Overexpres sion of Skp1B under the ecmA promoter inhibited tight aggregate formation even at 100% O2. No spores and few stalk cells were observed, confirming inability to pro gress past this early stage. Similar results were observed with unfortunately a strain overexpressing the closely related isoform Skp1A, or when either Skp1 was expressed under control of the cotB pro moter. However, overexpressing mutant Skp1A3, which cannot be modified, did not interfere with aggregation, and wild type Skp1 overexpression failed to inhibit cyst formation in the ab sence of PhyA. These strains did not form cyst like structures or spores at lower O2 levels, implying that high O2 also provides an add itional, possibly metabolic, function important for devel opment.
The opposing effects of Skp1 overexpression and blocking its modification suggests that modification stimulates Skp1 activity, which can be modeled as break down of a hypothet ical Inhibitors,Modulators,Libraries activator of cyst formation. In comparison, the requirement of Skp1 glycosylation Inhibitors,Modulators,Libraries for sporulation suggests that for this later developmental step, Skp1 contributes to the breakdown of a hypothet Cilengitide ical inhibitor of sporulation. Without modification, Skp1 is not activated and the inhibitor accumulates. However, overexpression of Skp1 in the phyA Inhibitors,Modulators,Libraries background allows sporulation, which can be interpreted as providing add itional activity to compensate for lack of activation by modification. Similar effects were observed irrespective of the promoter used, or whether wild type Skp1A or B, or mutant Skp1, was overexpressed.
How ever, overexpression of Skp1 at very high levels did not rescue sporulation in phyA cells as well, which might reflect a dominant negative Inhibitors,Modulators,Libraries effect toward SCF complex formation. Separate effects on activators and inhibitors may depend on involvement of distinct F box proteins. Discussion Three novel observations regarding selleck Imatinib development under submerged conditions are presented here, i In the pres ence of high O2 and absence of stirring, cell differenti ation occurs in a radially symmetrical rather than the typical linearly polarized pattern. With their outer husk like cortex and interior germinative cells, these struc tures have the organization of multicellular cysts as occur in animal tissues. The cyst like structures are dis tinct from other terminal states formed by Dictyoste lium, including the dormant unicellular microcyst and the multinucleated macrocyst. Although conditions leading to the formation of cyst like structures are not known to occur naturally, its O2 dependence is likely to be relevant to interpreting O2 signaling in normoxia as outlined below. ii Skp1 hydroxylation is limited by O2 availability.