Early heart development in the chick embryo: effects of isotretinoin on cell proliferation, α-actin synthesis, and development of contractions

Isotretinoin is a potent retinoic acid used in the treatment of skin disorders. Though very effective, it is teratogenic if administered during pregnancy, and its teratogenic effect may be related to the normal activity of retinoids as signalling molecules in the embryo. Although its exact mechanism of action is unknown, it has been suggested that it causes its characteristic pattern of defects that includes heart defects, by inhibiting the migration of neural crest cells. However, other effects on cells are known. We studied early cardiac cell proliferation using incorporation of bromodeoxyuridine (BrdU) and detection with a monoclonal anti-BrdU. Proliferation in heart tissue of whole embryo cultures was inhibited in medium with 10(-6) M isotretinoin to 62% of the control level in myocardium. We studied its effects in culture on precardiac explant development in the absence of the neural crests. Culture of precardiac mesodermal-endodermal explants revealed that development of heart vesicles from the mesoderm was little affected, but the development of heartbeat was inhibited depending on dose in the 10(-5) to 10(-7) M range. The effect on development of contractions was augmented in the presence of serum; it could be duplicated by all-trans-retinoic acid, and it was reversible. Synthesis of the alpha-actin isotype, analyzed by isoelectric focusing, was found to be inhibited or delayed. The results suggest multiple effects of retinoids on growth, morphogenesis, and differentiation of early cardiac tissue, and are discussed in relation to the potential role of retinoids in early embryogenesis.     

Wnt signal transduction and the formation of the myocardium

Soon after fertilization, vertebrate embryos grow very rapidly. Thus, early in gestation, a sizeable yet underdeveloped organism requires circulating blood. This need dictates the early appearance of a contractile heart, which is the first functional organ in both the avian and mammalian embryo. The heart arises from paired mesodermal regions within the anterior half of the embryo. As development proceeds, these bilateral precardiac fields merge at the midline to give rise to the primary heart tube. How specific areas of nondifferentiated mesoderm organize into myocardial tissue has been a question that has long intrigued developmental biologists. In recent years, the regulation of Wnt signal transduction has been implicated as an important event that initiates cardiac development. While initial reports in Drosophila and the bird had implicated Wnt proteins as promoters of cardiac tissue formation, subsequent findings that the WNT inhibitors Dkk1 and crescent possess cardiac-inducing activities led to the contrary hypothesis that WNTs actively inhibit cardiogenesis. This seeming contradiction has been resolved, in part, by more recent information indicating that Wnts stimulate multiple signal transduction pathways. In this review, we will examine what is presently known about the importance of regulated Wnt activity for the formation of the heart and the development of the myocardium and discuss this information in context of the emerging complexity of Wnt signal transduction.     

Analysis of chlorophyll fluorescence reveals stage specific patterns of chloroplast-containing cells during Arabidopsis embryogenesis

The basic body plan of a plant is established early in embryogenesis when cells differentiate, giving rise to the apical and basal regions of the embryo. Using chlorophyll fluorescence as a marker for chloroplasts, we have detected specific patterns of chloroplast-containing cells at specific stages of embryogenesis. Non-randomly distributed chloroplast-containing cells are seen as early as the globular stage of embryogenesis in Arabidopsis. In the heart stage of embryogenesis, chloroplast containing cells are detected in epidermal cells as well as a central region of the heart stage embryo, forming a triangular septum of chloroplast-containing cells that divides the embryo into three equal sectors. Torpedo stage embryos have chloroplast-containing epidermal cells and a central band of chloroplast-containing cells in the cortex layer, just below the shoot apical meristem. In the walking-stick stage of embryogenesis, chloroplasts are present in the epidermal, cortex and endodermal cells. The chloroplasts appear reduced or absent from the provascular and columella cells of walking-stick stage embryos. These results suggest that there is a tight regulation of plastid differentiation during embryogenesis that generates specific patterns of chloroplast-containing cells in specific cell layers at specific stages of embryogenesis.     

