Digestive gland ultrastructure of the tunicate,Halocynthia roretzi(Ascidiacea:Pyuridae)in relation to function

Objective:To examine the glycogen storage and lipid digestion,as well as detoxification of the digestive gland of the tunicate,Halocynthia roretzi.Methods:Tunicates used in this study were collected from tunicate aquafarm located in Hansan Bay on the southern coast of Korea.Light and electron microscopy was performed.Results:The digestive gland was divided into the tubular and blind ampulla portions.Fine vacuolar granules were present,and lipofuscin granules were confirmed in the cytoplasm of the epithelia of the blind ampulla portion.Epithelial cells of the blind ampulla portion could be classified into three types.Conclusions:The results indicate that these three types of cells are involved in glycogen storage,lipid digestion and detoxification.

Identification of Monitoring Organ in Bivalves for Early Warning of Paralytic Shellfish Toxins Accumulation

Bivalve farming plays a dominant role in mariculture in China.Paralytic shellfish toxins(PSTs)can be accumulated in bivalves and cause poisoning the consumers.A sensitive detection of PSTs can provide early warning to decrease poisoning events in bivalve consuming.PSTs are traditionally examined using the whole soft-tissues.However,PSTs accumulation varies dramatically in different tissues of bivalves.Some tough tissues/organs(such as mantle),which account for a large proportion of the total soft body,exhibit a lower accumulation of PSTs and make the toxin extraction time-and reagent-consuming,potentially decreasing the accuracy and sensitivity of PSTs monitoring in bivalves.To develop a sensitive and cost-effective approach for PSTs examination in massively farmed bivalves,we fed three commercially important bivalves,Yesso scallop Patinopecten yessoensis,Pacific oyster Crassostrea gigas,and blue mussel Mytilus edulis with PSTs-producing dinoflagellate Alexandrium catenella,and detected PSTs concentration in different tissues.For all three bivalve species,the digestive gland accumulated much more PSTs than other tissues,and the digestive gland’s toxicity was significantly correlated with the PSTs toxicity of the whole soft-tissues,with r^(2)=0.94,0.92,and 0.94 for Yesso scallop,Pacific oyster,and blue mussel,respectively.When the toxicity of the whole soft-tissues reached 80μgSTXeq(100g)^(−1),the regulatory limit for commercial shellfish,the digestive gland’s toxicity reached 571.48,498.90,and 859.20μgSTXeq(100g)^(−1) in Yesso scallop,Pacific oyster,and blue mussel,respectively.Our results indicate that digestive gland can be used for the sensitive and cost-effective monitoring of PSTs in bivalves.

Involvement of clustered oyster Wnt genes in gut formation

Genes encoding Wnt ligands play important roles in organ development. The Wnt10-Wnt6-Wnt1-Wnt9 cluster widely presents in many metazoan genomes, indicating the importance of gene arrangement. Hypothesis has been proposed that they may be coordinately regulated. However, few expression correlations were identified in model animals. We analyzed the tissue expression pattern of clustered oyster Wnt10, Wnt6, Wnt1, and Wnt9 a genes in this study. The results indicated the highest expression level in adult gut system of these clustered W nt genes, except for Wnt6, which had highest expression in mantle. Further whole-mount immunofluorescence assay indicated that Wnt6 protein was restricted to gut region in oyster larvae. These results suggest the possible important role of the W nt10-Wnt6-Wnt1-Wnt9 cluster in oyster gut formation.