Prepped for the Long Sleep

Hibernation-related proteins are common even in non-hibernating animals, a study shows.

By Jyoti Madhusoodanan | July 30, 2014

FLICKR, MARC DALMULDERThe inactivity of hibernation is marked by dramatic decreases in body temperature, heart rates, respiration, and metabolism. From bears to chipmunks, cyclically fluctuating levels of a liver protein complex are thought to be an important part of this extreme adaptive response.

But the same proteins—members of the hibernation protein (HP) complex, which are produced exclusively in the liver—may also regulate more subtle seasonal rhythms in non-hibernating animals, such as cows and tree squirrels, according to research published today (July 30) in The Journal of Experimental Biology.

Comparing the genomes of several mammals, neurobiologist G. William Wong of the Johns Hopkins University School of Medicine in Baltimore, Maryland, and his colleagues discovered homologs of HP complex genes in several species that do not hibernate, including pigs, elephants, dolphins, rabbits, and sheep. Wong attributed the finding, in part, to a surge in sequenced genomes. “Nobody had bothered to look [for these genes] before,” he said. “In the last few years, so many mammalian genomes have been sequenced, which led us to the question of whether these [HP complex] genes are unique.”

These genes clustered on the same chromosome fairly near to one another, leading the researchers to at first believe they were conserved throughout mammalian evolution. But the researchers did not find these genes in the mouse, rat, dog, chicken, and human genomes.

To elucidate how these genes might work in non-hibernators, the researchers focused on cows. The three proteins in the HP complex—HP-20, HP-25, and HP-27—were found circulating in bovine blood and recovered from the cows’ cerebrospinal fluid (CSF). In samples collected over a four-year period, the researchers found CSF levels of the proteins oscillated cyclically during winter, summer, and fall; the highest annual levels of HP complex were seen in samples collected in February.

Although the discovery of the gene sequences was not unexpected, “we were surprised to find that the biochemistry and regulation of hibernation protein complex in non-hibernating animals was basically identical to that of the hibernators,” said Wong.

When the researchers treated the brains of mice with bovine HP complex proteins, they observed a decrease in the animals’ food intake, but found no change in their body temperature, respiration, or overall metabolism. This suggested that HP complex proteins may also regulate circannual physiologies, such as mating, migration, or food intake, in non-hibernators. “Most animals have seasonal physiology in the wild, and lab animals are not always reflective of that,” said Wong.

Sheep, cattle, rabbits, and pigs are all known to experience seasonal oscillations of reproductive hormones. Lemurs in Madagascar are known to hibernate through dry seasons. And the lesser hedgehog tenrec, which also carries HP complex genes, conserves energy through the winter by keeping its body temperature between 18°C and 25°C.

Still, the potential roles HP complex proteins in non-hibernators remains unclear. The chromosomal locations identified in this study “may be good places to look for circannual promoters,” said biologist Matthew Andrews of the University of Minnesota, Duluth, who was not involved in the study.

While prior work suggested that hibernation genes were specific to hibernators, these new data suggest that differential gene expression, rather than the presence or absence of certain proteins, may be responsible for mammalian hibernation.

The work “demonstrates the universality of these genes,” said Andrews. “It really is a fine example of how the genes involved in hibernation are found in other mammals, but in other organisms they might be used for different purposes at different times of the year.”

M. Seldin et al., “Seasonal oscillation of liver-derived hibernation protein complex in the central nervous system of non-hibernating mammals,” The Journal of Experimental Biology, doi:10.1242/jeb.095976, 2014.

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Avatar of: James V. Kohl

James V. Kohl

Posts: 525

July 31, 2014

Article excerpt: "These genes clustered on the same chromosome fairly near to one another, leading the researchers to at first believe they were conserved throughout mammalian evolution. But the researchers did not find these genes in the mouse, rat, dog, chicken, and human genomes."

My comment: In the context of mutation-initiated natural selection and the evolution of biodiversity, do mutations lead to conserved chromosomal rearrangements in some mammals but not in others? I ask because of comments by PZ Myers from his attack on John A. Davison, which prefaced his attack on me.   

"Evolution was all due to chromosome rearrangements, which somehow are not mutations, and he also somehow ignored the existence of allelic differences between species:"  

In my model, the allelic differences between species of mammals and all vertebrates and invertebrates are nutrient-dependent and pheromone-controlled like they are in other species from microbes to man. Ecological variation leads to nutrient-dependent alternative splicings of pre-mRNA and pheromone-controlled amino acid substitutions that differentiate cell types, which are manifested in morphological and behavioral phenotypes.

What experimental evidence of biologically-based cause and effect led to PZ Myers attacks, and why didn't he tell anyone about the biological basis for his ridiculously pseudoscientific opinion?

How can scientific progress be made if people like PZ Myers do not explain how experimental evidence led to their claims that serious scientists, like Dobzhansky are cranks?   "...the so-called alpha chains of hemoglobin have identical sequences of amino acids in man and the chimpanzee, but they differ in a single amino acid (out of 141) in the gorilla." (1973) 

Avatar of: vm123456


Posts: 61

August 2, 2014

whoah. HP proteins cause decreased food intake. If there are no side effects (which i think unlikely since we tried many appetite suppressant before) it could be a big seller amng the obese

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