鸡胚原肠胚期原条细胞命运决定于其所处的局部微环境

在果蝇、斑马鱼、鸡等三胚层动物胚胎早期发育的原肠胚期,原条两侧的上胚层细胞进入原条经历上皮-间充质转化(EMT),迁移进入囊胚腔,形成松散的中胚层细胞,位于原条不同部位的细胞其迁移路线和分化命运不同,如前部原条细胞贡献于体节和心脏等,而后部原条细胞则迁移至胚外形成血岛。为了研究细胞的迁移途径及分化命运是否会随着细胞所处不同部位微环境的改变而改变,利用传统的移植技术,将宿主鸡胚原条前部的一部分细胞用GFP阳性的相同时期鸡胚原条组织替换,培养一段时间后,用荧光体视显微镜追踪GFP阳性细胞的迁移途径。结果发现,从供体原条后部移植到宿主原条前部的细胞遵循原条前部细胞迁移的路线,反之亦然;原位杂交结果显示移植后的GFP阳性细胞分化为所处部位的细胞类型。上述结果表明:鸡胚原肠胚期原条细胞迁移和分化的命运决定于细胞所处的微环境或者说局部基因表达的时空性。     

2011年第6期《遗传》封面说明

PTEN(Phosphatase and tensin homolog)是一种重要的抑癌基因,具有非常广泛的生物学活性,例如在细胞的生长发育、迁移、凋亡和信号传导等均发挥重要作用。本文主要是研究PTEN基因在早期胚胎原肠胚期后部原条细胞迁移的     

PTEN基因对早期胚胎神经嵴细胞迁移的作用研究

目的 初步探讨PTEN基因在早期神经嵴细胞迁移中的作用.方法 首先胚胎整体的原位杂交和免疫荧光方法检测鸡胚胎内源性的PTEN基因及蛋白水平的表达情况;其次,利用鸡胚胎体内半侧神经管转染的方法,使神经管一侧PTEN基因过表达,对侧神经管为正常对照侧;最后,通过Pax7的整体胚胎免疫荧光表达观察PTEN基因对其标记的部分神经嵴细胞迁移的影响.结果 内源性PTEN基因在mRNA和蛋白水平表达显示,其在早期胚胎HH4期的神经板即开始明显的表达;通过半侧过表达PTEN基因后观察到过表达PTEN基因侧的头部神经嵴细胞迁移与对照侧相比明显受到抑制,但对躯干部的影响并不明显.结论 PTEN基因可能抑制早期胚胎头部神经嵴细胞的迁移.     

斑马鱼原肠胚细胞运动

在斑马鱼原肠胚期, 细胞通过重排形成3个胚层：内胚层, 中胚层和外胚层。细胞重排的过程包含了3种极为保守的运动形式, 即外包运动、内卷运动和集中延伸运动。其中, 脊索前板祖细胞的前部延伸对于中内胚层祖细胞的定位以及最终分化形成胚层尤为重要。脊索前板祖细胞也是目前研究体内细胞运动机制的良好模型。原肠胚期细胞运动受诸多信号通路调控, 如Wnt/PCP信号通路, 但细胞行为的分子机制尚不明确。目前细胞粘附和细胞骨架重排是研究斑马鱼原肠胚期细胞运动的热点之一。此外, 胚胎外组织(卵黄合胞体层)对于原肠胚细胞运动的影响也受到了更多的关注。文章主要探讨了在斑马鱼原肠胚期细胞运动过程中控制细胞行为的关键因素以及一些尚未理清的问题, 并为将来在细胞水平上构建完整的原肠运动调控分子的图谱提供参考。     

TGF_β相关蛋白在爪蟾早期胚胎中的免疫组织化学的研究

在爪蟾早期胚胎中,存在能与抗TGF_β-1抗体结合的蛋白,我们称之为TGF_β-相关蛋白。用免疫细胞化学方法,检测到在囊胚(分期8)中,TGF_β相关蛋白主要分布在植物半球靠近囊胚腔底部的一些细胞内;在早期原肠胚(分期10.5)中仍只分布在植物半球卵黄团中,但距囊胚腔较远,与背唇无明显的关系;在晚期原肠胚(分期12)中,它主要分布在原肠腔四周,原肠腔腹方的内胚层细胞中含量高于原肠腔背方的中胚层细胞;在早期神经胚中(分期14),整个内胚层细胞都分布有TGF_β相关蛋白,而且它还存在于背部中胚层(预定体节和脊索)中,但分布不均匀,靠近原始肠腔的部分含有TGF_β相关蛋白,而靠近神经板的部分则不具有它;在晚期神经胚(分期20)中,它仅分布在卵黄团中央区域的内胚层细胞内。点免疫测定的结果印证了以上的观察。此外,还断定从卵裂期到分期27的胚胎,存在着两个TGF_β相关蛋白的高合成区域。第一个区间为分期7至分期8;第二个区间为分期12至分期14。在分期14胚胎中,它的含量最高。根据TGF_β相关蛋白在胚胎中分布的时空特性,讨论了它可能的功能。     

