Figure 5: Centrosome theoretical geometrical model: from 2D rotational polarity to 3D spherical polarity. A: (top view): the MC (internal circle subdivided in 9 intensely coloured sectors) is responsible for “longitude” that is transmitted to the whole PCM (external annulus, weakly coloured), whose γ-TuRCs (small bars) acquire an inclination parallel to the corresponding centriolar blade; each MC blade faces one meridian wedge. In each wedge, all the γ-TuRCs have the same longitudinal inclination. B: after the intervention of the DC, that imposes a rotational inclination corresponding to that of its blades, each γ-TuRC acquires also the latitude inclination which is added to that of longitude. There is a double inclination: first each γ-TuRC is parallel to the corresponding blade of the MC, then it acquires the inclination parallel to the corresponding DC blade; the eccentric positioned DC is responsible for “latitude” (two opposed spherical caps and three parallel spherical disks): this second centriole/protractor is composed of two symmetric hemi-protractors/goniometers. C: all the γ-TuRCs contained in the same cap or disc (coloured circles) whatever their longitudinal orientation, are rotated to acquire the same latitudinal orientation, identical in the same cap or disk. So, two 2D circumferential-rotational polarities are merged to realize a 3D spherical polarity. (From: M. Regolini Centrosome: a geometrical model Lambert Academic Publishing Germany 2014)