Rapid protamine evolution suppresses meiotic drive in Drosophila

Area of Science:

• Evolutionary biology
• Genetics
• Reproductive biology

Background:

• Spermatogenesis involves replacing histones with protamines, crucial for sperm function.
• Protamines evolve rapidly in many species, but the evolutionary drivers are unknown.
• The protamine Mst77F is essential for male fertility in Drosophila melanogaster.

Purpose of the Study:

• Investigate the causes and consequences of rapid protamine Mst77F evolution.
• Understand the role of Mst77F in DNA compaction and male fertility.
• Determine the selective pressures driving protamine evolution.

Main Methods:

• Utilized in vivo gene replacement in Drosophila melanogaster.
• Compared DNA compaction in X- and Y-chromosome-bearing sperm.
• Assessed male fertility and progeny sex ratios following gene replacement.

Main Results:

• Mst77F ortholog replacements caused defects in X-chromosome sperm DNA compaction.
• This resulted in reduced numbers of X-bearing mature sperm and male-biased progeny.
• Mst77F is essential for suppressing sex-ratio distortion in Drosophila yakuba, though not for male fertility.

Conclusions:

• Relentless pressure to suppress sex chromosomal meiotic drive drives rapid protamine evolution.
• Protamines play a critical role in ensuring accurate chromosome segregation during meiosis.
• Rapid protamine evolution is a mechanism to maintain reproductive fitness and prevent meiotic drive.