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Centrosomes help orchestrate cell division, building an apparatus of microtubules called the mitotic spindle, which pulls apart the duplicated chromosomes so that each of the two daughter cells gets a complete set of chromosomes. The centrosome contains about a hundred different proteins, including the main protein for making microtubules, called gamma tubulin.

The UCSC researchers studied the development of centrosomes in the eggs of two parasitic wasps (Nasonia vitripennis and Muscidifurax uniraptor). Using fluorescently labeled antibodies that recognize and bind to gamma tubulin and other centrosomal proteins, they demonstrated the presence of these proteins in accessory nuclei and showed that the accessory nuclei appear to give rise to centrosomes.

Accessory nuclei bud off from the membrane of the nucleus, the cellular structure that contains the chromosomes. By the time the egg is fully developed, it contains several hundred accessory nuclei that look much like the nucleus except that they don't contain chromosomes. Late in the development of the egg cell, the accessory nuclei disintegrate and centrosomes appear in the same locations in the cell.

"Right before the egg is laid, the membranes of the accessory nuclei break down, and at the same time the centrosomes begin to form," Ferree said.

One of the most striking aspects of this mechanism is the large number of accessory nuclei and centrosomes that form in the developing eggs of these Hymenopteran insects.

"You only need two centrosomes, and they make hundreds of them. So they go through a lot of work to make a male," Sullivan said. "A lot of energy goes into making these centrosomes, and if the egg gets fertilized they don't use them--the centrosome from the sperm is used preferentially."

Centrosomes remain somewhat mysterious structures, Ferree said, bu
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Source:University of Pittsburgh Medical Center