Stimulus-dependent translocation of egg-laying hormone encoding mRNA into the axonal compartment of the neuroendocrine caudodorsal cells

Abstract

To get insight into the stimulus-dependent translocation of mRNA encoding neuropeptides to the axonal compartment of neurons, we investigated this process in the egg-laying hormone producing caudodorsal cells of the mollusk Lymnaea stagnalis. The axonal compartment including the nerve terminals of these neurons harbors high amounts of mRNA encoding the egg-laying hormone precursor. We determined how a sensory stimulus, that results in egg-laying, affected the amount of egg-laying hormone encoding transcripts in the axon endings. Four hours after stimulation high amounts of transcripts were detected in the axonal compartment and maximum values were reached after 8 h. Transcript levels in the somata were affected in a similar fashion, although the increase was not as pronounced as in the axons. Next, we investigated the ultrastructural localization of egg-laying hormone encoding transcripts in axons and axon terminals by means of electron microscopic in situ hybridization and showed that transcripts were localized in the axoplasm. By means of conventional electron microscopy we showed that axon terminals of egg-laying hormone producing neurons contained large amounts of polyribosomes. Together, these data support the notion that egg-laying hormone encoding transcripts are translated in the axonal compartment.

Egg-Laying in the Cuttlefish Sepia officinalis

“…Moreover, large amounts of mRNAs were found in the OGs, MNGs, and ANGs of egg-laying females. Similar observations were reported in the pond snail Lymnaea stagnalis by van Minnen and Bergman [17]. High amounts of mRNAs encoding the egg-laying hormone were detected in the nerve terminals after a stimulus, as well as polyribosomes, supporting that the translation of egg-laying hormone transcripts could occur in the axonal compartment.…”

Stimulus‐dependent regulation and cellular expression of genes encoding neuropeptides, prohormone convertases, α‐amidating enzyme and 7B2 in identified Lymnaea neurons

“…a change of the animal from non‐refreshed water to clean water (the clean‐water stimulus), for which it is known that de novo synthesis of ELH and other peptides occurs (reviewed by Geraerts et al . 1991; Ter Maat 1992), and ELH transcripts can be readily measured (Van Minnen and Bergman 2002).…”

“…3). The level of ELH prohormone transcript is enhanced up to 6 h after egg‐laying (Van Minnen and Bergman 2002); at that time the transcripts of the processing enzymes are already back to prestimulus levels. This might be explained by the fact that the ELH processing enzymes could still be active within the subcellullar compartments, and therefore, de novo synthesis of the enzyme transcripts is not required.…”

“…Alternatively, the different subcellular localization of the ELH prohormone transcript vs. the LPC and L7B2 transcripts could explain their different kinetics. ELH prohormone transcript is localized both in the somal and the axonal compartment of CDCs (Van Minnen 1994; Van Minnen and Bergman 2002).…”

LFRFamides: a novel family of parasitation‐induced ‐RFamide neuropeptides that inhibit the activity of neuroendocrine cells in Lymnaea stagnalis

“…Thus, in total about 30 neurons express the LFRFa gene. As environmental stimulation in Lymnaea never resulted in an increase in the number neuropeptide‐expressing cells (see for instance, van Minnen and Bergman 2003), up‐regulation of LFRFa gene expression during parasitation is most likely due to an increased expression in these 30 neurons, and not to an increase in the number of LFRFa‐expressing neurons.…”