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. 2010 Sep;217(3):214-22.
doi: 10.1111/j.1469-7580.2010.01268.x. Epub 2010 Jul 21.

Expression and Cell Localization of Brain-Derived Neurotrophic Factor and TrkB During Zebrafish Retinal Development

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Free PMC article

Expression and Cell Localization of Brain-Derived Neurotrophic Factor and TrkB During Zebrafish Retinal Development

A Germanà et al. J Anat. .
Free PMC article

Abstract

Brain-derived neurotrophic factor (BDNF) signaling through TrkB regulates different aspects of neuronal development, including survival, axonal and dendritic growth, and synapse formation. Despite recent advances in our understanding of the functional significance of BDNF and TrkB in the retina, the cell types in the retina that express BDNF and TrkB, and the variations in their levels of expression during development, remain poorly defined. The goal of the present study is to determine the age-dependent changes in the levels of expression and localization of BDNF and TrkB in the zebrafish retina. Zebrafish retinas from 10 days post-fertilization (dpf) to 180 dpf were used to perform PCR, Western blot and immunohistochemistry. Both BDNF and TrkB mRNAs, and BDNF and full-length TrkB proteins were detected at all ages sampled. The localization of these proteins in the retina was very similar at all time points studied. BDNF immunoreactivity was found in the outer nuclear layer, the outer plexiform layer and the inner plexiform layer, whereas TrkB immunoreactivity was observed in the inner plexiform layer and, to a lesser extent, in the ganglion cell layer. These results demonstrate that the pattern of expression of BDNF and TrkB in the retina of zebrafish remains unchanged during postembryonic development and adult life. Because TrkB expression in retina did not change with age, cells expressing TrkB may potentially be able to respond during the entire lifespan of zebrafish to BDNF either exogenously administered or endogenously produced, acting through paracrine mechanisms.

Figures

Fig. 1
Fig. 1
TrkB and BDNF mRNA and protein are expressed in eyes of zebrafish. Cell lysates of eyes obtained from zebrafish were used to detect expression of TrkB and BDNF using RT-PCR (A). Lane 1, marker. Lane 2, negative control. Lanes 3 and 4, detection of TrkB and BDNF at 10 dpf. Lanes 5 and 6, detection of TrkB and BDNF at 20 dpf. Lanes 7 and 8, detection of TrkB and BDNF at 30 dpf. Lanes 9 and 10, detection of TrkB and BDNF at 40 dpf. Lanes 11 and 12, detection of TrkB and BDNF at 50 dpf. Lanes 13 and 14, detection of TrkB and BDNF at 180 dpf. Lane 15, detection of β-actin. Cell lysates of eyes obtained from zebrafish were used to detect expression of TrkB and BDNF using Western blot (B). Detection of TrkB at 10 (lane 1), 20 (lane 2), 30 (lane 3), 40 (lane 4), 50 (lane 5), and 180 (lane 6) dpf. Detection of BDNF at 10 (lane 7), 20 (lane 8), 30 (lane 9), 40 (lane 10), 50 (lane 11), and 180 (lane 12) dpf.
Fig. 2
Fig. 2
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at 10 dpf. BDNF immunoreactivity (A and C) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B,D) was restricted to the inner plexiform layer. Scale bars: 100 μm (A,B) and 40 μm (C,D).
Fig. 3
Fig. 3
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at 20 dpf. BDNF immunoreactivity (A,C) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B,D) was restricted to the inner plexiform layer. Scale bars: 100 μm (A,B) and 40 μm (C,D).
Fig. 4
Fig. 4
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at dpf. BDNF immunoreactivity (A) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B) was restricted to the inner plexiform layer. Scale bar: 100 μm (A,B).
Fig. 5
Fig. 5
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at 40 dpf. BDNF immunoreactivity (A,C) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B,D) was restricted to the inner plexiform layer. Scale bars: 100 μm (A,B) and 35 μm (C,D). GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; ONL, outer nuclear layer; OPL, outer plexiform layer; RPE, retinal pigment epithelium.
Fig. 6
Fig. 6
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at 50 dpf. BDNF immunoreactivity (A,C) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B,D) was restricted to the inner plexiform layer. Scale bars: 100 μm (A,B) and 40 μm (C,D).
Fig. 7
Fig. 7
Immunohistochemical localization of TrkB and BDNF in the retina of zebrafish at 180 dpf. BDNF immunoreactivity (A,C) was observed in the outer nuclear layer, outer plexiform layer and inner plexiform layer, whereas TrkB immunoreactivity (B,D) was restricted to the inner plexiform layer. Scale bars: 40 μm (A,B) and 20 μm (C,D). GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; ONL, outer nuclear layer; OPL, outer plexiform layer; RPE, retinal pigment epithelium.

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