Ovarian maturation in crustaceans is temporally orchestrated by two processes: oogenesis and vitellogenesis. The peptide hormone vitellogenesis-inhibiting hormone (VIH), by far the most potent negative regulator of crustacean reproduction known, critically modulates crustacean ovarian maturation by suppressing vitellogenin (VTG) synthesis. In this study, cDNA encoding VIH was cloned from the eyestalk of Pacific white shrimp, Litopenaeus vannamei, a highly significant commercial culture species. Phylogenetic analysis suggests that L. vannamei VIH (lvVIH) can be classified as a member of the type II crustacean hyperglycemic hormone family. Northern blot and RT-PCR results reveal that both the brain and eyestalk were the major sources for lvVIH mRNA expression. In in vitro experiments on primary culture of shrimp hepatopancreatic cells, it was confirmed that some endogenous inhibitory factors existed in L. vannamei hemolymph, brain, and eyestalk that suppressed hepatopancreatic VTG gene expression. Purified recombinant lvVIH protein was effective in inhibiting VTG mRNA expression in both in vitro primary hepatopancreatic cell culture and in vivo injection experiments. Injection of recombinant VIH could also reverse ovarian growth induced by eyestalk ablation. Furthermore, unilateral eyestalk ablation reduced the mRNA level of lvVIH in the brain but not in the remaining contralateral eyestalk. Our study, as a whole, provides new insights on VIH regulation of shrimp reproduction: 1) the brain and eyestalk are both important sites of VIH expression and therefore possible coregulators of hepatopancreatic VTG mRNA expression and 2) eyestalk ablation could increase hepatopancreatic VTG expression by transcriptionally abolishing eyestalk-derived VIH and diminishing brain-derived VIH.

Vibrio alginolyticus is a Gram-negative bacterium and has been recognized as an opportunistic pathogen in humans as well as marine animals. However, the virulence mechanisms for this species of Vibrio have not been elucidated. This study characterized multiple mechanisms that induce cell death in fish cells upon infection with a V. alginolyticus strain, ZJO. The bacterium required its type III secretion system (T3SS) to cause rapid death of infected fish cells. Dying cells exhibited some features of apoptotic cells, such as membrane blebbing, nuclear condensation and DNA fragmentation. Further studies showed that caspase-3 was activated by the T3SS of the ZJO strain, confirming that infection with V. alginolyticus rapidly induces T3SS-dependent apoptosis in fish cells. Infection with the ZJO strain also led to membrane pore formation and release of cellular contents from infected fish cells, as evidenced by lactate dehydrogenase release and the uptake of a membrane-impermeable dye. Importantly, inhibition of apoptosis did not prevent ZJO-infected cells from releasing cellular contents and did not block cell rounding. Taken together, these data demonstrate that infection with V. alginolyticus may promote at least three different T3SS-dependent events, which lead to the death of fish cells. This study provides an important insight into the mechanism used by Vibrio species to cause host-cell death.

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Benthodytes marianensis sp. nov., is described from the Mariana Trench at the depth of 5567 m. This is the thirteenth species in Benthodytes Théel, 1882. The new species has a broad brim around the body, dark violet skin, 9 pairs of large dorsal papillae with other papillae of equal or smaller size situated elsewhere, forming two zigzag rows, and some minute papillae scattered around the anterior region. Body wall ossicles are rods, crosses with three or four arms and central apophyses, and crosses of an unusual type. Crosses with four arms and central bipartite, tripartite and tetrapartite apophyses and peculiar cross-shaped ossicles with high apophyses ending in two horizontal arms are present in the dorsum. Large rod-shaped ossicles with bipartite apophyses and crosses with three or four arms and rudimentary apophyses are present on the ventrum. B. marianensis is morphologically most similar to B. incerta, but it is distinguished from B. incerta by the number and arrangement of dorsal large papillae, the broad brim and details of ossicle morphology. The phylogenetic analyses based on (16S, COI) and nuclear genes (H3) all confirm the morphological identification.