Examining the Role of Phosphorylation in the Gain and Loss of the Elasticity of the Tethers that Connect Separating Anaphase Chromosomes in Crane-Fly Spermatocytes

This thesis deals with elasticity of the tethers that connect anaphase chromosomes in crane-fly spermatocytes. Chromosomes move backwards after reaching the poles when Calyculin A (CalA), an inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A), is added in early anaphase. CalA added in later anaphase causes increasingly less backwards movement. Inhibiting only PP2A with low concentrations of okadaic acid does not result in backwards movement. I suggest that as anaphase progresses tethers are dephosphorylated by PP1. I next studied phosphorylation by inhibiting protein kinase C (PKC), PKA and general kinase activity, followed by (or simultaneous with) treatment with CalA in early anaphase. Chromosomes still moved backwards in these experiments. The main findings of this thesis are that the loss of tether elasticity during anaphase is due to dephosphorylation, presumably by PP1, that neither PKC nor PKA act during anaphase, and that tether phosphorylation likely occurs prior to anaphase.