Target of rapamycin signaling inhibits autophagy in sea cucumber Apostichopus japonicus

Autophagy mediated by mTOR pathway is a particularly important immune defense mechanism in the pathogens infected mammals. However, the role of TOR in echinoderm autophagy is largely unknown. Here, a cDNA encoding TOR protein was cloned and characterized from sea cucumber Apostichopus japonicus (designated as AjTOR) and its biological functions were also investigated. The AjTOR gene encoded a peptide of 2499 amino acids with the representative domains of DUF3385, FAT, FRB, PI3Kc, and FATC, which exhibited highly conservation with vertebrate orthologs. Phylogenetic analysis supported that AjTOR belonged to a new member of TOR family. Moreover, tissues distribution analysis indicated that AjTOR was ubiquitously expressed in all the tested tissues, with the highest transcription in muscle. Vibrio splendidus infection in vivo and LPS challenge in vitro could both significantly down-regulate the mRNA expression of AjTOR. What's more, transmission electron microscopy observations showed that rapamycin treatment resulted in rapid formation of autophagosomes in coelomocytes both at 3 and 6 h, however, injection with mTOR activator of MHY1485 showed an inhibitory effect on autophagosomes formation compared to the control, suggesting blocking the expression of AjTOR could accelerates autophagy signals. Our findings supported that AjTOR served as a negative regulator in sea cucumber authophay.

The role of matrix metalloprotease (MMP) to the autolysis of sea cucumber (Stichopus japonicus)

BACKGROUND

Sea cucumber (Stichopus japonicus) is easy to autolysis in response to a variety of environmental and mechanical factors. In the current study, collagen fibres were extracted from fresh sea cucumber body wall and then incubated with endogenous matrix metalloprotease (MMP) of sea cucumber. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), chemical analysis and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis were utilized to demonstrate the changes in collagen fibres, collagen fibrils and collagen proteins. Moreover, a verification experiment was also carried out to confirm the contribution of MMP to the autolysis of sea cucumber.

RESULTS

Endogenous MMP caused complete depolymerization of collagen fibres into smaller collagen fibril bundles and collagen fibrils due to the fracture of proteoglycan interfibrillar bridges. Meanwhile, endogenous MMP also caused partial degradation of collagen fibrils by releasing soluble hydroxyproline and pyridinium cross-links. Furthermore, the treatment with MMP inhibitor (1,10-phenanthroline) prevented the autolysis of tissue blocks from S. japonicus dermis.

CONCLUSION

Endogenous MMP was the key enzyme in the autolysis of sea cucumber, while its action still focused on high-level structures of collagens especially collagen fibres. © 2019 Society of Chemical Industry.

[The ultrastructural patterns of germinal and yolk granules in oocytes and embryonic cells of the holothurian Apostichopus japonicus]

The yolk germinal granules in oocytes and embryonic cells of Apostichopus japonicus were studied by transmission electron microscopy. Analysis of the features of synthesis and utilization of yolk granules made it possible to reveal ultrastructural criteria to distinguish between granules of the forming and utilized yolk, and germinal granules. Based on these findings, the authors suppose that identification of germ plasm elements in oocytes and embryonic cells of A. japonicus is quite possible with ultrastructural analysis only, and does not require utilizing molecular markers.

[The ultrastructural patterns of germinal and yolk granules in oocytes and embryonic cells of the holothurian Apostichopus japonicus]

The yolk germinal granules in oocytes and embryonic cells of Apostichopus japonicus were studied by transmission electron microscopy. Analysis of the features of synthesis and utilization of yolk granules made it possible to reveal ultrastructural criteria to distinguish between granules of the forming and utilized yolk, and germinal granules. Based on these findings, the authors suppose that identification of germ plasm elements in oocytes and embryonic cells of A. japonicus is quite possible with ultrastructural analysis only, and does not require utilizing molecular markers.