[Spontaneous and radiation-induced chromosome breaks]

Area of Science:

• Cytogenetics
• Cell Biology
• Radiation Biology

Background:

• Acentric chromosome fragments are common in cells undergoing mitosis.
• Their precise location during cell division can provide insights into the mechanisms of chromosome breakage and repair.

Purpose of the Study:

• To investigate the location of acentric chromosome fragments in various plant and animal cell types.
• To determine if fragment location correlates with the induction method (spontaneous vs. irradiation).
• To elucidate the timing of chromosome breaks during the cell cycle.

Main Methods:

• Microscopic analysis of chromosome morphology at metaphase and anaphase.
• Observation of acentric fragments in root cells of pea, cornea and bone marrow of rats and mice, and fibroblast cultures (mouse and human).
• Comparison of fragment location in non-irradiated and irradiated cells.

Main Results:

• Acentric fragments were observed both inside and outside the equatorial plate across all studied cell types.
• Spontaneously occurring fragments were predominantly located outside the equatorial plate.
• Irradiation-induced fragments were mainly found within the equatorial plate.
• A model is proposed where spontaneous breaks occur before prometaphase, leading to random distribution and subsequent movement to poles, while irradiation-induced breaks may complete later in mitosis.

Conclusions:

• The timing of chromosome breakage relative to the cell cycle influences the final location of acentric fragments.
• Spontaneous chromosome breaks appear to occur earlier in mitosis than those induced by irradiation.
• These findings are consistent across diverse plant and animal cell systems, highlighting conserved mechanisms in chromosome dynamics.