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A new joint collaboration between Tel Aviv University, Columbia University’s Medical Center, and the Cold Spring Harbor Laboratory (CSHL) has demonstrated that life events can effect the genetic heritage of an organism’s immediate descendants. The Columbia team was able to show that transgenerational memory is passed on through an organism’s short RNAs for at least three generations.

“It shows that our experiences shape our inheritance… and that’s there’s a memory of our ancestors’ lives,” Tel Aviv’s Oded Rechavi, lead researcher on the project, told The Speaker.

The study, “Starvation-Induced Transgenerational Inheritance of Small RNAs in C. elegans,” was completed by Leah Houri-Ze’evi, Sarit Anava, Wee Siong Sho Goh, Sze Yen Kerk, Gregory J. Hannon and Oliver Hobert, in addition to Rechavi. The study was supported by the Howard Hughes Medical institute and was published in the June 10 edition of Cell.

In its research, the team demonstrated that drastic environmental changes, such as famine, can cause genetic changes that are passed down through at least three consecutive generations.

The team demonstrated this using roundworms. The team starved roundworms for six days and examined their cells. The starved roundworms were found to have developed a specific set of small RNAs.

Small RNAs are a type of non-coding RNA (ncRNA), functional RNA molecules that are not translated into protein (as are DNA). Many ncRNAs have been newly identified in recent years, and have not yet been validated for their function. Small RNAs are involved in various aspects of genetic expression.

“Small RNA-induced gene silencing can persist over several generations via transgenerationally inherited small RNA molecules in C. elegans,” stated Rachavi. Starvation induced changes in the roundworms’ small RNA were inherited by subsequent generations. The genetic inheritance took place apparently independent of DNA involvement.

Based on evidence of human famines and animal studies, it had long been suspected that starvation can affect the health of descendants, but the means by which such genetic inheritance was conveyed was not known.

“[E]vents like the Dutch famine of World War II have compelled scientists to take a fresh look at acquired inheritance,” said Oliver Hobert, PhD, professor of biochemistry and molecular biophysics and Howard Hughes Medical Institute Investigator. Animal studies have been conducted showing that, like humans who give birth during famine, animals such as rats can be caused to produce thin or obese offspring.

Roundworms were used in another small RNA-related study in 2011, when they were used to show that virus immunity developed during a parent’s life could be passed on to offspring for many generations through small RNA viral-silencing.

Hobert suspected that the small RNAs were somehow finding their way into the worms’ sperm and egg cells. “When the worms reproduced, the small RNAs could have been transmitted from one generation to the next in the cell body of the germ cells, independent of the DNA.”

How small RNAs were entering germ cells, and what types of biological experiences were registered by small RNA changes, Rechavi told The Speaker, “is a completely uncharted area.”

Rechavi said that the response to an organism’s environment was, however, “not necessarily only dietary related. In theory… any response that would produce a strong systemic small RNA response could be heritable. It’s not clear exactly how small RNAs find their way to the germline, but in worms several genes that enable cell-to-cell transfer of small RNAs have been discovered.”

In Rechavi’s previous work he has demonstrated that human immune cells, such as T or NK cells, can exchange small RNAs with other cells, and that some small RNAs can be found circulating in human blood.

“In general, I would suspect that it would be worth ‘memorizing,’ or producing a heritable response,” Rechavi told us, “cues which are really important for the survival of the organism.”

The implications of the study include that the biology of inheritance is more complicated than previously thought.

“[They] suggest that we should be aware of other things—beyond pure DNA changes—that may have a long-term impact on the health of an organism,” said Dr. Hobert. “In other words, something that happened to one generation, whether famine or some other traumatic event, may be relevant to the health of its descendants for generations.”

The study has also been said to give weight to the long-dismissed Lamarckian theory of genetics, which proposed that organisms adapt to their environment and pass on adaptations to offspring. Lamarckian genetics has traditionally been contrasted with Darwinian genetics, which theorized that all mutations were random, and the randomly mutated offspring were selected by nature according to their success surviving and reproducing.

Next for Rechavi and his team is to further pursue an understanding of the effects of environment on genetics. “We are testing how stable these effects are,” Dr. Rechavi told us. “exactly how the small RNAs are produced, and which regulated genes are most important in the process. We are also interested in examining the generality of this mechanism. This could be an important mechanism that acts side by side along with the traditional DNA-based inheritance mechanism.”

By Day Blakely Donaldson

Researchers testing the amount of plastic garbage polluting the earth’s oceans have discovered a mystery. Instead of finding evidence of the millions of tons of durable plastic garbage expected to litter the ocean surface, they found only tens of thousands.

