We performed conventional and molecular cytogenetic studies on the Favitespentagona Esper, 1795, a scleractinian coral mostly found along the west coast of Japan. Karyotype analysis of F.pentagona by G-banding revealed a karyogram containing a homogenously staining region (HSR) on chromosome 10 in more than 50% of the examined metaphase spreads. This HSR consisted of sequences from 18S ribosomal RNA (rRNA) genes, as demonstrated by fluorescence in situ hybridization (FISH) and DNA sequencing. We highlighted the development of four chromosomal FISH markers from repetitive genes such as U2 small nuclear RNA linked to 5S rRNA sequence (U2 snRNA-5S), 18S rRNA, histone H3, and uncharacterized gene FP-9X. The chromosomal locations of the U2 snRNA-5S and 18S RNA were on the terminal end of long arm of chromosomes 2 and 10, respectively, while the histone H3 and the uncharacterized gene were located near the centromeres of chromosomes 1 and 9, respectively. These FISH markers will improve the karyotyping of F.pentagona from mitotic preparations which helps in widening our understanding of coral genetic structure and chromosome organization. In addition, these improvements in karyotyping will provide the basis in constructing of chromosome-level genome assembly for F.pentagona.
Keywords: FISH; HSR; chromosome; histone; karyotype; rRNA; scleractinian coral.
Rei Kawakami, Takahiro Taguchi, Joshua Vacarizas, Masumi Ito, Takuma Mezaki, Akira Tominaga, Satoshi Kubota.