Giardia and the other diplomonads are unique in their possession of two nuclei that are similar in appearance, DNA content, transcription, and time of replication. Trophozoites have a ploidy of four and the ploidy of cysts is eight, which in turn raises the question of how
Giardia maintains homogeneity between the chromosomes of the same and opposite nuclei.
Giardia has been assumed to be primitively asexual and with no means of transferring DNA between nuclei. These assumptions make it very difficult to explain the remarkably low level of allelic heterozygosity (< 0.01%) in the genome isolate, WB. However, all these assumptions are now in doubt with the identification of meiotic genes in
Giardi, evidence for recombination among isolates, and the evidence for exchange of genetic material between nuclei during the process of encystation.
from Anaerobic Parasitic Protozoa: Genomics and Molecular BiologyFurther reading:Labels: Allelic heterozygosity, Diplomonads, Giardia WB, Ploidy, Trophozoites
Diplomonads are a group of mitochondrion-lacking, binucleated flagellates found in anaerobic or micro-aerophilic environments. Most research on diplomonads has focused on Giardia, which is a major cause of water-borne enteric disease in humans and other animals. The first diplomonad to have its genome sequenced was a Giardia isolate (WB) and the 11.7 million basepair genome is compact in structure and content with simplified basic cellular machineries and metabolism. Currently the genomes of several other Giardia isolates and diplomonads (the fish pathogens Spironucleus vortens and S. salmonicida) are being sequenced.
from Anaerobic Parasitic Protozoa: Genomics and Molecular Biology
Further reading:Labels: Binucleated flagellates, Diplomonads, Giardia, Giardia lamblia, Spironucleus, Spironucleus salmonicida, Spironucleus vortens, Water-borne enteric disease
In a forthcoming book on
anaerobic protozoa, internationally acclaimed researchers critically review the most important aspects of research on anaerobic parasitic protozoa, providing the first coherent picture of their genomics and molecular biology since the publication of the genomes.
Chapters are written from a molecular and genomic perspective and contain speculative models upon which future research efforts can be based. Topics include: the genomes of
Entamoeba histolytica,
Trichomonas vaginalis,
Giardia and other diplomonads; the cytoskeletons of
Entamoeba histolytica,
Giardia lamblia and
Trichomonas vaginalis; genomic analyses and manipulation of gene expression in
Entamoeba histolytica; nuclear and chromosomal structure and replication in
Giardia; and the mitochondrion-like organelles of a fourth anaerobe,
Blastocystis.
from Anaerobic Parasitic Protozoa: Genomics and Molecular BiologyFurther reading:Labels: Blastocystis, Diplomonads, Entamoeba histolytica, Giardia, Giardia lamblia, Mitochondrion-like organelles, Trichomonas vaginalis