Bissen S T, Weisblat D A
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Dev Biol. 1991 Jul;146(1):12-23. doi: 10.1016/0012-1606(91)90442-6.
Zygotic transcription was analyzed in embryos of the glossiphoniid leech Helobdella triserialis by autoradiographic detection of tritiated uridine incorporated in the presence or absence of low concentrations of alpha-amanitin. RNA synthesis was first detected after the second cleavage and alpha-amanitin-sensitive RNA synthesis was first detected during the divisions yielding the embryonic stem cells, or teloblasts. RNA synthesis increased as development progressed, and the bulk of alpha-amanitin-sensitive RNA synthesis was found in two classes of cells, the blast cells, which are the progeny of the teloblasts, and the micromere-derived cells. The time during which zygotic gene products are required was determined by observing the developmental consequences of alpha-amanitin exposure. Zygotes microinjected with alpha-amanitin underwent the first several cleavages with normal timing and symmetry, but underwent aberrant cleavages and produced supernumerary large blastomeres during the time that the control embryos generated teloblasts. Once the teloblasts were formed, the microinjection of alpha-amanitin did not affect the production of blast cells by the teloblasts, but it did block the divisions and movements of the blast cells and the micromere-derived cells. These data suggest that zygotic transcription is activated during the early cleavages of Helobdella embryos and that newly synthesized transcripts are required for the generation of teloblasts. Thus, there is an early, critical period of messenger RNA synthesis essential for teloblast production that is distinct from the later phase of messenger RNA synthesis required for cell divisions and cell movements during gastrulation.
通过放射自显影检测在有或无低浓度α-鹅膏蕈碱存在的情况下掺入的氚标记尿苷，对光蛭科水蛭三带扁蛭的胚胎中的合子转录进行了分析。在第二次卵裂后首次检测到RNA合成，而α-鹅膏蕈碱敏感的RNA合成首次在产生胚胎干细胞或端细胞的分裂过程中检测到。随着发育的进行，RNA合成增加，并且大部分α-鹅膏蕈碱敏感的RNA合成存在于两类细胞中，即作为端细胞后代的胚细胞和源自小分裂球的细胞。通过观察α-鹅膏蕈碱暴露的发育后果来确定需要合子基因产物的时间。显微注射α-鹅膏蕈碱的合子在正常时间和对称性下经历了最初的几次卵裂，但在对照胚胎产生端细胞的时间段内经历了异常卵裂并产生了额外的大型卵裂球。一旦形成端细胞，显微注射α-鹅膏蕈碱并不影响端细胞产生胚细胞，但确实阻断了胚细胞和源自小分裂球的细胞的分裂和运动。这些数据表明，合子转录在三带扁蛭胚胎的早期卵裂过程中被激活，并且新合成的转录本是产生端细胞所必需的。因此，存在一个对端细胞产生至关重要的信使RNA合成的早期关键时期，这与原肠胚形成期间细胞分裂和细胞运动所需的信使RNA合成的后期阶段不同。
