AP Biology class blog for discussing current research in Biology

Tag: Hearing

Attention all Concert Attendees: Hearing Loss Is Potentially Reversible

Organ of cortiThe most common cause of hearing loss is the damage and loss of cells that grow the hairs inside the inner ear.  These cells are aptly named cochlear hair cells.  Repetitive exposure to loud environments, such as construction zones, concerts, or military bases can damage these cells, which, until recently, were thought to be irreplaceable.  Normally, these cells enter the G0 phase after initial development ends when the organism is mature, which makes them similar to the brain cells we learned about in class.  When a cell is in the G0 phase, it is frozen in the cell cycle, so the cell does not proceed through mitosis.  This means that once the organism is done growing, there is no replacement of the damaged cells, as no cells are dividing.  

In the animal kingdom, however, these cells are known to regenerate.  Birds and fish have a mechanism which relies on a gene called ERBB2.  The artificial expression of this gene in mammals has also been proven to trigger cell growth in a trial led by Jingyuan Zhang, PhD.  They found that activating the ERBB2 gene triggered a cascading series of cellular responses which made the active cochlear hair cells multiply as well as trigger stem cells to become cochlear hair cells. 

The research found that the activation of the ERBB2 gene caused stem-cell like development through the expression of a few proteins.  The most important protein to this process, SPP1, signals the CD44 receptor, which exists on cochlear hair cells.  The theory is that because these receptors are triggered, they somehow promote mitosis in the cells.  The promotion of mitosis, the process of cell division in the cell cycle, would mean that these cells could be reproduced and the damaged cells could be replaced by new cells. 

When this process was tested in adult mice, this cascade happened as previously shown in growing mice, meaning that the possibility of the development of new cochlear hair cells is possible in mature mammals, it just needs to be stimulated correctly.  

The next step in the research is to determine whether or not these new cochlear hair cells are functioning mechanically. I don’t know about you, but I would maybe not stop wearing my earmuffs to use a jackhammer if I were you.  

Embryo Gene Editing can Ensure Offspring Do Not Inherit a Deafness Gene!

Denis Rebrikov, A scientist in Russia has done research regarding ways in which he can edit the genome sequence of an embryo in order to prevent the fetus from developing certain gene mutations, specifically in this case a hearing problem or possible complete deafness. His plans are very controversial to some, who believe the possible risks of very harmful mutations to DNA that would be passed onto direct and future offspring, outweigh the possible benefits. However, some people find this scientific possibility to be worth the risk, if it means not passing a potentially very harmful gene down to offspring. If these methods are done correctly, it should alter the genome sequence in the embryo so that future offspring off that embryo will not inherit the negative mutation.

One couple shared their story in detail, in which both parties have a hearing deficiency, the man with partial deafness, and the woman completely deaf. Their biggest hope is to have children who will not inherit hearing issues, because of the apparent challenges they have had to face themselves because of them. They would be the first couple to perform this gene editing on an IVF embryo, so they obviously have some reservations. One of those being publicity, but more importantly the potential risks of using the CRISPR genome editor. They already have a daughter with hearing loss, but they never chose to test her genes for mutations, nor did they get her a cochlear implant to aid her hearing, because of the potential risks of that. When they finally tested her genes, they learned that she had the same common hearing loss mutation called 35delG in both her copies of a gene called GJB2. The parents then tested themselves, realizing they were both 35delG homozygous, meaning their daughter’s mutations were not unique to her, they had been inherited.

If either the mother or father had a normal copy of the GJB2 gene, a fertility clinic could have more easily created embryos by IVF and tested a few cells in each one to select a heterozygote–with normal hearing–to implant. At this stage, Denis Rebrikov informed them that CRISPR genome editing would be their only option. However, the process presents possibly deal breaking risks, such as mosaicism, in which a gene edit might fail to fix the deafness mutation, which could create other possible dangerous mutations like genetic disorders or cancer. The couple has not decided to go through with the editing just yet, but it is something they are open to in the future as more possible new research or test subjects become available.

Explaining the CRISPR Method: “The CRISPR-Cas9 system works similarly in the lab. Researchers create a small piece of RNA with a short “guide” sequence that attaches (binds) to a specific target sequence of DNA in a genome. The RNA also binds to the Cas9 enzyme. The modified RNA is used to recognize the DNA sequence, and the Cas9 enzyme cuts the DNA at the targeted location… Once the DNA is cut, researchers use the cell’s own DNA repair machinery to add or delete pieces of genetic material, or to make changes to the DNA by replacing an existing segment with a customized DNA sequence.” -US National Library of Medicine Genetics Home Reference


Woman with a hearing aid 

If you had the opportunity to alter something in the gene’s of your baby’s embryo, would you? Under what circumstances would you consider this, and what risks might stop you from deciding to do it? Comment down below.



The solution to hearing loss: listening to things?

When we think of hearing loss, we typically think that it’s because the person listens to too many loud things, and that they should try to give their ears a break by hearing as little as possible. However, according to researchers as Case Western Reserve, the solution to preventing deafness might be to use your ears.

