Nitric oxide level regulates the embryonic development of the pond snail Lymnaea stagnalis : pharmacological, behavioral, and ultrastructural studies

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

Knockdown of Snail inhibits epithelial-mesenchymal transition of human laryngeal squamous cell carcinoma Hep-2 cells through the vitamin D receptor signaling pathway

It has been well documented that Snail plays a decisive role in various tumors. However, the direct effect of Snail on laryngeal squamous cell carcinoma (LSCC) has not been elaborated. In this study, we firstly detected the expression of Snail in 14 samples of patients with LSCC and found that its content was high in cancer tissues compared with adjacent tissues. Then we established LSCC Hep-2 cells with Snail silencing and validated the knockdown efficiency by Western blotting and real-time PCR. Results showed that silencing of Snail significantly inhibited the ability of adhesion, migration, and invasion of Hep-2 cells. Further study revealed that knockdown of Snail suppressed the epithelial-mesenchymal transition (EMT) process of Hep-2 cells, as evidenced by downregulation of matrix metallopeptidase (MMP)-2, MMP-9, integrin subunit beta 1 (ITGβ1), β-catenin, vimentin, N-cadherin, and fibronectin and upregulation of vitamin D receptor (VDR) and E-cadherin. Additionally, transfection with the small interfering RNA of VDR reversed the effect induced by Snail silencing in Hep-2 cells. Taken together, these results demonstrate that knockdown of Snail can inhibit the EMT process of LSCC cells through the VDR signaling pathway in vitro.

Nitric oxide acts as a positive regulator to induce metamorphosis of the ascidian Herdmania momus

Marine invertebrates commonly have a biphasic life cycle in which the metamorphic transition from a pelagic larva to a benthic post-larva is mediated by the nitric oxide signalling pathway. Nitric oxide (NO) is synthesised by nitric oxide synthase (NOS), which is a client protein of the molecular chaperon heat shock protein 90 (HSP90). It is notable, then, that both NO and HSP90 have been implicated in regulating metamorphosis in marine invertebrates as diverse as urochordates, echinoderms, molluscs, annelids, and crustaceans. Specifically, the suppression of NOS activity by the application of either NOS- or HSP90-inhibiting pharmacological agents has been shown consistently to induce the initiation of metamorphosis, leading to the hypothesis that a negative regulatory role of NO is widely conserved in biphasic life cycles. Further, the induction of metamorphosis by heat-shock has been demonstrated for multiple species. Here, we investigate the regulatory role of NO in induction of metamorphosis of the solitary tropical ascidian, Herdmania momus. By coupling pharmacological treatments with analysis of HmNOS and HmHSP90 gene expression, we present compelling evidence of a positive regulatory role for NO in metamorphosis of this species, in contrast to all existing ascidian data that supports the hypothesis of NO as a conserved negative regulator of metamorphosis. The exposure of competent H. momus larvae to a NOS inhibitor or an NO donor results in an up-regulation of NOS and HSP90 genes. Heat shock of competent larvae induces metamorphosis in a temperature dependent manner, up to a thermal tolerance that approaches 35°C. Both larval/post-larval survival and the appearance of abnormal morphologies in H. momus post-larvae reflect the magnitude of up-regulation of the HSP90 gene in response to heat-shock. The demonstrated role of NO as a positive metamorphic regulator in H. momus suggests the existence of inter-specific adaptations of NO regulation in ascidian metamorphosis.

The dynamic nitric oxide pattern in developing cuttlefish Sepia officinalis

BACKGROUND

Nitric oxide (NO) is implied in many important biological processes in all metazoans from porifera to chordates. In the cuttlefish Sepia officinalis NO plays a key role in the defense system and neurotransmission.

RESULTS

Here, we detected for the first time NO, NO synthase (NOS) and transcript levels during the development of S. officinalis. The spatial pattern of NO and NOS is very dynamic, it begins during organogenesis in ganglia and epithelial tissues, as well as in sensory cells. At later stages, NO and NOS appear in organs and/or structures, including Hoyle organ, gills and suckers. Temporal expression of NOS, followed by real-time PCR, changes during development reaching the maximum level of expression at stage 26.

CONCLUSIONS

Overall these data suggest the involvement of NO during cuttlefish development in different fundamental processes, such as differentiation of neural and nonneural structures, ciliary beating, sensory cell maintaining, and organ functioning.

Distribution of NADPH-diaphorase activity in the central nervous system of the young and adult land snail Megalobulimus abbreviatus

Nitric oxide (NO) is a gas produced through the action of nitric oxide synthase that acts as a neurotransmitter in the central nervous system (CNS) of adult gastropod mollusks. There are no known reports of the presence of NOS-containing neurons and glial cells in young and adult Megalobulimus abbreviatus. Therefore, NADPH-d histochemistry was employed to map the nitrergic distribution in the CNS of young and adult snails in an attempt to identify any transient enzymatic activity in the developing CNS. Reaction was observed in neurons and fibers in all CNS ganglia of both age groups, but in the pedal and cerebral ganglia, positive neurons were more intense than in other ganglia, forming clusters symmetrically located in both paired ganglia. However, neuronal NADPH-d activity in the mesocerebrum and pleural ganglia decreased from young to adult animals. In both age groups, positive glial cells were located beneath the ganglionic capsule, forming a network and surrounding the neuronal somata. The trophospongium of large and giant neurons was only visualized in young animals. Our results indicate the presence of a nitrergic signaling system in young and adult M. abbreviatus, and the probable involvement of glial cells in NO production.

