Nitric oxide signaling in invertebrates |
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Authors: | Jon W Jacklet |
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Institution: | (1) Department of Biological Sciences, University at Albany, SUNY, 12222 Albay, NY |
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Abstract: | Nitric oxide (NO) is an unconventional neurotransmitter and neuromodulator molecule that is increasingly found to have important
signaling functions in animals from nematodes to mammals. NO signaling mechanisms in the past were identified largely through
experiments on mammals, after the discovery of NO's vasodilatory functions. The use of gene knock out mice has been particularly
important in revealing the functions of the several isoforms of nitric oxide synthase (NOS), the enzyme that produces NO.
Recent studies have revealed rich diversity in NO signaling. In addition to the well-established pathway in which NO activates
guanylyl cyclase and cGMP production, redox mechanisms involving protein nitrosylation are important contributors to modulation
of neurotransmitter release and reception. NO signaling studies in invertebrates are now generating a wealth of comparative
information. Invertebrate NOS isoforms have been identified in insects and molluscs, and the conserved and variable amino
acid sequences evaluated. Calcium-calmodulin dependence and cofactor requirements are conserved. NADPH diaphorase studies
show that NOS is found in echinoderms, coelenterates, nematodes, annelids, insects, crustaceans and molluscs. Accumulating
evidence reveals that NO is used as an orthograde transmitter and cotransmitter, and as a modulator of conventional transmitter
release. NO appears to be used in diverse animals for certain neuronal functions, such as chemosensory signalin, learning,
and development, suggesting that these NO functions have been conserved during evolution.
The discovery of NO's diverse and unconventional signaling functions has stimulated a plethora of enthusiastic investigations
into its uses. We can anticipate the discovery of many more interesting and some surprising NO signaling functions. |
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Keywords: | Nitric oxide cyclic GMP nitric oxide synthase NADPH diaphorase neuromodulation transmitter |
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