HgCl2-sensitive aquaporins are not involved in melanosome aggregation in Xenopus laevis melanophores
(English)Manuscript (preprint) (Other academic)
Melanophores are cells specialized for transport of pigment-filled organelles called melanosomes. Melanosomes are aggregated in the center of a melanophore or dispersed throughout the cytoplasm by motor proteins moving along the actin and microtubule cytoskeleton. In angelfish (Pterophyllum scalare), aggregation of melanosomes (as compared to dispersion) increases the height of the central part of melanophores by 300%. Our objective was to detennine whether such a height increase also occurs in frog (Xenopus laevis) melanophores. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that elevation of the melanophore plasma membrane is due to local swelling caused by influx of water through HgCl2-sensitive aquaporins and subsequent polymerization of actin. Confocal microscopy revealed a 30% increase in height in X. laevis melanophores during melatonin-induced aggregation. This was not due to actin polymerization, because it also occurred when aggregation was induced by the polymerization inhibitor latrunculin B. The nitric oxide (NO) synthase inhibitor L-NAME induced dispersion and lowered the plasma membrane, which suggests that NO is involved in the upward movement. Furthermore, neither dispersion nor aggregation was affected by inhibition of water flux through HgCl2 sensitive aquaporins. Together, these observations imply that melanosomes in X. laevis melanophores are driven upwards during aggregation by a mechanism other than actin polymerization, possibly involving microtubules, intermediate filaments, or a motor protein that may be regulated by NO. Furthermore, influx of water through HgCl2-sensitive aquaporins is probably not necessary for aggregation-induced elevation of the cell membrane, because both aggregation and dispersion can occur in the presence of HgCl2.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-80030OAI: oai:DiVA.org:liu-80030DiVA: diva2:545073