Learning Objectives: Cochlear sensory epithelial cells stop proliferation from the apical turn, while the earliest differentiated cochlear hair cell originates from the basal turn. Up to now, very few studies have been done to characterize the vestibular hair cells proliferation and differentiation. Planar cell polarity (PCP) is a special cell arrangement regularity. Vestibular organ has special cell polarity, with hair cell arrangement closely correlated with the function of vestibule. Whether the PCP establishment has the relationship with vestibular HC differentiation is still unknown .In this study, By collecting the embryonic utricles at the different stages, first we observed the 3D-schematic view of PCP in E18.5 mouse vestibular system, which showed the different PCP in five sensory organs. We choose utricle as an example, we found that the number of Edu/Myosin7a double positive cells peaks at E11.5 in medial extrastriola(MES) and striola zone of utricle. In the lateral extrastriola(LES), the number peaks at E13.5. Besides, at E12.5, P27 and Math1 positive cells were mainly observed in striola. At E13.5, P27 and Math1 positive cells occur in striola and MES. Edu positive cells decrease first in striola and then in MES. Interestingly, the PCP of hair cells stereocilia bundles also established first in the striola and MES region at E13.5. After overexpression of Emx2 in the E13.5 utricle epithelia, PCP of cultured utricle epithelia was disturbed, the orientation of HCs along the supposed LPR(line of polarity reversal) was not opposite, especially the orientation of the hair bundle arranged as a circular. Here we discovered the regional difference in the timing of terminal mitosis of hair cell precursors could account for the difference in their planar cell polarity . PCP of utricle epithelia regional establishment is consistant with HC proliferation and differentiation. Emx2 plays the role of the regional polarity formation in the developing utricle epithelia.
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