Variation of protein kinase C-α expression in eyestalk removal-activated ovaries in whiteleg shrimp, Litopenaeus vannamei.

The regulation of female reproduction in crustaceans is controlled by a variety of hormones. Previous studies of hormone-initiated cellular mechanisms controlling ovarian maturation focused mainly on those initiated by inhibitory hormones. In order to facilitate research on ovarian development, it is necessary to gain a better understanding of factors that promote ovarian growth on the cellular level. Here, we used eyestalk ablation to firstly induce a state of ovarian maturation in Litopenaeus vannamei. Gonadosomatic index, hemolymph vitellogenin (Vg) concentrations, and Vg gene transcript levels in the ovaries were significantly elevated at 1 and 2 weeks after eyestalk ablation (P < 0.05). Correspondingly, immunoblot analysis revealed a remarkable decrease in anti-PKC-α immunoreactivity in both cytosol and membrane fractions of ovarian tissue homogenates: it was strongly apparent in intact animals, but decreased with time after eyestalk ablation, showing a stronger tendency to do so in the membrane fraction than in the cytosol fraction. Considered overall, the data presented strongly suggest that PKC-α isoform plays a role in the regulation of ovarian growth in L. vannamei through a negative-based regulating mechanism.

Molecular phylogeny of ten intertidal hermit crabs of the genus Pagurus inferred from multiple mitochondrial genes, with special emphasis on the evolutionary relationship of Pagurus lanuginosus and Pagurus maculosus.

The hermit crab genus Pagurus exhibits high species diversity and a wide geological distribution. Despite the high species diversity of hermit crabs in the western Pacific coast of Japan, molecular phylogenetic studies of these species have yet to be conducted. To investigate their molecular phylogeny and genetic diversity, we obtained nearly complete mitochondrial genome sequences for ten Pagurus species found along the Pacific coast of Japan by next-generation sequencing, which were compared to other congeners deposited in the GenBank database. The genomes ranged from 13,458 to 16,401 base pairs in length, possessing 13 protein-coding genes, 2 rRNAs, and 22 tRNA genes. Based on the reconstructed phylogeny, we found that (1) Japanese Pagurus species separated into three groups, nested within the Northern Pacific species. (2) Pagurus lanuginosus and Pagurus maculosus, showed high morphological similarities, implying close kinship. Indeed, these two species were genetically closest to each other, compared to the remaining species studied. (3) An unspecified specimen sampled from the deep sea, which morphologically resembled Pagurus, might be a member of the Pagurus genus, but is genetically distant from the other Japanese Pagurus species. The novel data reported here may provide new perspectives for systematic studies of hermit crabs; these results provide important information that will facilitate population-level research and identifying intraspecific variation of these non-model, but ecologically important, decapod species.

Assessment of the Effects of Double-Stranded RNAs Corresponding to Multiple Vitellogenesis-Inhibiting Hormone Subtype I Peptides in Subadult Female Whiteleg Shrimp, Litopenaeus vannamei.

Vitellogenesis-inhibiting hormone (VIH) negatively regulates reproduction in shrimp and other decapod crustaceans. In order to assess the effects of transcriptional silencing by multiple VIH subtype I sinus gland peptides (SGPs) on ovarian maturation in female whiteleg shrimp, Litopenaeus vannamei, we synthesized five dsRNAs targeting Liv-SGP-A, -B, -C, -F, and -G and injected them into subadults. The following treatments were employed: sgpG-dsRNA (targeting Liv-SGP-G), sgpC-dsRNA (targeting Liv-SGP-C), and mixed-dsRNA (targeting Liv-SGP-A, -B, and -F). The expression of Liv-SGP-G in eyestalks was significantly decreased at 10, 20, and 30 days after the injection of sgpG-dsRNA In addition, it was significantly decreased at 10 and 30 days after the injection of mixed-dsRNA. The expression of vitellogenin (Vg) gene expression in the ovaries, and concentrations of Vg protein in the hemolymph, were not changed by the administration of any dsRNA treatment (the ovaries remained immature in all treated individuals and contained mostly oogonia and previtellogenic oocytes). Although the administration of dsRNAs corresponding to multiple VIHs did not promote ovarian maturation, this is the first report of the co-transcriptional repression of Liv-SGP-G by the injection of dsRNA for homologous genes (Liv-SGP-A, -B, and -F). These results indicate that subadults can respond to the techniques of transcriptional silencing.

The complete larval development of Pagurus maculosus Komai & Imafuku, 1996 (Decapoda, Anomura, Paguridae) reared in the laboratory, and a comparison with sympatric species.

The complete larval development of the hermit crab Pagurus maculosus, is described and illustrated based on specimens reared in the laboratory at 15 °C and 33-35 PSU. Newly hatched larvae invariably passed through a short prezoeal stage (10 minutes to 2 hours), four zoeal stages (each of 7 days,) and one megalopal stage (14 days). Distinct morphological features of each larval stage of the present study are compared with other closely related species in Japanese waters, and we found many differences in morphology and the duration of zoeal stages between them. We mentioned significant diagnostic characters separating this species from other congeners in Japanese waters that include the presence of red-yellowish chromatophores on the maxillipeds. This is the first report of complete larvae development of Pagurus maculosus.

The complete larval development of Pagurus lanuginosus De Haan, 1849 (Decapoda, Anomura, Paguridae) reared in the laboratory, with emphasis on the post-larval stage.

The complete larval development of Pagurus lanuginosus is described and illustrated including the first description of the post-larval stage. Specimens were reared in the laboratory at 15°C and 33.5-35.02 PSU. Newly hatched larvae passed through a short prezoeal stage (10 minutes to 2 hours), four zoeal stages (6, 6, 6, 8 days), and one megalopal stage (10 days). We compared the morphological features of each larval stage with those of the preceding two descriptions on the same species, and found many differences in morphology and the duration between zoeal stages. We concluded that significant diagnostic characters separating this species from other congeners in Japanese waters include the presence of two pairs of yellowish chromatophores on the carapace in the zoeal stages, a translucent body flecked with red chromatophores, and two pairs of red chromatophores on the carapace in the megalopal stage.