Structure and ultrastructure of eyes of tornaria larvae of Glossobalanus marginatus
Structure and ultrastructure of eyes of tornaria larvae of Glossobalanus marginatus
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DOI：
10.1007/s13127-015-0206-x
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发表时间：
2015-06-01
影响因子：
1.6
通讯作者：
Stach, Thomas
中科院分区：
文献类型：
--
作者：
Braun, Katrin;Kaul-Strehlow, Sabrina;Stach, Thomas
肠道蠕虫或橡子蠕虫是保留了许多半形性特征的海洋后口动物。因此，在后口和原口的进化比较中，肠口是最有意义的。在本研究中，我们用连续切片的方法重建和描述了边缘舌象幼虫的眼睛，并进行了透射电子显微镜观察。边缘毛虫Metschnikoff晚期/Krohn早期幼虫的外翻眼为表皮结构，由两排共13个遮光色素细胞和两排13个感光细胞组成。色素细胞形成一个相对较宽的浅杯，使杯状眼睛在光学上不适合图像生成。光敏细胞具有大量增大的微绒毛和未修饰的顶端纤毛。因此，我们的超微结构研究证实了边缘毛虫眼睛中的感光细胞是一种明显的横纹体型。初步的免疫组织化学实验通过证明龙卷风眼光感受器与一种针对横纹体海胆感光色素(Sp-Opsin4)设计的抗体的免疫阳性反应来支持这些发现。对活体动物的观察表明，Metschnikoff晚期/Krohn早期的旋毛虫幼虫是负趋光性的，可能与即将发生的变态相一致。
Enteropneusts or acorn worms are marine deuterostomes that have retained many plesiomorphic characters. Thus, enteropneusts are of prime interest in evolutionary comparisons between deuterostomes and protostomes. In the present study, the larval eyes of Glossobalanus marginatus were reconstructed and described based on serial sectioning for transmission electron microscopy. The everse eyes of the late Metschnikoff/early Krohn-stage tornaria larvae of G. marginatus are epidermal structures consisting of two rows of in total 13 shading pigment cells and another two rows of 13 photoreceptor cells. The pigment cells form a shallow cup with a relatively wide opening, making the cup-shaped eye optically unsuitable for picture generation. We demonstrate that the photosensitive cells possess numerous enlarged microvilli and an unmodified apical cilium. Our ultrastructural studies thus corroborate the photoreceptor cells in the eye of G. marginatus to be of a clearly rhabdomeric type. Preliminary immunohistochemical experiments support those findings by demonstrating immunopositive reaction of the tornarian eye photoreceptors with an antibody designed against rhabdomeric sea urchin photopigment (Sp-Opsin4). Observations of living animals indicate that Late Metschnikoff/early Krohn-stage tornaria larvae are negatively phototactic, probably concordant with imminent metamorphosis.