Although a crucial moment in human development, scientists have never been certain how the half-genomes of the maternal egg cell and paternal sperm merge to form one human genome. Researchers this week described the enzyme SPRK1 as being critical to the process, and a potential target in fertility treatments.

Sperm are weird cells, in more ways than one. Up to twenty times smaller than a normal human cell, their genomes are wound around the structural protein, protamine, rather than histone for more condensed packing. Upon fertilisation with an oocyte, this structural arrangement is rapidly reversed to allow for parental genome reprogramming and activation.

Researchers at the University of San Diego School of Medicine reported that the SRPK1, a splicing kinase enzyme, catalyses the phosphorylation of protamine, unravelling the sperm genome and allowing exchange of these proteins with histone in the fertilised oocyte.

Moreover, their work published in Cell last week, demonstrated coordinated chromatin remodelling in both the paternal and maternal genomes upon fertilisation, despite the genomes still residing in distinct pronuclei. Chromatin reorganisation of both cell types must take place to permit transcription. This paves the way for future studies to investigate how the sperm genome communicates with that of the maternal in fertilised eggs.

As the lead author Xiang-Dong Fu explains “We have a ton of new ideas now. And the better we understand every step in the process of spermatogenesis, fertilization and embryogenesis, the more likely we are to be able to intervene when systems malfunction for couples struggling with reproductive issues.”

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