One mystery has been the origin of the centrosome, an essential cellular component that is ordinarily derived from the sperm after fertilization. A new study led by researchers at the University of California, Santa Cruz, describes a remarkable process by which the egg cells of Hymenopteran insects make new centrosomes from scratch. The process involves enigmatic cellular structures called accessory nuclei, the function of which has not been explained since they were first discovered in the 1960s.
"Centrosomes arise from other centrosomes through duplication, but there is no centrosome in the egg that could give rise to new ones. We found that the accessory nuclei seed the formation of new centrosomes in unfertilized eggs," said Patrick Ferree, a graduate student in molecular, cell, and developmental biology at UCSC.
Ferree is first author of a paper describing the new findings in the April 18 issue of the journal Current Biology. Coauthor William Sullivan, professor of molecular, cell, and developmental biology at UCSC, said the findings have implications for understanding basic cell biology, the evolution of Hymenopteran insects, and centrosomal anomalies in cancer cells. The study also shows just how much remains to be discovered about the diversity of life at the cellular level, he said.
"You would think we’d have identified all the structures in the cell by now, but 90 percent of the material in cell biology textbooks comes from research on nine or ten organisms," Sullivan said. "Every time I look at a honeybee now, I think about these amazing structures they have, and it implies that among the millions of other species there must be cellular mechanisms we haven’t even imagined."
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, but researchers may be able to learn more about them by purifying accessory vesicles and studying their protein components.
Accessory nuclei have been observed in other species besides Hymenopteran insects, and they may have other functions in addition to making centrosomes, he said. They may also hold clues to the evolutionary origin of the Hymenoptera. Because the males of these insects develop from unfertilized eggs, they have half the number of chromosomes that females have--in technical terms, the males are haploid and the females are diploid.
This situation, known as haplodiploidy, results in interesting genetic relationships that are thought to underlie the complex social behavior of Hymenopteran insects. One of the key steps in the evolution of social insects, therefore, may have been the development of a mechanism for making centrosomes from scratch.
"The Hymenoptera were probably derived from a species that had accessory nuclei, and in the evolution of haplodiploidy the accessory nuclei were co-opted as a way of building centrosomes," Sullivan said.
Tim Stephens | EurekAlert!
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy