The detection of light intensity and subsequent phototaxis are essential for the fitness of sea urchins in intertidal and shallow subtidal waters, where light intensity varies in accordance with the depth and other hydrographic conditions. The molecular basis of photoresponse, however, remains largely unknown. We compared the expression of SiOpsin4, SiPax6, and SiOpsin5 among tube feet, coelomocytes, gonads, and gut of the sea urchin Strongylocentrotus intermedius. All three genes showed the significantly highest expression in tube feet. To test whether r‐opsin genes (for example, Opsin4) and Pax6 in tube feet, rather than chaopsin genes (for example, Opsin5), are involved in the molecular responses to light intensity, we investigated the expression of Opsin4, Pax6, and Opsin5 among four light intensities. Both Opsin4 and Pax6 expressions were significantly higher in the sea urchins at 1,500 lx than at 100, 300, and 700 lx, indicating a co‐upregulation of Opsin4 and Pax6 expressions in sea urchins exposed to the high light intensity (for example, 1,500 lx). However, there was no significant difference of SiOpsin5 expression among the four light intensity groups. Consistent with our hypothesis, there was no significant difference in either Opsin4 or Pax6 expression between the two light intensity environments (low light intensity environment: 50–100 lx; high light intensity environment: 330–1400 lx). This indicates that positive phototaxis and negative phototaxis probably regulate the expression of Opsin4 and Pax6 to a similar level when sea urchins are exposed to the high and low light intensities, respectively. The present study provides new insights into the molecular basis of light intensity detection and subsequent phototaxis of eyeless species.

中文翻译：

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光照强度对中间型海胆Strongylocentrotus intermedius的Opsin4，Opsin5和Pax6表达的影响

光强度的检测和随后的趋光性对于潮间带和浅潮带下海水中海胆的适应性至关重要，在这些潮汐和浅潮下水中，光强会根据深度和其他水文条件而变化。然而，光响应的分子基础仍然是未知的。我们比较了海胆Strongylocentrotus intermedius的管脚，粒细胞，性腺和肠道中SiOpsin4，SiPax6和SiOpsin5的表达。这三个基因在管脚中均显示出最高的表达。测试管脚中是否存在r-opsin基因（例如Opsin4）和Pax6，而不是chaopsin基因（例如Opsin5）），参与了对光强度的分子响应，我们研究了Opsin4，Pax6和Opsin5在四种光强度中的表达。既Opsin4和Pax6的表达均在海胆在1500 LX比在100显著更高，300，和700 LX，指示的共同上调Opsin4和Pax6的在暴露于高光强度海胆表达式（例如，1500 LX ）。但是，在四个光强度组之间，SiOpsin5表达没有显着差异。与我们的假设一致，Opsin4或两种光强度环境之间的Pax6表达（低光强度环境：50–100 lx；高光强度环境：330–1400 lx）。这表明当海胆分别暴露于高光和低光强度下时，正趋光性和负趋光性可能会将Opsin4和Pax6的表达调节到相似的水平。本研究为光强检测的分子基础和无眼物种的后续趋光性提供了新的见解。