Spatially restricted patterns of expression of the homeobox-containing gene Hox 2.1. during mouse embryogenesis

The mouse Hox 2.1 gene contains a homeobox sequence and is therefore a candidate for a vertebrate gene involved in the control of embryonic patterning or positional specification. To investigate this possibility, we have used in situ hybridization to determine the pattern of Hox 2.1 expression during mouse embryogenesis. At 8.5 days post coitum, Hox 2.1 is expressed at a low level in the posterior neuroectoderm and mesoderm, and in the neuroectoderm of the presumptive hindbrain. At 12.5 days p.c., Hox 2.1 is expressed in an anteroposterior restricted domain extending from the hindbrain throughout the length of the spinal cord, predominantly in the dorsal region. Between 12.5 and 13.5 days p.c. the domain becomes localized to the occipital and cervical regions. We also detect Hox 2.1 RNA in the embryonic lung, stomach, mesonephros and metanephros, as well as in myenteric plexus, dorsal root ganglia and the nodose ganglion, and in mature granulocytes. The embryonic expression of Hox 2.1 in neural tissue is compared with that of Hox 3.1, which also shows anteroposterior restricted domains of gene expression. These patterns of expression are not clearly consistent with Hox 2.1 or Hox 3.1 having roles in segmental patterning. However, the data are consistent with these genes having regulatory roles in anteroposterior positional specification in the neuroectoderm and mesoderm, and suggest that Hox 2.1 may also have functions during organogenesis.     

Growth and specification: fly Pax6 homologs eyegone and eyeless have distinct functions

Development requires not only the correct specification of organs and cell types in the right places (pattern), but also the control of their size and shape (growth). Many signaling pathways control both pattern and growth and how these two are distinguished has been something of a mystery. In the fly eye, a Pax6 homolog (eyeless) controls eye specification together with several other genes. Now Dominguez et al.1 show that Notch signaling controls eye growth through a second Pax6 protein (Eyegone). In mice and humans the single Pax6 gene appears to encode both specification and growth controlling proteins through alternative mRNA splicing.     

Axis specification in the Drosophila embryo.

Three genetic hierarchies control cell-fate specification in largely distinct regions of the antero-posterior axis of the Drosophila embryo, whereas a single hierarchy specifies dorso-ventral cell fates. Molecular genetic analysis of these hierarchies is leading to increased understanding of the nature of the regulatory circuitry that controls regional cell-fate specification.     

Generation of regionally specified neural progenitors and functional neurons from human embryonic stem cells under defined conditions

To model human neural-cell-fate specification and to provide cells for regenerative therapies, we have developed a method to generate human neural progenitors and neurons from human embryonic stem cells, which recapitulates human fetal brain development. Through the addition of a small molecule that activates canonical WNT signaling, we induced rapid and efficient dose-dependent specification of regionally defined neural progenitors ranging from telencephalic forebrain to posterior hindbrain fates. Ten days after initiation of differentiation, the progenitors could be transplanted to the adult rat striatum, where they formed neuron-rich and tumor-free grafts with maintained regional specification. Cells patterned toward a ventral midbrain (VM) identity generated a high proportion of authentic dopaminergic neurons after transplantation. The dopamine neurons showed morphology, projection pattern, and protein expression identical to that of human fetal VM cells grafted in parallel. VM-patterned but not forebrain-patterned neurons released dopamine and reversed motor deficits in an animal model of Parkinson's disease.     

tcl-2 encodes a novel protein that acts synergistically with Wnt signaling pathways in C. elegans

