Gao Tong, Roisin-Bouffay Celine, Hatton R Diane, Tang Lei, Brock Debra A, DeShazo Tiffany, Olson Laura, Hong Wan-Pyo, Jang Wonhee, Canseco Elvia, Bakthavatsalam Deenadayalan, Gomer Richard H
Howard Hughes Medical Institute, MS-140, Rice University, 6100 S. Main Street, Houston, TX 77005-1892, USA.
Eukaryot Cell. 2007 Sep;6(9):1538-51. doi: 10.1128/EC.00169-07. Epub 2007 Jul 27.
Developing Dictyostelium cells form aggregation streams that break into groups of approximately 2 x 10(4) cells. The breakup and subsequent group size are regulated by a secreted multisubunit counting factor (CF). To elucidate how CF regulates group size, we isolated second-site suppressors of smlA(-), a transformant that forms small groups due to oversecretion of CF. smlA(-) sslA1(CR11) cells form roughly wild-type-size groups due to an insertion in the beginning of the coding region of sslA1, one of two highly similar genes encoding a novel protein. The insertion increases levels of SslA. In wild-type cells, the sslA1(CR11) mutation forms abnormally large groups. Reducing SslA levels by antisense causes the formation of smaller groups. The sslA(CR11) mutation does not affect the extracellular accumulation of CF activity or the CF components countin and CF50, suggesting that SslA does not regulate CF secretion. However, CF represses levels of SslA. Wild-type cells starved in the presence of smlA(-) cells, recombinant countin, or recombinant CF50 form smaller groups, whereas sslA1(CR11) cells appear to be insensitive to the presence of smlA(-) cells, countin, or CF50, suggesting that the sslA1(CR11) insertion affects CF signal transduction. We previously found that CF reduces intracellular glucose levels. sslA(CR11) does not significantly affect glucose levels, while glucose increases SslA levels. Together, the data suggest that SslA is a novel protein involved in part of a signal transduction pathway regulating group size.
发育中的盘基网柄菌细胞形成聚集流，这些聚集流会分裂成约2×10⁴个细胞的群体。这种分裂以及随后的群体大小受一种分泌型多亚基计数因子（CF）调控。为阐明CF如何调控群体大小，我们分离了smlA⁻的第二位点抑制子，smlA⁻是一种由于CF分泌过多而形成小群体的转化体。smlA⁻ sslA1(CR11)细胞由于在sslA1编码区起始处的插入而形成大致野生型大小的群体，sslA1是编码一种新蛋白质的两个高度相似基因之一。该插入增加了SslA的水平。在野生型细胞中，sslA1(CR11)突变形成异常大的群体。通过反义技术降低SslA水平会导致形成更小的群体。sslA(CR11)突变不影响CF活性的细胞外积累或CF成分countin和CF50，这表明SslA不调控CF的分泌。然而，CF会抑制SslA的水平。在存在smlA⁻细胞、重组countin或重组CF50的情况下饥饿培养的野生型细胞形成较小的群体，而sslA1(CR11)细胞似乎对smlA⁻细胞、countin或CF50的存在不敏感，这表明sslA1(CR11)插入影响CF信号转导。我们之前发现CF会降低细胞内葡萄糖水平。sslA(CR11)对葡萄糖水平没有显著影响，而葡萄糖会增加SslA水平。综合来看，这些数据表明SslA是一种新蛋白质，参与了调控群体大小的部分信号转导途径。
