Sperm is usually at rest until signals are received to activate motility. Thus, while many sperm proteins are components of the eukaryotic 9+2 axoneme that powers the sperm flagellum and constitutes a well-known set of proteins, the proteins that regulate flagellar motility in this non-regenerative system may differ from other cells that produce cilia. or using flagella for motility.
Some insect sperm, reportedly those with associated microtubules around the axoneme (the 9+9+2 axoneme), display unusual waveforms when motile. A new study by UC Riverside describes a complete portrait of all the proteins in the insect’s sperm. It allows scientists to find the specific proteins that maintain sperm quality while they are inactive and also activate them to swim.
Cathy Thaler, UCR cell biologist and the study’s first author, said: “During mating, mosquitoes mate tail to tail and the males transfer sperm to the female reproductive tract. It can be kept there for a while, but it still has to get from point A to point B to complete fertilization.”
“Key to completing that journey are the specialized proteins secreted during ejaculation that activate the sperm flagella or ‘tails’ that power their movement.”
Richard Cardullo, UCR biology professor and corresponding author of the new study, said: “Without these proteins, the sperm cannot enter the egg cells. They will remain immobile and eventually degrade.”
Scientists isolated as many as 200 male mosquitoes from a larger population for this study. They then extracted enough sperm from the small reproductive organs for mass spectrometry equipment to detect and identify the proteins.
Previously, scientists determined that sperm use calcium to enter a reproductive tract to stimulate forward movement. In this study, scientists created the finished protein profile, identified calcium channel proteins, and designed experiments to target these channels.
This form of protein profiling offers an approach to mosquito control that is more environmentally friendly than other technologies that can have unforeseen, harmful consequences.
Thaler said, “We’ve stopped spraying pesticides everywhere because that kills everything, good insects and bad, and harms other animals.”
Cardullo said, “Our work lays the foundation for a form of biological control that most agree is preferable.”
“The operative word is control, rather than extermination. While immobilizing the sperm would be 100% effective for the treated mosquitoes, it is not possible or desirable to kill all mosquitoes. This technology would change the ratio of fertile to infertile males in a given mosquito population, rather than eradicate them all.”
The team hopes that information about sperm motility regulators in Culex will also apply to other species of mosquitoes. As climate change intensifies, many other mosquitoes, such as those that transmit malaria, are migrating to the Northern Hemisphere.
The study could help control populations of Culex, the common house mosquito that transmits brain-swelling encephalitis and West Nile virus.
- Catherine D. Thaler, Kaira Carstens et al. Using the sperm proteome of Culex pipiens to identify elements essential for mosquito reproduction. PloS One. DOI: 10.1371/journal.pone.0280013