The effect of the growth hormone of Lymnaea stagnalis on (Bi)carbonate movements, especially with regard to shell formation

Arrested Sexual Development in Queen Conch (Lobatus gigas) Linked to Abnormalities in the Cerebral Ganglia

In the Florida Keys, queen conchs (Lobatus gigas) occur in two spatially distinct regions: nearshore in habitats immediately adjacent to the shoreline and offshore in habitats along the reef tract south of the islands. Our previous research demonstrated that adult conchs nearshore are not reproductively active, showing deficiencies in their gonadal condition compared to their offshore counterparts. Because sexual development in gastropods is controlled by hormones secreted by the cerebral ganglia, we hypothesized that the reproductive deficiencies seen in nearshore queen conchs involved the cerebral ganglia. We collected nearshore and offshore adults and made histological comparisons of their gonads and cerebral ganglia. Our results confirmed that gonadal maturity was delayed and that gamete production was reduced in nearshore conchs compared to offshore animals. These gonadal deficiencies in nearshore conchs were associated with abnormal cerebral ganglion histology (i.e., significant hypertrophy of ganglion cells and significantly lower density of ganglion cells). In addition, the shells of nearshore conchs were significantly lighter, which is particularly consequential because shell formation in gastropods is also mediated by hormones secreted by the cerebral ganglia. Given these results, it is apparent that some yet unidentified factor(s) is interfering with hormone production in the cerebral ganglia, to the detriment of gonad development and shell formation.

Molecular modularity and asymmetry of the molluscan mantle revealed by a gene expression atlas

Background

Conchiferan molluscs construct a biocalcified shell that likely supported much of their evolutionary success. However, beyond broad proteomic and transcriptomic surveys of molluscan shells and the shell-forming mantle tissue, little is known of the spatial and ontogenetic regulation of shell fabrication. In addition, most efforts have been focused on species that deposit nacre, which is at odds with the majority of conchiferan species that fabricate shells using a crossed-lamellar microstructure, sensu lato.

Results

By combining proteomic and transcriptomic sequencing with in situ hybridization we have identified a suite of gene products associated with the production of the crossed-lamellar shell in Lymnaea stagnalis. With this spatial expression data we are able to generate novel hypotheses of how the adult mantle tissue coordinates the deposition of the calcified shell. These hypotheses include functional roles for unusual and otherwise difficult-to-study proteins such as those containing repetitive low-complexity domains. The spatial expression readouts of shell-forming genes also reveal cryptic patterns of asymmetry and modularity in the shell-forming cells of larvae and adult mantle tissue.

Conclusions

This molecular modularity of the shell-forming mantle tissue hints at intimate associations between structure, function, and evolvability and may provide an elegant explanation for the evolutionary success of the second largest phylum among the Metazoa.

Reproduction-related genes in the pearl oyster genome

Molluscan reproduction has been a target of biological research because of the various reproductive strategies that have evolved in this phylum. It has also been studied for the development of fisheries technologies, particularly aquaculture. Although fundamental processes of reproduction in other phyla, such as vertebrates and arthropods, have been well studied, information on the molecular mechanisms of molluscan reproduction remains limited. The recently released draft genome of the pearl oyster Pinctada fucata provides a novel and powerful platform for obtaining structural information on the genes and proteins involved in bivalve reproduction. In the present study, we analyzed the pearl oyster draft genome to screen reproduction-related genes. Analysis was mainly conducted for genes reported from other molluscs for encoding orthologs of reproduction-related proteins in other phyla. The gene search in the P. fucata gene models (version 1.1) and genome assembly (version 1.0) were performed using Genome Browser and BLAST software. The obtained gene models were then BLASTP searched against a public database to confirm the best-hit sequences. As a result, more than 40 gene models were identified with high accuracy to encode reproduction-related genes reported for P. fucata and other molluscs. These include vasa, nanos, doublesex- and mab-3-related transcription factor, 5-hydroxytryptamine (5-HT) receptors, vitellogenin, estrogen receptor, and others. The set of reproduction-related genes of P. fucata identified in the present study constitute a new tool for research on bivalve reproduction at the molecular level.

Protein synthesis in vitro by mantle tissue of the land snail Otala lactea: possible insulin-like peptide function

Mantle-collar tissue from adult land snails Otala lactea continuously incorporated labelled amino acids over a 72-h period of incubation in modified culture medium. Acid-saline extract of cerebral ganglia stimulated protein synthesis by the mantle-collar tissue in vitro. This effect was dose-dependent, with the minimum and maximum doses at 0.5 and 2 cerebral ganglion equivalents, respectively. The protein synthesis-stimulating factor(s) from the cerebral ganglia appeared to be proteinaceous and hydrophobic in nature. The cerebral ganglion extract was fractionated by means of a size-exclusion HPLC column. The biological activity was induced by three fractions with estimated molecular masses of 0.82, 1.88, and 4.33 kilodaltons (kDa). Porcine insulin antiserum abolished the activity of the 4.33- and 1.88-kDa fractions but had no significant effect on the activity of the 0.82-kDa fraction. The results suggest the existence in the cerebral ganglia of more than one factor with protein synthesis-stimulating activity. One of these factors could be related to mammalian insulin. Porcine insulin, however, had no significant effect on protein synthesis by the mantle collar in vitro.

