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Release of mature starfish oocytes from interphase arrest by microinjection of human centrosomes
Abstract:
Mature oocytes (unfertilized eggs) are arrested at definite cell-cycle stages which vary from species to species. In frogs and mammals, the oocytes are arrested at the second metaphase of meiosis whereas in echinoderms they are blocked later, at the pronucleus stage. What causes the maturing oocytes to stop at some point in the cell cycle is not entirely clear. In frogs, the metaphase arrest seems to be maintained by a cytostatic factor. In echinoderms, which stop at interphase, no such a factor has so far been found. The fertilization process, beyond the introduction of paternal chromosomes, releases the oocyte from cell-cycle arrest and provides a functional centrosome to replace the endogenous centrosome which is apparently lost during oogenesis in most species. Several lines of evidence suggest that release from cell-cycle arrest is mediated by a Ca2+ burst which is associated with fertilization, and it is known that the functional centrosome provided by the sperm is necessary for mitotic spindle formation and cleavages. We report here that microinjection of purified human centrosomes into mature starfish oocytes is sufficient to release them from arrest at interphase and to support many cleavages leading to the occasional formation of normal embryos. In this species centrosome induced re-entry into the cell cycle does not require a transient calcium burst nor does it require intact microtubules.
Insights
Mature oocytes arrest at specific cell cycle stages. Injecting human centrosomes into starfish oocytes releases them from arrest, enabling cell division and embryo formation without calcium or intact microtubules.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Oocytes arrest at distinct cell cycle stages, varying by species (e.g., metaphase in frogs/mammals, pronuclear stage in echinoderms).
- The mechanisms causing cell cycle arrest in oocytes are not fully understood, with cytostatic factors implicated in some species but not others.
- Fertilization releases oocytes from arrest, introduces paternal chromosomes, and provides a functional centrosome, essential for cell division.
Purpose of the Study:
- To investigate whether centrosomes alone can induce cell cycle re-entry in arrested oocytes.
- To determine if calcium bursts or intact microtubules are necessary for centrosome-mediated cell cycle progression.
- To explore the potential for centrosome injection to support embryonic development.
Main Methods:
- Microinjection of purified human centrosomes into mature starfish oocytes.
- Observation of oocyte cell cycle progression and cleavage following centrosome injection.
- Assessment of the requirement for calcium transients and intact microtubules for induced cell cycle re-entry.
Main Results:
- Microinjection of human centrosomes successfully released mature starfish oocytes from interphase arrest.
- Centrosome injection supported multiple cell cleavages, occasionally leading to the formation of normal embryos.
- Centrosome-induced re-entry into the cell cycle did not require a transient calcium burst or intact microtubules.
Conclusions:
- Functional centrosomes are sufficient to induce cell cycle re-entry in oocytes arrested at interphase.
- The sperm-provided centrosome's role in initiating cell cycle progression may be independent of the calcium burst typically associated with fertilization.
- This finding offers insights into the regulation of cell cycle control and the essential role of centrosomes in early embryonic development.