Preadaptations and Convergent Evolution

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Rigil Kent (February 05, 2010, 23:46:20 PM):
Still, it is a motor protein.

http://en.wikipedia.org/wiki/Motor_protein
Teleological (February 05, 2010, 23:50:46 PM):
It is a "direct voltage-to-force converter". I guess you can envision the organism generating voltage impulses to drive the motor to aid it in locomotion. I still think mechanosensing is the most likely explanation, besides, there are plenty of other motor proteins that can do the job of locomotion as well.
Rigil Kent (February 06, 2010, 00:03:22 AM):
http://www3.interscience.wiley.com/journal/123198229/abstract?CRETRY=1&SRETRY=0

Have a look at this article on the shaping (elongating and stiffening) the hair cell (called electromotility). To me this seems more mechanical than mechanosensory. So the question is, does prestin respond to signal, or does it generate a signal? Is it a motor or a dynamo?

Mintaka
rwenzori (February 06, 2010, 06:53:35 AM):
Bit anti-scientific to throw your arms up in the air and say: "look, we can't find a function, therefor we are just going to assume it is junk."


I'm just sticking to the scientific definition, old boy - one that has been shoved in front of your uncomprehending face numerous times in the past only to be ignored because it does not correlate well with your preconceived notions:


Quote
In evolutionary biology and molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a chromosome or a genome for which no function has been identified.



BTW, is a "caricuture" a cute comical depiction? ;D
Teleological (February 06, 2010, 14:31:06 PM):
http://www3.interscience.wiley.com/journal/123198229/abstract?CRETRY=1&SRETRY=0

Have a look at this article on the shaping (elongating and stiffening) the hair cell (called electromotility). To me this seems more mechanical than mechanosensory. So the question is, does prestin respond to signal, or does it generate a signal? Is it a motor or a dynamo?

Mintaka

I couldn't access the above link. I forgot to add the references in the first post though, apologies for that. Here they are:

Dallos, P., & Fakler, B. (2002). PRESTIN, A NEW TYPE OF MOTOR PROTEIN Nature Reviews Molecular Cell Biology, 3 (2), 104-111 DOI: 10.1038/nrm730

Li, Y., Liu, Z., Shi, P., & Zhang, J. (2010). The hearing gene Prestin unites echolocating bats and whales Current Biology, 20 (2) DOI: 10.1016/j.cub.2009.11.042

Weber T, Gopfert MC, Winter H, Zimmermann U, Kohler H, Meier A, Hendrich O, Rohbock K, Robert D, & Knipper M (2003). Expression of prestin-homologous solute carrier (SLC26) in auditory organs of nonmammalian vertebrates and insects. Proceedings of the National Academy of Sciences of the United States of America, 100 (13), 7690-5 PMID: 12782792

Gleitsman, K., Tateyama, M., & Kubo, Y. (2009). Structural rearrangements of the motor protein prestin revealed by fluorescence resonance energy transfer AJP: Cell Physiology, 297 (2) DOI: 10.1152/ajpcell.00647.2008

Teeling, E. (2009). Hear, hear: the convergent evolution of echolocation in bats? Trends in Ecology & Evolution, 24 (7), 351-354 DOI: 10.1016/j.tree.2009.02.012

Check out the Gleitsman article (as well as Dallos):
Prestin is not a motor protein like ATPases or spindle proteins that walk on microtubules. It also undergoes conformational changes, however it is voltage regulated and not an enzymatic-activity-based motor.

Look at the structure of the cochlea and the location of the cilia (the outer hair cells - OHCs) (from Dallos):


When OHCs stimulated by incoming sound waves, the mechanosensitive ion channels in the stereocilia membrane of OHCs become activate, thereby changing the voltage-potential of the membrane. This voltage potential is converted into mechanical movement (as a result of prestin motor action), and in the ear this movement is used to amplify sound waves whereby the OHCs mechanically vibrate up and down due to the structural rearrangements of the motor protein, prestin.

The inner hair cells are the sensory receptors and transmit the amplified sound information to the brain. So to answer your question, prestin responds to a signal that mechanically alters the cell membrane potential of OHCs, and the amplifies this signal by generating another mechanical signal. It is an amplifier to put is simply. And the same mutations (an example of convergent evolution) in bats, some dolphins, as well as whales allowed it to be sensitive enough for echolocation.



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