Centrosome, cell geometry and tissue topology. the biological 3d reference system of metazoa

Despite decades of studies and researches, morphologists have no good ideas to propose a theoretical model explaining anisotropy andbilateral symmetryof Metazoa development: the main problem consists in the transition from a linear (1D) genetic code to spatial (3D)cells and tissuesorganization. Here,a simple metazoan developing systemis attentively reviewed, sea urchin pluteus skeleton formation. During this process chemical gradients (morphogens) do not show the geometrical propertiesfor programming and controlling anisotropy, bilateral symmetry and 3D orientation necessary to solve the topological problems of developing tissues in Metazoa: it is possible to conclude that, by a topological point of view, without an intrinsic cellular spherical (3D) reference system (the centrosome, with its orthogonal enantiomorphouscentrioles) capable of driving the orientation and positioning of receptors, junctions, cell division planes and extracellular matrix fibers, developmental programs cannot be performed.