Lucini C, de Girolamo P, Maruccio L, Lamanna C, Castaldo L, Vega J A
Dipartimento di Strutture, Funzioni e Tecnologie Biologiche, Facoltà di Medicina Veterinaria, Napoli, Italy.
Cell Tissue Res. 1999 May;296(2):323-30. doi: 10.1007/s004410051292.
Neurotrophins, acting through their high-affinity signal-transducing Trk receptors, are involved in the development, differentiation and maintenance of discrete neuron populations in the higher vertebrates. Furthermore, the presence of Trk receptors in some non-neuronal tissues, including the endocrine cells of the gut, could indicate an involvement of neurotrophins also in these tissues. Recently, neurotrophins and neurotrophin receptor proteins have been identified in the lower vertebrates and invertebrates, whose amino acid sequences are highly homologous with those found in mammals. The present study investigates the occurrence and distribution of Trk-like proteins in the neurons and gut endocrine cells in five species of teleost. Single and double immunolabeling was carried out on fresh and paraffin-embedded tissue using commercially available antibodies against sequences of the intracytoplasmic domain of the mammalian Trk. Western-blot analysis, carried out on samples of stomach and intestine of bass, identified proteins whose estimated molecular masses (140 kDa, 145 kDa and 143-145 kDa) were similar to those reported for full-length TrkA, TrkB and TrkC in the higher vertebrates. TrkA-like immunoreactivity was found in the enteric nervous system plexuses of three fish species. Trk-like immunoreactivity was observed in the endocrine cells as follows: sparse TrkA-like immunoreactive endocrine cells were detected only in the intestine: TrkB-like immunoreactive cells were detected only in the stomach; and TrkC-like immunoreactive cells were found both in the intestine of the carp and in the stomach of the bass, where they also showed TrkB-like immunoreactivity. These findings confirm the occurrence and distribution of Trk-like proteins in teleosts. These proteins are closely related to the Trk neurotrophin receptors of mammals. The functional significance of Trk-like proteins in both neuronal and non-neuronal cells of teleosts is still not clear.
神经营养因子通过其高亲和力的信号转导Trk受体发挥作用，参与高等脊椎动物中离散神经元群体的发育、分化和维持。此外，在包括肠道内分泌细胞在内的一些非神经组织中存在Trk受体，这可能表明神经营养因子也参与这些组织的活动。最近，在低等脊椎动物和无脊椎动物中发现了神经营养因子和神经营养因子受体蛋白，它们的氨基酸序列与哺乳动物中的高度同源。本研究调查了五种硬骨鱼的神经元和肠道内分泌细胞中Trk样蛋白的存在和分布情况。使用针对哺乳动物Trk胞质内结构域序列的市售抗体，对新鲜和石蜡包埋组织进行单重和双重免疫标记。对鲈鱼的胃和肠样本进行的蛋白质印迹分析，鉴定出估计分子量（140 kDa、145 kDa和143 - 145 kDa）与高等脊椎动物中全长TrkA、TrkB和TrkC报道的分子量相似的蛋白质。在三种鱼类的肠神经系统丛中发现了TrkA样免疫反应性。在内分泌细胞中观察到Trk样免疫反应性如下：仅在肠道中检测到稀疏的TrkA样免疫反应性内分泌细胞；仅在胃中检测到TrkB样免疫反应性细胞；在鲤鱼的肠道和鲈鱼的胃中都发现了TrkC样免疫反应性细胞，在这些部位它们还表现出TrkB样免疫反应性。这些发现证实了硬骨鱼中Trk样蛋白的存在和分布。这些蛋白与哺乳动物的Trk神经营养因子受体密切相关。硬骨鱼神经元和非神经元细胞中Trk样蛋白的功能意义仍不清楚。