胚胎干细胞向内胚层分化的分子机制及其组学研究进展

胚胎干细胞(ESC)在发育过程中分化为内胚层、中胚层和外胚层3个胚层.其中内胚层进一步向终末细胞的分化,是形成整个消化道和呼吸道,以及肝脏、胰腺等器官的基础.ESC形成内胚层主要经历以下几个分化阶段:外胚叶的分化、原条的形成、内胚层与中胚层的分离以及定型内胚层的形成.本文主要从信号通路、转录因子以及表观遗传调控等几个方面综述胚胎干细胞向内胚层分化的分子机制,并重点介绍其组学研究进展,以期为该领域研究者提供重要参考信息.     

鸡胚早期发育过程中细胞迁移的基因调控

鸡胚是发育生物学研究的经典动物模型,通过基因导入技术调节胚胎发育的基因功能,研究鸡胚早期发育过程中的细胞迁移,有助于更好地诠释相关先天性疾病的发生发展过程。在早期胚胎发育的过程中,原肠胚期三胚层的形成、心管的发生及神经嵴的发育都伴随着显著的细胞迁移过程。该文将结合近年来国内外对该过程的研究进展,介绍这三个不同时期细胞的迁移及相关基因调控。     

Nodal信号的研究进展

早期胚胎发育过程中,组织者能够诱导胚胎组织形成完整的体轴。研究表明细胞之间的信息交流是脊椎动物胚胎诱导作用的基础。Nodal作为早期胚胎诱导信号的关键成分,参与了中胚层和内胚层的形成、前-后体轴的位置确定和左-右体轴特化等一系列关键事件,表明Nodal信号在脊椎动物早期发育过程中具有重要作用。     

小鼠早期胚胎发育期间TGF-β_1免疫组织化学定位

用兔抗人血小板TGF-β_1 N末端1—29氨基酸残基人工合成多肽抗血清作探针以及免疫荧光和免疫酶染色技术,分析了1—12天小鼠早期发育期间胚胎的TGF-β_1物质分布。结果表明,着床前胚胎包括卵裂细胞,桑椹胚和胚泡的ICM及滋养外胚层等细胞均显示TGF-β_1阳性免疫荧光染色。免疫酶染色还证明,沿囊胚腔顶部单层排列的原始内胚层细胞比邻近的ICM细胞有较深的染色反应。随着胚胎着床和进一步发育,7天龄胚胎中胚层早期形成阶段,紧靠中胚层一侧的外胚层胞质中含有浓集的棕色颗粒;各胚层的部分区域也存在着染色强度上差别。8—12天龄胚胎中,体节,心壁、间质细胞和肠道以及卵黄囊的脏壁中胚层均有显著的TGF-β_1免疫酶阳性物质。这些结果表明,着床前小鼠胚胎富含TGF-β_1物质,着床后的胚外组织,例如卵黄囊也为胚胎进一步发育提供了富含TGF-β_1物质的微环境;同时也提示,小鼠早期胚胎发育期间的胚泡形成,ICM细胞分化出原始内胚层,卵柱期中胚层形成,以及以后的神经管、体节和肢芽形成阶段等一系列形态发生和器官形成过程中,TGF-β_1可能是参与重要作用的一种生长调节因子。     

胚胎干细胞向中内胚层分化的调控机制

在哺乳动物胚胎发育过程中,中内胚层(mesendoderm)也被称为原条(primitive streak),是中胚层和内胚层分化的过渡时期。中内胚层的存在时间较短,但成功的中内胚层分化对随后进行的中胚层与内胚层发育至关重要。发育生物学的研究极大地推动了人们对胚胎发育的认识,同时,越来越多体外分化系统的建立也加深了对环境信号如何影响胚层分化的理解。近些年来,通过表观遗传的研究,人们逐渐认识到染色体结构与组蛋白修饰的改变也在分化发育过程中起到重要作用。通过胚胎干细胞定向诱导中内胚层分化来探究相关分子机制,不仅有助于对早期胚胎发育的了解,也有助于临床应用与疾病治疗。现总结了TGF-β信号、Wnt信号和FGF信号调控中内胚层分化的研究现状,并概述了这些信号如何与表观修饰共同调控胚胎干细胞向中内胚层分化的进展。     

