Twin Genes: Researchers Discover Second Stress Response Hormone in Louisiana Garfish

May 15, 2015 1:19 PM
BATON ROUGE – Karen Maruska, LSU assistant professor of biological sciences and 2013 recipient of the Ralph E. Powe Faculty Enhancement Award from Oak Ridge Associated Universities, and postdoctoral scholar Brian Grone at the University of California, San Francisco, have uncovered the long lost twin of one of the most extensively studied genes in the brain. The researchers’ discovery, documented in the May edition of The Journal of Comparative Neurology, will provide valuable insight into the evolution of this family of genes and their role in controlling stress and other physiological functions.

Corticotropin-releasing hormone, or CRH, is a well-known gene whose product relays signals throughout the brain and controls the physiological responses that enable animals to react to different and sometimes life threatening situations. The hormone’s powerful biological effects have been studied for 35 years and documented in more than 10,000 scientific publications.

“Mostly, this research effort began as an interesting observation, but the availability of lots of sequenced genomes from many different animals allowed us to make the discovery that this CRH2 gene was actually present in many species, but absent in some others,” said Maruska.

Maruska and Grone searched huge databases of genetic information for CRH genes. In their search, the new gene was found in species ranging from the coelacanth – a now rare order of fish – to reptiles, birds and mammals. Both CRH1 and CRH2 would have been present in the ancient vertebrates that walked from the seas onto land for the first time.

To understand the functions of this newly discovered CRH2 gene, Maruska and Grone looked for its expression in the Louisiana native spotted garfish. Gars are ancient fishes with similarities to both the ancestors of bony fishes and tetrapods, or four-limbed vertebrates.

“We used the gar fish to determine where in the brain this new CRH2 gene might be expressed and where it was expressed compared to the previously known CRH1 gene,” Maruska said. “Seeing where it is located in the brain can give some insight into its function because we know a little about what different brain regions do in terms of regulating behaviors like feeding, stress, reproduction and aggression.”

The researchers used a technique called “in situ hybridization” to label specific neurons in the brain that express CRH2. Neurons containing CRH2 will appear as a purple color so that they can be examined under a microscope to determine their location in the brain. Surprisingly, CRH2 messenger ribonucleic acid, or mRNA, was found restricted to a small part of the hindbrain that is not thought to be involved in most stress responses. Instead, this part of the brain may be important for regulating feeding behavior in varying conditions.

“Though the discovery of CRH2 is a significant and exciting step, more research is needed to understand how CRH2 functions to affect brain activity, physiology and behaviors,” Maruska said. “With our publication, we hope that more researchers will look at CRH2 in different species and attempt to determine its function.”

Maruska’s work is supported in part by the Powe Award and a Louisiana Board of Regents Research Competitiveness Subprogram grant.


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