Killian C E, Wilt F H
Department of Zoology, University of California, Berkeley 94720.
Dev Biol. 1989 May;133(1):148-56. doi: 10.1016/0012-1606(89)90306-0.
In this report we further characterize the expression of the gene that encodes the 50-kDa spicule matrix protein (SM50) during development of the sea urchin Strongylocentrotus purpuratus. Quantitative measurements of SM50 mRNA levels using the single-stranded probe excess titration technique indicate that SM50 transcript levels attain a maximum level of 8000 to 10,000 transcripts per embryo by the gastrula stage, representing 120 to 200 SM50 mRNAs per primary mesenchyme cell. Experiments analyzing run-on transcription in nuclei isolated at different stages of development indicate that the sharp increase in SM50 mRNA levels occurring at the time of primary mesenchyme ingression is concomitant with an increase in transcription of the SM50 gene. We have also analyzed the RNA sequences present on polyribosomes at different stages of development. These studies indicate that SM50 mRNA is present on polyribosomes as soon as it begins to accumulate (which is well in advance of overt spicule formation) and SM50 mRNA remains on polyribosomes through subsequent development. From estimates of the rate of SM50 protein synthesis based on these data, we calculated that the maximum amount of SM50 accumulated during development through the 4-day pluteus stage is approximately 7.4 pg/embryo. This approximation is concordant with the amount of SM50 actually found in the sea urchin embryo.
在本报告中，我们进一步描述了编码50 kDa骨针基质蛋白（SM50）的基因在紫海胆发育过程中的表达情况。使用单链探针过量滴定技术对SM50 mRNA水平进行定量测量表明，到原肠胚阶段，SM50转录本水平达到每个胚胎8000至10000个转录本的最高水平，相当于每个初级间充质细胞有120至200个SM50 mRNA。分析在不同发育阶段分离的细胞核中转录进行情况的实验表明，在初级间充质细胞内陷时SM50 mRNA水平的急剧增加与SM50基因转录的增加同时发生。我们还分析了不同发育阶段多核糖体上存在的RNA序列。这些研究表明，SM50 mRNA一旦开始积累（远在明显的骨针形成之前）就存在于多核糖体上，并且在随后的发育过程中SM50 mRNA一直留在多核糖体上。根据这些数据对SM50蛋白质合成速率的估计，我们计算出在发育到4天的长腕幼虫阶段期间积累的SM50的最大量约为7.4 pg/胚胎。这个近似值与在海胆胚胎中实际发现的SM50量一致。
