Journal Club: Imaging molecular transport in the hair cell stereocilia - LIVE!

on

Today's journal article

Miyoshi T, Vishwasrao HD, Belyantseva IA, Miyoshi J, Sajeevadathan M, Ishibashi Y, Adadey SM, Harada N, Shroff H, Friedman TB. "Single-molecule fluorescence microscopy reveals regulatory mechanisms of MYO7A-driven cargo transport in stereocilia of live inner ear hair cells." Nat Commun 16, 8149 (2025). https://doi.org/10.1038/s41467-025-63102-0

  • Nat Commun 16, 8149 (2025). 
  • DOI: https://doi.org/10.1038/s41467-025-63102-0

Why I picked this article

This is a very cool paper, using a custom-developed high-resolution methodology to image the movement of a protein called "myosin" along a highly specialised structure called the "stereocilia" in a live cell. 

Sensory hair cells are so-called "hair" cells because they have structures called "stereocilia" on the apical surface of the cell. Stereocilia are an amazing, specialised component of the cell responsible for converting mechanical movement into ion conduction across the hair cell membrane. In brief, bending of stereocilia opens ion channels on the stereocilia, causing depolarisation of hair cells (and hence allowing sensing of sounds in the auditory hair cells and balance in vestibular hair cells, respectively). Tiny stereocilia are packed full of different proteins like ion channels & structural proteins to enable this function. 

It's always so exciting to see inner ear research in the Nature Communications issues, which are high-impact journals and publications that are almost always very interesting and high-quality. 

About the research in this article

  • Technique: STELLA-SPIM microscopy
  • Target: Vestibular hair cells in utricles and saccules from P2-5 (postnatal day 2-5) mouse pups
  • Labelling: To visualise the target protein, hair cells were manipulated to express modified proteins with a tag (HaloTag-fusion protein). This was introduced to hair cells using a technique called Helios gene gun. 


Extracted from portions of Figure 1 & 2 - please see the original article. 

The study uses a very novel technique, and a series of different versions of the protein generated using DNA constructs. 

  • HaloTag-MYO7A-HMM - a version of the myosin 7a protein designed by the researcher, so that two molecules will bind together to "dimerise" at the desired timing. => these proteins moved continuously towards the tip of the stereocilia. 
  • HaloTag-MYO7A full length: closest to normal myosin 7a protein. => protein was found throughout the stereocilia.
  • HaloTag-MYO7A-RK/AA: has two mutations in the part of the myosin 7a protein ("RGSK") important for negatively controlling protein movement. => protein formed a blob and accumulated at the tip of the stereocilia.
  • HaloTag-MYO7A-ΔSH3-ΔM/F2: has modifications on a different part of the myosin 7a (SH3 and M), irrelevant to protein movement. => protein was found mostly throughout the stereocilia. 

In addition, researchers made further modifications to test if the movement of myosins within the stereocilia is dependent on being attached to the cell membrane or another protein called Harmonin. They observed:

  • When anchored to the membrane (via membrane-bound protein), myosin 7a did not move continuously/smoothly (but can move step-wise). 

  • When myosin 7a was bound to a part of harmonin b, tagged myosin 7 changed its location to be more at the stereocilia tip. 

Haruna's takeaway

This is a very big paper and very hard to describe in a short article! 

What should be highlighted is the fact that the new technique these researchers have developed enabled studying myosin movement in live stereocilia. This meant that not only the location of myosins, but also the movement patterns could be quantified, including the speed, smooth vs step-wise, and direction of the protein movement. By having the ability to quantify these parameters, it became possible to test different hypotheses. I would expect the research team to continue to use the technique to generate further modified versions of different anchoring proteins to further investigate the mechanism of myosin transport. 

Noting that the stereocilia of vestibular hair cells used in this study are very immature, I wonder how we expect the stereocilia and protein trafficking within stereocilia will change as the hair cells mature. It's so interesting to think about how protein movements in hair cells change to enable stereocilia to form, mature, and be maintained. 

 ------- 

This is Haruna's 3/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.