Bivalent orientation and behavior in crane-fly spermatocytes recovering from cold exposure

Meiotic spindle assembly involves precise kinetochore microtubule (kMT) interactions. In crane-fly spermatocytes, bivalents typically orient with sister kinetochores facing opposite poles. Cold exposure disrupts spindle dynamics and may alter bivalent orientation. Prior research has shown that cold stress can cause kinetochore misalignment during meiosis. However, the specific effects of cold recovery on bivalent orientation remain unclear. This gap motivated a detailed analysis of kMT configurations in cold-recovering cells. Existing studies suggest that spindle reorganization occurs during recovery from cold shock. This paper's contribution is a novel observation of bipolar malorientations in cold-recovering bivalents.

The aim was to investigate how cold exposure affects bivalent orientation in crane-fly spermatocytes. Specifically, the study focused on kinetochore microtubule (kMT) arrangements during recovery. The problem addressed is the lack of understanding about how cold stress influences meiotic orientation. Cold exposure is known to disrupt spindle dynamics, but recovery mechanisms are poorly defined. The motivation stems from the need to clarify how bivalents reorient after cold-induced stress. This paper proposes to examine whether cold recovery leads to persistent malorientations. The study also aims to compare maloriented configurations with those in untreated cells. The authors suggest that cold recovery may alter the stability of bivalent configurations.

The researchers examined crane-fly primary spermatocytes at metaphase using light microscopy. They focused on kinetochore microtubule (kMT) configurations in bivalents during recovery from cold exposure. Cells were exposed to 2 degrees Celsius and then allowed to recover at room temperature. The orientation of sister kinetochores was analyzed in both untreated and cold-recovering cells. Living cells were observed to track changes in bivalent configurations over time. Distances between homologous centromeres were measured to assess spatial relationships. Tilt angles relative to the spindle axis were calculated to determine bivalent positioning. Comparisons were made between untreated and cold-recovering cells to identify differences in orientation.

In cold-recovering cells, many metaphase bivalents showed bipolar malorientations. One or both homologues had kinetochore microtubules (kMTs) extending toward opposite poles. Sister kinetochores with most kMTs extending toward the same pole remained adjacent. Those with kMTs extending toward opposite poles were separated from each other. Distances between homologous centromeres were similar to properly oriented bivalents. Maloriented bivalents were tilted relative to the spindle axis in cold-recovering cells. Tilted configurations were rare in untreated cells but common in cold-recovering cells. Unipolar configurations in untreated cells reoriented quickly, unlike in cold-recovering cells.

The authors propose that cold-recovering cells show more stable bipolar malorientations. Bipolar malorientations arise upon initial spindle interaction and persist through metaphase. In contrast, unipolar malorientations in untreated cells reorient shortly after formation. The orientation process is affected during cold recovery, leading to persistent malorientations. Tilted bivalent configurations are more frequent in cold-recovering cells than in untreated ones. This suggests that cold exposure alters the dynamics of bivalent orientation recovery. The findings indicate that cold recovery may disrupt normal spindle-bivalent interactions. The authors suggest that this disruption leads to altered stability of bivalent configurations.