Molecular integration of inductive and mesoderm-intrinsic inputs governs even-skipped enhancer activity in a subset of pericardial and dorsal muscle progenitors.

Individual somatic muscles and heart progenitors are specified at defined positions within the mesodermal layer of Drosophila. The expression of the homeobox gene even-skipped (eve) identifies one specific subset of cells in the dorsal mesoderm, which give rise to particular pericardial cells and dorsal body wall muscles. Genetic analysis has shown that the induction of eve in these cells involves the combined activities of genes encoding mesoderm-intrinsic factors, such as Tinman (Tin), and spatially restricted signaling activities that are largely derived from the ectoderm, particularly those encoded by wingless (wg) and decapentaplegic (dpp). Here we show that a Dpp-activated Smad protein, phosphorylated Mad, is colocalized in eve-expressing cells during an extended developmental period. We demonstrate further that a mesodermally active enhancer of eve contains several Smad and Tin binding sites that are essential for enhancer activity in vivo. This enhancer also contains a number of binding sites for the Wg-effector Pangolin (Pan/Lef-1), which are required for full levels of enhancer activity. However, we find that their main function is to prevent ectopic enhancer activity in the dorsal mesoderm. This suggests that, in the absence of Wg signaling, Pan binding serves to abrogate the synergistic activities of Smads and Tin in eve activation while, in cells that receive Wg signals, Pan is converted into a coactivator that promotes eve induction. Together, these data show that the eve enhancer integrates several regulatory pathways via the combinatorial binding of the mesoderm-intrinsic regulator Tin and the effectors of the Dpp and Wg signals.     

Identification of common excitatory motoneurons in Drosophila melanogaster larvae

In insects, four types of motoneurons have long been known, including fast motoneurons, slow motoneurons, common inhibitory motoneurons, and DUM neurons. They innervate the same muscle and control its contraction together. Recent studies in Drosophila have suggested the existence of another type of motoneuron, the common excitatory motoneuron. Here, we found that shakB-GAL4 produced by labels this type of motoneuron in Drosophila larvae. We found that Drosophila larvae have two common excitatory motoneurons in each abdominal segment, RP2 for dorsal muscles and MNSNb/d-Is for ventral muscles. They innervate most of the internal longitudinal or oblique muscles on the dorsal or ventral body wall with type-Is terminals and use glutamate as a transmitter. Electrophysiological recording indicated that stimulation of the RP2 axon evoked excitatory junctional potential in a dorsal muscle.     

svp基因在果蝇副心肌细胞生长中的作用

果蝇心脏位于身体背部,是一个体节性重复的线性管状结构。在hedgehog（hh）基因的信号诱导下,seven-up（svp）基因调控果蝇的心脏发育,在每个体节的两个心肌细胞和两个副心肌细胞中表达。结果表明,在svp纯合突变体中,报告基因lacZ在心肌细胞中的表达图式正常,但在副心肌细胞中的表达图型明显异常,而且部分EPC细胞生长尺寸增加。某些体节的DA1肌肉祖细胞缺失,晚期突变体胚胎体壁肌肉细胞也呈现异常,表明基因svp的活性对果蝇副心肌细胞、DA1肌肉祖细胞和体壁肌肉细胞的分化是必须的,并且可能与EPC副心肌细胞的尺寸生长有关。     

