(ORDO NEWS) — Deep inside the ear there is a tiny thing you may not be aware of – a dead end tube called an endolymphatic sac.
Details of its function were discussed, but only in 2018 did scientists find out (at least partially) why this strange structure was.
According to the random discovery of zebrafish in fish, an endolymphatic sac can play the role of a kind of “safety valve” in the inner ear.
The story of this find begins a few years ago when the biologist at Harvard Medical School, Jan Swinburne, established a connection between the pulsating clot of cells in a developing fish, the zebrafish, and the process that protrudes from our inner ear.
Imagine that your inner ear is a long tube in the shape of a strange snail. At one end, it coils into a shell-like structure called a snail. On the other hand, where there would be snail eyes, there are three perpendicular loops called the labyrinth.
The fluid in the part of the cochlea’s shell transmits waves, which we interpret as sound, while the fluid in the loops acts as a biological level, giving information about where up.
Between these two structures, there are two chambers, called the utra and saccule. These cameras, in turn, are connected by a short, thin tube ending in a mysterious bag. Try presenting it in the diagram below:
Although no one is sure what he is for, there are some clues. It is understood that he plays a major role in Meniere’s disease, which is characterized by symptoms that include dizziness and tinnitus.
The disease is thought to be caused by an excess of fluid in the inner ear that over-inflates the structure, and since it has been shown that surgery on the endolymphatic sac helps relieve symptoms, this sac is probably related to fluid regulation.
Observing the work of the endolymphatic sac inside something as dense as a human head is easier said than done. But for zebrafish, Swinburne could use dyes to observe and record the movement of fluid slowly flowing in and then quickly emerging from the tiny structure.
There was only one question.
“We had all the notes on which the whole structure pulsated, and when Ian dyed the dye into the bag, we could see how the liquid flowed,” said Swinburne’s postdoctoral adviser Sean Megason in June 2018.
“But it was not clear how this fluid came out. Something strange seemed to be happening.”
Then the team was lucky. In a separate study of zebrafish in mutant fish with a variation of a specific genetic regulator, an endolymphatic sac was found to be larger than usual.
Whatever this mutated gene did, it seemed to cause an overflow of the structure and could not deflate properly, alluding to structural differences that could show how a normal bag works.
Using high resolution electron micrograph, the researchers found the answer. Inside the bag there were overlapping flap-like protrusions called lamellae protruding from the cells.
“Biologists like to say that structure determines function,” said Swinburne. “When we first saw the laemmli, everything fell into place.”
The cells lining the endolymphatic sac appear to have gaps between them to allow fluid to pass. These lamellas close the gaps, but as the pressure increases, they move apart until suddenly the entire bag flows like a sieve.
A closer look using more advanced microscopy methods showed that this is really what is happening.
“It looks like a cell that migrates, but they are part of the epithelium. This is a really strange cell biology,” said Swinburne.
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