Mechanisms orienting chromosomes in mitosis and meiosis

During cell division, exactly one copy of each chromosome must be delivered into each of two daughter cells, through mitosis. Gametes, such as eggs and sperm, receive only half the chromosome number of the parent cell through an adapted division called meiosis. A proteinaceous structure, the kinetochore, assembles at a specific site on each chromosome, called the centromere. Kinetochores attach to rope-like microtubules, which pull chromosomes apart. In mitosis, kinetochores on chromosome copies attach to microtubules growing from opposite sides, ensuring their segregation to different daughter cells after cell division. In the first step of meiosis, however, kinetochores on chromosome copies need to attach to microtubules growing from the same direction. Both the kinetochore itself and the pericentromere, the chromosomal region surrounding it, are important to set up these distinctly oriented attachments of chromosomes to microtubules.

We will use a simple model organism, baker’s yeast, together with frog eggs, which are more closely related to human eggs, to build a molecular picture of how chromosomes attach to microtubules in the correct orientation.

Our work could help us understand how eggs and sperm with the wrong number of chromosomes arise, which is a leading cause of birth defects and infertility.