Neuropeptide routing in the bag cells: kinetic differences in the appearance of newly labeled peptides in transport and secretion

Abstract

The bag cell neurons of Aplysia synthesize and secrete several peptides. Some of these, in addition to the egg-laying hormone (ELH), are strongly implicated in the various alterations of central neuronal activity that accompany an electrical discharge of the bag cells. Thus, the secreted peptides appear to play a variety of roles in the animal's physiology. We have been interested in the intracellular mechanisms that precede peptide secretion from the bag cells because of the evidence that most, if not all, of these peptides are derived from a common precursor. Our objective has been to determine if presumed products of this precursor are processed coordinately following their synthesis. We have concentrated on two peptides (ELH and the acidic peptide, AP) because they are most easily identified in our analytical systems. On pulse-chase radiolabeling of the cells in vitro, we found that labeled AP appears before labeled ELH in axonal transport. This observation is not easily accounted for by the assumption, taken from studies of other peptide-secreting cells, that a precursor to both peptides is loaded into secretory granules before further processing ensues. Since the initial disproportion in the representation of the peptides in transport is no longer detectable at long chase times (18 and 24 hr), we examined the possibilities that ELH production is delayed relative to that of AP or that AP is degraded more rapidly than ELH. No evidence was found for either process. The disproportion between the newly labeled peptides in transport was evident on analysis of the medium bathing bag cells depolarized after 24 hr of chase.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolytic processing of the Aplysia egg-laying hormone prohormone

“…Previously published results (34,35) have shown that nonstoichiometric amounts of ELH and AP have been recovered from tissue extracts, and it was suggested that ELH and AP peptide were differentially packaged, even though electron microscopy of bag cells has not demonstrated a new vesicle type. However, those results of a variable ELH͞AP ratio also can be explained by multiple forms of AP and ELH described here.…”

Hierarchical regulation of functionally antagonistic neuropeptides expressed in a single neuron pair

“…Vasopressin and galanin are also packaged into different DCV populations 20 . Bag cells and the atrial gland of Aplysia californica contain DCVs with distinct sets of neuropeptides, and even multiple peptides from the same propeptide are distributed across different vesicles [21][22][23][24] . To facilitate such segregation, at least the initial cleavage of propeptides has to occur in the Golgi apparatus, before their loading into secretory vesicles, as suggested in the processing of POMC 19 .…”

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted November 23, 2023. ; https://doi.org/10.1101/2023.11. 23.568473 doi: bioRxiv preprint the excitatory G protein-coupled receptor (GPCR) NPR-35. Our findings uncover a "wireless" microcircuit governing locomotion speed and body posture, unpredicted by the anatomical connectome.…”

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted November 23, 2023. ; https://doi.org/10.1101/2023.11. 23.568473 doi: bioRxiv preprint 6…”