Yazaki Ikuko, Abe Michio, Santella Luigia, Koyama Yumiko
Department of Biology, Tokyo Metropolitan University, Minamiohsawa 1-1, Hachiohji, Tokyo 192-0397, Japan.
Biol Cell. 2004 Mar;96(2):153-67. doi: 10.1016/j.biolcel.2003.11.009.
The micromeres, the first cells to be specified in sea urchin embryos, are generated by unequal cleavage at the fourth cell division. The micromeres differentiate autonomously to form spicules and dispatch signals to induce endomesoderm in the neighbouring macromeres cells in the embryo. Using a calcium indicator Fura-2/AM and a mixture of dextran conjugated Oregon green-BAPTA 488 and Rhodamine red, the intracellular calcium ion concentration ([Ca2+]i) was studied in embryos at the 16-cell stage. [Ca2+]i was characteristically elevated in the micromeres during furrowing at the 4th cleavage. Subsequently, Ca2+ oscillated for about 10 min in the micromeres, resulting in episodic high levels of [Ca2+]i. High [Ca2+]i regions were associated with regional localizations of the endoplasmic reticulum (ER), though not with ER accumulated at the vegetal pole of the micromeres during the 4th division. Pharmacological studies, using a blocker of IP3-mediated Ca2+ release (Xestospongin), a store-operated Ca2+ entry inhibitor (2 aminoethoxydiphenyl borate (2-APB)) and an inhibitor of stretch-dependent ion channels (gadolinium), suggest that the high [Ca2+]i and oscillations in the micromeres are triggered by calcium influx caused by the activation of stretch-dependent calcium channels, followed by the release of calcium ions from the endoplasmic reticulum. On the basis of these new findings, a possible mechanism for autonomous formation of the micromeres is discussed.
小分裂球是海胆胚胎中最早被指定的细胞，由第四次细胞分裂时的不均等分裂产生。小分裂球自主分化形成骨针，并发出信号诱导胚胎中相邻大分裂球细胞形成内胚层。使用钙指示剂Fura-2/AM以及葡聚糖偶联的俄勒冈绿- BAPTA 488和罗丹明红的混合物，研究了16细胞期胚胎中的细胞内钙离子浓度（[Ca2+]i）。在第四次分裂的沟裂过程中，小分裂球中的[Ca2+]i显著升高。随后，Ca2+在小分裂球中振荡约10分钟，导致[Ca2+]i出现间歇性高水平。高[Ca2+]i区域与内质网（ER）的区域定位相关，尽管在第四次分裂期间，ER并非聚集在小分裂球的植物极。药理学研究使用IP3介导的Ca2+释放阻滞剂（西司他汀）、储存操纵性Ca2+内流抑制剂（2-氨基乙氧基二苯硼酸（2-APB））和拉伸依赖性离子通道抑制剂（钆），表明小分裂球中高[Ca2+]i和振荡是由拉伸依赖性钙通道激活引起的钙内流触发的，随后内质网释放钙离子。基于这些新发现，讨论了小分裂球自主形成的可能机制。
