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

对胚胎第13天小鼠新皮质神经元发生的细胞周期调控进行了体外分析。将植入胶原凝胶的脑壁背内侧区外植体在微量培养液中孵育1小时，然后在含有BUDR的微量培养液中孵育1小时，30 mm后(体外1.5小时)，标记指数(LI，标记细胞/总细胞)为0.41，而先前在体内测定的LI为0.38。在接下来的7小时内，在持续暴露于BUDR的情况下，体外LI保持在0.4，然后线性上升，达到0.73。这些观察结果证实：(1)在体外培养的前1.5小时内，存在细胞从G1到S的通量；(2)在接下来的7小时内，G1到S的通量被中断；(3)G1到S的通量随后被重新建立。在这个相同的系统中，有丝分裂图形只在暴露于BUDR 5小时后才被标记，但随后超过2小时，所有有丝分裂都被标记。相比之下，在活体中，所有有丝分裂都变成了…在BUDR暴露2小时内标记的更多。这暗示着从S到M期的过程有一个短暂的停滞，这个停滞在外植体生长的5小时内就被克服了。重建的细胞周期为19.2小时，G1期为6.3-8.3小时，S期为8.8小时，G2-M期为2.0-4.0小时。周期(0，64)的离开(Q)分数是体内数值的两倍。三分之二的Q组分细胞仍然留在心室上皮细胞中，导致生长分数为0.73，而活体细胞的生长分数为1.0。在体外脑壁移植块中也检测了碱性成纤维细胞生长因子(b-FGF)和缝隙连接解偶联剂1-辛醇的结果。LI定位于皮质内侧带和外侧带的区段，分别对应于1区和40区。在40区，暴露于b-成纤维细胞生长因子的外植体的总LI高于对照外植体，而暴露于正辛醇的外植体的总LI低于对照组。这些观察表明，b-成纤维细胞生长因子减少了Q组分，而1-辛醇增加了这一组分。较少

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