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Published on: August 3, 2012
Early expression of pituitary adenylate cyclase-activating polypeptide and activation of its receptor in chick
N M Erhardt1, E A Fradinger, L A Cervini
1Department of Biology, University of Victoria, Victoria, British Columbia, Canada, V8W 2Y2.
Insights
Pituitary adenylate cyclase-activating polypeptide (PACAP) plays a role in early chick brain development. This study found evidence of a PACAP autocrine/paracrine system in developing chick neuroblasts.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- Pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing factor (GRF) are peptides with known roles in the nervous and endocrine systems.
- Their specific involvement in early avian brain development remains largely uncharacterized.
Purpose of the Study:
- To investigate the presence and function of PACAP and GRF in early chick brain development.
- To determine if these peptides can activate intracellular signaling pathways in developing chick neuroblasts.
Main Methods:
- Primary neuroblast-enriched cell cultures were established from embryonic day 3.5 chick brains.
- Cyclic adenosine monophosphate (cAMP) production was measured in response to various species-specific forms of PACAP and GRF.
- Immunocytochemistry, Western blot, and RT-PCR were used to detect peptide synthesis, receptor presence, and gene expression.
Main Results:
- Physiological concentrations of PACAP27 (human/salmon, chicken, tunicate) dose-dependently increased cAMP levels up to 5-fold.
- PACAP38 responses varied by species, with human PACAP38 showing a 5-fold increase and salmon PACAP38 showing no significant response.
- GRF peptides did not significantly increase cAMP, except for a small, significant increase with a tunicate GRF27-like peptide.
- PACAP38 peptide synthesis and the presence of PACAP/GRF mRNAs and a PACAP receptor mRNA were confirmed in the cultured cells.
Conclusions:
- This study provides the first evidence for an autocrine/paracrine system involving PACAP in early chick brain development.
- The findings suggest that PACAP acts on developing neuroblasts, utilizing its receptor to modulate intracellular cAMP levels.
- GRF's role appears limited or species-specific in this developmental context.
Abstract:
To investigate the involvement of pituitary adenylate cyclase- activating polypeptide (PACAP) and GH-releasing factor (GRF) during early chick brain development, we established neuroblast- enriched primary cell cultures derived from embryonic day 3.5 chick brain. We measured increases in cAMP generated by several species-specific forms of the peptides. Dose-dependent increases up to 5-fold of control values were measured in response to physiological concentrations of human/salmon, chicken, and tunicate PACAP27. Responses to PACAP38 were more variable, ranging from 5-fold for human PACAP38 to 4-fold for chicken PACAP38, to no significant response for salmon PACAP38, compared with control values. The responses to PACAP38 may reflect a greater difference in peptide structure compared with PACAP27 among species. Increases in cAMP generated by human, chicken, and salmon/carp GRF were not statistically significant, whereas increases in response to lower-range doses of tunicate GRF27-like peptide were significant, but small. We also used immunocytochemistry and Western blot to show synthesis of the PACAP38 peptide. RT-PCR was used to demonstrate that messenger RNAs for PACAP and GRF and a PACAP-specific receptor were present in the cells. This is a first report suggesting an autocrine/paracrine system for PACAP in early chick brain development, based on the presence of the ligand, messages for the ligand and receptor, and activation of the receptor in neuroblast-enriched cultures.
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