Almazan Eugene Matthew P, Ryan Joseph F, Rouhana Labib
Department of Biological Sciences, Wright State University, Dayton, OH, United States.
Whitney Laboratory of Marine Biosciences, University of Florida, St. Augustine, FL, United States.
Front Cell Dev Biol. 2021 Nov 26;9:777951. doi: 10.3389/fcell.2021.777951. eCollection 2021.
Detection of chemical stimuli is crucial for living systems and also contributes to quality of life in humans. Since loss of olfaction becomes more prevalent with aging, longer life expectancies have fueled interest in understanding the molecular mechanisms behind the development and maintenance of chemical sensing. Planarian flatworms possess an unsurpassed ability for stem cell-driven regeneration that allows them to restore any damaged or removed part of their bodies. This includes anteriorly-positioned lateral flaps known as auricles, which have long been thought to play a central role in chemotaxis. The contribution of auricles to the detection of positive chemical stimuli was tested in this study using , a North American planarian species known for its morphologically prominent auricles. Behavioral experiments staged under laboratory conditions revealed that removal of auricles by amputation leads to a significant decrease in the ability of planarians to find food. However, full chemotactic capacity is observed as early as 2 days post-amputation, which is days prior from restoration of auricle morphology, but correlative with accumulation of ciliated cells in the position of auricle regeneration. Planarians subjected to x-ray irradiation prior to auricle amputation were unable to restore auricle morphology, but were still able to restore chemotactic capacity. These results indicate that although regeneration of auricle morphology requires stem cells, some restoration of chemotactic ability can still be achieved in the absence of normal auricle morphology, corroborating with the initial observation that chemotactic success is reestablished 2-days post-amputation in our assays. Transcriptome profiles of excised auricles were obtained to facilitate molecular characterization of these structures, as well as the identification of genes that contribute to chemotaxis and auricle development. A significant overlap was found between genes with preferential expression in auricles of and genes with reduced expression upon knockdown in , suggesting that has a conserved role in regulating auricle development and function. Models that distinguish between possible contributions to chemotactic behavior obtained from cellular composition, as compared to anatomical morphology of the auricles, are discussed.
化学刺激的检测对生命系统至关重要，也有助于提升人类的生活质量。由于嗅觉丧失随着年龄增长愈发普遍，预期寿命的延长激发了人们对理解化学传感发育和维持背后分子机制的兴趣。涡虫扁虫具有干细胞驱动的再生能力，这种能力无与伦比，使它们能够恢复身体任何受损或被切除的部分。这包括位于前部的称为耳状突的侧翼，长期以来人们一直认为耳状突在趋化作用中起核心作用。本研究使用一种以其形态突出的耳状突而闻名的北美涡虫物种，测试了耳状突对阳性化学刺激检测的贡献。在实验室条件下进行的行为实验表明，通过截肢去除耳状突会导致涡虫寻找食物的能力显著下降。然而，早在截肢后2天就观察到了完全的趋化能力，这比耳状突形态恢复提前了几天，但与耳状突再生位置的纤毛细胞积累相关。在耳状突截肢前接受X射线照射的涡虫无法恢复耳状突形态，但仍能恢复趋化能力。这些结果表明，虽然耳状突形态的再生需要干细胞，但在没有正常耳状突形态的情况下，仍能实现趋化能力的一些恢复，这与我们实验中截肢后2天趋化成功得以重建的初步观察结果相符。获取切除耳状突的转录组图谱，以促进对这些结构的分子表征，以及鉴定有助于趋化作用和耳状突发育的基因。在 耳状突中优先表达的基因与 在 敲低后表达降低的基因之间发现了显著重叠，表明 在调节耳状突发育和功能方面具有保守作用。本文讨论了与耳状突解剖形态相比，区分细胞组成对趋化行为可能贡献的模型。