In the 1970s, the National Academy of Sciences estimated that 45,000 tons of plastic garbage reached the world’s oceans every year. Today the world produces five times as much plastic as it produced in the 70s, so researches expected to find evidence of millions of tons of plastic garbage in the oceans. They were surprised that after looking at over 3,000 samples, they found only 7,000 – 35,000 tons of plastic garbage.

The research was conducted by ecologists at the University of Cadiz in Spain. The report, “Plastic debris in the open ocean,” was completed by Andrés Cózara, Fidel Echevarríaa, Ignacio González-Gordilloa, Xabier Irigoienb, Bárbara Úbedaa, Santiago Hernández-Leónd, Álvaro T. Palmae, Sandra Navarrof, Juan García-de-Lomasa, Andrea Ruizg, María L. Fernández-de-Puellesh, and Carlos M. Duartei, and was published by the National Academy of Sciences.

The researchers do not know where the missing garbage has gone. The researchers did find clues, however. A primary piece of evidence was that far fewer plastic fragments under 5 millimeters were found than larger fragments.

The researchers guessed that somehow the smallest pieces of plastic were finding their way to deeper waters.

Another guess was that mesopelagic fish, which inhabit the oceans at 660-3,300 feet below the surface, were feeding on the plastic fragments when they came to the surface at night. The researchers pointed out that the normal food of these fish is roughly the same size–zooplankton. When the fish excrete the debris, it may sink deeper, or the debris may be carried deeper when the fish die.

Another finding was that bacteria was growing on the plastic fragments. The bacteria’s weight may be pushing the fragments down, the researchers suggested.

These guesses were phrased by the researcher this way: “Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered.”

The surprising finding led the researchers to conclude a further question was pending. “Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean,” the researchers stated.

By Sid Douglas

PNAS

Global Ocean Commission

Two marine researchers have published a report on two prominent near-bottom fish species of the northern seas, looking at how the two species fared in the warming waters of the past decade. The researchers looked at Bering Sea walleye pollock and Atlantic cod, and proposed that the differences in how the two species fared may be indicative of how other species will variously thrive or suffer during global warming.

The northern waters of both the cod and the pollock have warmed over the past decade, but one of the species appears to have prospered, while the other has diminished. “These response patterns appear to be linked to a complex suite of climatic and oceanic processes that may portend future responses to warming ocean conditions,” stated the researchers.

The report, “Distinct impact of tropical SSTs on summer North Pacific high and western North Pacific subtropical high,” was written by Anne B. Hollowed of the Alaska Fisheries Center’s National Marine Fisheries Service and Svein Sundby of the Institute of Marine Research, and was published in Science Magazine.

The report explained that Atlantic cod stock biomass has steadily increased since the 1980s, paralleling an increase in northern oceanic tempertures. Atlantic Cod, which spawn in the southern end of their territory, are thought to require warm temperatures to produce strong year classes. “During warming phases,” the report read, “the spawning stock biomass gradually builds up and the cod spawn rather north,” whereas in cooler phases spawning takes place further south. A similar trend of increasing fish stocks accompanied the warming period between the 1920s and the 1940s. The recent success of Atlantic cod stocks is thought to be the result of warmer weather, in addition to the effects of fishing limitations.

On the other hand, Bering Sea pollock–the largest fish stock in the northeast Pacific Ocean–declined in the early 2000. The stock began rising again before 2010, but did not reach pre-2000 levels.

The habitat and diet of pollock is thought to account for the difference. Bering Sea pollock feed throughout the middle and outer shelf regions and generally avoid bottom waters below 0 degrees Celsius–and so are usually found in the southern Bering Sea. The fish expand across the shelf in warmer years. The pollock stock is made up of several age groups, each of which has been affected by prey availability and the ability to accumulate winter stores of energy.

The pollock are thought to be affected by temperature most significantly in the first year of their life–due to the effects of temperature on their first summer.

The report concluded, “The response of seafloor fish species in the border regions between the boreal and Arctic domains to climate variability may provide clues to how future antrhopogenic climate change will influence fish stocks and marine ecosystems at high latitudes.”

The report also made more specific predictions about the future of Atlantic cod and Bering Sea pollock. The cod, which have already reached the shelf break and the deep polar basin, can advance no further north, and so may now advance eastward along the Siberian shelf as new habitats open up due to the loss of sea ice at the Siberian shelf and the Northeast Passage. The pollock face an uncertain future, because the suite of interacting processes that govern their health is more complex, and because sea ice is expected to continue to form in fall and winter, leaving a cold remnant in summer, making the cold pools inhospitable to the fish.

by Sid Douglas

Nature