The Glycosylphosphatidylinositol Anchor: A Linchpin for Cell Surface Versatility of Trypanosomatids.

The use of glycosylphosphatidylinositol (GPI) to anchor proteins to the cell surface is widespread among eukaryotes. The GPI-anchor is covalently attached to the C-terminus of a protein and mediates the protein's attachment to the outer leaflet of the lipid bilayer. GPI-anchored proteins have a wide range of functions, including acting as receptors, transporters, and adhesion molecules. In unicellular eukaryotic parasites, abundantly expressed GPI-anchored proteins are major virulence factors, which support infection and survival within distinct host environments. While, for example, the variant surface glycoprotein (VSG) is the major component of the cell surface of the bloodstream form of African trypanosomes, procyclin is the most abundant protein of the procyclic form which is found in the invertebrate host, the tsetse fly vector. Trypanosoma cruzi, on the other hand, expresses a variety of GPI-anchored molecules on their cell surface, such as mucins, that interact with their hosts. The latter is also true for Leishmania, which use GPI anchors to display, amongst others, lipophosphoglycans on their surface. Clearly, GPI-anchoring is a common feature in trypanosomatids and the fact that it has been maintained throughout eukaryote evolution indicates its adaptive value. Here, we explore and discuss GPI anchors as universal evolutionary building blocks that support the great variety of surface molecules of trypanosomatids.

To the Surface and Back: Exo- and Endocytic Pathways in Trypanosoma brucei.

Trypanosoma brucei is one of only a few unicellular pathogens that thrives extracellularly in the vertebrate host. Consequently, the cell surface plays a critical role in both immune recognition and immune evasion. The variant surface glycoprotein (VSG) coats the entire surface of the parasite and acts as a flexible shield to protect invariant proteins against immune recognition. Antigenic variation of the VSG coat is the major virulence mechanism of trypanosomes. In addition, incessant motility of the parasite contributes to its immune evasion, as the resulting fluid flow on the cell surface drags immunocomplexes toward the flagellar pocket, where they are internalized. The flagellar pocket is the sole site of endo- and exocytosis in this organism. After internalization, VSG is rapidly recycled back to the surface, whereas host antibodies are thought to be transported to the lysosome for degradation. For this essential step to work, effective machineries for both sorting and recycling of VSGs must have evolved in trypanosomes. Our understanding of the mechanisms behind VSG recycling and VSG secretion, is by far not complete. This review provides an overview of the trypanosome secretory and endosomal pathways. Longstanding questions are pinpointed that, with the advent of novel technologies, might be answered in the near future.

18S rRNA gene sequence-structure phylogeny of the Trypanosomatida (Kinetoplastea, Euglenozoa) with special reference to Trypanosoma.

Parasites of the order Trypanosomatida are known due to their medical relevance. Despite the progress made in the past decades on understanding the evolution of this group of organisms, there are still many open questions that require robust phylogenetic markers to increase the resolution of trees. Using two known 18S rRNA gene template structures (from Trypanosoma cruzi Chagas, 1909 and Trypanosoma brucei Plimmer and Bradford, 1899), individual 18S rRNA gene secondary structures were predicted by homology modeling. Sequences and their secondary structures, automatically encoded by a 12-letter alphabet (each nucleotide with its three structural states, paired left, paired right, unpaired), were simultaneously aligned. Sequence-structure trees were generated by neighbor joining and/or maximum likelihood. The reconstructed trees allowed us to discuss not only the big picture of trypanosomatid phylogeny but also a comprehensive sampling of trypanosomes evaluated in the context of trypanosomatid diversity. The robust support (bootstrap > 75) for well-known clades and critical branches suggests that the simultaneous use of 18S rRNA sequence and secondary structure data can reconstruct robust phylogenetic trees and can be used by the trypanosomatid research community for future analysis.

In Vitro Cellular Division of Trypanosoma abeli Reveals Two Pathways for Organelle Replication.

Since the observation of the great pleomorphism of fish trypanosomes, in vitro culture has become an important tool to support taxonomic studies investigating the biology of cultured parasites, such as their structure, growth dynamics, and cellular cycle. Relative to their biology, ex vivo and in vitro studies have shown that these parasites, during the multiplication process, duplicate and segregate the kinetoplast before nucleus replication and division. However, the inverse sequence (the nucleus divides before the kinetoplast) has only been documented for a species of marine fish trypanosomes on a single occasion. Now, this previously rare event was observed in Trypanosoma abeli, a freshwater fish trypanosome. Specifically, from 376 cultured parasites in the multiplication process, we determined the sequence of organelle division for 111 forms; 39% exhibited nucleus duplication prior to kinetoplast replication. Thus, our results suggest that nucleus division before the kinetoplast may not represent an accidental or erroneous event occurring in the main pathway of parasite reproduction, but instead could be a species-specific process of cell biology in trypanosomes, such as previously noticed for Leishmania. This "alternative" pathway for organelle replication is a new field to be explored concerning the biology of marine and freshwater fish trypanosomes.

In vitro cellular division of trypanosoma abeli reveals two pathways for organelle replication

Since the observation of the great pleomorphism of fish trypanosomes, in vitroculture has become an important tool to support taxonomic studies investigat-ing the biology of cultured parasites, such as their structure, growth dynamics,and cellular cycle. Relative to their biology, ex vivo and in vitro studies haveshown that these parasites, during the multiplication process, duplicate andsegregate the kinetoplast before nucleus replication and division. However,the inverse sequence (the nucleus divides before the kinetoplast) has onlybeen documented for a species of marine fish trypanosomes on a single occa-sion. Now, this previously rare event was observed inTrypanosoma abeli,afreshwater fish trypanosome. Specifically, from 376 cultured parasites in themultiplication process, we determined the sequence of organelle division for111 forms; 39% exhibited nucleus duplication prior to kinetoplast replication.Thus, our results suggest that nucleus division before the kinetoplast may notrepresent an accidental or erroneous event occurring in the main pathway ofparasite reproduction, but instead could be a species-specific process of cellbiology in trypanosomes, such as previously noticed forLeishmania. This "al-ternative" pathway for organelle replication is a new field to be explored con-cerning the biology of marine and freshwater fish trypanosomes.

In vitro cellular division of trypanosoma abeli reveals two pathways for organelle replication

Since the observation of the great pleomorphism of fish trypanosomes, in vitroculture has become an important tool to support taxonomic studies investigat-ing the biology of cultured parasites, such as their structure, growth dynamics,and cellular cycle. Relative to their biology, ex vivo and in vitro studies haveshown that these parasites, during the multiplication process, duplicate andsegregate the kinetoplast before nucleus replication and division. However,the inverse sequence (the nucleus divides before the kinetoplast) has onlybeen documented for a species of marine fish trypanosomes on a single occa-sion. Now, this previously rare event was observed inTrypanosoma abeli,afreshwater fish trypanosome. Specifically, from 376 cultured parasites in themultiplication process, we determined the sequence of organelle division for111 forms; 39% exhibited nucleus duplication prior to kinetoplast replication.Thus, our results suggest that nucleus division before the kinetoplast may notrepresent an accidental or erroneous event occurring in the main pathway ofparasite reproduction, but instead could be a species-specific process of cellbiology in trypanosomes, such as previously noticed forLeishmania. This "al-ternative" pathway for organelle replication is a new field to be explored con-cerning the biology of marine and freshwater fish trypanosomes.