PATTERNING THE DORSAL LONGITUDINAL FLIGHT MUSCLES (DLM) OF DROSOPHILA- INSIGHTS FROM THE ABLATION OF LARVAL SCAFFOLDS

The six Dorsal Longitudinal flight Muscles (DLMs) of Drosophila develo p from three larval muscles that persist into metamorphosis and serve as scaffolds for the formation of the adult fibers, We have examined t he effect of muscle scaffold ablation on the development of DLMs durin g metamorphosis, Using markers that are specific to muscle and myoblas ts we show that in response to the ablation, myoblasts which would nor mally fuse with the larval muscle, fuse with each other instead, to ge nerate the adult fibers in the appropriate regions of the thorax, The development of these de novo DLMs is delayed and is reflected in the d elayed expression of erect wing, a transcription factor thought to con trol differentiation events associated with myoblast fusion, The newly arising muscles express the appropriate adult-specific Actin isoform (88F), indicating that they have the correct muscle identity, However, there are frequent errors in the number of muscle fibers generated, A blation of the larval scaffolds for the DLMs has revealed an underlyin g potential of the DLM myoblasts to initiate de novo myogenesis in a m anner that resembles the mode of formation of the Dorso-Ventral Muscle s, DVMs, which are the other group of indirect flight muscles, Therefo re, it appears that the use of larval scaffolds is a superimposition o n a commonly used mechanism of myogenesis in Drosophila. Our results s how that the role of the persistent larval muscles in muscle patternin g involves the partitioning of DLM myoblasts, and in doing so, they re gulate formation of the correct number of DLM fibers.