Haberman Adam S, Isaac Daniel D, Andrew Deborah J
Department of Cell Biology, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205-2196, USA.
Dev Biol. 2003 Jun 15;258(2):443-53. doi: 10.1016/s0012-1606(03)00140-4.
The Drosophila salivary gland is a simple tubular organ derived from a contiguous epithelial primordium, which is established by the activities of the homeodomain-containing proteins Sex combs reduced (SCR), Extradenticle (EXD), and Homothorax (HTH). EGF signaling along the ventral midline specifies the salivary duct fate for cells in the center of the primordium, while cells farther away from the source of EGF signal adopt a secretory cell fate. EGF signaling works, at least in part, by repressing expression of secretory cell genes in the duct primordium, including fork head (fkh), which encodes a winged-helix transcription factor. FKH, in turn, represses trachealess (trh), a duct-specific gene initially expressed throughout the salivary gland primordium. trh encodes a basic helix-loop-helix PAS-domain containing transcription factor that has been proposed to specify the salivary duct fate. In conflict with this model, we find that three genes, dead ringer (dri), Serrate (Ser), and trh itself, are expressed in the duct independently of trh. Expression of all three duct genes is repressed in the secretory cells by FKH. We also show that SER in the duct cells signals to the adjacent secretory cells to specify a third cell type, the imaginal ring cells. Thus, localized EGF- and Notch-signaling transform a uniform epithelial sheet into three distinct cell types. In addition, Ser directs formation of actin rings in the salivary duct.
果蝇唾液腺是一个简单的管状器官，由连续的上皮原基发育而来，该原基是由含同源结构域的蛋白质性别梳减少（SCR）、额外齿（EXD）和同胸（HTH）的活性建立的。沿腹中线的表皮生长因子（EGF）信号决定了原基中心细胞的唾液导管命运，而离EGF信号源较远的细胞则采用分泌细胞命运。EGF信号至少部分通过抑制导管原基中分泌细胞基因的表达来发挥作用，这些基因包括叉头（fkh），它编码一种翼状螺旋转录因子。FKH反过来又抑制无气管（trh），这是一种最初在整个唾液腺原基中表达的导管特异性基因。trh编码一种含有碱性螺旋-环-螺旋PAS结构域的转录因子，有人提出它决定唾液导管的命运。与该模型不同的是，我们发现三个基因，死环（dri）、锯齿（Ser）和trh本身，在导管中独立于trh表达。所有这三个导管基因的表达在分泌细胞中被FKH抑制。我们还表明，导管细胞中的SER向相邻的分泌细胞发出信号，以确定第三种细胞类型，即成虫环细胞。因此，局部的EGF和Notch信号将均匀的上皮片转化为三种不同的细胞类型。此外，Ser指导唾液导管中肌动蛋白环的形成。
