Hagfish are a species with one of the longest lineages on Earth, now with genome sequencing they may help us better understand the evolution of vertebrates.
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So, what is a hagfish anyway? It doesn’t sound very appetizing. And it’s true, you definitely wouldn’t want to eat one. They produce an enormous amount of slime (and suffocate their prey in it), have no jaw, and importantly, have no vertebrae. But how can a species be a vertebrate without any vertebrae? By having a skull, apparently. So how did the hagfish come to be, and how did vertebrae get involved- did one come before the other? A new study conducted recently by Marlétaz, F. et al seeks to answer these questions by looking at the genetics of the Hagfish (Marlétaz et al., 2023).
In the past, there has been debate about whether Hagfish share a common ancestor with another species, the Lamprey, or whether they are simply their own species, and don’t belong to any certain grouping (Janvier, 2015) (Mallat & Sullivan, 1998). This debate becomes important when considering the bigger picture, how did vertebrates evolve? Scientists now understand that early vertebrates likely evolved through the entire genome of certain species being copied and passed on in duplicates to their offspring. But questions remain concerning how and when this happened, and they have been difficult to solve due to the shear amount of time that has passed since these events happened, which results in degradation of ancient DNA and lots of mutation since those times in the living organisms. Despite these problems, the geneticists involved in this study have found a way to answer these questions, big and small, using new methods and techniques.
The major findings of this study were that there is solid evidence showing Hagfish share a common ancestor with Lamprey, another wormy looking scavenger fish, and can safely be grouped into one category together (cyclostomes), and that Lamprey and Hagfish both experienced whole genome duplications, but Hagfish also experienced condensing of their genome, in what are known as ‘chromosomal fusions’. This is an important finding because it shows that the differences between Hagfish and Lamprey (the presence of vertebrae) happened after their branching off from a common ancestor, meaning that Hagfish underwent a series of major changes that resulted in their simplified body lay out, lacking vertebrate, while Lamprey already had them. These findings, however, were not easy to come by, and took an array of genetic testing methods and analysis in order to find, producing much other interesting information along the way. Once it was found that Hagfish and Lamprey had similar genomes, but that Lamprey often had several copies of genes or regions of the genome found on one chromosome in the Hagfish, it needed to be examined whether this was due to a second duplication of the genome in Lamprey or chromosomal fusion in Hagfish. This was accomplished using data analysis algorithms which processed the likelihood of both events, being calibrated on other well known similar genetic splitting events. Also interesting is the finding that Lamprey and Hagfish both share gene clusters (known as Hox clusters) which are important to altering DNA so that cells may become different types of tissues (like a hair cell, an eye cell, a nerve cell, etc). Knowing these similarities between Lamprey and Hagfish leads to continuation of the question, how did vertebrates evolve? Using RNA-sequencing data, the team was also able to identify specific genes which may have led to the genetic differences between non vertebrates and vertebrates we see today, including 22 genes involved in formation of embryos and hormone systems. Specifically in Hagfish, there was an interesting process noted in which Hagfish actually eliminate part of their genome at programmed times in their life, a process which needs to be studied more.
So, what next? Well, the epigenetic factors which control the programmed degradation of the Hagfish, and possibly the Lampreys, DNA and cellular death would definitely be a topic to research if I were in charge. But what’s the use of this? Why do we need evolutionary genetic research in the first place, especially concerning concepts so distant as the evolution of vertebrates? While it’s true that this research is not actively aiding in the development of treatments for curable diseases or cancers like other genetic research today, the benefit to simply understanding how our genome evolved, and the complexities which it holds, are enormous. Just looking at the idea of programmable cell death as has been seen in Hagfish, one can imagine the possibilities which this could have in cancer treatment, a disease characterized by rapid cell duplication. These genetic searches produce not only significant findings for evolutionary geneticists, but for others as well.
Janvier, P. Facts and fancies about early fossil chordates and vertebrates. Nature 520, 483–489 (2015). https://doi.org/10.1038/nature14437
Mallatt, J. & Sullivan, J. 28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes. Mol. Biol. Evol. 15, 1706–1718 (1998
Marlétaz, F. et al. The hagfish genome and the evolution of vertebrates. Nature https://doi.org/
10.1038/s41586-024-07070-3 (2024)
Rory Mullis, Class of 2026, romullis@davidson.edu
© Copyright 2022 Department of Biology, Davidson College, Davidson, NC 28036.
Not being familiar with hagfish, I thought it would be interesting to read this paper and was not disappointed. I enjoyed getting to know more about the different methods for doing phylogeny in related species. Specifically, I thought it was interesting to learn that some algorithims are based on the likely hood of known events which occured in other species. I would be interested to know what other species provide relevant information for comparison in the hagfish and lamprey. For instance, can any two other species which experienced similar gene duplication events or condensation be used to develop an algorithim in hagfish/ lamprey? Lastly, the programmed elimination of certain parts of the genome sounds like a very interesting trait. I wonder what the hagfish lifespan looks like then. Do they shift ranges over their lifespan? Do they change diets rapidly at a certain point in life? I wonder what would make such a trait viable for them. Overall, very interesting paper, Rory.
Hey Rory,
I thoroughly enjoyed reading your article; it provided intriguing insights into the relationship between lampreys and hagfish, shedding light on their common ancestry and the potential divergence of the two species. I’m particularly fascinated by the chromosomal duplications and fusions observed in hagfish. What could have triggered these genetic events, and how do they contribute to the evolutionary path of the species?
Moreover, the revelation that hagfish can selectively delete parts of their genome at certain life stages is truly remarkable. I’ve never encountered such a mechanism in any other organism before. It’s intriguing to consider how these regulatory processes function and their implications for hagfish biology.
Looking forward to hearing more about these captivating discoveries!