Direct and indirect requirements of Shh/Gli signaling in early pituitary development

Induction of early pituitary progenitors is achieved through combined activities of signals from adjacent embryonic tissues. Previous studies have identified a requirement for oral ectoderm derived Sonic Hedgehog (Shh) in specification and/or proliferation of early pituitary progenitors, however how different Gli genes mediate Shh signaling to control pituitary progenitor development has not yet been determined. Here we show that Gli2, which encodes a major Gli activator, is required for proliferation of specific groups of pituitary progenitors but not for initial dorsoventral patterning. We further show that the action of Gli2 occurs prior to the closure of Rathke' pouch. Lastly, we show that Shh/Gli2 signaling controls the diencephalic expression of Bone morphogenetic protein 4 (Bmp4) and Fibroblast growth factor 8 (Fgf8), two genes that are known to play critical roles in patterning and growth of Rathke's pouch. Our results therefore suggest both cell-autonomous and non-cell-autonomous requirements for Gli2 in regulation of pituitary progenitor specification, proliferation and differentiation.     

Shh、Gli1和VEGF蛋白在大肠癌组织中的表达及临床意义

Sonic Hedgehog(Shh)、Gli1蛋白和血管内皮生长因子表达在大肠癌的发生发展过程中的作用还不清楚.通过免疫组化法检测78例大肠癌及30例正常组织中Shh、Gli1和VEGF的表达,并与临床病理因素进行相关性分析,研究三者在大肠癌中的作用.研究发现,Shh、Gli1和VEGF蛋白在大肠癌癌组织中的阳性率分别为32%、71.7%和76.9%,与正常组织(6.0%、3.3%和3.3%)相比,差异有统计学意义(P0.05).Shh、Gli1和VEGF蛋白表达与患者年龄、肿瘤大小、组织学类型等均无关(P0.05),VEGF和Gli1蛋白表达与淋巴结转移状况和Duke分期有关(P0.05),而Shh蛋白表达仅与Duke分期有关(P0.05).Spearman相关分析显示,Shh与Gli1表达正相关(r=0.349,P0.05),Gli1与VEGF表达正相关(r=0.865,P0.05).Shh与VEGF表达正相关(r=0.403,P0.05).结果表明Shh、Gli1和VEGF在大肠癌发生、发展中呈协同和相互调节作用,Shh、Gli1和VEGF的表达参与大肠癌的生长、侵袭和转移过程.三者的联合检测可作为判断大肠癌预后,筛选高危转移患者的有效指标,同时也可用于指导大肠癌的药物治疗.     

Impaired endochondral bone development and osteopenia in Gli2-deficient mice

Mice homozygous for targeted disruption of the zinc finger domain of Gli2 (Gli2(zfd/zfd)) die at birth with developmental defects in several organ systems including the skeleton. The current studies were undertaken to define the role of Gli2 in endochondral bone development by characterizing the molecular defects in the limbs and vertebrae of Gli2(zfd/zfd) mice. The bones of mutant mice removed by cesarian section at E16.5 and E18.5 demonstrated delayed endochondral ossification. This was accompanied by an increase in the length of cartilaginous growth plates, reduced bone tissue in the femur and tibia and by failure to develop the primary ossification centre in vertebral bodies. The growth plates of tibiae and vertebrae exhibited increased numbers of proliferating and hypertrophic chondrocytes with no apparent alteration in matrix mineralisation. The changes in growth plate morphology were accompanied by an increase in expression of FGF2 in proliferating chondrocytes and decreased expression of Indian hedgehog (Ihh), patched (Ptc) and parathyroid-hormone-related protein (PTHrP) in prehypertrophic cells. Furthermore, there was a reduction in expression of angiogenic molecules in hypertrophic chondrocytes, which was accompanied by a decrease in chondroclasts at the cartilage bone interface, fewer osteoblasts lining trabecular surfaces and a reduced volume of metaphyseal bone. These results indicate that functional Gli2 is necessary for normal endochondral bone development and that its absence results in increased proliferation of immature chondrocytes and decreased resorption of mineralised cartilage and bone formation.     

Thalamic development induced by Shh in the chick embryo

Patterning of the early neural tube is achieved in part by the inductive signals, which arise from neuroepithelial signaling centers. The zona limitans intrathalamica (ZLI) is a neuroepithelial domain in the alar plate of the diencephalon which separates the prethalamus from the thalamus. The ZLI has recently been considered to be a possible secondary organizer, effecting its inductions via sonic hedgehog (Shh), a signaling molecule which drives morphogenetic information for the thalamus. Using experimental embryological techniques involving the generation of chimeric embryos, we show that the formation of the ZLI in the diencephalic alar plate is due to an interaction between the prechordal and epichordal plate neuroepithelia. We also provide evidence that Shh expression in the ZLI underlies the morphogenetic activity of this putative diencephalic organizer. Ectopic Shh led to the auto-induction of its own gene expression in host cells, as well as to the expression of other genes involved in diencephalic regionalization and histogenesis. Analysis of long-term surviving embryos after Shh ectopic expression demonstrated that Shh was able to induce thalamic structures and local overgrowth. Overall, these results indicate that Shh expressed in the ZLI plays an important role in diencephalic growth and in the development of the thalamus.     

