Cells respond to external signals by modifying their internal state and their environment. In multicellular organisms in particular, cellular differentiation and intra-cellular signaling are essential for the coordinated development of the organism. While some of the major players of these complex interaction networks have been identified, much less is known of the quantitative rules that govern their interaction with one another and with other cellular components (affinities, rate constants, strength of non linearities such as feedback or feedforward loops, etc.). To investigate these interactions (a prerequisite before understanding or modeling them), one needs to develop means to control or interfere spatially and temporally with these processes.
In the preceding context, we have retained the principle of a small lipophilic molecule to photo-activate several properly engineered proteins in vivo. We have adopted a steroid-related inducer as various proteins (e.g. Engrailed, Otx2, Gal4, p53, kinases such as Raf-1, Cre and Flp recombinases) fused to a steroid receptor were shown to be activated by binding of an appropriate ligand.[1] In its absence, the receptor forms a cytoplasmic assembly with a chaperone complex: the fusion-protein is inactivated. Its function is restored in the presence of the steroid ligand which binds to the receptor and disrupts the complex.
The present non-invasive optical method has been implemented for the fast control of protein activity down to the single cell level in a live zebrafish embryo.[2] In particular, we labeled single cells transiently (by activating a fluorescent protein) or irreversibly (by activating a Cre recombinase in an appropriate transgenic animal). The present method could be used more generally to investigate important physiological processes (for example in embryogenesis, organ regeneration and carcinogenesis) with high spatio-temporal resolution (single cell and faster than minute scales).
References
1 D. Picard, Curr. Op. Biotech.,1994, 5, 511-515.
2 D. K. Sinha et al., ChemBioChem. 2010, 11, 653-663 ;Zebrafish, 2010