Mutations in tcl-2 cause defects in the specification of the fates of the descendants of the TL and TR blast cells, whose polarity is regulated by lin-44/Wnt and lin-17/frizzled, during Caenorhabditis elegans development. In wild-type animals, POP-1/TCF/LEF, is asymmetrically distributed to the T cell daughters, resulting in a higher level of POP-1 in the nucleus of the anterior daughter. The POP-1 asymmetric distribution is controlled by lin-44 and lin-17. However, in tcl-2 mutants, POP-1 is equally distributed to T cell daughters as is observed in lin-17 mutants, indicating that, like lin-17, tcl-2 functions upstream of pop-1. In addition, tcl-2 mutations cause defects in the development of the gonad and the specification of fate of the posterior daughter of the P12 cell, both of which are controlled by the Wnt pathway. Double mutant analyses indicate that tcl-2 can act synergistically with the Wnt pathway to control gonad development as well as P12 descendant cell fate specification. tcl-2 encodes a novel protein. A functional tcl-2::gfp construct was weakly expressed in the nuclei of the T cell and its descendants. Our results suggest that tcl-2 functions with Wnt pathways to control T cell fate specification, gonad development, and P12 cell fate specification.     

The rate of fluid shear stress is a potent regulator for the differentiation of mesenchymal stem cells

We have previously demonstrated that the rate of fluid shear stress (ΔSS) can manipulate the fate of mesenchymal stem cells (MSCs) to osteogenic or chondrogenic cells. However, whether ΔSS is comparable to other two means of induction medium and substrate stiffness that have been proven to be potent in differentiation control is unknown. In this study, we subjected MSCs to 1–7 days of osteogenic or chondrogenic chemical induction, or 1–4 days of 37 or 86 kPa of substrate stiffness induction, followed by 20 min of Fast ΔSS (0–0′) or Slow ΔSS (0–2′), which is a laminar FSS that linearly increased from 0 to 10 dyn/cm ² in 0 (Fast) or 2 min (Slow) and maintained at 10 dyn/cm ² for a total of 20 min. We found that 20 min of ΔSS could compete with 5 days' chemical and 2 days' substrate stiffness inductions. Our study confirmed that ΔSS is a powerful tool to control the differentiation of MSCs, which stressed the possible application in MSCs linage specification.     

视黄酸对赤子爱胜蚓再生头尾轴形成的影响

为了探讨视黄酸对蚯蚓再生的影响,用视黄酸处理了从不同部位剪切的蚯蚓体段．观察其存活率、重量和再生长度的变化。结果表明,有头无尾的体段存活率受视黄酸影响较小,而无头有尾的处理受视黄酸影响较大;视黄酸处理后30d,各处理再生长度和存活率均小于对照;视黄酸对蚯蚓再生有明显影响,能延迟和干扰再生,影响头部的形成。视黄酸影响蚯蚓再生的作用方式可能是通过干扰前后体轴的形成,从而影响蚯蚓再生图式形成。     

Upregulation of <Emphasis Type="Italic">Slc38a1</Emphasis> Gene Along with Promotion of Neurosphere Growth and Subsequent Neuronal Specification in Undifferentiated Neural Progenitor Cells Exposed to Theanine

We have shown marked promotion of both cluster growth and neuronal specification in pluripotent P19 cells with overexpression of solute carrier 38a1 (Slc38a1), which is responsible for membrane transport of glutamine. In this study, we evaluated pharmacological profiles of the green tea amino acid ingredient theanine, which is a good substrate for glutamine transporters, on proliferation and neuronal specification in neural progenitor cells from embryonic rat neocortex. Sustained exposure to theanine, but not glutamine, accelerated the growth of neurospheres composed of proliferating cells and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) reducing activity at concentrations of 1–100 μM in undifferentiated progenitor cells. Such prior exposure to theanine promoted spontaneous and induced commitment to a neuronal lineage with concomitant deteriorated astroglial specification. Selective upregulation was seen in the expression of Slc38a1 in progenitor cells cultured with theanine. Similarly significant increases in cluster growth and MTT reducing activity were found in P19 cells cultured with theanine for 4 days. Luciferase activity was doubled in a manner sensitive to the deletion of promoter regions in P19 cells with a luciferase reporter plasmid of the Slc38a1 promoter after sustained exposure to theanine for 4 days. Overexpression of X-box binding protein-1 led to a marked increase in luciferase activity in P19 cells transfected with the Slc38a1 reporter plasmid. These results suggest that theanine accelerates cellular proliferation and subsequent neuronal specification through a mechanism relevant to upregulation of Slc38a1 gene in undifferentiated neural progenitor cells.     

