Looking Closely at Germ Cell Development

Researchers use superresolution to better understand the formation of germ granules

Germ cells are special types of stem cells that give rise to sperm and egg – the cells that combine during reproduction to create the next generation. Dr. Alexey Arkov and his lab at Murray State University (USA) work to better understand the molecules that are critical for germ cell development using the fruit fly model organism for their experiments.

In their recent publication, Dr. Arkov and his team focus on better understanding the formation of germ granules – unique molecular complexes which contain both RNA and protein and are required for germ cell development. They used the ZEISS Airyscan superresolution technology to look at specific proteins integrated into these granules to better understand how these important molecules assemble.

We interviewed Dr. Arkov to learn a bit more about his research and his use of the Airyscan superresolution technology.

Could you explain a bit more about germ granules and why they are a subject of interest for your lab and scientific discovery?

Germ granules have been found in over 80 animals, as diverse as rotifer and humans, and they are assembled from components, which are crucial for germ cell development. We would like to understand why these important components are put together in the granules to provide insights into the developmental mechanisms of germ cell specification. Furthermore, these germ granules provide a paradigm to study the assembly and function of large and dynamic RNA-protein structures, which lack the membrane, since many other membraneless RNA-protein granules are assembled in different types of cells. 

Did the Airyscan superresolution technology reveal anything novel compared to past data?

Superresolution microscopy has been used to image germ granules, however, in our work we focused on protein components of the granules, which have not been explored in the same detail by superresolution microscopy approaches in the fruit fly model as RNA components of the granules. When we looked at the protein localization in the granule with the Airyscan superresolution technology, we were surprised to find that individual proteins are not randomly distributed in the granule but rather assemble as separate clusters, which only partially overlap in the same granule.  

Imaris Snapshot
Distinct partially overlapping protein clusters assemble into germ granules. Posterior pole of early fruit fly embryo was immunostained to label two protein components of germ granules, Tudor (green) and Aubergine (red). An optical section image obtained with ZEISS Airyscan superresolution technology shows multiple individual germ granules formed from distinct Tudor and Aubergine clusters overlapping at the “interaction hubs”.

Was there anything in your publication that you are particularly excited about or that surprised you?

Proteins, described in our publication, associate with each other directly, therefore, it was really surprising to see that these proteins overlap in the granule only partially. We refer to these regions of proteins’ partial overlap as “interaction hubs”.  Overall, our data indicate that at least some protein building blocks of the granules assemble as distinct modules linked at the “interaction hubs”. Therefore, building the germ granule may be somewhat similar to building a structure from LEGO pieces or creating a mosaic art. 

3D reconstruction of individual germ granule. Multiple optical sections were used for 3D rendering of a single germ granule from fruit fly embryo’s posterior pole using Imaris software (Oxford Instruments). Tudor and Aubergine protein clusters within the granule are indicated with green and red respectively.     

Based on your findings here, where do you see your research going next?

We are in the process of studying additional components of the granules to see whether they follow the same assembly pathway as the proteins characterized in our publication. Also, we are characterizing germ granule-like structures in other cell types. We are using superresolution microscopy as well as genetics, biochemistry and structural methodology to decipher the precise assembly mechanism of these RNA-protein granules and, importantly, how this ordered and structured assembly contributes to function that these granules perform in the cell.

Learn More

Read the full article “Protein components of ribonucleoprotein granules from Drosophila germ cells oligomerize and show distinct spatial organization during germline development

Learn more about ZEISS Airyscan, the superresolution detector for ZEISS confocal microscopes.

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