Early expression of pituitary adenylate cyclase-activating polypeptide and activation of its receptor in chick neuroblasts

Melatonin mediates monochromatic green light-induced satellite cell proliferation and muscle growth in chick embryo

Background

Green light penetrates the skull and has directly affected on the secretion of melatonin in plasma, which regulates the endocrine activities to influence the muscle growth, satellite cell mitotic activity and quality properties of meat from the embryonic period to posthatch in chick. Pituitary adenylate cyclase-activating polypeptide 6–38 (PACAP6-38) could inhibit the synthesis and secretion of pineal melatonin. Finding a new way for exploring the mechanism of light-regulated muscle growth in ovo is essential for promoting the productive performance in poultry.

Methods

Chick embryos were exposed to darkness (D-group) and green light (G-group) throughout the embryonic period, and injected with PACAP6-38 or saline at embryonic day 8. Plasma hormone, skeletal muscle fiber areas, satellite cell proliferation activity, paired domain homeobox transcription factor 7 and myogenic regulatory factors were observed.

Results

By saline treatment, the percentage of proliferating cell nuclear antigen immunoreactive cells and mitotic activity of satellite cells in skeletal muscle were higher in G-group than those of in D-group at post-hatching day 0. With the increase of plasma melatonin, green light promoted the secretion of growth hormone (GH) and insulin like factor 1 (IGF-1) in plasma, the satellite cell proliferation, the size of muscle fiber, as well as the mRNA expressions of Pax7, myogenic regulatory factors and IGF-1R. After PACAP6-38 treatment to inhibit the secretion of melatonin in ovo, aforementioned parameters were remarkably decreased and the difference of these parameters was disappeared between D-group and G-group.

Conclusion

These data indicated that stimulation with monochromatic green light during incubation enhanced the secretion of melatonin and up-regulation of GH-IGF-1 axis to activate the satellite cells proliferation and myofiber formation, involving the expression of Pax7 and myogenic regulatory factors.

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP1-38) Exerts Both Pro and Anti-Apoptotic Effects on Postnatal Retinal Development in Rat

PACAP1-38, a ubiquitous and multifunctional regulator has been in the focus of neurotoxicity research due to its impressive neuroprotective potential. Although the literature extensively demonstrated its repressive effect on the apoptotic machinery in neurodegenerative models, there is a striking absence of analysis on its role in normal development. We performed quantitative analyses on caspase activity in developing retina upon 100, 50, 25 or 1 pmol intravitreal PACAP1-38 injection from postnatal day 1 (P1) through P7 in Wistar rats. Retinas were harvested at 6, 12, 18, 24 or 48 h post-injection. Apoptotic activity was revealed using fluorescent caspase 3/7 enzyme assay, western blots and TUNEL assay. Unexpectedly, we found that 100 pmol PACAP1-38 increased the activity of caspase 3/7 at P1 and P5 whereas it had no effect at P7. At P3, as a biphasic effect, PACAP1-38 repressed active caspase 3/7 at 18 h post-injection while increased their activity in 24 h post-injection. Amounts, smaller than 100 pmol, could not inhibit apoptosis whereas 50, 25 or 1 pmol PACAP1-38 could evoke significant elevation in caspase 3/7 activity. TUNEL-positive cells appeared in the proximal part of inner nuclear as well as ganglion cell layers in response to PACAP1-38 treatment. The fundamental novelty of these results is that PACAP1-38 induces apoptosis during early postnatal retinogenesis. The dose as well as stage-dependent response suggests that PACAP1-38 has a Janus face in apoptosis regulation. It not only inhibits development-related apoptosis, but as a long-term effect, facilitates it.

PAC1-expressing structures of neural retina alter their PAC1 isoform splicing during postnatal development

