Good J Randall, Cabral Matthew, Sharma Sujata, Yang Jun, Van Driessche Nancy, Shaw Chad A, Shaulsky Gad, Kuspa Adam
Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, 77030, USA.
Development. 2003 Jul;130(13):2953-65. doi: 10.1242/dev.00523.
The tag genes of Dictyostelium are predicted to encode multi-domain proteins consisting of serine protease and ATP-binding cassette transporter domains. We have identified a novel tag gene, tagA, which is involved in cell type differentiation. The tagA mRNA accumulates during the first four hours of development, whereas TagA protein accumulates between two and ten hours of development and decreases thereafter. Wild-type cells express tagA in prespore cells and mature spores, defining tagA expression as prespore specific. However, tagA mutant cells that activate the tagA promoter do not sporulate, but instead form part of the outer basal disc and lower cup of the fruiting body. tagA mutant aggregates elaborate multiple prestalk cell regions during development and produce spores asynchronously and with low viability. tagA mutants produce about twice as many prestalk cells as the wild type as judged by a prestalk cell reporter construct. When mixed with wild-type cells, tagA(-) cells become overrepresented in the prestalk cell population, suggesting that this phenotype is cell-autonomous. These results suggest that TagA is required for the specification of an initial population of prespore cells in which tagA is expressed. Expression profiling uncovered a delay in the transcriptional program between 2 and 6 hours, coincident with TagA expression, revealing an early function for TagA. TagA also appears to play a general role in cell fate determination since tagA mutants express a spore coat protein gene (cotB) within vacuolated cells that form part of the stalk and they express a prestalk/stalk-specific gene (ecmB) within cells that become spores. The expression of TagA at two hours of development, the observed coincident delay in the transcriptional program and the subsequent mis-expression of cell-type specific genes provide evidence for cell fate determination beginning in some cells much earlier than previously believed.
盘基网柄菌的标签基因预计编码由丝氨酸蛋白酶和ATP结合盒转运蛋白结构域组成的多结构域蛋白。我们鉴定出了一个新的标签基因tagA，它参与细胞类型分化。tagA mRNA在发育的前四个小时积累，而TagA蛋白在发育的两到十个小时之间积累，之后减少。野生型细胞在前孢子细胞和成熟孢子中表达tagA，将tagA的表达定义为前孢子特异性。然而，激活tagA启动子的tagA突变细胞不能形成孢子，而是形成子实体外基盘和下杯的一部分。tagA突变聚集体在发育过程中形成多个前柄细胞区域，并异步产生孢子且活力较低。通过前柄细胞报告构建体判断，tagA突变体产生的前柄细胞数量大约是野生型的两倍。当与野生型细胞混合时，tagA(-)细胞在前柄细胞群体中所占比例过高，表明这种表型是细胞自主的。这些结果表明，TagA是表达tagA的初始前孢子细胞群体特化所必需的。表达谱分析发现，在2至6小时之间的转录程序出现延迟，这与TagA的表达一致，揭示了TagA的早期功能。TagA似乎在细胞命运决定中也发挥着普遍作用，因为tagA突变体在形成柄一部分的空泡化细胞中表达孢子壁蛋白基因（cotB），并且在变成孢子的细胞中表达前柄/柄特异性基因（ecmB）。在发育两小时时TagA的表达、观察到的转录程序的同步延迟以及随后细胞类型特异性基因的错误表达，为细胞命运决定在某些细胞中比以前认为的要早得多开始提供了证据。
