An international team of scientists has discovered that microRNA operates across and not just within cells to perform a vital role in the development of organisms.
You can read about the discovery by Professor Yrjö Helariutta at the Institute of Biotechnology of the University of Helsinki, Finland, and colleagues, including researchers in Sweden and the US, online in the 21 April issue of Nature.
MicroRNA, also called miRNA, comprises short RNA (ribonucleic acid) molecules found in many types of cell. It was only discovered about ten years ago, yet it plays a vital role in silencing genes in plants and animals.
It works by binding to messenger RNA (mRNA), the molecules that interpret gene information to make proteins.
The researchers in this study have now shown that microRNA operates across cells as well as within cells.
Helariutta describes microRNA as the “dark energy” of biology:
“They were in the shadows for a long time,” he said in a statement to the press.
“Researchers had seen phenomena that were not understood, until microRNA was discovered in the 1990s,” explained Helariutta.
In the Nature study, he and his colleagues focused on plants, but they said the results also apply to animals.
From previous studies they already knew that microRNA played an important role in ontogeny: the development of an organism from its single-cell beginnings to a fully-fledged adult.
The research could be relevant to many areas of medicine as well as biology. For example, some cancers are linked to deficiencies in ontogeny, and microRNA also affects the development of the vascular or circulation system.
A key question for plant biologists is how cells tell each other where they are as the plant and its various organs develop, so that the correct pattern of growth takes place.
For example, in plant roots, there is a central vascular cylinder containing cell types that conduct water (the protoxylem and metaxylem) arranged in a circular pattern around the centre (if you look at a cross section it looks a bit like the patterns you see in a kaleidoscope).
Helariutta and colleagues showed that this patterning “occurs through crosstalk between the vascular cylinder and the surrounding endodermis mediated by cell-to-cell movement of a transcription factor in one direction and microRNAs in the other”.
They also found that microRNAs made inside the cells acted to degrade target mRNA that encoded transcription factors outside the cells, and concluded that:
“The resulting differential distribution of target mRNA in the vascular cylinder determines xylem cell types in a dosage-dependent manner.”
Helariutta said that it might be possible to make use of microRNA communication between cells in medicine, for instance to calm down genes that have gone awry: this has already been tested successfully in plants, he said.
“Cell signalling by microRNA165/6 directs gene dose-dependent root cell fate.”
Annelie Carlsbecker, Ji-Young Lee, Christina J Roberts, Jan Dettmer, Satu Lehesranta, Jing Zhou, Ove Lindgren, Miguel A Moreno-Risueno, Anne Vatén, Siripong Thitamadee, Ana Campilho, Jose Sebastian, John L Bowman, Ykä Helariutta and Philip N. Benfey.
DOI:10.1038/nature08977
Source: University of Helsinki.
Written by: Catharine Paddock, PhD