The large variation in size among cetacean species, including dolphins, whales and porpoises, is largely explained by the activity of specific genetic regions, according to a recent study by scientists from the Institute of Biology of the University of Campinas (IB- Unicamp) of Brazil.
Blue whales (Balaenoptera musculus), for example, can grow to be a giant 30 meters (98 ft) long, while the bottlenose dolphin (Tursiops truncated) usually does not exceed 3.5 meters. The new research not only helps explain these huge size differences, but may also advance cancer treatments.
The researchers examined the DNA sequence that precedes the protein-coding part of a gene, called the promoter region. Examination of the promoter region of a gene called NCAPG revealed intriguing relationships among cetaceans.
Furthermore, it is possible that the identified regulatory sequence could play a role in managing any uncontrolled cell proliferation in animals adapted for massive growth.
Cetaceans are divided into two well-defined groups; Mysticeti, which includes all baleen whales such as humpbacks, and Odontoceti, which includes whales with teeth, such as sperm whales and dolphins. However, despite such a distinct evolutionary classification, the entire group of aquatic mammals could be divided in another way.
“We found in the promoter region of the gene NCAPG a division between those that measure more or less than 10 meters: giants and non-giants,” says Felipe Silva, first author of the new article and geneticist at IB-Unicamp.
Previous research by the same group revealed that the NCAPG The gene appears to be favored by evolution in giant cetaceans. New findings about the promoter and coding regions of this gene suggest that it plays an important role in making cetaceans grow to enormous sizes.
Gene activity depends largely on the promoter region, which is like a regulator of gene expression. Silva and his team discovered that size-controlling proteins were more active in giant cetaceans, driven by their specific promoters. On the other hand, cetaceans with lengths less than 10 meters had those same genes that acted as inhibitors, limiting the production of these proteins and, consequently, the size of the animal.
“Our findings do not modify the evolutionary tree of the group, but they constitute new evidence that giant size has a genomic basis,” says geneticist Mariana Nery from IB-Unicamp.
Proteins that regulate body size were more active in giant cetaceans, explaining why the sperm whale (Physeter macrocephalus), which is giant but has teeth, is most closely related to Mysticeti, which are also giant but lack teeth.
Those same genes were inhibitory in cetaceans shorter than 10 meters, explaining the genetic link between the 8.8-meter-long toothless common minke whale (Balaenoptera acutorostrata), and other non-giant toothed cetaceans.
“Analysis of other genes confirms the evolutionarily established groups,” explains Nery, “which means that the characteristics of minke whales and sperm whales are probably convergent adaptations: similar traits that evolve independently in separate groups through different pathways. “.
Despite the expectation that tumors will occur in animals with large numbers of cells, giant cetaceans have an exceptionally low incidence of cancer.
The researchers then analyzed the regulatory regions of four genes whose protein-coding sequences had been previously studied. Non-coding sequences, which include regulatory elements such as promoters and enhancers, play a role in coordinating the timing and location of gene expression.
“It was important to analyze the coding and non-coding parts of the genomes of these cetaceans, since both were significant for these traits, which evolved very quickly in these animals, as the analysis also demonstrated,” explains Silva.
The team speculated that these regulatory regions could not only have an effect on the size of cetaceans but could also influence their ability to suppress cancer.
“Humans also have these genes, so it would be interesting to know more about how they inhibit tumor formation in these animals,” says Nery.
“This knowledge could help develop future cancer treatments by activating or inhibiting specific regions of the genome, for example.”
The research has been published in BMC Ecology and Evolution.