Natural tissue remodeling as trigger for tumor initiation?

Colinda Scheele    

Oncogenic clones frequently emerge in normal tissues as we age, progressively colonizing their host tissues for decades while remaining fully functional. This suggests that tissues pos-sess a remarkable capacity to manage the presence of mutant cells while maintaining func-tional and morphological normalcy. This phenomenon is particularly surprising in heavily re-modeled tissues, such as the mammary gland, where oncogenic clones are effectively kept in check.

To uncover the mechanisms driving this resistance to transformation, we developed a dynamic mammary organoid system that replicates the complex life cycle of the mammary gland. Our culture approach recreates the intricate branched morphology of the mammary gland, reflect-ing the post-pubertal stage. Starting with these branched organoids, we further stimulated them to mimic estrus cycle remodeling, followed by pregnancy, lactation, and involution-like stages. We validated our mammary organoid model across different reproductive stages at the transcriptomic, protein, and morphological levels, identifying high similarities between our organoids and their in vivo counterparts.

Using our dynamic organoid models, we investigated resistance mechanisms against onco-genic transformation by sporadically inducing different oncogenes, coupled with fluorophore expression. Through a combination of live imaging, quantitative clonal analysis, and cellular phenotyping, we mapped the impact of various remodeling stages on mutant cell behavior and spread, identifying resistance mechanisms at both tissue and cellular levels. By coupling these cellular dynamics with live recordings of pathway activity using signaling reporters and timed single-cell transcriptomics, we further elucidated the molecular pathways driving this tissue-intrinsic resistance to oncogenic transformation.