Saele Oystein, Smáradóttir Heiddís, Pittman Karin
Department of Biology, University of Bergen, High Technology Center, 5020 Bergen, Norway.
J Morphol. 2006 Jun;267(6):730-8. doi: 10.1002/jmor.10437.
Early molecular markers for flatfish metamorphosis and eye migration must be linked to the ethmoid region, the earliest part of the flatfish cranium to change, as well as chondral and dermal ossification processes. Serial sections, morphological landmarks, and stereology were used to determine where and when the remodeling of tissues and asymmetry occurs in the head region of metamorphosing Atlantic halibut, Hippoglossus hippoglossus. Not all parts of the head remodel or migrate, and those that do may be asynchronous. Normal metamorphosis limits the torsion of the Atlantic halibut head to the anterior part of the neurocranium and excludes the tip of the snout and the general jaw area. The first cranial structure displaying eye migration-related asymmetric development is the paraethmoid part of the ethmoid cartilage. In early eye migration the medial frontal process moves apace with the eyes, whereas near completion the migrating eye moves significantly closer to the frontal process. Structures of the jaw remain mostly symmetrical, with the exception of the adductor mandibulae muscle and the bone maxillare, which are larger on the abocular than on the ocular side, the muscle occupying the space vacated by the migration of the eye. Thus, normal eye migration involves a series of temperospatially linked events. In juveniles lacking eye migration (arrested metamorphosis), the dermal bone, the prefrontal, does not develop. The two abnormal paraethmoids develop symmetrically as two plate-like structures curving anteriorly, whereas normal elongate fused paraethmoids curve at their posterior. The abocular side retrorbital vesicles are largest in volume only after the completion of normal eye migration. Factors involved in completion of normal metamorphosis and eye migration in flatfish affect chondral and dermal ossification signals in the ethmoid group, as well as remodeling of the mineralized frontal, a series of linked events not involving the entire neurocranium.
比目鱼变态和眼睛迁移的早期分子标记必须与筛骨区域相关联，筛骨区域是比目鱼颅骨最早发生变化的部分，同时也与软骨和真皮骨化过程相关。连续切片、形态学标志和体视学被用于确定正在变态的大西洋庸鲽（Hippoglossus hippoglossus）头部区域组织重塑和不对称现象发生的位置和时间。并非头部的所有部分都会重塑或迁移，而且那些发生重塑或迁移的部分可能并不同步。正常变态将大西洋庸鲽头部的扭转限制在脑颅的前部，不包括吻端和一般的颌部区域。显示与眼睛迁移相关的不对称发育的第一个颅骨结构是筛骨软骨的副筛骨部分。在眼睛迁移早期，内侧额突与眼睛同步移动，而在迁移接近完成时，迁移的眼睛明显更靠近额突。颌部结构大多保持对称，但除外展下颌肌和上颌骨，它们在无眼侧比有眼侧更大，该肌肉占据了眼睛迁移腾出的空间。因此，正常的眼睛迁移涉及一系列时空相关的事件。在缺乏眼睛迁移（变态停滞）的幼鱼中，真皮骨——额骨——不发育。两个异常的副筛骨对称发育为两个向前弯曲的板状结构，而正常的细长融合副筛骨在其后部弯曲。只有在正常眼睛迁移完成后，无眼侧的眶后囊体积才最大。比目鱼正常变态和眼睛迁移完成所涉及的因素会影响筛骨组中的软骨和真皮骨化信号，以及矿化额骨的重塑，这是一系列不涉及整个脑颅的相关事件。
