Lizard and Frog Prestin: Evolutionary Insight into Functional Changes

Abstract

The plasma membrane of mammalian cochlear outer hair cells contains prestin, a unique motor protein. Prestin is the fifth member of the solute carrier protein 26A family. Orthologs of prestin are also found in the ear of non-mammalian vertebrates such as zebrafish and chicken. However, these orthologs are electrogenic anion exchangers/transporters with no motor function. Amphibian and reptilian lineages represent phylogenic branches in the evolution of tetrapods and subsequent amniotes. Comparison of the peptide sequences and functional properties of these prestin orthologs offer new insights into prestin evolution. With the recent availability of the lizard and frog genome sequences, we examined amino acid sequence and function of lizard and frog prestins to determine how they are functionally and structurally different from prestins of mammals and other non-mammals. Somatic motility, voltage-dependent nonlinear capacitance (NLC), the two hallmarks of prestin function, and transport capability were measured in transfected human embryonic kidney cells using voltage-clamp and radioisotope techniques. We demonstrated that while the transport capability of lizard and frog prestin was compatible to that of chicken prestin, the NLC of lizard prestin was more robust than that of chicken’s and was close to that of platypus. However, unlike platypus prestin which has acquired motor capability, lizard or frog prestin did not demonstrate motor capability. Lizard and frog prestins do not possess the same 11-amino-acid motif that is likely the structural adaptation for motor function in mammals. Thus, lizard and frog prestins appear to be functionally more advanced than that of chicken prestin, although motor capability is not yet acquired.

Synchronized Progression of Prestin Expression and Auditory Brainstem Response during Postnatal Development in Rats

“…NLC and electromotility are fully coupled in mammalian OHCs [21, 23, 24] and the former could be evaluated accurately [16–19]. Our NLC measurements show that, for apical OHCs, the function of prestin first appears at P9 and reached mature level at P14 (Figure 4).…”

“…Cells showing any signs of shrinkage, swelling, or damage were excluded from the patch-clamp recording. Nonlinear capacitance (NLC) was measured as described in our previous publications [16–19]. The recording patch pipette was pulled by a pipette puller (P97, Sutter) and back-filled with the intracellular solution (140 CsCl, 10 EGTA, 2 MgCl 2 , and 10 HEPES in mM, 305 mOsm and pH 7.35).…”

Prestin at year 14: Progress and prospect

“…Two other studied found that prestin can act as a weak Cl − /HCO3 − antiporter (Mistrik et al, 2012) or as a weak electrogenic anion transport (Schanzler and Fahlke, 2012). It is worth noting that recent studies using radioactive anion uptake techniques failed to detect anion uptakes in mammalian prestin (Tan et al, 2011; Tang et al, 2013). In spite of the fact that it is still controversial whether prestin retains transport function, it is quite certain that its transport capability is significantly diminished as prestin gains motor function in mammals during evolution (Tan et al, 2011; Schanzler and Fahlke, 2012).…”

The Effects of Urethane on Rat Outer Hair Cells

“…Healthy young Sprague Dawley rats of either sex (21–28 days old, body weight 40–70 g) exhibiting normal hearing were used for the experiments. The CM measurements and whole-cell patch recordings were performed as previously described [26, 27]. These methods are briefly described as follows.…”