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This study characterizes the spawning phenomena of the honeycomb grouper (Epinephelus merra), which is a lunar-synchronized spawner that spawns a few days after full moon. To elucidate the aggregation characteristics of wild honeycomb groupers, the numbers of males and females at the spawning grounds were counted before and after the full moon. Approximately 20 males were consistently observed at the spawning grounds throughout the study period. Females appeared several days after full moon and rapidly increased in number, peaking four days after full moon (41 individuals). The maturation status of the females aggregating at the spawning grounds was investigated. The gonadosomatic index increased rapidly three days after full moon, and ovulation was confirmed. Individuals with ovulatory eggs were present for three days, after which the number of females at the spawning grounds decreased. Additionally, the role of males in final oocyte maturation (FOM) and ovulation in females during the spawning phase was investigated in captivity. FOM was induced in females reared in water with mature males, suggesting that male pheromones in the water induced FOM via activation of the hypothalamic–pituitary–gonadal axis. This suggests that spawning at the natural spawning grounds was the result of male–female interactions via pheromones., Cells, 11 (3), art. no. 484; 2022

Groupers are widely distributed in tropical and subtropical areas worldwide, are key species to coastal ecosystems, and valuable fishery targets. To facilitate artificial seed production technology for grouper aquaculture, the mechanisms of reproduction and gonad development are being elucidated for these important species. In addition, since groupers are sexually dimorphic fish with female-first maturity (protogynous hermaphrodite fish), research is being conducted to clarify the ecological mechanism of sex change and their reproductive physiology, focusing on the endocrine system. In recent years, research on groupers has also been conducted to understand changes in the coastal environment caused by ocean warming and man-made chemicals. However, due to difficulties associated with conducting research using wild populations for breeding experiments, knowledge of the physiology and ecology of these fish is lacking, especially their reproductive physiology. In this review, we present information on the reproductive physiology and endocrinology of groupers obtained to date, together with the characteristics of their life history., Cells, 11(5), art. no. 825; 2022

Antimicrobial peptides (AMPs) are found widespread in nature and possess antimicrobial and immunomodulatory activities. Due to their multifunctional properties, these peptides are a focus of growing body of interest and have been characterized in several fish species. Due to their similarities in amino-acid composition and amphipathic design, it has been suggested that neuropeptides may be directly involved in the innate immune response against pathogen intruders. In this review, we report the molecular characterization of the fish-specific AMP piscidin1, the production of an antibody raised against this peptide and the immunohistochemical identification of this peptide and enkephalins in the neuroepithelial cells (NECs) in the gill of several teleost fish species living in different habitats. In spite of the abundant literature on Piscidin1, the biological role of this peptide in fish visceral organs remains poorly explored, as well as the role of the neuropeptides in neuroimmune interaction in fish. The NECs, by their role as sensors of hypoxia changes in the external environments, in combination with their endocrine nature and secretion of immunomodulatory substances would influence various types of immune cells that contain piscidin, such as mast cells and eosinophils, both showing interaction with the nervous system. The discovery of piscidins in the gill and skin, their diversity and their role in the regulation of immune response will lead to better selection of these immunomodulatory molecules as drug targets to retain antimicrobial barrier function and for aquaculture therapy in the future

Gonadotropin-releasing hormone (GnRH) is one of the most important neuroendocrine regulators for animal reproduction. GnRH-like peptide (GnRH-like)has recently been shown to play a critical reproductive role mainly in gametogenesis or steroidogenesis in the gonads of some molluscs, including cephalopods. However, its involvement in gonadal sex differentiation remains unknown. Here, we show the expression profile of GnRH-like in the brain of the cephalopod kisslip cuttlefish, Sepia lycidas, throughout gonadal sex differentiation, by quantitative real time RT-PCR and immunohistochemistry. We found that GnRH-like could be detected in the brain at a sexually undifferentiated stage, and its expression level significantly increased upon initiation of gonadal sex differentiation. However, no significant difference in GnRH-like expression levels was observed between sexes during gonadal sex differentiation. Additionally, we demonstrated immunoreactivity of GnRH-like in glial cells or immature neurons, which are mainly distributed in the non-reproductive related area of the cephalopod brain, suggesting the immature function of the reproductive endocrine axis during early ontogenesis. Our results demonstrate for the first time, the expression profile of GnRH-like during early ontogenesis in cephalopods., General and Comparative Endocrinology, 304, art.no.113718; 2021

