Behavioural response of different epithelial tissues of sea cucumber (Apostichopus japonicus) to light and differential expression of the light-related gene Pax6

ABSTRACT In this study, we evaluated the behavioural characteristics of the epithelial tissues of sea cucumber (Apostichopus japonicus) subjected to illumination. The behavioural results indicated that the tentacles, tube feet, and spines were sensitive to light with structural changes. Among the three epithelial tissues, the tentacles were the most sensitive with the shortest reaction and recovery times, whereas the tube feet and spines had longer reaction times. Quantitative real-time PCR (q-PCR) was used to analyse the changes of Pax6 expressions before and after illumination in the tentacles, tube feet and spines. Q-PCR results indicated that Pax6 expressions in the three above tissues after illumination were higher than that before illumination. We hypothesised that sea cucumber may not have independent photoreceptors, but the epithelial tissues were capable of exhibiting a behavioural response to light. This will allow us to re-examine the functions of all epithelial tissues of sea cucumbers.