Epithelial-mesenchymal cell transformation in the embryonic heart can be mediated, in part, by transforming growth factor beta

Progenitor cells of the valves and membranous septa of the vertebrate heart are formed by transformation of a specific population of endothelial cells into mesenchyme. Previous studies have shown that this epithelial-mesenchymal cell transformation is mediated by a signal produced by the myocardium of the atrioventricular (AV) canal and transferred across the extracellular matrix. Data are presented here that transforming growth factor beta (TGF beta 1 or TGF beta 2), in combination with an explant of ventricular myocardium, will produce an epithelial-mesenchymal transformation by cultured AV canal endothelial cells in vitro. Alone, neither component is capable of producing this effect. The factor provided by the ventricular explant cannot be substituted by either epidermal growth factor or basic fibroblast growth factor. Further experiments show that an antibody that blocks TGF beta activity is effective in preventing the epithelial-mesenchymal cell transformation normally produced by AV canal myocardium. Control antibodies are without effect. By immunological criteria, a member of the TGF beta family of molecules can be demonstrated in the chicken embryo and heart at the time overt valvular formation begins. Together, these data show that TGF beta 1 can produce mesenchymal cell formation in vitro and provide evidence that a member of the TGF beta family is present and plays a role in the process of epithelial-mesenchymal cell transformation in the embryonic heart.     

Plastidic protein Cdf1 is essential in Arabidopsis embryogenesis

Arabidopsis cell growth defect factor-1 (Cdf1 in yeast, At5g23040) was originally isolated as a cell growth suppressor of yeast from genetic screening. To investigate the in vivo role of Cdf1 in plants, a T-DNA insertion line was analyzed. A homozygous T-DNA insertion mutant (cdf1/cdf1) was embryo lethal and showed arrested embryogenesis at the globular stage. The Cdf1 protein, when fused with green fluorescent protein, was localized to the plastid in stomatal guard cells and mesophyll cells. A promoter-β-glucuronidase assay found expression of Cdf1 in the early heart stage of embryogenesis, suggesting that Cdf1 was essential for Arabidopsis embryogenesis during the transition of the embryo from the globular to heart stage.     

Involvement of gibberellin and cytokinin in the formation of embryogenic cell clumps in carrot (Daucus carota)

Somatic embryogenesis of carrots is a typical example of the totipotency of plant cells. However, little is known about the process of change from somatic cells to embryogenic cells. To test the involvement of plant hormones in the acquisition process of embryogenic potency, we investigated the effects of plant growth regulators and their inhibitors on auxin-induced direct somatic embryogenesis of carrots. Gibberellin (GA) inhibited the early stage of embryogenic cell differentiation/development to the globular stage and uniconazole, an inhibitor of GA synthesis, promoted the secondary embryogenesis from the primary embryo. Purine riboside, an anticytokinin, inhibited direct somatic embryogenesis, and this effect was nullified by the application of cytokinin (CK). These results show that GA and CK regulate the early stage of auxin-induced somatic embryogenesis in carrots.     

Mechanisms regulating the origins of the vertebrate vascular system

In order to sustain growth, differentiation, and organogenesis, vertebrate embryos must form a functional vascular system early in embryonic development. Intrinsic interest in this process as well as the promise of potential clinical applications has led to significant progress in understanding the mechanisms governing the formation of the vascular system, however the earliest stages of vascular development--the emergence of committed endothelial precursors from the mesoderm--remain unclear. A review of the current literature reveals an unexpected diversity and heterogeneity with respect to where vascular endothelial cells originate in the embryo, when they become committed and the mechanisms governing how endothelial cells acquire their identity. Spatially, a widespread region of the early mesoderm possesses the ability to give rise to vascular endothelial cells; temporally the process is not limited to a small window during embryogenesis, but rather, may continue throughout the lifespan of the organism. On the molecular level, recent findings point to several determinative pathways that regulate, modulate, and extend the scope of the Flk1/VEGF signaling system. An expanding array of novel gene products implicated in endothelial cell type determination appear to act synergistically, with different combinations of factors leading to diverse cellular responses, varying patterns of differentiation, and considerable heterogeneity of endothelial cell types during embryogenesis.     

Localization of bFGF-like proteins as punctate inclusions in the preseptation myocardium of the chicken embryo.

Immunocytochemistry has been employed to map the appearance of bFGF-like proteins in precardiac and preseptation myocardial cells between stages 6 and 15 of chicken embryogenesis. Stage 6 embryos exhibited no staining, with the exception of a subtle signal in endoderm cells. At subsequent stages, staining was observed only in cells of the developing myocardium, first appearing at the time of heart tube fusion (stage 9+) as punctate cytoplasmic aggregates. While the expression of bFGF-like antigen was temporally similar to that of myosin heavy chain, their staining patterns differed in that bFGF-like proteins were nonsarcomeric and did not extend into the inflow or outflow tracts. Western blotting of heparin agarose affinity-isolated proteins from stage 15 hearts revealed an antigen migrating at approximately 19 kDa. In contrast with the unique localization of bFGF-like proteins in myocardial cells, FGF receptor (FGFR) staining was widely distributed in the embryo; however, concentrated deposits of FGFR were detected in endothelial and myocardial cells, which diminished in the myocardium but not in the endothelium by stage 15. These results suggest that FGF-like proteins may have autocrine and/or paracrine functions during early cardiac morphogenesis.     

