A supernumerary chromosome segment in Locusta migratoria

Area of Science:

• Genetics
• Molecular Biology
• Cytogenetics

Background:

• Supernumerary chromosome segments can arise from various mechanisms, including amplification.
• Nucleolus organizer regions (NORs) are crucial for ribosome biogenesis and contain GC-rich DNA sequences.

Purpose of the Study:

• To investigate the origin and characteristics of a supernumerary heterochromatic segment in Locusta migratoria.
• To determine the potential functional implications of this segment on nucleolus formation and gene expression.

Main Methods:

• Chromosome banding techniques (e.g., GC-specific banding) were used to analyze the heterochromatic segment.
• Analysis of nucleolus size in embryo prophase cells of heterozygous and homozygous individuals.
• Examination of offspring for evidence of segment accumulation.

Main Results:

• A female Locusta migratoria was identified as heterozygous for a distal supernumerary heterochromatic segment on the M6 autosome, adjacent to the NOR.
• Chromosome banding revealed the segment's heterochromatic nature and composition of GC-rich DNA, similar to the NOR.
• Heterozygous embryos exhibited larger nucleoli compared to homozygous ones, suggesting the presence of rRNA genes in the extra segment.
• No accumulation mechanism for the segment was observed in 213 offspring.

Conclusions:

• The supernumerary heterochromatic segment likely originated from the amplification of GC-rich DNA sequences from the distal NOR of the M6 chromosome.
• The segment appears to be transcriptionally active, contributing to increased nucleolus size in heterozygous individuals.
• While no accumulation was detected, the findings provide insights into chromosome evolution and gene regulation in Locusta migratoria.