Question

Describe three classes of spindle microtubules including their functions, locations, and the polarity:

o Aster microtubules

o Kinetochore microtubules

o Interpolar microtubules

Answer 1

Spindle microtubules are in fact protein fibres which are composed of about 45 different proteins that arise from the centriole. There are three different classes of spindle microtubules; Aster microtubules, Kinetochore microtubules and Interpolar microtubules. The main function of these microtubules is to pull and push the sister chromatids apart toward opposite spindle poles. The description for each spindle microtubules is given below:

1. Aster microtubules - They are star shapes radial microtubules found in animal cell. These structures can be seen around each pair of centrioles during mitosis. They are formed in the actin skeleton and communicate with the cell cortex and assist in spindle orientation. The main function of aster microtubules is the establishment of cell geometry. It plays a major role in the exact positioning and orientation of the mitotic spindle apparatus and thereby involved in deciding the cell division site based on the geometry and polarity of the cells.
2. Kinetochore microtubule - Also known as K fibres. Spindle microtubules thet attach to the kinetochores of chromosome and guide the chromosomes during mitotic or meiotic chromosome segregation. The major functions of these microtubules are; tracking the attachment of chromosomes to the spindle microtubules, it also delays the cell cycle progression by activating a checkpoint pathway if any defects are detected. It also helps to power the movements of chromosomes on the spindle. The exact location of kinetochore microtubules is on the centromere and connects the chromosome to microtubule polymers during mitosis and meiosis.
3. Interpolar microtubules - It is also called polar microtubules. These are spindle microtubules that arises from each pole and overlap at the spindle midzone. These microtubules are the most abundant and active class of microtubules during mitosis. They are arranged parallel to each other but in opposite directions. They plays an important role in pushing the spindle apparatus apart during mitosis.