Intra-tumoral heterogeneity is a hallmark of glioblastoma that challenges treatment efficacy. However, the mechanisms that set up tumor heterogeneity and tumor cell migration remain poorly understood. Herein, we present a comprehensive spatiotemporal study that aligns distinctive intra-tumoral histopathological structures, oncostreams, with dynamic properties and a specific, actionable, spatial transcriptomic signature. Oncostreams are dynamic multicellular fascicles of spindle-like and aligned cells with mesenchymal properties, detected using ex vivo explants and in vivo intravital imaging. Their density correlates with tumor aggressiveness in genetically engineered mouse glioma models, and high grade human gliomas. Oncostreams facilitate the intra-tumoral distribution of tumoral and non-tumoral cells, and potentially the collective invasion of the normal brain. These fascicles are defined by a specific molecular signature that regulates their organization and function. Oncostreams structure and function depend on overexpression of COL1A1. Col1a1 is a central gene in the dynamic organization of glioma mesenchymal transformation, and a powerful regulator of glioma malignant behavior. Inhibition of Col1a1 eliminates oncostreams, reprograms the malignant histopathological phenotype, reduces expression of the mesenchymal associated genes, induces changes in the tumor microenvironment and prolongs animal survival. Oncostreams represent a pathological marker of potential value for diagnosis, prognosis, and treatment.

Tumor heterogeneity is a hallmark of cancer and a determinant of malignant behavior. How tumor heterogeneity arises is thus of fundamental importance. Gliomas display oncostreams, self-organizing multicellular fascicles of elongated, aligned, collectively motile glioma cells, that establish dynamic heterogeneity throughout gliomas. Gliomas exhibit two collective motion patterns: streams, displaying bidirectional collective motion, and flocks, displaying unidirectional collective motion. Oncostreams function as highways to facilitate the intratumoral spread of tumoral and non-tumoral cells. Detailed quantitative and deep learning analysis of rodent and human gliomas uncovered that the density of oncostreams correlates positively with glioma aggressiveness. Our study establishes the self-organizing dynamic nature of gliomas, and its role in setting up dynamic tumor heterogeneity and consequently tumor malignant behavior.

Layer 5 pyramidal neurons of sensory cortices project corticofugal axons to myriad of sub-cortical targets, thereby broadcasting high-level signals important for perception and learning. Recent studies suggest dendritic Ca2+ spikes as key biophysical mechanisms supporting corticofugal neuron function: These long-lasting events drive burst firing, thereby initiating uniquely powerful signals to modulate sub-cortical representations and trigger learning-related plasticity. However, the behavioral relevance of corticofugal dendritic spikes is poorly understood. We shed light on this issue using 2-photon Ca2+ imaging of auditory corticofugal dendrites as mice engage in a sound-discrimination task. Unexpectedly, only a minority of dendritic spikes were triggered by sound. Rather, task-related dendritic activity mostly occurred following sound termination and reflected instrumental actions, irrespective of reward consumption. Temporally selective silencing of this motor-related activity impaired auditory discrimination learning. Thus, corticofugal systems contribution to learning and plasticity may be largely motor, rather than sensory in nature.