Intron-containing globin genes in the insect Chironomus thummi

Area of Science:

• Molecular Biology
• Evolutionary Genetics

Background:

• Previously, all known chironomid globin genes were reported as intronless.
• This suggested the ancestral chironomid globin gene lacked introns.

Purpose of the Study:

• To investigate the presence and functionality of introns in Chironomus thummi globin (Gbs) II beta and IX genes.
• To understand the evolutionary implications of intron presence/absence in chironomid globin genes.

Main Methods:

• Polymerase chain reaction (PCR) amplification of genomic DNA using specific oligonucleotide primers.
• Sequencing of PCR-generated DNA fragments to confirm intron presence and structure.
• Comparison of gene sequences (exons and intron-spanning regions) between related genes and species.

Main Results:

• The coding regions of Chironomus thummi globin (Gbs) II beta and IX genes are interrupted by introns (64 nucleotides in Gb II beta).
• These intron-containing genes possess functional transcription and translation signals.
• Intron-spanning regions of Gb II beta and IX genes show higher similarity than their exons, suggesting potential gene correction.
• Homologous Gb II beta and IX genes in C. tentans were found to be intronless.

Conclusions:

• Intron-containing chironomid globin genes in C. thummi are functional.
• The findings present alternative evolutionary scenarios: either introns were lost in multiple lineages or recently acquired in specific C. thummi sublineages.
• The intron status of chironomid globin genes is more complex than previously assumed, requiring re-evaluation of evolutionary models.