被子植物的早期胚胎形态建成

被子植物早期胚胎形态建成是其有性生殖过程中一个重要发育阶段。在这一阶段中,被子植物形体基本特征形成,包括顶-基轴极性建立、不同细胞层分化以及分生组织形成。合子极性直接与顶基细胞命运相关,但其极性产生机理仍然不明。研究表明,WOX家族转录因子、生长素定向运输以及生长素响应应答可能参与了早期顶-基模型建成;辐射对称模型的建立可能由细胞与细胞间相互作用来介导;生长素流可能参与胚胎顶端组织形成。该文对近年来被子植物早期胚胎形态建成过程中的合子极性建立与生长、合子分裂及其顶基细胞的形成、胚根原特化及根极的形成、辐射对称模式及表皮原特化、顶端分生组织特化及子叶起始等方面的研究进展进行了综述。     

From stem cell to embryo without centrioles

Centrosome asymmetry plays a key role in ensuring the asymmetric division of Drosophila neural stem cells (neuroblasts [NBs]) and male germline stem cells (GSCs) [1-3]. In both cases, one centrosome is anchored close to a specific cortical region during interphase, thus defining the orientation of the spindle during the ensuing mitosis. To test whether asymmetric centrosome behavior is a general feature of stem cells, we have studied female GSCs, which divide asymmetrically, producing another GSC and a cystoblast. The cystoblast then divides and matures into an oocyte, a process in which centrosomes exhibit a series of complex behaviors proposed to play a crucial role in oogenesis [4-6]. We show that the interphase centrosome does not define spindle orientation in female GSCs and that DSas-4 mutant GSCs [7], lacking centrioles and centrosomes, invariably divide asymmetrically to produce cystoblasts that proceed normally through oogenesis-remarkably, oocyte specification, microtubule organization, and mRNA localization are all unperturbed. Mature oocytes can be fertilized, but embryos that cannot support centriole replication arrest very early in development. Thus, centrosomes are dispensable for oogenesis but essential for early embryogenesis. These results reveal that asymmetric centrosome behavior is not an essential feature of stem cell divisions.     

多细胞生物干细胞不对称分裂的内在调节机制研究进展

多细胞生物的发育是从一个受精卵分化成多种类型细胞的过程。细胞多样性形成的基础是不等分裂,不等分裂是干细胞自我更新和自我维持的关键。干细胞不等分裂有细胞内和细胞外两种调节机制。果蝇神经干细胞增殖和分化、植物胚胎发育、表皮气孔形成及根内皮层的分化,是研究不等细胞分裂调节机制最多的发育背景。本综述介绍了果蝇神经干细胞和植物胚胎发育早期、表皮气孔发生及根皮层内皮层中细胞不等分裂内在调节机制的研究进展。     

Genetic control of early events in protoplast division and regeneration pathways in sunflower

Experiments were conducted to identify the genetic factors controlling protoplast division and to determine eventual relations between genetic factors involving organogenesis, somatic embryogenesis and protoplast division in sunflower. The present study involved protoplast culture and two traits: total division per 100 protoplasts (TOTD) and asymmetric division per 100 protoplasts (ASYD) were scored in 52 recombinant inbred lines (RILs) from a cross between PAC-2 and RHA-266. Asymmetric division is an early event in the formation of embryoids from protoplasts. Analysis of variance indicated the existence of highly significant differences among parental genotypes and their RILs. Heritability for the two protoplast division parameters (TOTD and ASYD) was high (0.87 and 0.89, respectively) and genetic gain expressed as percentage of the best parent for 10% of the selected RILs was significant. Twelve putative loci associated with total division per 100 protoplasts were identified. Eleven QTLs were also detected for asymmetric division per 100 protoplasts. The QTLs present high significant LOD scores and sum to a high percentage of phenotypic variance. The percentage of phenotypic variation explained by each QTL ranged from 2% to 24%. Some segments of the linkage groups I, XV and XVII are likely to contain genes important for organogenesis, somatic embryogenesis and protoplast division, as clustering of QTLs for these characters were described. The QTLs identified in these three linkage groups should be involved in cell division and in early events associated with cell differenciation. Received: 15 December 1999 / Accepted: 30 December 1999     

EARLY DEVELOPMENT OF THE BARLEY EMBRYO: FINE STRUCTURE

The ultrastructure of early stages in embryogenesis in barley was examined. Post-fertilization shrinkage does not occur. Plasmodesmata were not observed in cell walls of the zygote and outer cell walls of embryos. There is little evidence of cellular specialization in earliest embryonic stages, and planes of cell division tend to be irregular although a pattern of cell disposition characteristic of some grass embryos can be discerned. The embryo appears polarized after 2–3 division cycles, but no evolving of dorsiventrality occurs during this period. A basal supensor cell “anchors” the embryo during early embryogenesis, but by about five division cycles the embryo loses its attachment to the nucellus and is completely surrounded by endosperm. An increase in number of ribosomes and mitochondria takes place during early embryogenesis, and mitochondrial dimensions are reduced. A shift in vacuole distribution occurs.     

小鼠着床前胚胎发育中调控因子的时序表达及功能

哺乳动物着床前胚胎发育最基本的问题之一是高度分化的卵母细胞如何过渡到全能性的卵裂球。这一转换过程受到了多种调控因子正或负的调控作用,这些特定调控因子在着床前胚胎发育过程中呈现出较为显著的时空表达特征,它们对早期胚胎的进一步正常发育有重要的作用。研究这些调控因子在着床前胚胎发育中的表达模式和调控机制,将有助于我们对早期胚胎发育机制的进一步了解。作者主要对近些年来有关生长因子与细胞因子（如：PAF、IL－1、IGF、MIF）以及特定转录因子（如：SP1、TBP、mTEF、eIF、myc、c-jun等）在小鼠着床前胚胎发育中的时空表达及其相应功能的研究做一简要介绍。     

被子植物胚胎发育的分子调控

被子植物的胚胎发育受到精确的遗传调控。从双受精开始到种子成熟,胚胎发育经历了合子激活、细胞分裂与分化、极性建立、模式形成、器官发生和储藏物质累积等重要过程。过去20年来的分子遗传学研究鉴定了很多调控胚胎发生的基因．为了解胚胎形成的分子机理提供了大量信息。本文对这一领域的主要研究进展进行了简要评述,重点阐述了植物的早期胚胎发生过程,对尚未解决的科学问题及未来发展方向进行了综合分析。