US scientists Victor Ambros and Gary Ruvkun won the 2024 Nobel Prize in Medicine for the discovery of microRNA and its crucial role in how multicellular organisms grow and live, the award-giving body said on Monday.

The Nobel Assembly said in a statement that the laureates discovered a new class of tiny RNA molecules, which play a crucial role in gene regulation.

“Their groundbreaking discovery revealed a completely new principle of gene regulation that turned out to be essential for multicellular organisms, including humans,” the assembly said.

Their work helped explain how cells specialise and develop into different types, such as muscle and nerve cells, even though all the cells in an individual contain the same set of genes and instructions for growing and staying alive.

Thomas Perlmann, secretary of the Nobel committee for physiology, said he had reached Ruvkun by phone, waking him up early in the US morning, but he was eventually happy and “very enthusiastic”. He had not yet reached Ambros, he said.

“(Ruvkun’s) wife answered. It took a long time till he came to the phone and he was very tired,” Perlmann said at a press conference.

Ambros is a professor at the University of Massachusetts Medical School, while Ruvkun is a professor at Harvard Medical School and is also affiliated with Massachusetts General Hospital in Boston.

Last year’s medicine prize was awarded to the runaway favourites Katalin Kariko, a Hungarian scientist, and US colleague Drew Weissman, for discoveries that paved the way for COVID-19 vaccines that helped curb the pandemic.