Let me explain. There are tiny hairs in your ear (stereocilia) which allow you to hear by vibrating. When overly loud noise hits these hair bundles, they whip back and forth, damaging them. However, if they are constantly stimulated with gentle sound, the movement of the hair bundles actually allows them to readjust, repair, and maintain the health of the hairs of the inner ear. The researchers looked at zebrafish, whose hair bundles move back and forth constantly at amazing speeds, which reinforced the idea. In more detail, the proteins that constitute the hair bundles have a higher turnover rate when under stimulation, meaning that the proteins in your ear hairs are replaced more often, allowing the hair to repair itself. Ears not used much retain the useless broken proteins, leading to poor hearing. Ear hairs used a lot are like muscles when working out: yeah, they’re a bit torn, but they’ll be stronger when they grow back.


The research team says they haven’t proven stereocilia repair themselves, and that they still need to look into more detail for that process (link for the more academically inclined). However, the theory looks very promising.

I find it interesting that biological organisms have a tendency to heal through usage, as it almost seems counterproductive to me. I typically think of rest and recuperation when I think of healing, but apparently biology wants you to just keep on chuggin’. What other systems or things do you think we have that heal with use?


Quite simply.

To heal your hearing,

One needs to whip their hair back and forth.)

Moles Can Smell In Stereo

BSC Photography

We humans can see and hear in stereo. This is what leads to our 3D vision and allows us to find things easily because of our depth perception. Similarly our ability to hear in stereo allows us to roughly locate where a sound is coming from and how far away it is. But humans can’t smell in stereo, and it was widely believed that no mammal could naturally. That is until a study came out which indicates that the eastern mole, which is nearly blind, locates it’s food with the help of stereo smell.


Kenneth Catania, who led the research, said he came into it as a skeptic. “I thought the moles’ nostrils were too close together to effectively detect odor gradients.” Catania’s interest began when he found that the eastern mole could locate food just as quickly as its cousin, the star-nosed mole, which has a far superior sense of touch. In further tests he found that the eastern mole was remarkably quick at locating food placed in a radial chamber, indicating that they had a very sensitive sense of smell. In addition, Catania found that when he covered a mole’s right nostril, it veered to the left consistently, and when he covered the left nostril, it veered to the left consistently. This discovery is what indicated that the moles had stereo smell. Catania says this discovery “suggests other mammals that rely heavily on their sense of smell, like dogs and pigs might also have this ability”

Gerbils Can You Hear Me?

80 to 90 percent of people suffer from inherited deafness. In a study, scientists have reversed deafness in gerbils. This is a huge step in gene therapy research this month making the possibility of using gene therapy as a cure for deftness one step closer. Genetic therapy is the use of genetic material such as DNA to manipulate a cell and is generally used to treat inherited diseases; in this case scientists used human embryonic stem cells. The gerbils in the study were born deaf. This type of deafness is a birth defect caused by damage to hair cells in the inner ear. These inner ear hair along with auditory neurons which translate sound vibrations from the inner-ear cells to electrical signals are how you can hear. Scientists specifically worked on gerbils whose deafness was caused by a mutation in a gene coding for a protein called vesicular glumamate transporter-3. Even minor alterations to a protein’s primary structure ,such as the movement of a double bond, will cause major defects in the tertiary structure and the function of the protein. The mutated protein in this study vesicular glutamate transporter-3 controls the consumption of glutamate (neurotransmitter) into synaptic vesicles, which join two nerve cells, of the neural cells. This is clearly groundbreaking news this month and has proved the various use of stem cells. How do you feel about the use of embryonic stem cell research? Feel free to comment!!



Sorry, What Did You Say?

Credit: Cyclone

Are you able to zone out in a noisy room and just focus on one thing? I know that I am able to do this when I am really into a book and I block every other sound out when I am reading. Are you able to focus on only one voice in a room of many?

A recent study has shown that the brain has the ability to focus so intensely that it can make a single voice seem like the only sound in a room full of other noises. Nima Mesgarani and Edward Chang of the University of California, San Francisco, studied what happens in the brains of people who are trying to follow one of two talkers. Scientists call this scenario “cocktail party problem.” In the study, electrodes were placed under the skulls of three people for an epilepsy treatment. The electrodes picked up high gamma waves from nerve cells. The pattern and strength of the high gamma waves reflect which sounds the people were paying attention to. The scientists gave the test subjects a signal word and told them to focus on that speaker once that word was spoken. Throughout this experiment, the researchers recorded brain activity and sorted that activity into patterns that reflect voices and words. They found that before the signal word was uttered, the patterns in the brain showed up as a mishmash, but once that word was heard, the subjects’ attention focused on that one voice and their brain activity shifted to a pattern similar to that seen when the listener heard only a solo speaker.

Micheyl said, “scientists already knew that attention influences perception, but the new results demonstrate that this is a literal, direct reflection of auditory attention at the neural level.” These results help explain how people are able to pick out a single speaker from a multitude of incoming sounds. Scientists hope that with these results and a deeper understanding of the brain’s power to focus, it will be possible to better treat people who can’t sort out sound signals effectively, something that can decline with age.

The next time you are in class and feel like you can’t listen to your teacher because the rest of the students in your class are making a lot of noise, try to focus on only your teacher’s voice. Your brain has the power to do this, so if you put your mind to it, you will be able to see that it isn’t so hard to listen to one person amidst a group of jumbled noises!

Powered by WordPress & Theme by Anders Norén

Skip to toolbar