Bate M, Rushton E, Frasch M
Department of Zoology, Cambridge University, UK.
Dev Suppl. 1993:149-61.
In wild-type embryos of Drosophila melanogaster, the formation of differentiated larval muscles is preceded by the segregation of small numbers of progenitor or founder cells in the embryonic mesoderm. The founder cells, characterised by the expression of genes encoding putative transcription factors such as S59 or vestigial, fuse with neighbouring myoblasts to form syncytial precursors of individual muscles. Founder cell segregation is deranged in embryos mutant for any of the neurogenic genes: enlarged clusters of cells expressing S59 or vestigial are detected at the sites where small numbers of founder cells segregate in the wild type. In addition, muscle differentiation is deranged in such embryos in a way that appears to be closely linked to the extent of epidermal disruption caused by the neurogenic phenotype: myoblast fusion is limited to regions of the mesoderm beneath the residual epidermis left by the hyperplasia of the nervous system, and late expression of S59 and vestigial is lost from mesoderm not lying within the margins of the residual epidermis. Thus neurogenic gene functions appear to be required both for the normal segregation of founder cells and for muscle differentiation. It is not clear whether either of these requirements reflects an essential function for any or all of the neurogenic genes within the mesoderm itself.
在黑腹果蝇的野生型胚胎中，分化的幼虫肌肉形成之前，胚胎中胚层会先分离出少量祖细胞或奠基细胞。这些奠基细胞的特征是表达编码假定转录因子（如S59或vestigial）的基因，它们与相邻的成肌细胞融合，形成单个肌肉的合胞体前体。在任何神经源性基因突变的胚胎中，奠基细胞的分离都会紊乱：在野生型中少量奠基细胞分离的部位，会检测到表达S59或vestigial的细胞簇增大。此外，在这类胚胎中，肌肉分化也会紊乱，其方式似乎与神经源性表型引起的表皮破坏程度密切相关：成肌细胞融合仅限于神经系统增生后残留表皮下方的中胚层区域，而S59和vestigial的晚期表达在不在残留表皮边缘内的中胚层中消失。因此，神经源性基因功能似乎对于奠基细胞的正常分离和肌肉分化都是必需的。目前尚不清楚这些需求是否反映了中胚层本身内任何或所有神经源性基因的基本功能。
