Sex-inducing effects toward planarians widely present among parasitic flatworms.

Various parasitic flatworms infect vertebrates for sexual reproduction, often causing devastating diseases in their hosts. Consequently, flatworms are of great socioeconomic and biomedical importance. Although the cessation of parasitic flatworm sexual reproduction is a major target of anti-parasitic drug design, little is known regarding bioactive compounds controlling flatworm sexual maturation. Using the planarian Dugesia ryukyuensis, we observed that sex-inducing substances found in planarians are also widespread in parasitic flatworms, such as monogeneans and flukes (but not in tapeworms). Reverse-phase HPLC analysis revealed the sex-inducing substance(s) eluting around the tryptophan retention time in the fluke Calicophoron calicophorum, consistent with previous studies on the planarian Bipalium nobile, suggesting that the substance(s) is likely conserved among flatworms. Moreover, six of the 18 ovary-inducing substances identified via transcriptome and metabolome analyses are involved in purine metabolism. Our findings provide a basis for understanding and modifying the life cycles of various parasitic flatworms.

Establishment of the immunological self in juvenile Patiria pectinifera post-metamorphosis.

Ontogeny of the immune system is a fundamental immunology issue. One indicator of immune system maturation is the establishment of the immunological self, which describes the ability of the immune system to distinguish allogeneic individuals (allorecognition ability). However, the timing of immune system maturation during invertebrate ontogeny is poorly understood. In the sea star Patiria pectinifera, cells that have dissociated from the embryos and larvae are able to reconstruct larvae. This reconstruction phenomenon is possible because of a lack of allorecognition capability in the larval immune system, which facilitates the formation of an allogeneic chimera. In this study, we revealed that the adult immune cells of P. pectinifera (coelomocytes) have allorecognition ability. Based on a hypothesis that allorecognition ability is acquired before and after metamorphosis, we conducted detailed morphological observations and survival time analysis of metamorphosis-induced chimeric larvae. The results showed that all allogeneic chimeras died within approximately two weeks to one month of reaching the juvenile stage. In these chimeras, the majority of the epidermal cell layer was lost and the mesenchymal region expanded, but cell death appeared enhanced in the digestive tract. These results indicate that the immunological self of P. pectinifera is established post-metamorphosis during the juvenile stage. This is the first study to identify the timing of immune system maturation during echinodermal ontogenesis. As well as establishing P. pectinifera as an excellent model for studies on self- and non-self-recognition, this study enhances our understanding of the ontogeny of the immune system in invertebrates.

Lineage-specific evolution of zona pellucida genes in fish.

The zona pellucida (ZP) protein constitutes the egg envelope, which surrounds the vertebrate embryo. We performed a comprehensive study on the molecular evolution of ZP genes in Teleostei by cloning and analyzing the expression of ZP genes in fish of Anguilliformes in Elopomorpha, Osteoglossiformes in Osteoglossomorpha, and Clupeiformes in Otocephala to cover unsurveyed fish groups in Teleostei. The present results confirmed findings from our previous reports that the principal organ of ZP gene expression changed from ovary to liver in the common ancestors of Clupeocephala. Even fish species that synthesize egg envelopes in the liver carry the ovary-expressed ZP proteins as minor egg envelope components that were produced by gene duplication during the early stage of Teleostei evolution. The amino acid repeat sequences located at the N-terminal region of ZP proteins are known to be the substrates of transglutaminase responsible for egg envelope hardening and hatching. A repeat sequence was found in zona pellucida Cs of phylogenetically early diverged fish. After changing the synthesis organ, its role is inherited by the N-terminal Pro-Gln-Xaa repeat sequence in liver-expressed zona pellucida B genes of Clupeocephala. These results suggest that teleost ZP genes have independently evolved to maintain fish-specific functions, such as egg envelope hardening and egg envelope digestion, at hatching.

Galactose-Binding C-Type Lectin Promotes Cellular Aggregation of Coelomocytes in Sea Cucumber.

Echinoderms have a large coelomic cavity containing coelomocytes. When the coelomic fluid is removed from the cavity, the cells aggregate immediately. We found that a fraction or an extract of the intestine of the sea cucumber, Apostichopus japonicus, markedly accelerated cellular movement and aggregation on a glass slide, and this effect was clearly inhibited by galactose. We successfully purified the aggregation-promoting factor, a 16 kDa protein, from the intestine. TOF-MS analysis followed by de novo sequencing revealed that the protein is a C-type lectin. RNA-seq data and cDNA cloning demonstrated the factor to be a novel lectin, named AjGBCL, consisting of 158 aa residues in the mature form. Microscopic observation revealed that most of the aggregating cells moved toward aggregates and not to an intestinal fragment, suggesting that AjGBCL is not a chemoattractant but a cellular aggregation-inducing factor that may induce aggregates to release chemoattractant. We report, for the first time, an endogenous molecule that promotes coelomocyte aggregation in echinoderms.

Enantioselective synthesis of 8-azabicyclo[3.2.1]octanes via asymmetric 1,3-dipolar cycloadditions of cyclic azomethine ylides using a dual catalytic system.

The first example of asymmetric 1,3-dipolar cycloadditions between diazo imine-derived cyclic azomethine ylides and acryloylpyrazolidinone using a rhodium(ii) complex/chiral Lewis acid binary system is reported. The asymmetric cycloadditions afforded optically active 8-oxabicyclo[3.2.1]octanes with high diastereo- and enantioselectivities (up to >99 : 1 dr, 99% ee). A switch of exo/endo-selectivity was observed depending on the diazo substrates.