Prof. Lendert Gelens
KU Leuven

Upon fertilization, the early Xenopus leavis frog egg quickly divides about ten times to go from a single cell with a diameter of a millimeter to several thousands of cells of somatic cell size (tens of microns). Such frog eggs can be deconstructed into their basic components, such as lipids, yolk, organelles, cytoplasm, etc. Using Xenopus frog egg cytoplasmic extracts, many cellular processes have been reconstituted and studied in vitro.

Biochemically, clock-like transitions between interphase (during which DNA is copied) and mitosis (during which the cell divides) can be recreated in cell-free extracts. The transition from interphase to mitosis has been shown to be controlled by biochemical waves traveling through the cytoplasm. Such waves ensure that cell division is properly coordinated in the large frog egg. Homogenized extracts can also spontaneously self-organize into various cellular spatial structures when mixing isolated components back together. For example, nuclei form around DNA and can replicate its genetic information. Moreover, microtubules are known to form a wide range of spatial patterns, such as a mitotic spindle, a critical structure to segregate the copied DNA between daughter cells. Altogether, a cytoplasmic extract is able to form a realistic pattern of cell-like structures that preserve the ability to divide when sperm is added.

Here, I will discuss some of our recent experimental and modeling efforts to understand how such waves and patterns form in the frog cytoplasm, and what their role is in organizing the cell division cycle.