Domains of movement in the zebrafish gastrula

The mechanisms controlling cell movements during vertebrate gastrulation are not known. Studies using the zebrafish embryo show promise at identifying these mechanisms, combining an embryo that is accessible and optically clear with mutations that affect early development. In this article we describe the movements of cells during the midblastula, early epiboly and gastrulation stages of the zebrafish, correlating 'domains of movement' with embryonic morphology. We suggest that these domains of movement may parallel the 'zones of movement' of Xenopus.     

诱导心脏发生的早期信号通路

心脏是胚胎发生过程中最早形成的器官 .心脏前体的特化是组织间及细胞与细胞之间相互作用的结果 ,这一过程包含了诱导信号作用的时间和空间完整程序 .以脊椎动物和无脊椎动物作为模式动物 ,总结了在早期心脏发生中发挥重要作用的诱导信号通路 :BMP Dpp ,Wnt Wingless ,FGF及Notch信号通路 ,并阐述了信号通路之间的通讯 (crosstalk)以及信号通路与心脏发生相关的关键转录调节因子之间的协同诱导作用 .     

山黧豆胚胎发育过程中ODAP和一些大分子物质含量的变化

应用微量分析方法检测了山黧豆胚胎发育过程中ODAP毒素含量和核酸、蛋白质、糖类等大分子物质含量变化。结果表明：每粒种子的ODAP含量随着胚的发育而增加。每粒种子DNA量随着细胞的迅速分裂而增加,R、蛋白质、淀粉含量随着胚的发育而成倍地增加,当进入心形胚时这些物质的增加更为迅速。如以每克干重中的含量来表示,那么ODAP,DNA及可溶性糖含量则随胚的发育而下降,其它大分子物质含量在胚发育前期升高;进入心形胚时,这些物质达到最高峰;到鱼雷胚时,这些物质含量开始下降;直到胚基本分化完全时,降到最低点;只有酸性蛋白质含量一直保持增长。     

Bone morphogenetic proteins in vertebrate hematopoietic development

During embryonic development, the hematopoietic system is the first to generate terminally differentiated, functional cell types. The urgent necessity for the early formation of blood and blood vessels during embryogenesis means that the induction, expansion, and maturation of these systems must be rapidly and precisely controlled. Bone morphogenic proteins (BMPs) have been implicated in hematopoietic development in the vertebrate embryo and stimulate the proliferation and/or differentiation of human cord blood hematopoietic stem cells (HSC) and embryonic stem cells in vitro. Here we review the mechanisms of action and potential roles of these soluble signaling molecules in vertebrate hematopoiesis.     

Drastic expression change of transposon-derived piRNA-like RNAs and microRNAs in early stages of chicken embryos implies a role in gastrulation

Recent studies have shown that endogenous small RNAs regulate a variety of biological processes during vertebrate development; however, little is known about the role of small RNAs in regulating developmental signaling pathways during early embryogenesis. In this study, we applied Illumina sequencing to characterize an unexpected endogenous small RNA catalog and demonstrated a dramatic transition from transposon-derived piRNA-like small RNAs (pilRNAs) to microRNAs (miRNAs) in pre- and post-gastrula chicken embryos. The comprehensive expression profile of chicken miRNAs at the pre- and post-gastrula stages revealed that most known and new miRNAs were dynamically regulated during development. In addition to embryonic stem cell-related miRNAs, Gene Ontology (GO) analysis showed that miRNAs enriched in early stage chicken embryos targeted multiple signal transduction pathways associated with the reproductive process and embryogenesis, including Wnt and TGF-β, which specifies the neural fate of blastodermal cells. Intriguingly, a large cohort of pilRNAs primarily derived from the active and most abundant transposable elements (TEs) were enriched in chicken stage X blastoderms. Within stage X blastoderms, pilRNAs were specifically localized to the primordial germ cells (PGCs), indicating their post-zygotic origin. Together, these findings imply a role for small RNAs in gastrulation in early stage chicken embryos.     

