Which organelle is involved in the formation of the spindle prior to nuclear division?

The centrosome is the organelle responsible for the formation of the spindle apparatus prior to nuclear division, specifically during mitosis and meiosis. It serves as the main microtubule organizing center in animal cells and consists of a pair of centrioles surrounded by pericentriolar material. During the cell cycle, the centrosome duplicates and each centrosome moves to opposite poles of the cell, ultimately leading to the assembly of microtubules that form the spindle fibers. These fibers are crucial for the accurate segregation of chromosomes into daughter cells, ensuring that each new cell ends up with the correct number of chromosomes.

The other options do not play this specific role in spindle formation. The centriole contributes to the structure of the centrosome but is not the sole organelle responsible for spindle assembly. The nucleus contains genetic material and is the site of transcription but does not play a direct role in spindle formation. Mitochondria are the powerhouses of the cell, providing energy through ATP production, and are not involved in the processes of nuclear division or spindle formation.