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L.E. Paraoanu, E. Christ, P.G. Layer; Co–Expression of Neurexin–1ß and Acetylcholinesterase Preceding Synaptogenesis in the IPL of Chicken Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):565.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: ß–neurexins and their ligands, the neuroligins, have been implicated in synaptogenesis. Neuroligin–1 belongs to the family of cholinesterase–like cell adhesion proteins, which all share a homologous domain with cholinesterases, suggesting that ChEs themselves may be implicated in non–enzymatic cell–cell interactions by binding to neurexins. To assess this postulated interaction, we describe here the expression patterns of AChE and neurexin–1ß during embryonic development of the chick retina and compare them with the expression of neuroligin–1. Methods: Distinct regions of the mRNAs of neurexin–1 and neuroligin–1 were amplified from cDNA by the PCR using specific primers. The expression patterns of neurexin–1ß and neuroligin–1 were analyzed by in situ hybridization on chick embryonic retina sections, corresponding to the E4 up to E19 (E, embryonic day). In parallel, the expression of AChE was investigated by enzyme histochemistry and immuno–histochemistry. Results: In situ hybridisation revealed an early appearance of neurexin–1ß, the first signal being detected at E6 in the future ganglion cell layer. At E9, neurexin–1ß transcripts appeared not only in the GCL, but also in the inner half of the INL. Until stage E19, the staining remained localized to the GCL and inner half of the INL. An antibody against AChE labeled postmitotic neurons which later will undergo synaptogenesis. The first cells to be stained are ganglion cells, followed by amacrine cells situated in the INL. A strong labeling of sublaminae in the IPL can be associated with the formation of synaptic connections. In summary, it was shown that both neurexin–1ß and AChE, two genes whose protein products are involved in neurotransmission, became detectable in differentiating chicken retinal cells long before synaptogenesis, whereby their spatial expression patterns overlapped closely. The expression of both markers was intense during the differentiation of neurons that send their axons and dendrites into the inner plexiform layer to form synapses (ganglion, amacrine and bipolar cells). Conclusions: This study suggests that neurexin–1ß and AChE could represent mutual binding partners functioning in the development and/or maturation of synaptic connections in the chicken retina, particularly so in the inner plexiform layer.
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