EFFECT OF GROWTHFACTOR (S) ON CEREBRAL HISTOGENESIS : ANALYSIS ON TISSUE CULTRED EXPLANT

研究了胚胎第13天小鼠新皮层神经发生过程中细胞周期调控的变化。将脑壁后内侧区域的外植体植入胶原凝胶中，在微量培养基中孵育1小时，然后在含BUdR的微量培养基中孵育1小时。BUdR作用30mm（体外1.5小时）后，标记指数（LI，标记/总细胞数）为0.41，而先前测定的体内LI为0.38。在接下来持续暴露于BUdR的7小时内，体外LI保持在0.4，然后线性上升至渐近线0.73。这些观察结果证实(1)细胞在体外培养的最初1.5小时内有从G1到S的通量，(2)这种G1到S的通量在随后的7小时内中断，但(3)随后G1到S的通量重新建立。在同样的系统中，只有在暴露于BUdR 5小时后才标记有丝分裂图，然后在2个多小时后所有的有丝分裂都被标记。相比之下，在体内，所有的有丝分裂在暴露于BUdR 2小时后都变得…由此可见，在从S相到M相的过程中有一个短暂的停顿，这个停顿显然在外植后5小时内被克服。重建的细胞周期和G1、Sand合并G2-M期的持续时间估计分别为19.2、6.3 -8.3、8.8和2.0 -4.0小时。周期（0,64）的离开(Q)分数是体内值的两倍。三分之二的Q部分细胞留在心室上皮中，与体内的1.0相比，其生长分数低得多，为0.73。在体外脑壁外植体中还检测了碱性成纤维细胞生长因子（b-FGF）和间隙连接解偶联剂1-辛醇的影响。在皮质内侧区和外侧区测定LI，分别对应1区和40区。区域40中，b- fgf外植体的总体LI高于对照外植体，1-辛醇外植体的LI低于对照外植体。这些观察结果表明，b-FGF降低了Q分数，而1-辛醇增加了Q分数。少

Analysis of cell cycle regulation in neocortical neuronogenesis has been undertaken in vitro in the embryonic day 13 mouse. Explants of the dorsomedial region of the cerebral wall, implanted in collagen gel, were incubated for 1 hr in minimal medium and then in minimal medium containing BUdR.After 30 mm with BUdR (1.5 hr in vitro), the labeling index (LI, labeled/total cells) was 0.41 as compared to the previously determined LI of 0.38 in vivo. The in vitro LI remained at 0.4 over the next 7 hr of continued exposure to BUdR and then ascended linearly to asymptote at 0.73. These observations establish (1) that there is a flux of cells from G1 to S for the first 1.5 hr in vitro, (2) that this G1 to S flux is then interrupted for the following 7 hr but (3) that G1 to S flux is subsequently reestablished. In this same system, mitotic figures were first labeled only after a 5 hr exposure to BUdR but then over 2 more hours all mitoses became labeled. In vivo, by contrast, all mitoses become … More labeled during 2 hr of BUdR exposure. By implication there is a transient arrest in the progression from S to M phase which is evidently overcome within 5 hr of explantation. The duration of the reestablished cell cycle and those of G1, Sand combined G2-M phases were estimated to be 19.2, 6.3 -8.3, 8.8, and 2.0 -4.0 hr, respectively. The leaving (Q) fraction of the cycle (0,64) was twice the in vivo value. Two thirds of the Q fraction cells remained in the ventricular epithelium, resulting in a substantially low growth fraction of 0.73 as compared with 1.0 in vivo.Also examined in a cerebral wall explant in vitro was the consequences of basic fibroblast growth factor (b-FGF) and the gap junction uncoupling agent, 1-octanol. LI was determined in the sector of the medial and lateral cortical zones, corresponding to areas 1 and 40, respectively. In area 40, the overall LI in b-FGF-exposed explants was higher and that in 1-octanol-exposed explants was lower than the LI in control explants. Those observations suggest that b-FGF reduces Q fraction while 1-octanol increases the fraction. Less