Huddersfield Biologist's study sheds light on the origin of moder

Dr Martin Carr

Fri, 13 Sep 2013 14:23:00 BST

Dr Martin Carr, who was recently appointed as Lecturer in Molecular Biology at the University of Huddersfield, is part of an international team which recently published research providing new evidence about how animals evolved in the Cryogenic Era, approximately 700 million years ago.

It has long been assumed that early animals must have evolved a larger genome than the single-celled organisms which they evolved from, in order to build their complex multi-cellular bodies. However it hasn’t been possible to prove this without sequencing the whole genomes of the closest relatives of the animals.

Previous work by Dr Carr and his colleagues, undertaken at the University of York, established the identity of the closest unicellular relatives of animals. This, and other studies, highlighed a small amoeboid organism called Capsaspora owczarzaki. Capsaspora was already the target of research, due to its potential role as a biocontrol of schistosomiasis, a chronic disease which afflicts over 240 million people worldwide. However its close evolutionary relationship with animals meant that it is an ideal study organism for research into animal genomics.

Dr Carr is a member of an international team headed by Dr Iñaki Ruiz-Trillo of the Universitat de Barcelona, which has published the Capsaspora genome in Nature Communications and found that many of the genes previously believed to be unique to animals have a far earlier evolutionary origin. Surprisingly, they found that many genes involved in the formation of cell-to-cell connections, as well as complex gene regulation, were already present in the unicellular ancestor of animals. The team did find evidence for the formation of many gene families in the direct ancestors of modern animals, with many of the new families involved in communication between individual cells. This suggests that this group of genes in particular were necessary for the evolution of multicellularity in animals.

As part of the study, Dr Carr analysed two major components of the Capsaspora genome for the study. Firstly, despite sex never having been observed in Capsaspora, he found the genome contained a complete set of genes involved in sexual reproduction. The finding shows that Capsaspora can switch from sexual to asexual reproduction and places the origin of sex to over 1 billion years ago.

Dr Carr also investigated the presence of genetic parasites called transposable elements in the Capsaspora genome. Transposable elements cause detrimental mutations in their hosts’ genomes, yet despite their harmful nature they are almost universal in living organisms and make up approximately 70% of the human genome. Dr Carr showed that only 10% of the Capsaspora is made up from transposable elements, which he explains is a result of Capsaspora being more efficient than humans at removing the elements from their genomes. All of the transposable elements found in Capsaspora have evolutionary counterparts in animal genomes, indicating that they were present in the last common ancestor of Capsaspora and animals. This came as something of a surprise as, despite the parasitic relationship they have with their hosts, the transposable elements have survived in both animals and Capsaspora for at least 1 billion years.

The Capsaspora genome analysis has highlighted many of the genomic changes which occurred in the evolution of animals and has also shown that our distant unicellular ancestors had unexpectedly complex genomes. Dr Carr is now continuing his research into the evolutionary origins of animals at the University of Huddersfield by studying the ecology and genomics of our closest single-celled relatives, the choanoflagellates.

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