Catfish (Siluriformes) are characterized by unique morphologies, including enlarged jaws with movable barbels and taste buds covering the entire body surface. Evolution of these characteristics was a crucial step in their adaptive radiation to freshwater environments. However, the developmental processes of the catfish craniofacial region and taste buds remain to be elucidated; moreover, little is known about the molecular mechanisms underlying the morphogenesis of these structures. In Amur catfish (Silurus asotus), three pairs of barbel primordia are formed by 2 days post-fertilization (dpf). Innervation of the peripheral nerves and formation of muscle precursors are also established during early development. Taste buds from the oral region to the body trunk are formed by 4 dpf. We then isolated catfish cognates Shh (SaShh) and Fgf8 (SaFgf8), which are expressed in maxillary barbel primordium at 1–2 dpf. Further, SHH signal inhibition induces reduction of mandibular barbels with abnormal morphology of skeletal elements, whereas it causes no apparent abnormality in the trigeminal and facial nerve morphology. We also found that mandibular barbel lengths and number of taste buds are reduced by FGF inhibition, as seen in SHH signal inhibition. However, unlike with SHH inhibition, the abnormal morphology of the trigeminal and facial nerves was observed in FGF signal-inhibited embryos. The developmental processes of Amur catfish are consistent with those reported for other catfish species. Thus, developmental aspects of craniofacial structures and taste buds may be conserved in Siluriformes. Our findings also suggest that SHH signaling plays a crucial role in the formation of barbels and taste buds, without affecting nerve projection, while FGF signaling is required for the development of barbels, taste buds, and branchial nerves. Thus, SHH and FGF signaling plays key roles in the ontogenesis and evolution of some catfish-specific characteristics.

中文翻译：

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基于 FGF 和 SHH 的分子信号调节鲶鱼的触须和颅面发育

鲶鱼（鲶形目）具有独特的形态特征，包括扩大的下颚，带有可移动的触须和覆盖整个身体表面的味蕾。这些特征的进化是它们适应淡水环境辐射的关键一步。然而，鲶鱼颅面部和味蕾的发育过程仍有待阐明；此外，关于这些结构形态发生的分子机制知之甚少。在阿穆尔鲶鱼 (Silurus asotus) 中，受精后 2 天 (dpf) 形成了三对触须原基。周围神经的神经支配和肌肉前体的形成也在早期发育过程中建立。从口腔区域到躯干的味蕾由 4 dpf 形成。然后我们分离出鲶鱼同源Shh（SaShh）和Fgf8（SaFgf8），它们在 1-2 dpf 的上颌触须原基中表达。此外，SHH 信号抑制诱导下颌触须减少，骨骼元素形态异常，而三叉神经和面神经形态没有明显异常。我们还发现，抑制 FGF 会减少下颌触须长度和味蕾数量，如 SHH 信号抑制所示。然而，与 SHH 抑制不同，在 FGF 信号抑制的胚胎中观察到三叉神经和面神经的异常形态。阿穆尔鲶鱼的发育过程与报道的其他鲶鱼物种的发育过程一致。因此，颅面结构和味蕾的发育方面可能在鲶形目中得到保护。我们的研究结果还表明，SHH 信号在触须和味蕾的形成中起着至关重要的作用，而不影响神经投射，而 FGF 信号是触须、味蕾和鳃神经发育所必需的。因此，SHH 和 FGF 信号在一些鲶鱼特异性特征的个体发生和进化中起关键作用。