UH Scientists' Findings from Research Utilizing Hox Genes in Squid Published in Nature

UH researchers discover difference in use of gene set may be key to diversity of animal life forms existing today

University of Hawaiʻi at Mānoa
Heinz Gert de Couet, (808) 956-9367
Department of Zoology
Kristen Cabral, (808) 956-5039
Public Information Officer
Posted: Sep 17, 2003

University of Hawaiʻi at Mānoa and University of Houston researchers have for the first time discovered how squid develop some of their unique features. Their findings were recently reported in the journal Nature.

The first to examine an important set of genes called Hox genes in squid, UH scientists Patricia Lee, Mark Q. Martindale, Heinz Gert de Couet and University of Houston researcher Patrick Callaerts, found that this set of normally predictable genes present in animals, from flies to humans, is utilized in entirely different ways when it comes to squid. This finding is vastly different from the conventional view of the role of these genes in other animals. It gives scientists a key to understanding how an animal‘s body plan is shaped by evolution, and how the same set of genes, when used differently, may give rise to the diversity of life forms that are observed today.

The so-called Hox genes are a group of highly conserved genes that are normally involved in organizing the body into the regions of the head, thorax, and abdomen in almost all animals. Their role is to increase or decrease the activity of many other genes, effectively acting as a "master switch" in development. The researchers cloned these genes from the Hawaiian bobtail squid (Euprymna scolopes), which was used as a model organism in this study. Although squid, nautilus and octopus form a unique branch of the evolutionary tree, the Hox genes found in the bobtail squid are very similar to those in any other animal. However, when the researchers mapped these genes in squid embryos, they were surprised to find that they are involved in the development of the unique features that define a squid—the arm-like tentacles, the light organ, and in parts of the nervous system connected to unique light-sensing organs and the jet-propulsion system.

All animals present today evolved from a common ancestor. One of the fundamental issues in evolutionary biology is explaining how the tremendous diversity of animals evolved from now extinct animals. For new animal body plans to appear, changes in their embryonic development must occur. Using modern techniques, developmental biologists are now beginning to understand the molecular basis for these changes. While much of the molecular progress in developmental biology has been made on a few laboratory animal systems, the time is ripe for this information to be applied to understanding the origins of biological diversity.

Cephalopods (nautiluses, squids and octopuses) are diverse animals that possess a range of novel characters not found in their closely related sister groups (snails, clams, sea hares and their kin). Compelling evidence suggests that cephalopods, with their unique modes of jet propulsion, tentacles, ink glands, light organs, camera-like eyes, and profound cognitive abilities, evolved from a simple, opihi-like animal. To understand how this might have occurred, Lee et al. cloned a set of highly conserved genes (called Hox genes), that are normally involved in organizing body plans of animals ranging from flies to humans, from the local Hawaiian bobtail squid, Euprymna scolopes. They mapped the expression of these genes in the squid embryos, and their results indicate that Hox genes are involved in virtually all of the unique features that define cephalopods. The details of their results show that in cephalopods, and likely also in many other diverse invertebrate animals, these genes have been used in interesting and unpredictable ways that are not seen in vertebrates, such as mice and humans.

These results show that although "simple" animals like squids contain virtually all the same genes as humans, these genes are co-opted to give rise to evolutionary distinct structures. Further research of this sort at UH, taking advantage of the unique local fauna of Hawaiʻi, will reveal the ways that these genes, and gene networks, have been re-used during evolution to give rise to all the diverse animals around us.

This research was supported by federal grants from the National Science Foundation and a seed money award from the University Research Council of the University of Hawaiʻi.