A Cell Number-Counting Factor Regulates Levels of a Novel Protein, SslA, as Part of a Group Size Regulation Mechanism in Dictyostelium

Abstract

Developing Dictyostelium cells form aggregation streams that break into groups of ϳ2 ؋ 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.

Regulation of Ammonia Homeostasis by the Ammonium Transporter AmtA in Dictyostelium discoideum

“…3G). Since glucose has been suggested to increase aggregation size, we measured intracellular levels of glucose (34,22). We found that glucose levels in amtA Ϫ cells were higher than those in wild-type cells (Fig.…”

Phylogeny and Molecular Evolution of Tricyrtis (Liliaceae s.l.) Inferred from Plastid DNA matK Spacer Nucleotide Sequences

“…However, in Bayesian inference studies, T. nana has shown either a medium (rps16, Hong & Jury, 2011) or a slow (matK, Figure 2) evolutionary rate compared to the remainder of the genus. However, the generation time differences between T. nana and other Tricyrtis taxa are much less than for example between humans and Drosophila or Dictyostelium (Ehrenman et al, 2003;Gao et al, 2007;Hong, Qi, Brabant, Bosco, & Martinez, 2008) and may not be a significant factor in this case.…”

Gene Prioritization by Compressive Data Fusion and Chaining

“…Three out of the five validated bacterial growth genes– abpC , smlA and pten , are involved in actin polymerization and cell motility [ 33 – 36 ]. One explanation for the enrichment of these genes is that the availability of preexisting knockout strains may be enriched with cell motility genes.…”