Bcl6aa and bcl6ab are ubiquitously expressed and are inducible by lipopolysaccharide and polyI:C in adult tissues of medaka Oryzias latipes.

B-cell lymphoma-6 (Bcl6) is a transcriptional repressor that plays important roles in various physiological activities such as innate and adaptive immune response, lymphocyte differentiation, and cell cycle regulation in mammals. Two homologs of Bcl6a, namely Bcl6aa and Bcl6ab, are identified in teleost fish including medaka Oryzias latipes. The expression profiles of bcl6aa and bcl6ab in medaka were studied using reverse-transcription polymerase chain reaction and in situ hybridization. The transcripts of bcl6aa and bcl6ab were detected from very early embryos such as the four-cell stage until hatching. Bcl6aa and bcl6ab were clearly detected in the embryonic body from 5 days postfertilization onward by in situ hybridization. Bcl6aa was specifically expressed in the retina, whereas bcl6ab was expressed in entire embryonic body. The results referred to that both bcl6aa and bcl6ab originate maternally in the zygotes and may play major roles in embryogenesis of medaka. The transcripts of bcl6aa and bcl6ab were detected in all examined adult tissues, including immune organs such as the gill, spleen, kidney, liver, and intestine. The expression of bcl6aa and bcl6ab in the liver, spleen, head-kidney, and intestine could be upregulated or downregulated by lipopolysaccharide and polyriboinosinic-polyribocytidylic acid. These results indicate that both bcl6aa and bcl6ab may be involved in immune response in medaka.