The Origin of Mitochondria



Running head: THE ORIGINS OF MITOCHONDRIA The Origins of Mitochondria The origins of mitochondria remain an important object of professional interest. Dozens of researchers explored the origins of mitochondria and their implications for future research. This paper provides a brief summary of the article Microsporidia, Amitochondrial Protists, Possess a 70-kDa Heat Shock Protein of Mitochondrial Evolutionary Origin. The purpose, methods, and results of the study are discussed. The information from the article is compared to what other articles say. Recommendations for future research are provided. Keywords: mitochondria, origins, microsporidia, evolution. The Origins of Mitochondria The origins of mitochondria remain one of the most popular objects of professional interest. Much has been written and said about the structure of various genes and their implications for understanding the history of mitochondria. In this sense, the study conducted by Peyretaillade, Broussolle, Peyret, Metenier, Gouy and Vivares (1998) deserves special attention. The researchers claim that, based on previous studies, “three eukaryotic protozoan phyla, Microsporidia, Metamonada, and Parabasala were considered to be the earliest-diverging lineages among all extant protists” (Peyretaillade et al., 1998, p.683). As far as these organisms lack mitochondrial features, they were believed to originate from the earliest eukaryotes living before mitochondria (Peyretaillade et al., 1998). However, just recently, three nuclear-encoded genes with mitochondrial features have been found in a Trichomonas vaginalis genome (Peyretaillade et al., 1998). This being said, the researchers decided to test previous assumptions about the origins of mitochondria and re-assess the immunological evidence for the presence of mitochondrial features in Encephalitozoon hellem (Peyretaillade et al., 1998). The purpose of the study was to test a hypothesis that Microsporidia and Metamonada lacked even the most primitive forms of mitochondria (Peyretaillade et al., 1998). The researchers focused on the analysis of the hsp70 gene family, since the latter contains one nuclear gene encoding a protein expressed in mitochondrion (Peyretaillade et al., 1998). The hsp70 gene family is also very similar to ?-proteobacterial homologs, which is suggestive of mitochondrial evolutionary origins for HSP70-encoding genes (Peyretaillade et al., 1998). Peyretaillade et al. (1998) chose to explore the presence of an hsp70 gene sequence in E. cuniculi and E. hellem genomes. The presence or absence of mitochondrial features had to confirm or reject the mitochondrial origins of the hsp70 gene sequence (Peyretaillade et al., 1998). The researchers developed complex methodology, incorporating the elements of gene cloning and phylogenic analysis (Peyretaillade et al., 1998). Peyretaillade et al. (1998) obtained E. cuniculi and E. hellem samples and cloned the hsp70 gene, followed by pulsed-field gel electrophoresis and sequence analysis (Peyretaillade et al., 1998). The researchers found that the genomes of E. cuniculi and E. hellem had a single copy of the mitochondrially expressed HSP70 protein (Peyretaillade et al., 1998). In the meantime, other parasites have more than one mitochondrially expressed gene copies (Peyretaillade et al., 1998). These results suggest that the HSP70 protein evolved from mitochondrial-like species and, consequentially, cast doubts on the existence of amitochondrial eukaryotes (Peyretaillade et al., 1998). Not all researchers readily agree that the HSP70-gene sequences in E. cuniculi and E. hellem genomes are primarily connected to mitochondrial eukaryotes. While Peyretallade et al. (1998) focused on the analysis of hsp-70 genes, Andersson et al. (1998) devoted much of their time to the study of Rickettsia Prowazekii and its relation to the origins of mitochondria. Andersson et al. (1998) were able to describe the entire genome sequence of Rickettsia prowazekii, which is responsible for the development of epidemic typhus in humans. The Rickettsia prowazekii genome was found to contain a total of 834 protein-coding genes, which exhibited considerable similarities with mitochondrial genes (Andersson et al., 1998). ATP production in Rickettsia prowazekii is also similar to that in mitochondria (Andersson et al., 1998). Andersson et al. (1998) discovered that the R. prowazekii had the highest concentration of non-coding DNA, which can be degraded remnants of mitochondrial sequences. for this reason, Andersson et al. (1998) consider that the R. prowazekii genome sequence is the closest to mitochondria than any other genome sequence studied before. Apparently, the origins of mitochondria are not well understood. More often than not, researchers apply to phylogenic analysis, which poses too many questions. In the meantime, researchers cannot define where and how mitochondria originated and how the current state of genes and genome sequences can explain the origins of mitochondria. Peyretaillade et al. (1998) are right: immunocytochemical analyses should be used to reconsider the nature and origins of mitochondrial proteins and mitochondria-related genome sequences. Future researchers must focus on the analysis of other mitochondrial remnants. References Andersson, S.G., Zomorodipour, A., Andersson, J.O., Sicheritz-Ponten, T., Alsmark, U.C., Podowski, M., Naslund, A.K., Eriksson, A.S. &amp. Kurland, C.G. (1998). The genome sequence of Rickettsia prowazekii and the origin of mitochondria. Nature, 396, 133-143. Peyretaillade, E., Broussolle, V., Peyret, P., Metenier, G., Gouy, M. &amp. Vivares, C.P. (1998). Microsporidia, amitochondrial protists, possess a 70-kDa heat shock protein gene of mitochondrial evolutionary origin. Molecular Biology and Evolution, 15(6), 683-689.