MicroRNA controls breast growth

Researchers discover novel mechanism for the development of organs

In lactating mice lacking microRNAs 212 and 132, the milk ducts (dark red) in the mammary gland tissue are not fully grown (right). The result: These mice can not produce enough milk for their offspring. © MPI for biophysical chemistry
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Hormones, growth factors and several other proteins provide the necessary growth in the near term - the components that cause breast growth in mammals during puberty seemed largely known. But apparently hormones and proteins are not everything in the breast development: This has now German scientists found out in a new study. They were able to show that tiny ribonucleic acid molecules play a key role in this process.

In mice lacking the gene for microRNAs 212 and 132, the growth of their mammary glands during puberty was completely absent, the researchers from Göttingen, Frankfurt and Hannover report in the online edition of the journal "Nature Genetics".

For the first time, scientists have demonstrated in the animal model that small ribonucleic acid molecules - so-called microRNAs - also play an important role in organ development. "That was also a surprise for us, " says project leader Kamal Chowdhury from the Max Planck Institute for Biophysical Chemistry in Göttingen. "The mice used in our experiments still had all the hormones, growth factors and proteins that ensure normal breast development. But the absence of the gene for miRNAs miR-212 and miR-132 alone meant that the growth of the mammary glands, especially the milk ducts, was completely absent. "

microRNAs allow fine-tuning of protein production

It has been known for some years that microRNAs have very important regulatory functions. Although they do not code for proteins themselves, they are responsible for the fine-tuning of the production of specific proteins and thus play a key role in the metabolism. But the repertoire of small RNA molecules is far from exhausted.

"Through various experiments, we have been able to show the key role that this RNA family plays in the development of the mammary gland and where the molecules are thought to intervene in regulatory terms, " ​​explains Chowdhury. display

Connective tissue as site of use

The mammary gland, also known as the mammary gland, consists of the glandular tissue with the milk ducts and of the connective tissue with a supporting and regulating function. In the mouse, the glandular tissue is surrounded by connective tissue and clearly demarcated. Connective tissue also appears to be the place where miR-212 and miR-132 intervene in the developmental process, according to scientists.

For only here, as Chowdhury and his colleague Ahmet Ucar could prove with their experiments, the genes of these ribonucleic acid molecules are "switched on".

Molecular dimmer

The microRNA molecules, according to the researchers' model, seem to control the production of a protein called MMP-9. Similar to a dimmer, the microRNAs can downregulate the production of MMP-9, "explains Ucar. If the microRNAs are missing, more MMP-9 proteins will be produced and accumulate near the dairy. There, they seem to activate a signaling pathway, which then prevents the doses of milk from growing up in the dorsal tissue.

"Their regulatory function thus exerts these tiny RNA molecules by influencing the communication between the two tissues of the mammary gland, " says Ucar. Further experiments now have to check whether the microRNAs also regulate breast development in humans. What happens when the microRNAs work incorrectly, the scientists can only speculate about this. "If such malfunctions can, for example, lead to the development of tumors in the breast tissue, further studies have yet to show, " says Chowdhury.

(MPG, 08.11.2010 - DLO)