Origins of Sex

A study cataloguing the different types of protein found in sperm for the first time could help to unveil some of the questions surrounding infertility and the origin of sex, scientists claim. Researchers from the University of Bath identified 381 proteins present in sperm of the fruit fly, Drosophila melanogaster. This finding is a 50-fold increase in the proteins previously identified.

Writing in the journal Nature Genetics, the researchers claim that their study is the first to characterise the whole-cell protein components of a higher eukaryotic cell (a cell in which all the genetic components are contained within a nucleus). These components (known as the proteome) contain everything the sperm needs to survive and function properly and provide the basis for studies investigating why some sperm are more successful than others. The findings could be significant for researching infertility in men as around half of the genes of the fruit fly sperm proteome have comparable versions in humans and mice. Proteins carry out an immense range of functions, from forming structural materials to catalysing chemical reactions, so knowing exactly what proteins are in sperm is a great step forward in understanding.

"This study offers a tantalising glimpse into how we might begin to answer some of biology's most fundamental questions," said Dr Tim Karr from the University of Bath, who led the study. "Amazingly we know very little about what is in a sperm, which probably explains why we don't really understand sex, let alone how it evolved." He added: "Before we catalogued the sperm proteome, we only knew a few specific proteins in the Drosophila sperm. Being able to compare the structure and content of the proteomes of sperm from different species should help us understand the evolution and origin of sperm."
Research published in Nature Genetics today describes 381 proteins present in sperm of the fruit fly, Drosophila melanogaster. Whilst more proteins may be identified as research progresses, this study marks the first substantial ’whole-cell’ characterisation of the protein components of a higher eukaryotic cell (a cell in which all the genetic components are contained within a nucleus).

By comparing the sperm proteome of the fruit fly with other species, scientists will also be able to rewind evolution and work out the core sperm proteome – the most basic constituents a sperm needs for sexual reproduction. This will shed light on how sex itself evolved.