Vertebrates usually exhibit gonochorism, whereby their sex is fixed throughout their lifetime. However, approximately 500 species (~ 2%) of extant teleost fishes change sex during their lifetime. Although phylogenetic and evolutionary ecological studies have recently revealed that the extant sequential hermaphroditism in teleost fish is derived from gonochorism, the evolution of this transsexual ability remains unclear. We revealed in a previous study that the tunica of the ovaries of several protogynous hermaphrodite groupers contain functional androgen-producing cells, which were previously unknown structures in the ovaries of gonochoristic fishes. Additionally, we demonstrated that these androgen-producing cells play critical roles in initiating female-to-male sex change in several grouper species. In the present study, we widened the investigation to include 7 genera and 18 species of groupers and revealed that representatives from most major clades of extant groupers commonly contain these androgen-producing cells, termed testicular-inducing steroidogenic (TIS) cells. Our findings suggest that groupers acquired TIS cells in the tunica of the gonads for successful sex change during their evolution. Thus, TIS cells trigger the evolution of sex change in groupers., Scientific Reports, 11, art. no. 11117; 2021

To understand and obtain basic information on sex differentiation in the kisslip cuttlefish (Sepia lycidas), the gonadal sex differentiation process was investigated histologically. An undifferentiated gonad consisting of germ cells and somatic cells was found to form at a caudal site in the space between the internal yolk sacks of cuttlefish embryos at 14 and 21 days after spawning (DAS). Sexual dimorphism in the gonad was first detected at around 28 DAS. Meiotic oocytes were observed as the first visible morphological characteristic of ovaries in the gonads of some cuttlefish embryos at 28 DAS. In other individuals, neither meiotic germ cells,nor the appearance of a testicular structure, were observed in the gonad even after 10 days post hatching (DPH). Seminiferous tubules, consisting of a small number of spermatogonia and a surrounding basement membrane,were the first visible morphological characteristic of the testis in the male gonad, detected at around 20 DPH. This is the third report on the gonadal sex differentiation process in cephalopods., Heliyon, 5(6), art.no.e01948; 2019

博士(理学), 琉球大学

A sufficient supply of NADPH is a critical factor in L-lysine production by Corynebacterium glutamicum. Endogenous NAD-dependent glyceraldehyde 3-phosphate dehydrogenase (GAPDH) of C. glutamicum was replaced with nonphosphorylating NADP-dependent glyceraldehyde 3-phosphate dehydrogenase (GapN) of Streptococcus mutans, which catalyzes the reaction of glyceraldehyde 3-phosphate to 3-phosphoglycerate with the reduction of NADP(+) to NADPH, resulting in the reconstruction of the functional glycolytic pathway. Although the growth of the engineered strain on glucose was significantly retarded, a suppressor mutant with an increased ability to utilize sugars was spontaneously isolated from the engineered strain. The suppressor mutant was characterized by the properties of GapN as well as the nucleotide sequence of the gene, confirming that no change occurred in either the activity or the basic properties of GapN. The suppressor mutant was engineered into an L-lysine-producing strain by plasmid-mediated expression of the desensitized lysC gene, and the performance of the mutant as an L-lysine producer was evaluated. The amounts of L-lysine produced by the suppressor mutant were larger than those produced by the reference strain (which was created by replacement of the preexisting gapN gene in the suppressor mutant with the original gapA gene) by similar to 70% on glucose, similar to 120% on fructose, and similar to 100% on sucrose, indicating that the increased L-lysine production was attributed to GapN. These results demonstrate effective L-lysine production by C. glutamicum with an additional source of NADPH during glycolysis.

Hilly areas consisting of the Plio-Pleistocene in the large Quaternary basins of Japan are located adjacent to large urbanized regions and have been developed as residential suburbs by earthworks. The small valleys in these hilly areas are artificially filled in the developments....

Hilly areas consisting of the Plio-Pleistocene in the large Quaternary basins of Japan are located adjacent to large urbanized regions and have been developed as residential suburbs by earthworks. The small valleys in these hilly areas are artificially filled in the developments....