Cessation of gastrulation is mediated by suppression of epithelial-mesenchymal transition at the ventral ectodermal ridge

In the gastrula stage embryo, the epiblast migrates toward the primitive streak and ingresses through the primitive groove. Subsequently, the ingressing epiblast cells undergo epithelial-mesenchymal transition (EMT) and differentiate into the definitive endoderm and mesoderm during gastrulation. However, the developmental mechanisms at the end of gastrulation have not yet been elucidated. Histological and genetic analyses of the ventral ectodermal ridge (VER), a derivative of the primitive streak, were performed using chick and mouse embryos. The analyses showed a continued cell movement resembling gastrulation associated with EMT during the early tailbud stage of both embryos. Such gastrulation-like cell movement was gradually attenuated by the absence of EMT during tail development. The kinetics of the expression pattern of noggin (Nog) and basal membrane degradation adjacent to the chick and the mouse VER indicated a correlation between the temporal and/or spatial expression of Nog and the presence of EMT in the VER. Furthermore, Nog overexpression suppressed EMT and arrested ingressive cell movement in the chick VER. Mice mutant in noggin displayed dysregulation of EMT with continued ingressive cell movement. These indicate that the inhibition of Bmp signaling by temporal and/or spatial Nog expression suppresses EMT and leads to the cessation of the ingressive cell movement from the VER at the end of gastrulation.     

FGF signalling through RAS/MAPK and PI3K pathways regulates cell movement and gene expression in the chicken primitive streak without affecting E-cadherin expression

Background  

FGF signalling regulates numerous aspects of early embryo development. During gastrulation in amniotes, epiblast cells undergo an epithelial to mesenchymal transition (EMT) in the primitive streak to form the mesoderm and endoderm. In mice lacking FGFR1, epiblast cells in the primitive streak fail to downregulate E-cadherin and undergo EMT, and cell migration is inhibited. This study investigated how FGF signalling regulates cell movement and gene expression in the primitive streak of chicken embryos.     

PtdIns(3,4,5)P(3)-dependent and -independent roles for PTEN in the control of cell migration

BACKGROUND: Phosphatase and tensin homolog (PTEN) mediates many of its effects on proliferation, growth, survival, and migration through its PtdIns(3,4,5)P(3) lipid phosphatase activity, suppressing phosphoinositide 3-kinase (PI3K)-dependent signaling pathways. PTEN also possesses a protein phosphatase activity, the role of which is less well characterized. RESULTS: We have investigated the role of PTEN in the control of cell migration of mesoderm cells ingressing through the primitive streak in the chick embryo. Overexpression of PTEN strongly inhibits the epithelial-to-mesenchymal transition (EMT) of mesoderm cells ingressing through the anterior and middle primitive streak, but it does not affect EMT of cells located in the posterior streak. The inhibitory activity on EMT is completely dependent on targeting PTEN through its C-terminal PDZ binding site, but can be achieved by a PTEN mutant (PTEN G129E) with only protein phosphatase activity. Expression either of PTEN lacking the PDZ binding site or of the PTEN C2 domain, or inhibition of PI3K through specific inhibitors, does not inhibit EMT, but results in a loss of both cell polarity and directional migration of mesoderm cells. The PTEN-related protein TPTE, which normally lacks any detectable lipid and protein phosphatase activity, can be reactivated through mutation, and only this reactivated mutant leads to nondirectional migration of these cells in vivo. CONCLUSIONS: PTEN modulates cell migration of mesoderm cells in the chick embryo through at least two distinct mechanisms: controlling EMT, which involves its protein phosphatase activity; and controlling the directional motility of mesoderm cells, through its lipid phosphatase activity.     

