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Sphingomyelin (SM) is a constituent of cellular membranes, while ceramides (Cer) produced from SM on plasma membranes serve as a lipid mediator that regulates cell proliferation, differentiation, and apoptosis. In the skin, SM also is a precursor of Cer, an important constituent of epidermal permeability barrier. We investigated the role of epidermal SM synthase (SMS)2, an isoform of SMS, which modulates SM and Cer levels on plasma membranes. Although SMS2-knockout (SMS2-KO) mice were not neonatal lethal, an ichthyotic phenotype with epidermal hyperplasia and hyperkeratosis was evident at birth, which persisted until 2 weeks of age. These mice showed abnormal lamellar body morphology and secretion, and abnormal extracellular lamellar membranes in the stratum corneum. These abnormalities were no longer evident by 4 weeks of age in SMS2-KO mice. Our study suggests that (1) exposure to a dry terrestrial environment initiates compensatory responses, thereby normalizing epidermal ichthyotic abnormalities and (2) that a nonlethal gene abnormality can cause an ichthyotic skin phenotype., (© 2021 S. Karger AG, Basel.)

Objective: To set up an effective technique for isolating the single inner hair cells (IHCs) and observe morphological features to distinguish IHCs from other hair cells (OHCs) in vitro., Methods: Surface preparations contained rows of OHCs and IHCs were prepared from guinea pigs. The cluster and single IHCs were separated microsurgically combination with an enzymatic digestion. The clusters of IHCs were separated using two fine electrodes and transferred by a gentle suction using a glass micropipette., Results: On the average, one guinea pig cochlear yielded approximately 30 to 50 viable solitary IHCs. The cell body of the IHCs was pear or flask shape. The nucleus was located in the central of the cell body, and the cytoplasm was filled with the structured and scattered rough granules. The stereocilia were seen in the most of IHCs (93 out of 98). The stereocilia were aligned, almost lineally or in a "C" shape, in one side on the surface of the cuticular plate. The tight neck and the angle between the cuticular plate and the axis of the cell were observed in some IHCs but not obvious in most cases, which might be due to the orientation of the cells. The length of isolated IHCs was ranged from 13 to 31 microns and with an average of (22.45 +/- 4.14) micron (mean +/- s, n = 98). The diameter of IHCs was ranged from 7 to 15 microns and with an average of (11.95 +/- 1.59) micron. The length of stereocilia was ranged from 2 to 7.5 microns and with an average of (5.21 +/- 1.00) micron., Conclusion: Unambiguous solitary IHCs were successfully harvested from guinea pig cochlea using a microsurgical technique. The tight neck and the angle between the cuticular plate and the axis of the IHCs have been considered as an important landmark to distinguish the IHCs from OHCs.