Posttranslational isomerization of a neuropeptide in crustacean neurosecretory cells studied by ultrastructural immunocytochemistry.
Isomerization of the third amino acid residue (a phenylalanine) of crustacean hyperglycemic hormone (CHH) has been previously reported to occur as a late step of hormone precursor maturation in a few neurosecretory cells in the X-organ-sinus gland complex of the crayfish Orconectes limosus. In the present report, using conformation-specific antisera combined with immunogold labeling, we have studied, at the ultrastructural level, the distribution of L- and D-CHH immunoreactivity in CHH-secreting cells of the crayfish Astacus leptodactylus. Two CHH-secreting cell populations were observed, the first one (L-cells), the most numerous, exhibited only labeling for L-CHH. In the second one (D-cells), four secretory granule populations were distinguished according to their labeling: unlabeled, either L- or D- exclusively or both L- and D-granules. Labeling quantification by image analysis in D-cells showed a marked increase in D-labeling from the cell body to the axon terminal. However some L- and mixed granules remain in axon terminals. Our results demonstrate that Phe3 isomerization of CHH occurs within the secretory granules of specialized neurosecretory cells and progresses as the granules migrate along the axonal tract. The observation that not all the CHH synthesized is isomerized, and the great variability in the proportion of L- and D-immunoreactivity in granules in every cell region may suggest an heterogeneous distribution of the putative enzyme involved in Phe3 isomerization, a peptide isomerase, within the secretory pathway.
Gallois
Dominique
D
Groupe Biogenèse des Peptides Isomères, UMR CNRS 7079 Physiologie et Physiopathologie, Université Pierre et Marie Curie, Paris, France. dominique.gallois@snv.jussieu.fr
Brisorgueil
Marie-Jeanne
MJ
Conrath
Marie
M
Mailly
Philippe
P
Soyez
Daniel
D
D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins; D003400:Astacoidea / Q000145:classification / Q000166:cytology* / Q000378:metabolism*; D005088:Exocrine Glands / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry; D007447:Invertebrate Hormones; D007536:Isomerism; D008297:Male; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D009490:Neurosecretory Systems / Q000166:cytology* / Q000648:ultrastructure; D011499:Protein Processing, Post-Translational
D060829:Arthropod Proteins; D007447:Invertebrate Hormones; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C015947:hyperglycemic hormone, crustacean