Page L, Benson S
Department of Biological Sciences, California State University, Hayward 94542.
Exp Cell Res. 1992 Dec;203(2):305-11. doi: 10.1016/0014-4827(92)90003-q.
Sea urchin embryo micromeres form the primary mesenchyme, the skeleton-producing cells of the embryo. Almost nothing is known about nature and timing of the embryonic cues which induce or initiate spicule formation by these cells. A related question concerns the competence of the micromeres to respond to the cues. To examine competence in this system we have exposed cultured sea urchin micromeres to an inducing medium containing horse serum for various periods of time and have identified a period when micromeres are competent to respond to serum and form spicules. This window, between 30 and 50 h after fertilization, corresponds to the time when mesenchyme cells in vivo are aggregating and beginning to form the syncytium in which the spicule will be deposited. The loss of competence after 50 h is not due to impaired cell health since protein synthesis at this time is not significantly different from controls. Likewise the accumulation of a spicule matrix mRNA (SM 50) and a cell surface glycoprotein (msp 130), both indices of micromere/mesenchyme differentiation, still occurs in cells that have lost competence to respond to serum by forming spicules. These experiments demonstrate that the acquisition and loss of competence in these cells are regulated developmental events and establish an in vitro system for the identification of the molecular basis for inductive signal recognition and signal transduction.
海胆胚胎的小分裂球形成初级间充质，即胚胎中产生骨骼的细胞。对于诱导或启动这些细胞形成骨针的胚胎信号的性质和时间，人们几乎一无所知。一个相关的问题是小分裂球对这些信号作出反应的能力。为了研究这个系统中的反应能力，我们将培养的海胆小分裂球暴露于含有马血清的诱导培养基中不同时间，并确定了一个小分裂球有能力对血清作出反应并形成骨针的时期。这个窗口期在受精后30至50小时之间，与体内间充质细胞聚集并开始形成骨针将沉积其中的合胞体的时间相对应。50小时后反应能力的丧失并非由于细胞健康受损，因为此时的蛋白质合成与对照组并无显著差异。同样，骨针基质mRNA（SM 50）和细胞表面糖蛋白（msp 130）的积累，这两者都是小分裂球/间充质分化的指标，在已经失去通过形成骨针对血清作出反应能力的细胞中仍然会发生。这些实验表明，这些细胞中反应能力的获得和丧失是受发育调控的事件，并建立了一个体外系统来确定诱导信号识别和信号转导的分子基础。
