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The role of the hyaline spheres in sea cucumber metamorphosis: lipid storage via transport cells in the blastocoel.
EvoDevo ( IF 4.1 ) Pub Date : 2019-04-11 , DOI: 10.1186/s13227-019-0119-4
Josefina Peters-Didier 1 , Mary A Sewell 1
Affiliation  

Background For echinoderms with feeding larvae, metamorphic and post-settlement success may be highly dependent on larval nutrition and the accumulation of energetic lipids from the diet. In contrast to the sea urchins, starfish and brittle stars within the Phylum Echinodermata, sea cucumber metamorphosis does not involve formation of a juvenile rudiment, but instead there is a rearrangement of the entire larval body. Successful metamorphosis in sea cucumbers is often associated with the presence in the late auricularia stage of an evolutionary novelty, the hyaline spheres (HS), which form in the base of the larval arms. Known since the 1850s the function of these HS has remained enigmatic-suggestions include assistance with flotation, as an organizer for ciliary band formation during metamorphosis and as a nutrient store for metamorphosis. Results Here using multiple methodologies (lipid mapping, resin-section light microscopy, lipid and fatty acid analyses) we show definitively that the HS are used to store neutral lipids that fuel the process of metamorphosis in Australostichopus mollis. Neutral lipids derived from the phytoplankton diet are transported by secondary mesenchyme cells ("lipid transporting cells", LTC), likely as free fatty acids or lipoproteins, from the walls of the stomach and intestine through the blastocoel to the HS; here, they are converted to triacylglycerol with a higher saturated fatty acid content. During metamorphosis the HS decreased in size as the triacylglycerol was consumed and LTC again transported neutral lipids within the blastocoel. Conclusion The HS in A. mollis functions as a nutrient storage structure that separates lipid stores from the major morphogenic events that occur during the metamorphic transition from auricularia-doliolaria-pentactula (settled juvenile). The discovery of LTC within the blastocoel of sea cucumbers has implications for other invertebrate larvae with a gel-filled blastocoel and for our understanding of lipid use during metamorphosis in marine invertebrates.

中文翻译:

透明球在海参变态中的作用:通过囊胚腔中的运输细胞储存脂质。

背景对于以幼虫为食的棘皮动物,变质和定居后的成功可能高度依赖于幼虫的营养和饮食中高能脂质的积累。与棘皮动物门中的海胆、海星和海蛇尾相比,海参变态不涉及幼体雏形的形成,而是整个幼体的重新排列。海参的成功变态通常与在黑木耳晚期阶段的进化新奇的存在有关,透明球体(HS)形成于幼虫臂的基部。自 1850 年代以来,这些 HS 的功能一直很神秘——建议包括协助漂浮、作为变态过程中睫状带形成的组织者以及作为变态的营养储存。结果 在此使用多种方法(脂质映射、树脂切片光学显微镜、脂质和脂肪酸分析),我们明确表明 HS 用于储存中性脂质,这些脂质促进了南方刺参的变态过程。来自浮游植物饮食的中性脂质由次级间充质细胞(“脂质转运细胞”,LTC)运输,可能是游离脂肪酸或脂蛋白,从胃和肠壁通过囊胚腔到 HS;在这里,它们被转化为饱和脂肪酸含量更高的三酰基甘油。在变态过程中,随着三酰基甘油的消耗,HS 的大小减小,LTC 再次在囊胚腔内转运中性脂质。结论 A 中的 HS。mollis 作为一种营养储存结构,将脂质储存与在从 auricularia-doliolaria-pentactula (定居幼体)变质过渡期间发生的主要形态发生事件分开。海参囊胚腔内 LTC 的发现对其他具有凝胶填充囊胚腔的无脊椎动物幼虫以及我们对海洋无脊椎动物变态过程中脂质使用的理解具有重要意义。
更新日期:2020-04-22
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