Multicolor strategies for investigating clonal expansion and tissue plasticity.

Understanding the generation of complexity in living organisms requires the use of lineage tracing tools at a multicellular scale. In this review, we describe the different multicolor strategies focusing on mouse models expressing several fluorescent reporter proteins, generated by classical (MADM, Brainbow and its multiple derivatives) or acute (StarTrack, CLoNe, MAGIC Markers, iOn, viral vectors) transgenesis. After detailing the multi-reporter genetic strategies that serve as a basis for the establishment of these multicolor mouse models, we briefly mention other animal and cellular models (zebrafish, chicken, drosophila, iPSC) that also rely on these constructs. Then, we highlight practical applications of multicolor mouse models to better understand organogenesis at single progenitor scale (clonal analyses) in the brain and briefly in several other tissues (intestine, skin, vascular, hematopoietic and immune systems). In addition, we detail the critical contribution of multicolor fate mapping strategies in apprehending the fine cellular choreography underlying tissue morphogenesis in several models with a particular focus on brain cytoarchitecture in health and diseases. Finally, we present the latest technological advances in multichannel and in-depth imaging, and automated analyses that enable to better exploit the large amount of data generated from multicolored tissues.

Hedgehog interacting protein in the mature brain: membrane-associated and soluble forms.

Hedgehog interacting protein (Hip) is considered as a membrane protein implicated in sequestering the hedgehog (hh) morphogens during embryonic development. Here, we demonstrate that Hip transcription also occurs in cells scattered in discrete brain areas of adult rodents and we identify the presence of membrane-associated and soluble forms of Hip in the mature brain. Moreover, we show that soluble forms of Hip, present in the conditioned medium of HEK293 cells overexpressing Hip, inhibit Sonic hedgehog (Shh)-induced differentiation of C3H10T1/2 cells, a well-characterised response associated with Shh signalling. After transfection in HEK293 cells, Hip partitions with the raft component ganglioside GM1 during density gradient centrifugation. Analysis of tagged Hip constructs reveals that the putative transmembrane domain of Hip is not cleaved suggesting that other mechanisms are implicated in the release of its soluble forms. Taken together, these data are consistent with the involvement of both membrane-associated and soluble Hip in the regulation of Shh signalling in adult neural tissues.