What protein helps pinch animal cells in two during cell division?

The protein that plays a critical role in pinching animal cells apart during cell division is microfilaments, which are primarily composed of actin. During the process of cytokinesis, the division of the cytoplasm following mitosis, microfilaments form a contractile ring just beneath the plasma membrane of the cell. This contractile ring contracts, pulling the membrane inward and effectively "pinching" the cell into two separate daughter cells.

Microtubules, while important during cell division for the alignment and separation of chromosomes, do not play a direct role in the physical division of the cell's cytoplasm. Chromatin, which is composed of DNA and proteins, is involved in packaging genetic material and is not directly related to the mechanics of cytokinesis. Thus, the role of microfilaments, specifically through the action of actin, is vital for the successful separation of cellular components during this stage of cell division.