鱼类Ⅰ型与Ⅱ型胶原蛋白基因系统进化及其在有/无肌间骨代表鱼中的表达比较分析

研究在分析鱼类Ⅰ型与Ⅱ型胶原蛋白基因系统进化基础上, 以有肌间骨的团头鲂(Megalobrama amblycephala)和无肌间骨的尼罗罗非鱼(Oreochromis niloticus)为研究对象, 探究了Ⅰ型与Ⅱ型胶原蛋白基因在二者不同发育阶段及不同部位肌肉组织中的表达模式。系统进化分析结果显示, 胶原蛋白基因col1a1、col1a2和col2a1在有刺鱼和无刺鱼中均各自聚为一支, 团头鲂和罗非鱼3个基因的氨基酸同源性都在90%以下。不同部位肌肉组织(背部上方、尾部上方和尾部下方)的基因表达结果显示, 团头鲂col1a1a和col1a1b基因与罗非鱼该同源基因col1a1在不同肌肉组织中的表达模式存在明显差异。在团头鲂中, Ⅰ型与Ⅱ型胶原蛋白基因在背上肌肉中的表达量高于尾部; 而在罗非鱼中, 其表达模式则相反。团头鲂和罗非鱼不同发育时期的基因定量结果显示: 团头鲂col1a1a和col2a1b基因的表达在肌间骨出现以前(15 dph)和基本出现之后(50 dph)显著(P<0.01)增加, 且Ⅰ型胶原蛋白基因和col2a1b的相对表达量在不同时期差异明显, 其中col1a1a基因在50 dph的表达丰度极高; 与团头鲂相比, 罗非鱼中相应基因的表达量变化较小, 整体波动不大。研究揭示了Ⅰ型和Ⅱ型胶原蛋白在有刺鱼与无刺鱼肌肉中的表达模式, 结果表明col1a1在团头鲂和尼罗罗非鱼两种鱼类中表达模式显著不同(P<0.01), 推测其与肌间骨发育潜在相关。     

Analysis of the expression pattern of Mysidium columbiae wingless provides evidence for conserved mesodermal and retinal patterning processes among insects and crustaceans

The Wnt family includes a number of genes, such as wingless ( wg), which encode secreted glycoproteins that function in numerous developmental patterning processes. In order to gain a better understanding of crustacean pattern formation, a wg orthologue was cloned from the malacostracan crustacean Mysidium columbiae(mysid), and the expression pattern of this gene was compared with that of Drosophila wg. Although Drosophila wg is expressed in many developing tissues, such as the ventral neuroectoderm, M. columbiae wg (mcowg)expression is detected within only a subset of these tissues. mcowg is expressed in the dorsal part of each developing segment and within the developing eye, but not within the ventral neuroectoderm. Dorsal wg expression in Drosophila is required for heart and muscle development, and conservation of this dorsal wgexpression pattern suggests that mcowgmay function to pattern these tissues in mysids. Consistent with this, expression of Even-skipped (Eve) protein in heart precursor and muscle cells, which is dependent on Wg signaling in Drosophila, is also conserved in mysids. Within the developing mysid eye, mcowg is expressed in a pattern that is similar to the expression pattern of Drosophila wg in the fly eye disc. In Drosophila,Wg inhibits neural differentiation at the anterior margin of the eye disc and patterns the dorsal/ventral axis of the eye. These data indicate that mcowg may function similarly during mysid eye development. Analysis of mcowgexpression provides molecular evidence suggesting that the processes of heart, muscle, and eye patterning are likely to be conserved among insects and crustaceans.     

Cardioblast-intrinsic Tinman activity controls proper diversification and differentiation of myocardial cells in Drosophila

The NK homeobox gene tinman (tin) is required for the specification of the cardiac, visceral muscle and somatic muscle progenitors in the early dorsal mesoderm of Drosophila. Like its vertebrate counterpart Nkx2.5, the expression of tin is maintained in cardiac cells during cardiac maturation and differentiation; however, owing to the complete lack of a dorsal vessel in tin mutant embryos, the function of tin in these cells has not been defined. Here we show that myocardial cells and dorsal vessels can form even though they lack Tin, and that viable adults can develop, as long as Tin is provided in the embryonic precardiac mesoderm. However, embryos in which tin expression is specifically missing from cardial cells show severe disruptions in the normal diversification of the myocardial cells, and adults exhibit severe defects in cardiac remodeling and function. Our study reveals that the normal expression and activity of Tin in four of the six bilateral cardioblasts within each hemisegment of the heart allows these cells to adopt a cell fate as ;working' myocardium, as opposed to a fate as inflow tract (ostial) cells. This function of tin involves the repression of Dorsocross (Doc) T-box genes and, hence, the restriction of Doc to the Tin-negative cells that will form ostia. We conclude that tin has a crucial role within myocardial cells that is required for the proper diversification, differentiation, and post-embryonic maturation of cardiomyocytes, and we present a pathway involving regulatory interactions among seven-up, midline, tinman and Dorsocross that establishes these developmental events upon myocardial cell specification.