Verification of the expression of Piezo1 and Piezo2 ion channels in the mouse lens during the embryonic, postnatal and adult growth.
It has been proposed that in the absence of a blood supply and any direct innervation, the lens utilizes a variety of mechanosensitive ion channels to transduce changes to its internal and external environments into the activation of signaling pathways that alter fiber cell structure and hence overall lens function. One such mechanosensitive channel is Piezo1, the activation of which has been shown to phosphorylate Myosin light chain kinase (MLCK) and increase the expression of Transglutaminase 2 in fiber cells. To complement these functional studies, we have conducted a comprehensive mapping of the distribution of Piezo1 and Piezo2, the other member of this protein family, throughout all regions of the mouse lens. Using Western blotting, we first show that in addition to Piezo1, the mouse lens also expresses Piezo2. Using immunohistochemistry, we then show that both proteins are present throughout all regions of the lens, but are more concentrated in a discrete zone of high intensity labelling in mature fiber cells in the inner cortical region of the adult mouse lens. Despite being localized to the same localized ring the two proteins exhibited distinctly different subcellular distributions. In the outer cortex Piezo1 was more localized to the membrane, while Piezo2 was predominantly located in the cytoplasm of differentiating fiber cells. To determine at what stage of development this prominent ring of Piezo1/2 labelling was formed, immunohistochemistry was performed at different stages of embryonic and postnatal development. We found Piezo1 and Piezo2 to be both first expressed in the lens vesicle at E10, with both proteins exhibiting a constant level of cytoplasmic labelling across the whole lens throughout embryonic development and up to P6. This pattern of localisation changed from cytoplasmic to membranous at around P15 when the tunica vasculosa lentis was almost fully regressed and eye opening occurred. Our findings suggest that Piezo1/2 recruitment to the plasma membrane is developmentally regulated and associated with a key transitional stage of lens fiber cell maturation.