Identification of Actin Filament Interactors in Giardia lamblia

The deep-branching protozoan parasite Giardia lamblia is the causative agent of the intestinal disease giardiasis. Consistent with its proposed evolutionary position, many pathways are minimalistic or divergent, including its actin cytoskeleton. Giardia is the only eukaryote known to lack all canonical actin-binding proteins. Previously, our lab identified a number of non-canonical Giardia lamblia actin (GlActin) interactors; however, these proteins appeared to interact only with monomeric or globular actin (G-actin), rather than filamentous actin (F-actin). To identify interactors, we used a chemical crosslinker to preserve native interactions, followed by an anti-GlActin antibody, Protein A affinity chromatography, and liquid chromatography coupled to mass spectrometry. We found 46 putative actin interactors enriched in the conditions favoring F-actin. None of the proteins identified contain known actin-interacting motifs, and many lacked conserved domains. Each potential interactor was then tagged with the fluorescent protein mNeonGreen and visualized in live cells. We categorized the proteins based on their primary localization; localizations included ventral disc, marginal plate, nuclei, flagella, plasma membrane, and internal membranes. One protein from each category was co-localized with GlActin using immunofluorescence microscopy. We also co-immunoprecipitated one protein from each category and confirmed three interactions. Most of the localization patterns are consistent with previously demonstrated GlActin functions, but the ventral disc represents a new category of actin interactor localization. These results suggest a role for GlActin in ventral disc function, which has previously been controversial.

Two new genera and three new species of freshwater crabs (Crustacea: Pseudothelphusidae: Potamocarcinini) from Chiapas, Mexico

Two new genera, Sylvathelphusa n. gen. and Tzotzilthelphusa n. gen., and three new species, Sylvathelphusa kalebi n. sp., S. cavernicola n. sp. and Tzotzilthelphusa villarosalensis n. sp., of the tribe Potamocarcinini, family Pseudothelphusidae, are described from Chiapas, Mexico. Sylvathelphusa n. gen. is characterized by a male gonopod with the marginal plate between the caudal and mesial surfaces abruptly widening distally and forming a triangular apical projection; and a mesial process as a strong, acute spine forming a 90º angle with respect to the principal axis of the gonopod. Tzotzilthelphusa n. gen. exhibits a male gonopod strongly bent laterally in the distal third, and a mesial surface rounded distally with acute spinules. Sylvathelphusa n. gen. is similar to Potamocarcinus in gonopod morphology, in both straight and with a mesial process developed as strong tooth in a similar shape and position. Tzotzilthelphusa n. gen. is similar to Phrygiopilus in that the gonopods of both genera develop a supra-apical process that is a continuation of the mesial surface. The new taxa come from the Los Altos de Chiapas region and bring the total number of pseudothelphusid genera in Chiapas to 11.

Giardia muris and Giardia duodenalis groups: ultrastructural differences between the trophozoites

Trophozoites of the Giardia muris group from hamsters, domestic rats and mice and of the Giardia duodenalis group from hamsters and domestic rats were examined by transmission electron microscopy. The basic ultrastructure of the trophozoites was similar. Differences were shown in the morphology of the ventrolateral flange of the trophozoites of Giardia muris and Giardia duodenalis groups. Marginal plates are less developed in the species of the Giardia duodenalis group. In this group, the distal extremity of the lateral flange is short and thick and the marginal plate does not penetrate into the distal extremity of the flange. In the Giardia muris group, the ventro-lateral flange is well developed and narrow and the marginal plate penetrates the distal extremity of the flange. The osmiophilic lamella, which accompanies the dorsal surface of the marginal plate is seen only in the Giardia muris group.