Differential distribution and regulation of expression of synaptosomal-associated protein of 25 kDa isoforms in the Xenopus pituitary gland and brain

• Published in: Neuroscience Vol. 128; no. 3; pp. 531 - 543
• Main Authors: Kolk, S.M., Groffen, A.J.A., Tuinhof, R., Ouwens, D.T.W.M., Cools, A.R., Jenks, B.G., Verhage, M., Roubos, E.W.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2004; Elsevier
• Subjects: Adaptation, Physiological - physiology; alpha-MSH - metabolism; Amphibia; Animals; Biological and medical sciences; Brain - anatomy & histology; Brain - metabolism; DNA, Complementary - analysis; DNA, Complementary - genetics; docking/fusion complex; Exocytosis - physiology; exocytosis proteins; Freshwater; Fundamental and applied biological sciences. Psychology; in situ hybridization; Membrane Fusion - physiology; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Sequence Data; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - isolation & purification; Nerve Tissue Proteins - metabolism; Neurons - metabolism; Neurosecretory Systems - anatomy & histology; Neurosecretory Systems - metabolism; neurotransmitter release; Pituitary Gland - anatomy & histology; Pituitary Gland - metabolism; Protein Isoforms - genetics; Protein Isoforms - metabolism; real-time RT-PCR; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Skin Pigmentation - physiology; Synaptic Membranes - metabolism; Synaptosomal-Associated Protein 25; Up-Regulation - genetics; Vertebrates: nervous system and sense organs; Xenopus laevis; Xenopus laevis - anatomy & histology; Xenopus laevis - metabolism; DTT; real-time RT-PCR; BoNT; neurotransmitter release; SNARE; Ct; OD; RT-PCR; docking/fusion complex; exocytosis proteins; α-MSH; GAPDH; SNAP-25; in situ hybridization; Molecular hybridization; Molecular form; Endocrine gland; Central nervous system; Exocytosis; Encephalon; Polymerase chain reaction; Synaptosome; Distribution; Neurotransmitter; Pituitary gland; Release
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2004.06.059

Synaptosomal-associated protein of 25 kDa (SNAP-25) regulates various membrane fusion processes including exocytosis by endocrine and neural cells. To increase our understanding of the occurrence and regulation of SNAP-25 isoforms, we identified and characterized SNAP-25a and SNAP-25b mRNAs in the pituitary gland and brain of the amphibian Xenopus laevis. The proteins are strongly conserved and are resistant to botulinum neurotoxin A but not to botulinum neurotoxin E, as shown by Western blotting. The spatial distribution of the two SNAP-25 isoforms was assessed with in situ hybridization. Both SNAP-25a mRNA and SNAP-25b mRNA reside in cells in the pituitary distal lobe and, particularly, in the endocrine melanotrope cells in the pituitary intermediate lobe. The melanotrope cells are involved in the background adaptation process of the skin by releasing α-melanophore-stimulating hormone. Quantitation of the respective in situ hybridization signals in the Xenopus pars intermedia indicated a differential response, SNAP-25b mRNA being more highly expressed in black-adapted animals than SNAP-25a mRNA, and more than in white-adapted toads. This differential upregulation was also studied by real-time reverse transcriptase polymerase chain reaction, showing that in the intermediate pituitary lobe, both isoforms are physiologically controlled by the background light intensity stimulus, but with different intensities; in black-adapted animals SNAP-25b mRNA is upregulated by 3.33 times compared with white-adapted animals, but SNAP-25a only by 1.96 times. As to neural tissue, in situ hybridization showed that both isoforms coexist throughout the brain, sometimes with similar strengths, but in various areas either SNAP-25a mRNA or SNAP-25b mRNA expression is prevalent. It is speculated that each of the SNAP-25 isoforms in the Xenopus pituitary and brain has a distinct function in cellular fusion processes including secretion, and that their occurrence and regulation depend on the type of secreted neurotransmitter/hormone and/or the activity state of the cell.