Activity‐Dependent Dynamics of Coexisting Brain‐Derived Neurotrophic Factor, Pro‐Opiomelanocortin and α‐Melanophore‐Stimulating Hormone in Melanotrope Cells ofXenopus laevis

Journal of Neuroendocrinology - Tập 16 Số 1 - Trang 19-25 - 2004
L. C. Wang1, Hans Meijer1, Bruno M. Humbel2, Bruce G. Jenks1, Eric W. Roubos1
1Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences, University, of Nijmegen, The Netherlands
2Department of Molecular Cell Biology, Institute for Biomembranes, Utrecht University, The Netherlands.

Tóm tắt

AbstractBrain‐derived neurotrophic factor (BDNF) is involved as an autocrine factor in the regulation of the secretory activity of the neuroendocrine pituitary melanotrope cells ofXenopus laevis. We studied the subcellular distribution of BDNF inXenopusmelanotropes using a combination of high‐pressure freezing, cryosubstitution and immunoelectron microscopy. Presence of BDNF, pro‐opiomelanocortin (POMC) and α‐melanophore‐stimulating hormone (αMSH) within melanotrope secretory granules was studied by triple‐labelling immunoelectron microscopy. In addition, intracellular processing of BDNF was investigated by quantifying the number of immunogold particles in different stages of secretory granule maturation, in animals adapted to black or white background light conditions. The high‐pressure freezing technique provides excellent preservation of both cellular ultrastructure and antigenicity. BDNF coexists with POMC and αMSH within secretory granules. BDNF‐immunoreactivity increases along the secretory granule maturation axis (i.e. from electron‐dense, via moderately electron‐dense, to electron‐lucent secretory granules). Immature, low immunoreactive, electron‐dense secretory granules are assumed to contain mainly or even exclusively proBDNF. Strongly immunoreactive electron‐lucent secretory granules represent the mature granule stage in which proBDNF has been processed to mature BDNF. Furthermore, in moderately electron‐dense secretory granules, immunoreactivity is markedly (+79%) higher in black‐adapted than in white‐adapted animals, indicating that stimulation of melanotrope cell activity by the black background condition speeds up processing of BDNF from its precursor in this granule stage. It is concluded that, in theXenopusmelanotrope, BDNF biosynthesis and processing occur along the secretory granule maturation axis, together with that of POMC‐derived αMSH, and that the environmental light condition not only controls the biosynthesis and secretion of BDNF and of POMC end‐products, but also regulates the rate of their intragranular processing.

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Journal of Neuroendocrinology

Tập 16 Số 1

19-25

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