Gestation has traditionally been viewed as the mother’s domain, with dad doing little more than depositing his half of the genome. Now, a new study in fruit flies pinpoints a protein in sperm that regulates embryos’ earliest cell divisions.
Evolutionary biologists at Fred Hutchinson Cancer Research Center published a study Tuesday in the journal eLife showing that when dad flies are missing this protein, known as HP1E, fertilized eggs die before they can even hatch. The findings could point to new ways to study fertilization in humans and other animals.
In most cells of the body, be they fruit fly or human, DNA is packaged by a special set of proteins into an organization system known as chromatin. Think of chromatin as your cellular closet organizer: This highly ordered structure winds, loops and squishes the six feet of DNA that is your entire genome into its microscopic housing in every cell, known as nuclei.
If most of your nuclei are like a well-organized closet, sperm nuclei are more like a jam-packed storage unit. Unlike most cells, sperm don’t need to do anything with their DNA other than deliver it to the egg.
HP1E appears to help solve an unusual problem of sperm-meets-egg fertilization: That super-packed DNA has to be quickly unbundled and reformatted into the “normal” chromatin within mere minutes inside the egg before the embryo can begin to grow and divide in a process known as mitosis. How HP1E does this is still somewhat of a mystery, especially since the protein itself is not actually present during the unpacking step, but the discovery of a male protein involved in early embryo survival is somewhat surprising, the researchers said.
We sat down with two of the study authors, Drs. Harmit Malik and Mia Levine, to find out more about protein evolution, fruit fly sex and what their findings could mean for human fertility. Their answers have been edited for clarity and brevity.