Establishing three blastocyst lineages--then what?

Development of the mouse embryo to the blastocyst stage occurs over 3 to 4 days following fertilization of the oocyte. During this time, several molecular and morphological events take place that result in the formation of three distinct cell lineages: the trophectoderm, the epiblast, and the primitive endoderm. Many studies have investigated the processes that control lineage specification in the blastocyst including gene expression, cell signaling, cell-cell contact/positional relationships, and most recently, epigenetics. Here we review, at the molecular level, recent contributions to our understanding of the mechanisms that play a role in formation of these lineages. Additionally, we focus on the next steps in differentiation to highlight processes important in the development of those lineages that contribute to the extraembryonic tissues. In this context, we discuss the establishment of extraembryonic ectoderm and the contributions of parietal and visceral endoderm to yolk sac formation.     

EGF receptor and Notch signaling act upstream of Eyeless/Pax6 to control eye specification

The Drosophila compound eye is specified by the concerted action of seven nuclear factors that include Eyeless/Pax6. These factors have been called "master control" proteins because loss-of-function mutants lack eyes and ectopic expression can direct ectopic eye development. However, inactivation of these genes does not cause the presumptive eye to change identity. Surprisingly, we find that several of these eye specification genes are not coexpressed in the same embryonic cells-or even in the presumptive eye. We demonstrate that the EGF Receptor and Notch signaling pathways have homeotic functions that are genetically upstream of the eye specification genes, and show that specification occurs much later than previously thought-not during embryonic development but in the second larval stage.     

The little R cell that could

Drosophila eye development provides an excellent model system to study the role of inter-cellular signaling in the specification of unique cell fates. Behavioral screens by Benzer and his colleagues led to the identification of a gene, Sevenless, a receptor tyrosine kinase (RTK) receptor, required for the specification of the UV sensitive R7 cell. Genetic analysis further showed that the Ras/Raf/MAPK pathway function downstream of Sevenless in the specification of R7 fate. Signaling mediated by another RTK, EGFR and Notch have also been shown to function in either an antagonistic or a synergistic manner in the specification of cell fate during eye development. In some instances, these pathways are linked in a sequential manner by the regulation of the expression of Notch ligand, Delta by EGFR, while in others, these pathways function in a combinatorial fashion on enhancer elements to control target gene expression. In this review, we highlight the elegant genetic strategies used by several laboratories in early elucidation of the Sevenless pathway which helped link the RTK receptor to the Ras/Raf/MAPK cascade and discuss how EGFR and Notch signaling pathways are used in a reiterative manner and by combining in different modes, generate sufficient diversity required for the specification of unique cell fates.     

On signaling pathways: hematopoietic stem cell specification from hemogenic endothelium

Hematopoietic stem cells(HSCs) are specified and generated during the embryonic development and have remarkable potential to replenish the full set of blood cell lineages. Researchers have long been interested in clarifying the molecular events involved in HSC specification. Many studies have reported the development of methods for generating functional hematopoietic cells from pluripotent stem cells(PSCs-embryonic stem cells(ESCs) and induced pluripotent stem cells(i PSCs)) for decades. However, the generation of HSCs with robust long-term repopulation potential remains a swingeing challenge, of which a major factor contributing to this failure is the difficulty to define the intraembryonic signals related to the specification of HSCs. Since HSCs directly derive from hemogenic endothelium, in this review, we summarize both in vivo and in vitro studies on conserved signaling pathways that control the specification of HSCs from hemogenic endothelial cells.