FUN14 domain-containing protein 1 (FUNDC1) is a mitochondrial outer membrane protein which is responsible for hypoxia-induced mitophagy in mammalian cells. Knockdown of fundc1 is known to cause severe defects in the body axis of a rare minnow. To understand the role of Fundc1 in embryogenesis, we used zebrafish in this study. We used bioimaging to locate zebrafish Fundc1 (DrFundc1) with MitoTracker, a marker of mitochondria, and/or CellLight Lysosomes-GFP, a label of lysosomes, in the transfected ovary cells of grass carp. The use of Western blotting detected DrFundc1 as a component of mitochondrial proteins with endogenous COX IV, LC3B, and FUNDC1 in transgenic human embryonic kidney 293 T cells. DrFundc1 induced LC3B activation. The ectopic expression of Drfundc1 caused cell death and apoptosis as well as impairing cell proliferation in the 293 T cell line, as detected by Trypan blue, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and incorporation of BrdU. DrFundc1 up-regulated expression of both autophagy- and apoptosis-related genes, including ATG5, ATG7, LC3B, BECLIN1, and BAX in transgenic 293 T cells. A knockdown of Drfundc1 using short hairpin RNA (shRNA) led to midline bifurcation with two notochords and two spinal cords in zebrafish embryos. Co-injection of Drfundc1 mRNA repaired defects resulting from shRNA. Knockdown of Drfundc1 resulted in up- or down-regulation of genes related to autophagy and apoptosis, as well as decreased expression of neural genes such as cyclinD1, pax2a, opl, and neuroD1. In summary, DrFundc1 is a mitochondrial protein which is involved in mitophagy and is critical for typical body axis development in zebrafish.

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.

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T‐cell immunoglobulin (Ig) and mucin domain‐containing 1 (Tim‐1) and Tim‐4 are two members of the Tim family. In mammals, Tim‐1 and Tim‐4 are proteins mainly expressed in immune cells and are associated with immune response. In the present study, medaka Oryzias latipes' Tim‐1 (OlTim‐1) and OlTim‐4 were identified and characterized using bioinformatics analyses. With the use of reverse‐transcription polymerase chain reaction, the expression profiles of OlTim‐1 and OlTim‐4 were examined in embryos and adult fish and in immune tissues following the intraperitoneal injection of stimulants. The results revealed that OlTim‐1 possesses a cytoplasmic region, a transmembrane region, a mucin domain, and an Ig‐like domain, while OlTim‐4 is composed of two Ig‐like domains and a mucin domain, but without the transmembrane region and cytoplasmic region. OlTim‐1 and OlTim‐4 expressions are detectable from the gastrula stage on, indicating that they are zygotic genes. Furthermore, OlTim‐1 and OlTim‐4 are expressed ubiquitously in the adult. Administration of immune stimulants, namely lipopolysaccharides and polyinosinic:polycytidylic acid, significantly increased the expression levels of OlTim‐1 and OlTim‐4 in the liver and intestine within 1 day and in the head, kidney, and spleen within 3 to 4 days postinjection. These results suggest that OlTim‐1 and OlTim‐4 are possibly involved in both innate and adaptive immunities.