Although the transforming growth factor-beta (TGF-beta) pathway has been implicated in breast cancer metastasis, its in vivo dynamics and temporal-spatial involvement in organ-specific metastasis have not been investigated. Here we engineered a xenograft model system with a conditional control of the TGF-beta-SMAD signaling pathway and a dual-luciferase reporter system for tracing both metastatic burden and TGF-beta signaling activity in vivo. Strong TGF-beta signaling in osteolytic bone lesions is suppressed directly by genetic and pharmacological disruption of the TGF-beta-SMAD pathway and indirectly by inhibition of osteoclast function with bisphosphonates. Notably, disruption of TGF-beta signaling early in metastasis can substantially reduce metastasis burden but becomes less effective when bone lesions are well established. Our in vivo system for real-time manipulation and detection of TGF-beta signaling provides a proof of principle for using similar strategies to analyze the in vivo dynamics of other metastasis-associated signaling pathways and will expedite the development and characterization of therapeutic agents.

Summary Background In many organisms, germ cells are segregated from the soma through the inheritance of the specialized germ plasm, which contains mRNAs and proteins that specify germ cell fate and promote germline development. Whereas germ plasm assembly has been well characterized, mechanisms mediating germ plasm inheritance are poorly understood. In the Drosophila embryo, germ plasm is anchored to the posterior cortex and nuclei that migrate into this region give rise to the germ cell progenitors, or pole cells. How the germ plasm interacts with these nuclei for pole cell induction and is selectively incorporated into the forming pole cells is not known. Results Live imaging of two conserved germ plasm components, nanos mRNA and Vasa protein, revealed that germ plasm segregation is a dynamic process involving active transport of germ plasm RNA-protein complexes coordinated with nuclear migration. We show that centrosomes accompanying posterior nuclei induce release of germ plasm from the cortex and recruit these components by dynein-dependent transport on centrosome-nucleated microtubules. As nuclei divide, continued transport on astral microtubules partitions germ plasm to daughter nuclei, leading to its segregation into pole cells. Disruption of these transport events prevents incorporation of germ plasm into pole cells and impairs germ cell development. Conclusions Our results indicate that active transport of germ plasm is essential for its inheritance and ensures the production of a discrete population of germ cell progenitors endowed with requisite factors for germline development. Transport on astral microtubules may provide a general mechanism for the effective segregation of cell fate determinants.

Cnn and PLP directly interact at two defined sites to coordinate the cell cycle–dependent rearrangement and scaffolding activity of the centrosome to permit normal centrosome organization, cell division, and embryonic viability.

PLP levels are regulated by Centrobin and act to suppress mother centrosome maturation by blocking the localization of Polo kinase.