The development of membrane specializations in the receptor-bipolar-horizontal cell synapse of the chick embryo retina

Retinae of chick embryos and chicks one to six weeks after hatching were examined in ultrathin sections and in freeze-etch specimens. The development of the synaptic contacts between receptor cells and bipolar cells starts at the end of the second week of incubation with the enclosure of the dendritic prolongations, invaginating receptor terminals accompanied by the appearance of electron dense material at the synaptic contact sites. Subsequently receptor terminals become filled with synaptic vesicles which surround the synaptic lamellae that appear on the 16th day of incubation. The application of the freeze-fracture technique demonstrates that the differentiation of the synaptic membranes continues into the first week post hatching. E-fracture faces of the presynaptic membranes are characterized by crater-like structures, called synaptopores. Their number is rather small during incubation and increases after hatching. In the P-fracture faces of the dendrites, which are enclosed by the receptor terminals, small particle aggregations appear on the 16th day of incubation. These small particle clusters increase by the apposition of further particles which become arranged in lines and bring out a lattice-like aspect. This arrangement of particles in the inner part of the cell membrane is the morphological expression of the maturation process. The significance of these aggregations as a postsynaptic receptor for neurotransmitters in excitatory cells is discussed.     

The development of a zonula occludens in peripheral myelin of the chick embryo

Summary The development of the egg envelope and its incorporation into the larval cuticle of the polychaete Phragmatopoma lapidosa, was studied by correlative scanning and transmission electron microscopy. The mature egg possesses an envelope composed of five zones including an outer granular zone formed by the tips of the egg microvilli. The formation of the granules is described and their functions are discussed. The entire egg envelope is retained as the larval cuticle up to the 16 h trochophore stage. From this stage to about the 60 h larval stage, the envelope is gradually lost and replaced by a cuticle consisting of branching microvilli. The cuticle of the 20 day larva is composed of highly branching microvilli penetrating a homogeneous electron opaque cuticle. The possible functions of the cuticle among the Annelida are discussed.We thank Mrs. P.A. Linley, Mr. R. Koss, and Mr. G.D. Braybrook for technical assistance. Special appreciation is extended to Dr. Edward Ruppert for his contributions to many stimulating discussions during the course of this investigation. This study was partially supported by a National Research Council of Canada grant to F.S. ChiaContribution No. 76, Harbor Branch Foundation, Inc.     

Six1 is not involved in limb tendon development, but is expressed in limb connective tissue under Shh regulation

Mice deficient for the homeobox gene Six1 display defects in limb muscles consistent with the Six1 expression in myogenic cells. In addition to its myogenic expression domain, Six1 has been described as being located in digit tendons and as being associated with connective tissue patterning in mouse limbs. With the aim of determining a possible involvement of Six1 in tendon development, we have carefully characterised the non-myogenic expression domain of the Six1 gene in mouse and chick limbs. In contrast to previous reports, we found that this non-myogenic domain is distinct from tendon primordia and from tendons defined by scleraxis expression. The non-myogenic domain of Six1 expression establishes normally in the absence of muscle, in Pax3-/- mutant limbs. Moreover, the expression of scleraxis is not affected in early Six1-/- mutant limbs. We conclude that the expression of the Six1 gene is not related to tendons and that Six1, at least on its own, is not involved in limb tendon formation in vertebrates. Finally, we found that the posterior domain of Six1 in connective tissue is adjacent to that of the secreted factor Sonic hedgehog and that Sonic hedgehog is necessary and sufficient for Six1 expression in posterior limb regions.     

Changes in liver nuclear sap proteins during chick embryo development

Summary Nuclear sap proteins from liver of 12-, 15-, 19-day-old embryos and 1-day-old chicks were resolved by one-and two-dimensional gel electrophoresis. Although the protein patterns from various stages of development have remarkable similarities, some qualitative and quantitative differences were found among these patterns. The most pronounced changes were detected in protein with molecular weight of 100 K which was very abundant in nuclei of 12-day-old embryos and disappeared in nuclei of older embryos and in protein with molecular weight of 40 K which rapidly diminished after hatching.