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the secretin/glucagon/vasoactive intestinal peptide family, exerts various effects on neuronal development as mediated by the differential expression of PAC1 receptor (PAC1-R) isoforms. The expression changes of PAC1-R isoforms (Hip, Hop1) reported in correlation with retinal development suggest an isoform switch during the second postnatal week. Our aim is to determine the exact period of the isoform shift and to describe the PAC1-R-immunoreactive structures appearing from postnatal day 5 (P5) to P10 in the rat retina. The ratio of Hip and Hop1 receptors was assessed and changes in their expression were followed by Taqman and SybrGreen-based quantitative polymerase chain reaction. For the detection of PAC1-R-expressing retinal structures, anti-PAC1-R, anti-calbindin, anti-protein kinase C, anti-glutamine synthetase, anti-HPC1 and anti-Brn3a antibodies were utilized. At the transcript level, a marked decrease to an undetectable level was measured in Hip mRNA expression from P6 to P9. Hop1 expression appeared to be unchanged from P6 to P9, followed by a significant elevation at P10. A Hip/Hop1 isoform shift occurred between P6 and P7. Immunostaining showed strong PAC1-R labeling from P5 to P10 in ganglion, amacrine, horizontal and rod bipolar neurons and in glial Muller cell processes. The Hop1 isoform was predominantly expressed in various types of retinal cell beginning at P7, because of a dramatic reduction in Hip mRNA level. As the Hop1 receptor is coupled to different signaling cascades, this isoform shift might alter the physiological role of PACAP during this particular period.

Changes in the expression of PACAP-like compounds during the embryonic development of the earthworm Eisenia fetida

Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed at very early stages in the vertebrate nervous system, and its functions in the embryonic development have been shown by various studies. PACAP is an extremely conserved molecule in phylogeny; however, little is known about its presence and functions in invertebrates. Our previous studies have shown the occurrence of PACAP-like immunoreactivity in the invertebrate nervous system. The aim of this study was to investigate the presence and localization of PACAP-like compounds during the embryonic development of earthworms from cocoon deposition to hatching using immunological methods (radioimmunoassay, dot blot, immunohistochemistry). PACAP-like immunoreactive compounds were detected at very early stages of the embryonic development of the earthworm Eisenia fetida. No significant changes were observed during the early stages in the developing embryo, but a marked increase occurred before hatching. In contrast, during the embryonic development, the level of PACAP-like compounds gradually decreased in cocoon fluids. Immunohistochemistry revealed the presence of PACAP-like immunoreactive cell bodies and processes in the developing body wall, prostomium, pharyngeal wall, and central nervous system. Cells located in the body wall correspond to putative progenitor cells of primary sensory cells. In the present study, we also showed that the clitellum (reproductive organ) of sexually mature worms contained significantly higher levels of PACAP-like immunoreactivity than other regions of the same animals or the clitellar region of a non-reproducing animal. In summary, these observations provide a morphological basis and suggest a role of PACAP(-like peptides) in the reproductive and developmental functions of invertebrates.

Distribution and localization of pituitary adenylate cyclase-activating polypeptide-specific receptor (PAC1R) in the rostral migratory stream of the infant mouse brain

Pituitary adenylate cyclase-activating polypeptide (PACAP) is known to participate in the regulation of neuronal proliferation and differentiation. While these processes are considered to be mediated via PACAP's actions on the PACAP-specific receptor, PAC1R, the precise distribution of PAC1R during neurodevelopment has not yet to be elucidated in detail. The purpose of this study is to examine the distribution of PAC1R in the neurogenic region of the rostral migratory stream (RMS) from the apical subventricular zone (SVZa) to the olfactory bulb (OB) in infant mice using immunostaining. Co-immunostaining for PAC1R in a variety types of cell were carried out using different markers. These included the neural stem cell markers, nestin and glial fibrillary acidic protein (GFAP), a marker for migrating neuroblasts (doublecortin, DCX), a marker for immature neurons betaIII-tubulin, (Tuj1), and a marker for mature neurons, neuronal nuclei (NeuN). PAC1R-like immunoreactivity (LI) was observed in the RMS. However, the intensity of PAC1R- LI was different depending on the regions which were investigated. PAC1R-LI was strong in nestin- and GFAP-positive cells in the SVZa and was also observed in NeuN-positive cells in the OB. However, the intensities of PAC1R-LI in DCX- and Tuj1-positive cells were weaker than the other markers. These results suggest that PACAP may participate in the neurodevelopment with the stage-specific expression of PAC1R and that PACAP plays important roles in neurons as well as in glial cells.

