Ultrastructural search for homologues of pancreatic -cells in the intestinal mucosa of the mollusc Buccinum undatum

Identification and comparative analysis of the Tegillarca granosa haemocytes microRNA transcriptome in response to Cd using a deep sequencing approach

Background

MicroRNAs (miRNAs) are endogenous non-coding small RNAs (sRNAs) that can base pair with their target mRNAs, which represses their translation or induces their degradation in various biological processes. To identify miRNAs regulated by heavy metal stress, we constructed two sRNA libraries for the blood clam Tegillarca granosa: one for organisms exposed to toxic levels of cadmium (Cd) and one for a control group.

Results

Sequencing of the two libraries and subsequent analysis revealed 215 conserved and 39 new miRNAs. Most of the new miRNAs in T. granosa were up- or down-regulated in response to Cd exposure. There were significant differences in expression between the Cd and control groups for 16 miRNAs. Of these, five miRNAs were significantly up-regulated and 11 were significantly down-regulated in the Cd stress library. Potential targets were predicted for the 16 differential miRNAs in pre-miRNAs identified according to sequence homology. Some of the predicted miRNA targets are associated with regulation of the response to stress induced by heavy metals. Five differentially expressed miRNAs (Tgr-nmiR-8, Tgr-nmiR-21, Tgr-miR-2a, Tgr-miR-10a-5p, and Tgr-miR-184b) were validated by qRT-PCR.

Conclusion

Our study is the first large-scale identification of miRNAs in T. granosa haemocytes. Our findings suggest that some miRNAs and their target genes and pathways may play critical roles in the responses of this species to environmental heavy metal stresses.

Identification of insulin-like peptides in cerebral ganglia neurosecretory cells of the mussel Mytilus edulis

The immunostaining patterns of cerebral ganglia sections from the mussel Mytilus edulis with monoclonal antibodies raised against cerebral ganglia (CG) extracts were compared to those obtained with various polyclonal anti-insulin-like antibodies. One of the monoclonal antibodies (MAB 46) revealed clusters of positive cells in localization comparable to those revealed by the polyclonal antibodies. The nature of the antigen recognized by MAB 46 and the polyclonal antibodies was compared by gel filtration-HPLC of a cerebral ganglia extract. Similar peaks were revealed by the monoclonal and polyclonal antibodies. MAB 46 significantly inhibited the cerebral ganglia induced stimulation of amino-acid incorporation by mantle edge cell suspensions, suggesting that the antigen recognized by MAB 46 is involved in the control of growth.

Gut endocrine cells in the snail Helix aspersa

A microscopic study of the endocrine cells present in the gut of the snail Helix aspersa is made. Electron microscopy is necessary in most cases to identify the enteroendocrine cells, since neither silver impregnations nor immunocytochemical staining have rendered positive results. Endocrine cells are scarce and rest on the basement membrane. They display a clear cytoplasm and variable amounts of small (143 nm) secretory granules of diverse electron-density. They are ovoid or rounded and possess apical processes which extend into the lumen of the gut. The nucleus, located in the basal region of the cell, presents characteristic cytoplasmic indentations. Intraepithelial nerve bundles in contact with endocrine cells are present.

Phylogenetical aspects on islet hormone families: a minireview with particular reference to insulin as a growth factor and to the phylogeny of PYY and NPY immunoreactive cells and nerves in the endocrine and exocrine pancreas

A common feature in the phylogeny of the four islet hormones (insulin, somatostatin, glucagon, PP) is that they do not seem to occur in the most primitive metazoan animals investigated so far, namely the coelenterates. However, already in the earliest protostomian invertebrates, such as flatworms and annelids, somatostatin and PP immunoreactive nerve fibres were found. In highly developed forms of protostomian invertebrates, such as insects, all the four islet hormones are represented as immunoreactive nerve cells and nerve fibres in the brain. In deuterostomian invertebrates a brain-gut-axis has evolved as regards somatostatin and PP, whereas insulin and glucagon now seem to occur exclusively as cells of open type in the gut mucosa. This brain-gut-axis for somatostatin and PP persists in all the vertebrates. The insulin cells, however, leave the gut mucosa already in the earliest forms of vertebrates and then appear only as cells in the islet parenchyma and in the mucosa of the bile duct (Agnatha) or in the pancreatic ducts (Gnathostomi). To some extent, glucagon islet cells evolve in a similar manner; here, however, cells immunoreactive with the precursor hormone, glicentin (enteroglucagon), persist in the gastrointestinal tract mucosa. A few PYY immunoreactive cells have been found in the pancreatic islet parenchyma of reptiles and mammals, often as disseminated cells in the acinar tissue. In the pancreas of these phyla NPY only occurs in neurons and nerve fibres. In pilot studies the effects of hagfish insulin as a growth factor have been compared with those of pig insulin on Swiss 3T3 mouse embryonic fibroblasts.