The accumulation of whole genome sequence information for diverse vertebrate species had not encompassed elasmobranchs (sharks and rays) until recently. Although not so species-rich (1,200 species) as actinopterygian fishes，elasmobranchs occupy the majority of cartilaginous fishes and is a remarkably long-established lineage that has >400 million years of unique history. To overcome the long standing lack of genome-wide information，we analyzed whole genomes of three shark species，with stable sample supply from public aquariums，by optimizing DNA sequence data acquisition workflow. In general，the quality of whole genome sequence information determines the reliability of gene identification，and the cross-species relationship of individual genes identified therein should be investigated with molecular phylogenetic analysis to discern orthology and paralogy. This literacy for sequence data handling was exercised in our focused analysis on opsin genes，which revealed frequent loss of opsin genes in sharks，suggesting a decreased reliance of sharks on vision. Our spectroscopic experiment indicated a spectral tuning of the rhodopsin of deep-sea dwellers to exhibit the maximum absorption of the light with the wavelength of nearly 480 nm that is least attenuated in deep water. This approach that does not require tissue sampling from live animals is expected to unveil the visual ecology of rare marine species.

Two-day rhythms, referred to as circa‘bi’dian rhythms, have been reported in humans and mosquitos. However, these rhythms only appear in the laboratory or artificial conditions, and the functional mechanisms of 2-day rhythms were unknown. In this article I introduce clear circabidian rhythm of the large black chafer Holotrichia parallela (Coleoptera: Scarabaeidae) both in the laboratory and field. A mark recapture study showed that beetles repeatedly appeared on the same tree approximately every 2 days. However, the periodicity was not rigid. In the laboratory H. parallela appeared on the ground every 2 nights under 12-h light: 12-h dark conditions, and the rhythm continued under constant darkness with a period close to 48 h. Phase responses of the circabidian rhythm to light pulses suggested involvement of the circadian clock in the circabidian rhythm. Brain surgery suggested the optic lobe and some neurons in the pars intercerebralis are involved in the circabidian rhythm. A novel function of the circadian clock is proposed being characterized by the release of an output signal every two cycles to produce the 2-day rhythm. A neural circuit of circadian clock cells in the optic lobe to pars lateralis might be evolutionally conserved and used also for the generation of circabidian rhythm.

Mitocryptides including mitocryptide-1, mitocryptide-2, mitocryptide-3, and mitocryptide-CYC are a novel family of endogenous regulatory peptides that induce innate immune responses including neutrophilic migration and activation. More than 20 years have passed from the discovery of a firstly isolated mitocryptide; mitocryptide-1, and the physiological and pathophysiological significance of mitocryptides has been recently elucidated. Mitocryptides are physiologically produced by the enzymatic degradation of various mitochondrial proteins such as cytochrome c oxidase, cytochrome b, and cytochrome c. They are thought to be released from injured tissues caused by non-sterilized tissue damage such as trauma, burn and bacterial infection. They are proposed to be involved not only in proinflammatory responses but also in resolution and recovery from damage. Accumulation of mitocryptides in damaged tissues may cause serious symptoms including multi-organ failure. It is therefore important to elucidate their physiological and pathophysiological roles in innate immunity for the developments of therapies and therapeutic drugs against various inflammatory diseases.