Centromere specific antibody mediated karyotyping of Okinawan Oikopleura dioica

Oikopleura dioica is a ubiquitous marine tunicate that has been of biological interest due to features that include dioecious reproduction, short life cycle and vertebrate-like dorsal notochord while possessing relatively compact genome. The use of tunicates as a model organism, particularly with these characteristics, offers the advantage of facilitating studies in evolutionary development and furthering the understanding of enduring attributes found in the more complex vertebrates. At present, we are undertaking a novel initiative to sequence the genomes of Oikopleura individuals in populations found among the seas surrounding the Ryukyu Islands in southern Japan. To facilitate and validate genome assemblies, karyotyping was employed to count individual animals’ chromosomes in situ using centromere-specific antibodies directed against H3S28P, a prophase-metaphase cell cycle-specific marker of histone H3. New imaging data of embryos and oocytes stained with two different antibodies directed against the marker clearly show cell cycle-dependent changes to chromosome structure; interpretation of these data lead us to conclude that the Okinawan Oikopleura dioica has three pairs of chromosomes, similar to what was observed in Atlantic populations. The imaging data have been deposited to the open access EBI BioImage Archive for reuse while additionally providing representative images of two commercially available anti- H3S28P antibodies’ staining properties for use in epifluorescent and confocal based fluorescent microscopy.