Resum
A fundamental question in biology is how the myriad of specialized cell behaviors observed in a multicellular organism is encoded by a single genome sequence,
and which gene regulatory mechanisms orchestrate the spatiotemporal deployment and maintenance of these cell type-specific programs. Decades of genetic
and, more recently, genomic analyses have identified multiple layers of regulation,
including specific molecular players and their interactions. This regulation ultimately results in cell-specific gene expression profiles that define coordinated cell
cooperation at the tissue and whole-organism levels. However, the diversity and
evolutionary dynamics of cell types remain almost completely unexplored beyond
selected tissues in a few species, and so it is the gene regulatory networks that define them. Similarly, little is known about the emergence of complex genome regulatory mechanisms that support cell type-specific programs and cellular memory,
including genome spatial compartmentalization and chromatin dynamics. The advent of low-input, highly-multiplexed epigenomic and transcriptomic profiling
methods, even at single-cell resolution, and the broad applicability of these techniques to diverse systems, bypasses the need to obtain large amounts of biological
material by culturing or dissecting particular tissues or cell types. This paves the
way for the comparative multi-level analysis of cell differentiation in species and
ontogenetic stages that span an unprecedented phylogenetic breadth and represent
diverse levels of biological complexity: ranging from unicellular temporal differentiation dynamics and simple multicellular behaviors (as in some protistan eukaryotes), through loosely integrated and limitedly diversified ensembles of cell types
(as in early-branching animals), to organisms with elaborate tissue and body plan
organization (as in bilaterian animals). The comparative approach, through the prism of evolutionary theory and supported by a robust phylogenetic framework,
holds the promise of offering far-reaching insights into the fundamental principles
that govern cell biological systems and the associated molecular mechanisms of
genome regulation.
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