Centromeric dots in crane-fly spermatocytes: meiotic maturation and malorientation

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• During meiosis I in crane-fly spermatocytes, homologs typically orient sister kinetochores to the same pole, leading to malorientation.
• Previous studies identified treatments (temperature, chemical) that increase bipolar malorientations, causing lagging anaphase homologs.
• Giemsa staining reveals two dots in the centromeric region of each homolog, which appear separated in maloriented homologs.

Purpose of the Study:

• To determine if centromeric dot separation precedes or is a consequence of bipolar malorientation.
• To investigate the role of centromeric dot maturation in meiotic orientation.

Main Methods:

• Analysis of Giemsa-stained crane-fly spermatocytes.
• Measurement of center-to-center distances between sister centromeric dots in treated and untreated cells.
• Correlation of dot separation with the establishment of bipolar malorientation.

Main Results:

• In untreated cells, the distance between sister centromeric dots increases during meiosis I.
• Treated cells exhibited increased dot separation, similar to normal anaphase I distances, even before nuclear membrane breakdown.
• Extended meiotic arrest at low temperatures further increased centromeric dot separation.

Conclusions:

• Close apposition of centromeric dots aids normal orientation in meiosis I.
• A time-dependent maturation process causes centromeric dots to separate, facilitating sister kinetochore orientation to opposite poles in meiosis II.
• Premature or early meiosis I centromeric maturation may contribute to persistent bipolar malorientation.