Hughes S C, Krause H M
Banting and Best Department of Medical Research, University of Toronto, Charles H. Best Institute, Toronto, Ontario, M5G 1L6, Canada.
Development. 2001 Apr;128(7):1109-18. doi: 10.1242/dev.128.7.1109.
Embryos of higher metazoans are divided into repeating units early in development. In Drosophila, the earliest segmental units to form are the parasegments. Parasegments are initially defined by alternating stripes of expression of the fushi-tarazu and even-skipped genes. How fushi-tarazu and even-skipped define the parasegment boundaries, and how parasegments are lost when fushi-tarazu or even-skipped fail to function correctly, have never been fully or properly explained. Here we show that parasegment widths are defined early by the relative levels of fushi-tarazu and even-skipped at stripe junctions. Changing these levels results in alternating wide and narrow parasegments. When shifted by 30% or more, the enlarged parasegments remain enlarged and the reduced parasegments are lost. Loss of the reduced parasegments occurs in three steps; delamination of cells from the epithelial layer, apoptosis of the delaminated cells and finally apoptosis of inappropriate cells remaining at the surface. The establishment and maintenance of vertebrate metameres may be governed by similar processes and properties.
高等后生动物的胚胎在发育早期就被划分为重复单元。在果蝇中，最早形成的节段单元是副节。副节最初由腹分节基因和偶数跳基因交替表达的条纹所定义。腹分节基因和偶数跳基因如何界定副节边界，以及当腹分节基因或偶数跳基因功能出现异常时副节是如何消失的，这些问题从未得到充分或恰当的解释。在此我们表明，副节宽度在早期由条纹交界处腹分节基因和偶数跳基因的相对水平所界定。改变这些水平会导致副节宽窄交替。当偏移30%或更多时，增大的副节会保持增大状态，而缩小的副节则会消失。缩小的副节的消失分三步进行：细胞从上皮层分层、分层细胞凋亡，最后是表面残留的不适当细胞凋亡。脊椎动物体节的建立和维持可能受类似的过程和特性所调控。
