How fish got their spines

The movie "A Fish Called Wanda" shows Otto as a villain who effortlessly eats all the fish in Ken's tank. However, reality is much more difficult. One fan, at least, was admitted to hospital with a stuck fish in his throat after reenacting the scene. This was also a painful lesson in Ichthyology, the scientific study of fishes. It teaches that some fishes can be protected by their fin spines. There are two types of fin elements. Many fish species have two types of fin elements. "Ordinary" soft fin Rays are blunt and flexible, and are primarily used for locomotion. Fin spines are sharp and highly ossified. They are an evolutionary advantage because fin spines make fish less edible. The most diverse fish lineage, with over 18.000 members. These fishes have even developed separate "spiny Fins" that are made up of only spines. The evolution of fin spines is a key factor in the diversity and success of fishes. Researchers from the University of Konstanz, led by Joost Woltering (his PhD student and the first author of the study), have published a study in PNAS that shows how fin spines develop during embryonic development. The researchers also discuss how the different lineages of fish could have their own ancestral soft-rays that can be used to create spines. The study is focused on the Astatotilapia Burtoni, a model species of spiny-rayed fish. It has well-developed soft-rayed fin parts and spiny spines. Different developmental genes for soft-rays and spines. As a first step, team members determined the genetic profile of soft-ray fins and spiny fins in embryonic development. Rebekka Hch says, "What we saw in these first experiments was that a group of genes we knew about fin and limb development become differently activated when spines or soft-rays." These genes are called master regulator genes. They have been shown to control morphology in both the axial and limb skeleton. These genes are thought to be responsible for determining whether fin elements emerge looking like a spine, or soft-ray in fish fins. The team discovered genetic pathways that activate these master regulator genes. These pathways control the activity of the fins at different locations. Joost Woltering is an assistant professor at the University of Konstanz's Department of Biology and the senior author of this study. The scientists were able alter the number and soft-rays of the fins through their experiments. The BMP (bone-morphogenetic protein signaling) was modulated to produce the most dramatic results. Joost Woltering says that we saw changes in activation of master regulatory genes as well as so-called homeotic transforms in which soft-rays became spines or vice versa. Another observation was that the morphology and coloration of the fins changed in these fish. "Male Cichlids have bright yellow spots, but they are limited to the soft-rayed portion. Joost Woltering says that we found that a soft-ray transformed into a spine and the fin lost its yellow spots. This observation indicates that spines and soft-rays in spiny-rayed fish are integral parts of a larger developmental program that determines many of the fin's visible features. This principle is the same in different fish lineages. As the puzzle was assembled, the team realized that a deeply preserved patterning system had been re-employed during the evolution of the spiny Fin. "In fact, the genetic code which determines where spines will appear in the fin domain is active even in fins without spines. Rebekka Hch says this indicates that an ancestral pattern of genetics was used to make spines." The authors used this new insight to study fin patterning in catfish. This is a group of fish that has evolved their own fins. The genetic code for spines in the catfish was identical to the one found in the cichlid. Although there are some differences between spiny fish species it all suggests that there is an evolutionary-favored fin pattern that can be relied upon to produce spines. Next steps The team will continue to research genes that are downstream of the spine and soft-ray control gene genes. This will allow them to discover how they affect fin morphology and control ossification as well as cellular growth pathways. Joost Woltering concludes, "In the end, we want to gain better understanding of how anatomical structures emerge that make certain species more successful and how this contributed the amazing evolutionary diversity of the fish linesages." ### Here are some key facts THE EMBARGO ON PAPER WILL LIFT AT 3:00 U.S.EASTERN TIME (8:00 PM CEST) ON JULY 5th 2021! Original study: Rebekka, Ralf F. Scheiber, Alison Kickuth and Joost M. Woltering (2021). A BMP-gremlin–shh signaling network establishes spiny and soft-rayed fin domains for acanthomorph fish. PNAS ; DOI 10.1073/pnas.2101783118 ; DOI 10.1073/pnas.2101783118 Journalists have EurekAlert access to the embargoed articles! All the authors of this study are associated with the Department of Biology, University of Konstanz. Ralf F. Schneider is currently employed at the Helmholtz Centre for Ocean Research Kiel, (Geomar), and Alison Kickuth at Max Planck Institute of Molecular Cell Biology and Genetics. Contacts with scientists: Dr Joost Woltering at uni-konstanz.de, Professor Axel Meyer @ uni-konstanz.de BMP (bone-morphogenetic protein), and shh (sonic hedger) signaling pathways play a crucial role in the formation of fin patterns for fish development. They regulate the activity of master regulator genes (hoxa13, alx4) which determine whether developing fin elements will be soft- or spiny. Comparing fin spines of fishes from different lineages shows that they have evolved independently through repeated redeployment and conservation of a highly conserved genetic pattern. Funding: Deutsche Forschungsgemeinschaft, #WO-2165/2-1, European Research Council (ERC) #293700 and Young Scholar Fund of University of Konstanz Editor's Note: Download a photo by clicking https:/ / cms. uni-konstanz. de/fileadmin/ pi/fileserver/ 2021/ how_fish. jpg Caption: Two males from the cichlid fish Astatotilapia Burtoni. This is the model organism that was used in Hch et. al. to study the development of spine and soft-rays. Copyright: Joost Woltering Contact: University of Konstanz Communications and Marketing Telephone: +49 7531 88-353 Email: kum@unikonstanz.de uni.kn/en

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