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C. Hodel, M. Heidemann, M. Gesemann, O. Biehlmaier, S. C. F. Neuhauss; Expression of MyosinVII Paralogs in Zebrafish. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2716.
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The unconventional MyosinVII (Myo7) is a motor protein which can moves along actin filaments under ATP consumption. Its tail interacts with a variety of intracellular proteins. Mutations in Myo7a are associated with congenital deafness and Usher Syndrome 1B. Myo7 plays a role in intracellular transport mechanisms and in the interaction of the actin cytoskeleton with the cell membrane. Vertebrate genomes contain two highly conserved paralogs (Myo7a and Myo7b). Myo7a has been found in cochlear hair cells and in the retina, whereas Myo7b is restricted to the microvilli of intestinal and kidney cells. The cellular location of Myo7a in photoreceptors is controversial, possibly due to species differences.In zebrafish, the ortholog of Myo7a and its expression in hair cells of the inner ear and of lateral line neuromasts has been reported. The purpose of this study is to identify all Myo7 paralogs in the zebrafish genome and determine their developmental expression pattern.
Sequences were assembled and annotated using various genome and EST databases. Peptide antibodies against zebrafish Myo7 proteins were raised and used in immunhistochemical experiments to asses the protein distribution in the developing zebrafish. Localization studies were supplemented with transmission and scanning electron microscopy to reveal ultrastructural details. Expression of mRNA was determined by in situ hybridizations.
We found a second paralog of Myo7a and two Myo7b paralogs that we call Myo7a1 and Myo7a2 or Myo7b1 and Myo7b2, respectively.Myo7a1, which was already found in hair cells, is also expressed in the retina. Immunolabelings show staining in a longish structure along the cone outer segments, probably the accessory outer segment, and a faint staining in the inner retina. Myo7a2 is also expressed in hair cells, but not in retinal cells.
In zebrafish, Myo7a is expressed in hair cells and photoreceptors. In contrast to all other tested vertebrates, we surprisingly found no staining in the retinal pigment epithelium. A possible explanation is a compensatory expression of Myo7b, which in mammals is expressed in the microvilli of intestinal and kidney cells.
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