological conditions, such as cancer? Embryogenesis, and neurodevelopment in particular, comprise an elegant and well-orchestrated series of tightly regulated events, culminating in an organized and highly functioning organism. Cancer, on the other hand, can often be viewed as an uncontrolled, unrestrained, genetically chaotic disease, lacking the precise spatial and temporal rigidity associated with normal development. While appearing to be on opposite sides of the organizational spectrum, the similarities between early neurodevelopment and oncogenesis are numerous. 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 and years of gene-level analyses have provided a wealth of knowledge and mechanistic insight. As advances in next generation sequencing allow for deeper characterization of genetic programs, it is increasingly possible to explore various isoforms of cancer associated genes. It is widely known that neurotrophins and their receptors (TrkA, TrkB, TrkC) are instrumental for neurodevelopment and that they remain critical for proper neuronal functioning throughout life. Our work highlights a previously unidentified role for an alternatively spliced neurotrophin receptor in neurodevelopment, embryogenesis, transformation, and oncogenesis across multiple tumor types in humans and mice. This specific isoform, TrkB.T1, is the predominant NTRK2 isoform across embryonic organogenesis, and forced overexpression of this embryonic pattern causes multiple solid and nonsolid tumors in mice. TrkB.T1 also emerges as the predominant NTRK isoform expressed in a wide range of adult and pediatric tumors, including those harboring various NTRK fusions. This work hopes to address the fundamental question of how neurodevelopmental processes can go awry in cancer, while seeking to better characterize the role of TRKs, in normal developmental processes and oncogenesis.