The occurrence and in vitro effects of molecules potentially active in the control of growth in the marine mussel Mytilus edulis L

A molecular with a molecular weight, estimated by gel filtration, of approximately 22 kDa and immunoreactive to anti-human hypophysial growth hormone (hGH) has been identified by radioimmunoassay in the digestive gland and hemolymph of the mussel Mytilus edulis L. The dilution curve of this molecule was parallel to that of hGH, suggesting that the antigenic site of the Mytilus molecule is similar to that of hGH. Immunoreactive fractions resulting from gel filtration failed to stimulate protein synthesis in dispersed mantle-edge cells in vitro. No hGH-immunoreactive material was detected in the cerebral ganglia. It is thus clear that a small protein-synthesis-stimulating factor (PSSF), identified in the cerebral ganglia and hemolymph by its action in vitro on dispersed mantle-edge cells, is not analogous to the Mytilus hGH-immunoreactive molecule. Likewise, a somatostatin-immunoreactive molecule present in the hemolymph of Mytilus did not coelute with PSSF. Evidence is presented that PSSF is a hydrophilic peptide that stimulates DNA, RNA, and protein synthesis and that is not tissue specific. These characteristics suggest that PSSF is a growth hormone.

Neurohormonal control of growth and carbohydrate metabolism by the light green cells in Lymnaea stagnalis

The neuroendocrine light green cells (LGCs), 4 clusters of together approximately 150 giant neurons in the cerebral ganglia of the freshwater gastropod, Lymnaea stagnalis, have been suggested to be involved in the control of growth. The present study examines in greater detail this role and possible actions on energy metabolism. Growth indices (total body and organ wet and dry weights, as well as protein and DNA contents of the organs) and metabolic indices (tissue lipid, polysaccharide and glucose levels) were compared in LGC extirpated/reimplanted with control groups. LGC extirpation in rapidly growing juvenile snails immediately arrested growth, which was restored by reimplantation of cerebral ganglia with LGCs but not by cerebral ganglia without LGCs, indicating their neuroendocrine control of growth. The LGCs stimulate a pattern of organ growth, which is in proportion to the growth of the whole body except for the shell, which shows a disproportionally faster growth due to calcium deposition over the whole surface. The data on protein and DNA in the organs strongly suggest that the LGCs induce growth by stimulating cell multiplication. The LGCs maintain low tissue glycogen reserves and hemolymph concentrations of both glycogen and glucose. The secretions of these cells stimulate the uptake of glucose by the growing tissues with no apparent effects on lipid metabolism.

Electrotonic coupling and afterdischarges in the Light Green Cells: a comparison with two other cerebral ganglia neurosecretory cell types in the pond snail. Lymnaea stagnalis

Electrotonic coupling occurs between the growth hormone-producing Light Green Cells on the same but not the opposite side of the brain of Lymnaea. Long duration inhibitory post synaptic potentials occur spontaneously or can be evoked by nerve or connective stimulation. Afterdischarges, lasting for up to 1 min, are evoked by brief stimulation of the median lip nerves. Activity is confined to cells ipsilateral to the nerve being stimulated. The electrical properties of the Light Green Cells are compared with those of the Caudodorsal Cells and Canopy Cells.

A hormone dependent calcium-binding protein in the mantle edge of the freshwater snail Lymnaea stagnalis

By means of gel filtration and ion exchange chromatography on calcium-saturated Chelex-100, a calcium-binding fraction was isolated from the mantle edge of the freshwater snail lymnaea stagnalis. This fraction was not present in other tissues. Treatment with trypsin caused a disappearance of the calcium-binding capacity, proving that the active substance in this fraction is a protein (calcium-binding protein; CaBP). Removal of the growth hormone-producing neuroendocrine light green cells resulted in a strong decrease of the amount of CaBP. It is concluded that L. stagnalis possesses a hormone-dependent CaBP, probably responsible for the maintenance of a high calcium concentration in that part of the mantle that produces the outer crystalline layer of the shell.

Ultrastructural localization of carbonic anhydrase in tissues involved in shell formation and ionic regulation in the pond snail Lymnaea stagnalis

The ultrastructural localization of carbonic anhydrase (CA) was investigated with the cobalt-bicarbonate method in three epithelia of the pond snail Lymnaea stagnalis. In the epidermis a selective population of "positive cells" was observed. In these cells, CA is confined to the apical and to small parts of the lateral plasma membrane. In cells of the outer mantle epithelium, CA is localized in the lateral and basal parts of the plasma membrane. In cells of the ureter, CA was found apically as well as basally. The localization of CA is discussed in relation to the different functions of the epidermis (electrolyte uptake), mantle (HCO3- secretion, calcification) and ureter (electrolyte uptake, acid-base regulation).