A) Microtubule motor proteins contribute to the assembly and overall shape of th

Question

A) Microtubule motor proteins contribute to the assembly and overall shape of the mitotic spindle. Predict what effect the following situations will have on the spindle assembly dynamics and the shape of the spindle. Provide a short explanation for your answer.

i) overexpression of kinesin-14:

ii) overexpression of kinesin-5:

B) Sister chromatid segregation during anaphase is dependent on the cleavage of cohesin proteins that hold the sisters together. Predict what will happen to sister chromatid segregation in the following situations. Provide a short explanation for your answer. [Note: assume the only form of securin available in the cell is the one indicated].

i) non-degradable securin:

ii) a securin mutant that cannot associate with separase:

Explanation / Answer

Kinesin-14 Family Proteins basically Control Spindle Length by Cross-Linking and Sliding Microtubules.literature showed that Kinesin-14 is regulated by Ran via the association of a bipartite NLS in the tail of XCTK2 with importin /, which regulates its ability to cross-link microtubules during spindle formation. Kinesin-14 localize to the spindle poles and focus the MT minus ends. kinesin-14 and dynein localize to the poles where they function in spindle assembly and organization. So their overexpression would leads to pole and MT focusing, resulting in less protrusion of MT minus ends due to decreasing forces at the spindle midzone. Over expression may also cause polyploidy via kinesin-5-dependent microtubule protrusions leading to chromosome cut. Finally, kinesin-14 pkl1p also appeared to play a major role in spindle length control, as its overexpression may result in longer metaphase spindle compared to wild-type.

The kinesin-5 motors in generate outward forces and establish to maintain spindle bipolarity and contribute to microtubule flux. Kinesin-5 motors regulates their localization to the mitotic spindle. Kinesin-5 motors crosslink and slide apart antiparallel microtubules. Spindle assembly requires kinesin-5 activity and required for the establishment of a bipolar spindle. Inhibition of kinesin-5 leads to disruption of centrosomes and spindle poles. Therefore Kinestin overexpression would enhance the outward force and increase the integrity of microtubules and its bipolarity. Also it would increase cross link.

In case the securin is not degradable then sister chromatid would not be separated and be attached and sister chromatid would move together this will lead a cell with less or more no of chromosome. same will happen in either case if there is no association between securin and separase leads to failure of degradation of the cohesin rings that link the two sister chromatids.

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