Development of the circadian melatonin rhythm and the effect of PACAP on melatonin release in the embryonic chicken pineal gland. An in vitro study

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to participate in modulation of circadian rhythm and to stimulate melatonin (MT) secretion in both the rat and chicken pineal glands. In contrast to mammals, the main regulator of circadian rhythm in birds is the pineal gland, which begins its rhythmic MT production already during embryonic life. In the present study, we investigated the development of MT secretion in explanted embryonic chicken pineals and their responsiveness to PACAP in a perifusion system. Our results show that: (1) the circadian clock and/or the intracellular signal transduction system connecting the clock to MT synthesizing apparatus develop between the embryonic days 16-18 (E16-18), even in vitro. (2) Exposure of the embryonic chicken pineal gland to PACAP induces transitory increase in MT secretion but does not induce visible phase shift in the circadian rhythm. (3) Cyclic AMP (cAMP) efflux also responds to PACAP at or before day E13 in embryonic chicken pineal gland in vitro.

Effects of in ovo treatment with PACAP antagonist on general activity, motor and social behavior of chickens

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to influence nervous system development. The aim of the present study was to investigate the effects of in ovo treatment with the PACAP antagonist PACAP6-38 during embryonic life (E8 and E16) on motor activity and social behavior in chicken. Our results showed that a single injection of PACAP6-38 during the first half of embryonic life caused subtle transient changes in general behavior and motor control when compared to saline-treated controls. Increased activity and reduced anxiety were observed also in a novel environment at 2 days after hatching. However, most of these behavioral differences disappeared by 2 weeks. PACAP6-38-treatment during the first half of embryonic life resulted in markedly reduced social behavior, which was still present at 2 weeks of age. Treatment during the second half of embryonic life resulted in no behavioral differences between control and PACAP6-38-treated chicken. PACAP content in different brain areas was not different between control and PACAP6-38-treated chicken at 5 days or 3 weeks of age, but it decreased significantly with age in both groups. In summary, our results show that PACAP6-38 treatment at E8 caused transient changes in motor behavior, and long-lasting reduction in social behavior.

Developmental changes in the expression of growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide in zebrafish

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are structurally and functionally related members of the glucagon superfamily, a group of hormones important in development, growth, and metabolism. Our objectives were to determine the developmental expression pattern of the ghrh-pacap1 gene using the zebrafish model. The temporal and spatial expression pattern of the ghrh-pacap1 gene was examined by RT-PCR and in situ hybridization. In zebrafish, the ghrh-pacap1 mRNA transcript was expressed throughout development beginning at the transition between the blastula and gastrula periods. During midgastrulation, alternative splicing resulted in the generation of a novel transcript lacking the cryptic peptide. During the segmentation period, expression was localized to the neural tube, developing eye, and neural crest; strong expression was found in the developing cerebellum. Later in development, expression was localized in the hatching gland and developing pharyngeal arches. The temporal and spatial expression pattern of the ghrh-pacap1 transcript suggests that these hormones may modulate patterning during development.

Embryonic expression of pituitary adenylyl cyclase-activating polypeptide and its selective type I receptor gene in the frog Xenopus laevis neural tube

The genes encoding pituitary adenylyl cyclase-activating peptide (PACAP) and its selective type I receptor (PAC1) are expressed in the embryonic mouse neural tube, where they may be involved in neurogenesis and neural tube development. We examined here the early expression and potential actions of PACAP and PAC1 in the vertebrate developmental model Xenopus laevis. PACAP and PAC1 mRNAs were first detected by RT-PCR in stage 16-18 embryos (18 hours after fertilization). Two distinct PACAP precursor mRNAs were identified. One encoded both growth hormone-releasing hormone and PACAP, whereas the other encoded only full-length PACAP. Unlike that in the adult, the latter represented the predominant embryonic PACAP mRNA species. In situ hybridization revealed that PACAP and PAC1 mRNAs were restricted to neural cells. PAC1 gene expression was observed mainly in the ventricular zone in the ventral parts of the prosencephalon, mensencephalon, rhombencephalon, and anterior spinal cord. In contrast, PACAP mRNA was localized exclusively in postmitotic cells in the dorsolateral parts of the rhombencephalon and entire spinal cord. Most PACAP mRNA-containing cells were characterized as Rohon-Beard neurons. Exposure of early embryos to UV irradiation, which ventralizes embryos and inhibits neural induction, reduced the expression of PACAP and PAC1 genes. These results suggest that PACAP may be involved in the early development of the embryonic Xenopus neural tube.