Kinetochore development in two dicentric chromosomes in man. A light and electron microscopic study

Area of Science:

• Human cytogenetics
• Molecular biology
• Cellular biology

Background:

• Dicentric chromosomes, characterized by two centromeres, can arise from translocations and pose challenges to accurate chromosome segregation during cell division.
• Understanding centromere function and kinetochore assembly in dicentric chromosomes is crucial for comprehending genomic stability and aneuploidy.
• Previous studies have indicated variability in the behavior of dicentric chromosomes, but the precise mechanisms of kinetochore formation remain incompletely understood.

Purpose of the Study:

• To investigate the structural and functional characteristics of two distinct dicentric human chromosomes using advanced microscopy and molecular techniques.
• To elucidate the patterns of centromere activity and kinetochore development in dicentric chromosomes.
• To determine the influence of centromere inactivation on chromosome behavior during cell division.

Main Methods:

• Light and electron microscopy were employed to examine the ultrastructure of the dicentric chromosomes.
• C- and Cd-banding techniques were utilized to identify centromeric regions and assess their activity.
• Immunostaining with CREST antikinetochore antibody was performed to detect kinetochore formation.
• Detailed analysis of metaphase chromosomes was conducted to observe kinetochore development at the centromeres.

Main Results:

• One dicentric chromosome, tdic(5;13)(p12;p12), exhibited two primary constrictions and two active centromeres, with kinetochore development observed at both centromeres simultaneously.
• The second dicentric chromosome, tdic(21;21)(q22;q22), showed occasional two primary constrictions, but C- and Cd-banding revealed one active and one inactive centromere.
• CREST antibody reacted strongly with the active centromere and weakly with the inactive centromere of tdic(21;21), with electron microscopy confirming kinetochore development at only one centromere.

Conclusions:

• Dicentric human chromosomes can display differential centromere activity, leading to varied kinetochore formation and segregation patterns.
• The presence of an inactive centromere in tdic(21;21) suggests mechanisms for centromere inactivation that ensure proper chromosome function.
• These findings contribute to the understanding of chromosome stability and the potential consequences of dicentric chromosome formation in human genetics.