Even though they're in the animal kingdom's order of Carnivora – carnivorous species – Giant pandas spend up to 16 hours a day on their backsides eating bamboo. But contrary to the many jokes about the intelligence of these black and white bears, scientists have found that it's not because they're too dumb to know better. It's actually far more fascinating – and gives us insights into how what we eat impacts our genes.
An international team of researchers led by China West Normal University (CWNU) has found that tiny plant molecules from bamboo have infiltrated the bodies of giant pandas (Ailuropoda melanoleuca) to regulate gene expression, leading them to not just rely on but crave this vegetation.
Analysis of several bamboo species and the blood samples of seven giant pandas – three adult females, three adult males and one juvenile female – found that the animals had 57 plant-based microRNAs that bonded to the bears' RNA to directly influence a broad range of physiological mechanisms, including those related to smell, taste and even dopamine. So what may look like a tedious job, gnawing through 30 pounds of woody, bitter vegetation each day, for the pandas it could even be something that triggers pleasurable reward signals in the brain.
Like humans (and all living organisms), panda RNA (ribonucleic acid) molecules make up a hugely important part of the body's genetic code. RNA is essentially the messenger cell that instructs which proteins are made when and where – the "building blocks of life" as biologists say. One amusing way of thinking about it is that if DNA is the whole "cookbook," which never leaves the "library" of a cell, then RNA is just one recipe copied from that book, which takes these instructions to other cells to create the proteins needed.
MicroRNAs (miRNAs), on the other hand, don't make proteins but they do regulate gene expression, altering the production of those proteins when they bind to complementary mRNA molecules. The scientists in this study found 57 bamboo-derived miRNAs in the pandas' blood exosomes, influences broad physiological pathways.
This plant-to-animal ("cross-kingdom") genetic influence is, in a way, how pandas at some point got "tricked" by nature into being almost singularly focused on bamboo – and how it's been able to help sustain the survival of the species.
“MiRNA in bamboo can enter giant pandas’ bodies through diet, be absorbed by the intestine, enter the blood circulation, and then regulate when the giant panda’s RNA transfers information, thus playing a role in regulating the gene expression of giant pandas,” said Dr Feng Li, a researcher at CWNU and senior author of the study. “MiRNA in bamboo is also involved in the regulation of smell, taste, and dopamine pathways of giant pandas, all of which are related to their feeding habits."
Once in the bloodstream, the bamboo-derived miRNAs regulate genes that help with dietary adaptation, including being able to acutely taste bitterness – which may help the animals avoid toxic plants – and better extract and absorb nutrients. They also appear to influence the immune system and metabolism, enabling these big mammals to survive on such a specialist low- nutrient diet. So, not so stupid after all.
"Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses of the target genes for these miRNAs revealed their involvement in various pathways, including taste and olfactory signal transduction, digestion and absorption, and hormonal signal transduction," the authors wrote. "Furthermore, we found that plant-derived miRNAs can modulate dopamine metabolism in giant pandas, thereby influencing their food preferences. This study shows that plant-derived miRNAs can enter the bloodstream of giant pandas and exert cross-kingdom regulatory effects, potentially playing a vital role in their dietary adaptation process."
Interestingly, some of the bamboo-derived miRNAs were found to regulate dopamine pathways, driving food motivation and the reward system linked to it. So if eating bamboo is a pleasurable, satisfying experience for a panda, it's more likely to be solely driven to seek out this trigger.
The scientists found varying miRNA profiles in their animal samples, suggesting that these plant molecules also play an important function at different stages of life – such as in reproduction and development – but much more research is needed in this area.
“We showed that plant-derived miRNAs are present in the blood of giant pandas,” said Li. “Our study proved that bamboo used as food for giant pandas does affect the change of giant pandas’ feeding habits.”
This study goes beyond just finding out why pandas have such a restrictive and labor-intense diet – one that on face value seems to defy evolution. It gives us a fascinating insight into how plant miRNAs can cross into the animal kingdom to modulate genes. For humans, this opens the door to new therapeutics to treat a broad range of conditions, including metabolic disorders, as well as healthier crops and better conservation strategies.
It also suggests that environment-gene interactions are a lot more complex and interconnected than previously thought.
The study was published in the journal Frontiers in Veterinary Science.
Source: China West Normal University via Scimex
