Figure 10. Schematic illustration of how... | Rockefeller University Press

Figure 10.

$Figure 10. Schematic illustration of how a Plk4-dependent homeostatic clock might set daughter centriole length in flies. (i) The schematic shows an end-on view of a mother centriole (black skeleton) in mitosis, just after it has disengaged from its daughter. Plk4 starts to be recruited to mothers by the surrounding ring of Asl (red, only shown in part) but we speculate that a small fraction of Plk4 (pink star) is stabilized by binding to Ana2 (brown)—and potentially Sas-6 (green)—so defining the site where the daughter will form. (ii) This pool of Plk4 starts to recruit more Plk4 (blue arrow, recruiting to blue ellipse); the rate of this recruitment is dependent on the amount of Plk4 initially bound to Asl and Ana2, and it sets the period of daughter centriole growth by determining how quickly Plk4 will accumulate to trigger its own destruction. (iii) When the embryo enters S-phase, the Asl/Ana2-bound fraction of Plk4 is activated (filled pink stars), allowing it to recruit more Sas-6 and Ana2 (green/brown arrow); the kinase activity of the Plk4 influences the rate of Sas-6/Ana2 recruitment, and so the rate of centriole growth. (iv) Sas-6 and Ana2 levels reach a threshold that allows cartwheel assembly, whereas the local concentration of Plk4 continues to increase. (v) Centriolar Plk4 levels reach a critical concentration that triggers its destruction—centriolar Plk4 levels start to fall, but levels of the Asl/Ana2-bound Plk4 initially remain high enough that Sas-6 and Ana2 recruitment is not slowed, and cartwheel growth continues. (vi) Eventually, levels of the Asl/Ana2-bound Plk4 are too low to support Sas-6 and Ana2 recruitment, so their concentration falls below the threshold for cartwheel growth and the daughter centriole stops growing.$

Schematic illustration of how a Plk4-dependent homeostatic clock might set daughter centriole length in flies. (i) The schematic shows an end-on view of a mother centriole (black skeleton) in mitosis, just after it has disengaged from its daughter. Plk4 starts to be recruited to mothers by the surrounding ring of Asl (red, only shown in part) but we speculate that a small fraction of Plk4 (pink star) is stabilized by binding to Ana2 (brown)—and potentially Sas-6 (green)—so defining the site where the daughter will form. (ii) This pool of Plk4 starts to recruit more Plk4 (blue arrow, recruiting to blue ellipse); the rate of this recruitment is dependent on the amount of Plk4 initially bound to Asl and Ana2, and it sets the period of daughter centriole growth by determining how quickly Plk4 will accumulate to trigger its own destruction. (iii) When the embryo enters S-phase, the Asl/Ana2-bound fraction of Plk4 is activated (filled pink stars), allowing it to recruit more Sas-6 and Ana2 (green/brown arrow); the kinase activity of the Plk4 influences the rate of Sas-6/Ana2 recruitment, and so the rate of centriole growth. (iv) Sas-6 and Ana2 levels reach a threshold that allows cartwheel assembly, whereas the local concentration of Plk4 continues to increase. (v) Centriolar Plk4 levels reach a critical concentration that triggers its destruction—centriolar Plk4 levels start to fall, but levels of the Asl/Ana2-bound Plk4 initially remain high enough that Sas-6 and Ana2 recruitment is not slowed, and cartwheel growth continues. (vi) Eventually, levels of the Asl/Ana2-bound Plk4 are too low to support Sas-6 and Ana2 recruitment, so their concentration falls below the threshold for cartwheel growth and the daughter centriole stops growing.