Azpiazu N, Frasch M
Brookdale Center for Molecular Biology, Mount Sinai School of Medicine, New York, New York 10029.
Genes Dev. 1993 Jul;7(7B):1325-40. doi: 10.1101/gad.7.7b.1325.
Whereas the mechanisms of early Drosophila mesoderm formation have been studied in much detail, the subsequent processes determining regional identities within the mesoderm remain largely unknown. Here, we describe two homeo box genes, tinman (tin) and bagpipe (bap), which spatially subdivide the mesoderm and determine cell fates in the dorsal mesoderm. These two genes are components of a cascade of genetic interactions that result in the spatial restriction of tin mRNA to the dorsal mesoderm and in the activation of bap in segmental clusters of cells in this region. A subset of cells from those clusters segregate to form visceral mesoderm that differentiates into gut musculature. This indicates that the visceral mesoderm is derived from metamerically repeated primordia. In embryos mutant for bap, visceral mesoderm formation is strongly disrupted. Most cells of the visceral mesoderm fail to differentiate properly, and a portion of them are transformed into body wall musculature and gonadal mesoderm. In tin mutant embryos, bap expression is not activated in the dorsal mesoderm. Probably as a consequence, neither visceral mesoderm nor midgut musculature are formed in these mutants, and the absence of visceral mesoderm results in strong disruptions of endoderm migration and midgut morphogenesis. In addition to visceral mesoderm development, tin is required for the formation of the heart from dorsal mesoderm and for the specification of founder cells for particular body wall muscles.
虽然果蝇早期中胚层形成的机制已得到详细研究，但决定中胚层内区域特性的后续过程仍基本未知。在此，我们描述了两个同源异型盒基因，tinman（tin）和bagpipe（bap），它们在空间上对中胚层进行细分，并决定背侧中胚层中的细胞命运。这两个基因是一系列遗传相互作用的组成部分，这些相互作用导致tin mRNA在空间上局限于背侧中胚层，并在该区域的细胞节段簇中激活bap。这些细胞簇中的一部分细胞分离形成内脏中胚层，后者分化为肠道肌肉组织。这表明内脏中胚层源自分节重复的原基。在bap突变的胚胎中，内脏中胚层的形成受到严重破坏。内脏中胚层的大多数细胞无法正常分化，其中一部分细胞转变为体壁肌肉组织和性腺中胚层。在tin突变胚胎中，背侧中胚层中bap的表达未被激活。可能因此，这些突变体中既不形成内脏中胚层也不形成中肠肌肉组织，并且内脏中胚层的缺失导致内胚层迁移和中肠形态发生的严重破坏。除了内脏中胚层发育外，tin对于从背侧中胚层形成心脏以及特定体壁肌肉的起始细胞的特化也是必需的。