Analysis of extraembryonic mesodermal structure formation in the absence of morphological primitive streak

During mouse gastrulation, the primitive streak is formed on the posterior side of the embryo. Cells migrate out of the primitive streak to form the future mesoderm and endoderm. Fate mapping studies revealed a group of cell migrate through the proximal end of the primitive streak and give rise to the extraembryonic mesoderm tissues such as the yolk sac blood islands and allantois. However, it is not clear whether the formation of a morphological primitive streak is required for the development of these extraembryonic mesodermal tissues. Loss of the Cripto gene in mice dramatically reduces, but does not completely abolish, Nodal activity leading to the absence of a morphological primitive streak. However, embryonic erythrocytes are still formed and assembled into the blood islands. In addition, Cripto mutant embryos form allantoic buds. However, Drap1 mutant embryos have excessive Nodal activity in the epiblast cells before gastrulation and form an expanded primitive streak, but no yolk sac blood islands or allantoic bud formation. Lefty2 embryos also have elevated levels of Nodal activity in the primitive streak during gastrulation, and undergo normal blood island and allantois formation. We therefore speculate that low level of Nodal activity disrupts the formation of morphological primitive streak on the posterior side, but still allows the formation of primitive streak cells on the proximal side, which give rise to the extraembryonic mesodermal tissues formation. Excessive Nodal activity in the epiblast at pre‐gastrulation stage, but not in the primitive streak cells during gastrulation, disrupts extraembryonic mesoderm development.     

Hypoblast controls mesoderm generation and axial patterning in the gastrulating rabbit embryo

Gastrulation in higher vertebrate species classically commences with the generation of mesoderm cells in the primitive streak by epithelio-mesenchymal transformation of epiblast cells. However, the primitive streak also marks, with its longitudinal orientation in the posterior part of the conceptus, the anterior-posterior (or head-tail) axis of the embryo. Results obtained in chick and mouse suggest that signals secreted by the hypoblast (or visceral endoderm), the extraembryonic tissue covering the epiblast ventrally, antagonise the mesoderm induction cascade in the anterior part of the epiblast and thereby restrict streak development to the posterior pole (and possibly initiate head development anteriorly). In this paper we took advantage of the disc-shape morphology of the rabbit gastrula for defining the expression compartments of the signalling molecules Cerberus and Dickkopf at pre-gastrulation and early gastrulation stages in a mammal other than the mouse. The two molecules are expressed in novel expression compartments in a complementary fashion both in the hypoblast and in the emerging primitive streak. In loss-of-function experiments, carried out in a New-type culturing system, hypoblast was removed prior to culture at defined stages before and at the beginning of gastrulation. The epiblast shows a stage-dependent and topographically restricted susceptibility to express Brachyury, a T-box gene pivotal for mesoderm formation, and to transform into (histologically proven) mesoderm. These results confirm for the mammalian embryo that the anterior-posterior axis of the conceptus is formed first as a molecular prepattern in the hypoblast and then irrevocably fixed, under the control of signals secreted from the hypoblast, by epithelio-mesenchymal transformation (primitive streak formation) in the epiblast.Edited by D. Tautz     

Fate maps of the primitive streak in chick and quail embryo: ingression timing of progenitor cells of each rostro-caudal axial level of somites

Developmental fates of cells emigrating from the primitive streak were traced by a fluorescent dye Dil both in chick and in quail embryos from the fully grown streak stage to 12-somite stage, focusing on the development of mesoderm and especially on the timing of ingression of each level of somitic mesoderm. The fate maps of the chick and quail streak were alike, although the chick streak was longer at all stages examined. The anterior part of the primitive streak predominantly produced somites. The thoracic and the lumbar somites were shown to begin to ingress at the 5 somite-stage and 10 somite-stage in a chick embryo, and 6 somite-stage and 9 somite-stage in a quail embryo, respectively. The posterior part of the streak served mainly as the origin of more lateral or extra embryonic mesoderm. As development proceeded, the fate of the posterior part of the streak changed from the lateral plate mesoderm to the tail bud mesoderm and then to extra embryonic, allantois mesoderm. The fate map of the primitive streak in chick and quail embryo presented here will serve as basic data for studies on mesoderm development with embryo manipulation, especially for transplantation experiments between chick and quail embryos.     

BMP signaling in the epiblast is required for proper recruitment of the prospective paraxial mesoderm and development of the somites

Bmpr1a encodes the BMP type IA receptor for bone morphogenetic proteins (BMPs), including 2 and 4. Here, we use mosaic inactivation of Bmpr1a in the epiblast of the mouse embryo (Bmpr-MORE embryos) to assess functions of this gene in mesoderm development. Unlike Bmpr1a-null embryos, which fail to gastrulate, Bmpr-MORE embryos initiate gastrulation, but the recruitment of prospective paraxial mesoderm cells to the primitive streak is delayed. This delay causes a more proximal distribution of cells with paraxial mesoderm character within the primitive streak, resulting in a lateral expansion of somitic mesoderm to form multiple columns. Inhibition of FGF signaling restores the normal timing of recruitment of prospective paraxial mesoderm and partially rescues the development of somites. This suggests that BMP and FGF signaling function antagonistically during paraxial mesoderm development.