The PfAP2-G2 transcription factor is a critical regulator of gametocyte maturation.

Differentiation from asexual blood stages to mature sexual gametocytes is required for the transmission of malaria parasites. Here, we report that the ApiAP2 transcription factor, PfAP2-G2 (PF3D7_1408200) plays a critical role in the maturation of Plasmodium falciparum gametocytes. PfAP2-G2 binds to the promoters of a wide array of genes that are expressed at many stages of the parasite life cycle. Interestingly, we also find binding of PfAP2-G2 within the gene body of almost 3,000 genes, which strongly correlates with the location of H3K36me3 and several other histone modifications as well as Heterochromatin Protein 1 (HP1), suggesting that occupancy of PfAP2-G2 in gene bodies may serve as an alternative regulatory mechanism. Disruption of pfap2-g2 does not impact asexual development, but the majority of sexual parasites are unable to mature beyond stage III gametocytes. The absence of pfap2-g2 leads to overexpression of 28% of the genes bound by PfAP2-G2 and none of the PfAP2-G2 bound genes are downregulated, suggesting that it is a repressor. We also find that PfAP2-G2 interacts with chromatin remodeling proteins, a microrchidia (MORC) protein, and another ApiAP2 protein (PF3D7_1139300). Overall our data demonstrate that PfAP2-G2 establishes an essential gametocyte maturation program in association with other chromatin-related proteins.

A role for polyglucans in a model sea urchin embryo cellular interaction.

The enzymatic activities of commercially prepared glycosidases were verified by direct chemical assays using defined substrates and fixed and live sea urchin (Lytechinus pictus) embryos to determine if a model cellular interaction of interest to developmental biologists for over a century (interaction of archenteron tip and roof of the blastocoel) was mediated by glycans. Glycosidases (active and denatured) were incubated with microdissected archenterons and blastocoel roofs in a direct assay to learn if their enzymatic activities could prevent the normal adhesive interaction. Of the five glycosidases tested only ß-amylase (an exoglycosidase) immediately inhibited the interaction at relatively low unit activity. α-Amylase (an endoglycosidase) had no measurable effect, while other glycosidases (α-glucosidase, ß-glucosidase, ß-galactosidase) only substantially inhibited adhesion after a 12-h incubation. We demonstrated that the five glycosidases were active (not inhibited) in the presence of embryo materials, and that cleaved sugars could be detected directly after incubation of some enzymes with the embryos. The biochemical purity of the enzymes was examined using gel electrophoresis under denaturing conditions, and the absence of contaminating proteases was confirmed using Azocoll™ substrate. As we cannot entirely rule out the presence of minor contaminating enzymatic activities, only inhibitions of adhesion after very short incubations with enzyme were considered significant and biologically relevant. Although glycans in indirect experiments have been implicated in mediating the interaction of the tip of the archenteron and roof of the blastocoel, to our knowledge, this is the first study that directly implicates polyglucans with terminal 1,4-linked glucose residues in this adhesive event.

Adsorption of nonionic surfactants (CnEm) at the silica-water and cellulose-water interface.

The adsorption of nonionic surfactants to the silica-water and cellulose-water interfaces was studied using optical reflectometry (OR) and soft-contact atomic force microscopy imaging. The polyethylene oxide alkyl ethers C(14)E(6) and C(16)E(8) were shown to readily adsorb to both interfaces. The kinetics of the adsorption process as well as the equilibrium surface excess was determined using OR. In agreement with previous studies, the short headgroup surfactant C(14)E(6) adsorbed to a greater extent than the longer headgroup surfactant C(16)E(8) on silica. This trend was also observed for the cellulose-water interface. The structure of the adsorbed surfactant layer above the critical surface aggregation concentration (csac) was visualized using the soft contact imaging technique for both interfaces. On the silica surface, the layer structure for both surfactants mostly showed spherical aggregates, however, with some elongation into rods being more prevalent for C(14)E(6). Similar structures were observed on the cellulose surface, but imaging was more difficult due to the soft gel-like nature of the cellulose thin film in water. This suggests that these surfactants adsorb in a cooperative fashion above the critical micelle concentration (cmc) with a similar interaction between surfactant headgroup and surface for both silica and cellulose. No evidence was seen for the penetration of surfactant molecules into the cellulose surface or any solubilization of the interface.