Aoki Momoe, Shimizu Takashi
Division of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.
Dev Genes Evol. 2017 Jul;227(4):279-287. doi: 10.1007/s00427-017-0584-5. Epub 2017 Jun 17.
Early embryos of the clitellate annelid Tubifex (oligochaete) undergo a series of unequal spiral cell divisions before the descendants of the D quadrant micromeres (cells 2d and 4d) divide bilaterally. Here, we show that inhibition of zygotic transcription by microinjection of α-amanitin (transcription inhibitor) exclusively converts unequal cleavage in cell 2d (granddaughter of 2d) into equal cleavage while other unequal cleavages and ensuing bilateral cleavages in cells 4d and 2d (great-granddaughter of 2d) all proceed in a normal fashion in the presence of this inhibitor. These results differ significantly from those reported for embryos of another clitellate annelid Helobdella (leech), in which inhibition of transcription converts bilateral (symmetric) cleavages in cells DNOPQ"' and DM" (equivalent to 2d and 4d) into unequal (asymmetric) cleavages while having no apparent effect on unequal cleavage in DNOPQ" (equivalent to 2d). These differences imply distinct mechanisms for the control of the unequal-to-bilateral transition in the two clitellate annelids.
环节动物颤蚓（寡毛纲）的早期胚胎在D象限小卵裂球（细胞2d和4d）的后代进行双侧分裂之前，会经历一系列不等的螺旋式细胞分裂。在此，我们表明，通过显微注射α-鹅膏蕈碱（转录抑制剂）抑制合子转录，仅能将细胞2d（2d的孙女细胞）中的不等分裂转化为均等分裂，而在这种抑制剂存在的情况下，细胞4d和2d（2d的曾孙女细胞）中的其他不等分裂以及随后的双侧分裂均以正常方式进行。这些结果与另一种环节动物蛭类动物血红蛭胚胎的报道结果有显著差异，在血红蛭胚胎中，转录抑制会将细胞DNOPQ"'和DM"（相当于2d和4d）中的双侧（对称）分裂转化为不等（不对称）分裂，而对DNOPQ"（相当于2d）中的不等分裂没有明显影响。这些差异意味着两种环节动物在控制不等分裂向双侧分裂转变方面存在不同机制。