Antioxidants and total oxyradical scavenging capacity during grass shrimp, Palaemonetes pugio, embryogenesis

During embryogenesis in grass shrimp the capacity to scavenge oxyradicals increased as measured by the Total Oxyradical Scavenging Capacity (TOSC) assay. The increase in TOSC during embryogenesis was associated with increasing concentrations of a number of antioxidants, including coenzyme Q (ubiquinone), alpha-tocopherol and reduced glutathione. Glutathione concentrations ranged from 0.004 to 0.005 nmol/embryo in early embryo stages and reached concentrations between 0.16 to 0.23 nmol/embryo in late embryo stages. Ascorbate remained essentially constant (0.16-0.20 nmol/embryo) throughout embryogenesis and may provide the preponderance of TOSC during early embryo development. Carotenoids were associated with yolk lipovitellin and these antioxidants decreased as yolk was absorbed during embryogenesis. Astaxanthin and beta-carotene were identified in embryos with astaxanthin always the principal carotenoid. In early embryo stages there are maternally derived antioxidants but as embryogenesis proceeds there is an assembly of a complex antioxidant system by newly formed cells and tissues.     

Mesoderm progenitor cells of common origin contribute to the head musculature and the cardiac outflow tract

During early embryogenesis, heart and skeletal muscle progenitor cells are thought to derive from distinct regions of the mesoderm (i.e. the lateral plate mesoderm and paraxial mesoderm, respectively). In the present study, we have employed both in vitro and in vivo experimental systems in the avian embryo to explore how mesoderm progenitors in the head differentiate into both heart and skeletal muscles. Using fate-mapping studies, gene expression analyses, and manipulation of signaling pathways in the chick embryo, we demonstrate that cells from the cranial paraxial mesoderm contribute to both myocardial and endocardial cell populations within the cardiac outflow tract. We further show that Bmp signaling affects the specification of mesoderm cells in the head: application of Bmp4, both in vitro and in vivo, induces cardiac differentiation in the cranial paraxial mesoderm and blocks the differentiation of skeletal muscle precursors in these cells. Our results demonstrate that cells within the cranial paraxial mesoderm play a vital role in cardiogenesis, as a new source of cardiac progenitors that populate the cardiac outflow tract in vivo. A deeper understanding of mesodermal lineage specification in the vertebrate head is expected to provide insights into the normal, as well as pathological, aspects of heart and craniofacial development.     

The Arabidopsis Somatic Embryogenesis Receptor Kinase 1 Gene Is Expressed in Developing Ovules and Embryos and Enhances Embryogenic Competence in Culture

We report here the isolation of the Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (AtSERK1) gene and we demonstrate its role during establishment of somatic embryogenesis in culture. The AtSERK1 gene is highly expressed during embryogenic cell formation in culture and during early embryogenesis. The AtSERK1 gene is first expressed in planta during megasporogenesis in the nucellus [corrected] of developing ovules, in the functional megaspore, and in all cells of the embryo sac up to fertilization. After fertilization, AtSERK1 expression is seen in all cells of the developing embryo until the heart stage. After this stage, AtSERK1 expression is no longer detectable in the embryo or in any part of the developing seed. Low expression is detected in adult vascular tissue. Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype. However, seedlings that overexpressed the AtSERK1 mRNA exhibited a 3- to 4-fold increase in efficiency for initiation of somatic embryogenesis. Thus, an increased AtSERK1 level is sufficient to confer embryogenic competence in culture.     

The MADS domain protein AGL15 localizes to the nucleus during early stages of seed development.

Little is known about regulatory factors that act during the earliest stages of plant embryogenesis. The MADS domain protein AGL15 (for AGAMOUS-like) is expressed preferentially during embryogenesis and accumulates during early seed development in monocotyledonous and dicotyledonous flowering plants. AGL15-specific antibodies and immunohistochemistry were used to demonstrate that AGL15 accumulates before fertilization in the cytoplasm in the cells of the egg apparatus and moves into the nucleus during early stages of development in the suspensor, embryo, and endosperms. Relatively high levels of AGL15 are present in the nuclei during embryo morphogenesis and until the seeds start to dry in Brassica, maize, and Arabidopsis. AGL15 is associated with the chromosomes during mitosis, and gel mobility shift assays were used to demonstrate that AGL15 binds DNA in a sequence-specific manner. To assess whether AGL15 is likely to play a role in specifying the seed or embryonic phase of development, AGL15 accumulation was examined in Arabidopsis mutants that prematurely exit embryogenesis. lec1-2 mutants show an embryo-specific loss of AGL15 at the transition stage, suggesting that AGL15 interacts with regulators in the leafy cotyledons pathway.