TACS-3 – radially aligned collagen fibers associated with invasion. Combined MPE/SHG imaging of live intact PyVT mammary tumors indicates that (A) non-invading regions (*) possess taut collagen (TACS-2; white arrowhead) wrapped around the tumor, while regions of invasion (x) are linked to aligned collagen, with cells invading along radially aligned collagen fibers (TACS-3; black arrowheads). Examination of invasion at the tumor-stromal interface at higher magnification (B and C) clearly reveals the collagen alignment at specific regions of invasion (B) with tumor cells (*) in between, and in association with, aligned collagen fibers (C). (D) Example of an individual tumor cell attached to a collagen fiber leading away from the primary tumor. Additionally, tumor cells that have invaded across the tumor-stromal boundary can be visualized by separating the MPE and SHG signals or imaging with FLIM. (E) Combined MPE/SHG image of a TACS-3 region facilitating local invasion. The tumor-stromal boundary is not well preserved at this stage, but is roughly outlined in red. Examples of regions of cells that have invaded past the boundary are marked with an asterisk (t = the primary tumor). The red arrowhead indicates cells near the tumor boundary that are migrating along aligned collagen fibers away from the primary tumor. (F) MPE and SHG signal separation of the image shown in E. MPE signal is represented in red pseudo-color while SHG is shown in green pseudo-color. Note the interdigitation of aligned collagen fibers (green) into the tumor, with individual, or lines of, cells (* in E) migrating away from the tumor on collagen fibers. (G) FLIM micrograph of invading cells at the TACS-3 region shown in E and F. Collagen (blue; no fluorescence lifetime) can be distinguished from cells (green to yellow), confirming the presence of invading cells at the tumor-stromal boundary and cells that have migrated past the boundary in association with collagen. The color bar in G ranges represents the weighted mean ranging from 100 ps (blue) to 1 ns (red). Scale bars equal 25 μm in A, E, F, and G; 10 μm in B, C, and D.
Provenzano et al. BMC Medicine 2006 4:38 doi:10.1186/1741-7015-4-38