Nitric oxide inhibits metamorphosis in larvae of Crepidula fornicata, the slippershell snail

This paper concerns the role of nitric oxide (NO) in controlling metamorphosis in the marine gastropod Crepidula fornicata. Metamorphosis was stimulated by the nitric oxide synthase (NOS) inhibitors AGH (aminoguanidine hemisulfate) and SMIS (S-methylisothiourea sulfate) at concentrations of about 100-1000 micromol l(-1) and 50-200 micromol l(-1), respectively. Metamorphosis was not, however, induced by the NOS inhibitor l-NAME (l-N(G)-nitroarginine methyl ester) at even the highest concentration tested, 500 micromol l(-1). Moreover, pre-incubation with l-NAME at 20 and 80 micromol l(-1) did not increase the sensitivity of competent larvae to excess K(+), a potent inducer of metamorphosis in this species; we suggest that either l-NAME is ineffective in suppressing NO production in larvae of C. fornicata, or that it works only on the constitutive isoform of the enzyme. In contrast, metamorphosis was potentiated by the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-1-one) in response to a natural metamorphic inducer derived from conspecific adults. Because NO typically stimulates cGMP production through the activation of soluble guanylate cyclase, this result supports the hypothesis that NO acts as an endogenous inhibitor of metamorphosis in C. fornicata. The expression of NOS, shown by immunohistochemical techniques, was detected in the apical ganglion of young larvae but not in older larvae, further supporting the hypothesis that metamorphosis in C. fornicata is made possible by declines in the endogenous concentration of NO during development.

A Possible Stimulatory Effect of FMRFamide on Neural Nitric Oxide Production in the Central Nervous System of Helix lucorum L

The anatomical and functional relationship between neurons expressing nitric oxide (NO) synthase and molluscan cardioexcitatory (FMRFamide)-like neuropeptides was studied in the central ganglia of Helix lucorum (Pulmonata, Gastropoda), applying NADPHdiaphorase (NADPHd) histochemistry to visualize NO synthase and immunocytochemistry to demonstrate FMRFamide (FMRFa) at the light microscopic level. The NO production of the ganglia was detected by the colorimetric Griess determination of nitrite, a breakdown product of NO. Effects of the NO synthase substrate amino acid L-arginine, the NO synthase inhibitor Nomega-nitro-L-arginine (NOARG), synthetic FMRFa and the FMRFa sensitive ion channel blocker amiloride hydrochloride on nitrite production were also tested. NADPHd reaction labeled nerve cells and fibers in the procerebra, mesocerebra and metacerebra within the cerebral ganglia, and cell clusters in the postcerebral ganglia. FMRFa immunolabeling could be observed within subpopulations of NADPHd positive cells and in pericellular varicose fibers surrounding NADPHd stained neurons. Nitrite production of the ganglia was stimulated by L-arginine (10- 20 mM) but was decreased by NOARG (1-2 mM). Synthetic FMRFa (0.830-3.340 mM) increased the nitrite production in a dose dependent manner, but was ineffective in the presence of NOARG. Amiloride hydrochloride (7.890 mM) reduced the FMRFa evoked nitrite production in all ganglia. This is the first description of an anatomical relationship between putative NO producing and FMRFa containing cells, suggesting a possible regulatory role of FMRFa in the NO mediated signaling in an invertebrate nervous system.

Myenteric nitrergic neurons along the rat esophagus: evidence for regional and strain differences in age-related changes

Several studies have suggested an age-related reduction in the number of myenteric neurons in the lower gastrointestinal (GI) tract linked to changes in GI neuromuscular functions. The present study, combining protein gene product 9.5 immunostaining and NADPH-diaphorase histochemistry, aimed at quantifying the proportion of nitrergic neurons compared to the overall number of enteric neurons in the esophagus of young (3-4.5 months) and aged (18-20 months) Sprague-Dawley and Wistar rats. In both strains, the neuron numbers per ganglion in the cervical region were almost twice as high as in the other esophageal regions. Irrespective of age or strain, the esophagus harbored a very high proportion of intrinsic nitrergic neurons (greater than approximately 65%). Both strains showed with aging an overall neuronal loss of approximately 27%. While a significant increase (young: 64-71%; aged: 82-89%) was observed in all esophageal regions in the Wistar strain, the proportion of nitrergic neurons remained stable with aging in the Sprague-Dawley strain (range: 72-82%). In conclusion, the age-related reduction in the overall number of myenteric, nitrergic, and non-nitrergic neurons observed in the rat esophagus, appears to be highly region- and strain-dependent. Therefore, a protective mechanism against neuronal cell loss, selectively present in specific (nitrergic) enteric subpopulations, as suggested in earlier reports, cannot be put forward as a general phenomenon throughout the entire GI tract.