Early Muscle Cell Fate Determination During Embryogenesis

肌肉特异性基因调控因子MyoD家族的研究为了解成肌细胞决定和分化的调控机制提供了巨大的见解。但是肌肉发育生物学中仍然存在一个基本问题：是什么激活了肌源性转录因子？本研究的主要目的是确定多能中胚层干细胞形成肌源性命运的最早分子事件。这些实验旨在确定影响早期胚胎肌肉细胞决定的因素，并探索不属于肌原性程序的胚胎细胞分化为肌肉细胞的能力。海胆胚胎的发育非常清楚，其胚胎在早期发育过程中特别适合微操作，将成为实验生物。Venuti博士开发了一种体外实验，使她能够询问细胞外信号是否以及何时需要用于肌肉前体的确定和分化，或者它们是否自主发展。这些实验应该能够识别触发肌肉命运决定的信号或线索，并确定肌肉祖细胞何时开始参与。Venuti博士从海胆胚胎中克隆并鉴定了肌肉特异性基本螺旋-环-螺旋（b-HLH）转录因子SUM-1，并表明它在肌肉分化程序的早期就被激活。她已经证明SUM-1可以激活脊椎动物组织培养细胞和微注射海胆胚胎中的肌肉特异性报告因子。她将研究在过早时期和胚胎异位位置单独或与相互作用因素结合表达SUM-1的后果。为了确定直接调控SUM-1转录的因子，我们将对SUM-1启动子的顺式调控元件和反式调控因子进行表征。一旦确定了SUM-1启动子的重要时空调控元件，她将在体外试验中测试细胞外信号对这些元件的影响。这些实验的结合将有助于指导长期研究肌肉细胞命运的决定和细胞外信号在胚胎细胞决定肌生成命运中的作用。他们还将更好地了解肌源性转录因子，SUM-1和其他调节分子在这些决定事件中的作用。＊＊＊

9506346 Venuti Studies on the MyoD family of muscle specific gene regulatory factors have provided enormous insight into the mechanisms that regulate myoblast determination and differentiation. But a fundamental question that remains in muscle developmental biology is: what activates the myogenic transcription factors? The prime objective of this proposed research is to identify the earliest molecular events that commit a pluripotent mesodermal stem cell to a myogenic fate. These experiments are designed to identify factors that influence early embryonic muscle cell determination and explore the capacity of embryonic cells which are not part of the myogenic program to differentiate as muscle cells. The sea urchin embryo, whose development is extremely well understood and whose embryos are particularly amenable to micromanipulation during early development, will be the experimental organism. Dr. Venuti has developed an in vitro assay that will enable her to ask if and when extracellular signaling is required for the determination and differentiation of muscle precursors or if they develop cell autonomouqly. These experiments should identify the signals or cues that initiate the decision to follow a muscle fate and determine when muscle progenitors first become committed. Dr. Venuti has cloned and characterized the muscle specific basic helix-loop-helix (b-HLH) transcription factor, SUM-1, from the sea urchin embryo and shown that it is activated very early in the muscle differentiation program. She has shown that SUM-1 can activate muscle specific reporter elements in vertebrate tissue culture cells and in microinjected sea urchin embryos. She will examine the consequences of expressing SUM-1 at premature times and at ectopic locations in the embryo either alone or in combination with interacting factors. To identify factors that act directly to regulate the transcription of SUM-1, the cis regulatory elements and trans acting factors of the SUM-1 promoter wil l be characterized. Once important temporal and spatial regulatory elements of the SUM-1 promoter are identified, she will test the effects of the extracellular signals identified in in vitro assays on these elements. The combination of these experiments will help direct long term investigations into muscle cell fate determination and the role of extracellular signals in the decision of embryonic cells to commit to a myogenic fate. They will also provide a better understanding of the role of the myogenic transcription factor, SUM-1, and other regulatory molecules in these determination events. ***