Editing Archezoa (section)

== Original mitochondria lost ==
Eukaryotic protists lacking mitochondria were discovered to have experienced secondary mitochondrial loss, meaning that their ancestors once possessed mitochondria but that these mitochondria had, over time, been transformed, reduced, or lost. In some of these organisms, mitochondria had degraded into simpler double-membrane bound organelles known as [[mitosomes]] and [[hydrogenosomes]]. Some of both types of organelles are known to have fully lost their genome.<ref>{{Cite journal |last1=Embley |first1=T. Martin |last2=Hirt |first2=Robert P. |date=1998 |title=Early branching eukaryotes? |journal=Current Opinion in Genetics & Development |volume=8 |issue=6 |pages=624–629 |doi=10.1016/S0959-437X(98)80029-4 |pmid=9914207 |lang=en |url=https://linkinghub.elsevier.com/retrieve/pii/S0959437X98800294|url-access=subscription }}</ref><ref>{{cite journal |last=Roger |first=Andrew J. |year=1999 |title=Reconstructing early events in eukaryotic evolution |journal=The American Naturalist |volume=154 |issue=S4 |pages=S146–S163 |doi=10.1086/303290 |pmid=10527924 |bibcode=1999ANat..154S.146R |s2cid=32138852 |issn=0003-0147 |lang=en |url=https://www.journals.uchicago.edu/doi/10.1086/303290|url-access=subscription }}</ref> 

Initial discoveries found that amitochondriate organisms appeared to express mitochondrial Hsp60 and Hsp70 proteins from the nuclear DNA of the organism. This indicated that the ancestors of these organisms once possessed mitochondria which expressed these proteins, but that these genes had migrated to their nuclear DNA over time as a result of endosymbiotic gene transfer.<ref>{{cite journal |last1=Clark |first1=C.G. |last2=Roger |first2=A.J. |year=1995 |title=Direct evidence for secondary loss of mitochondria in Entamoeba histolytica |journal=Proc. Natl. Acad. Sci. USA |volume=92 |issue=14 |pages=6518–6521|doi=10.1073/pnas.92.14.6518 |pmid=7604025 |pmc=41549 |bibcode=1995PNAS...92.6518C |doi-access=free }}</ref><ref>{{cite journal |last=Roger |first=A.J. |year=1999 |title=Reconstructing early events in eukaryotic evolution |journal=Am. Nat. |volume=154 |issue=S4 |pages=S146–S163|doi=10.1086/303290 |pmid=10527924 |bibcode=1999ANat..154S.146R |s2cid=32138852 }}</ref>

As a result, the argument that some extant eukaryotes lacking mitochondria had emerged from the eukaryotic lineage before mitochondria were acquired was falsified.<ref>{{cite journal |last1=Embley |first1=T.M. |last2=Martin |first2=W. |year=2006 |title=Eukaryotic evolution, changes and challenges |journal=Nature |volume=440 |issue=7084 |pages=623–630|doi=10.1038/nature04546 |pmid=16572163 |bibcode=2006Natur.440..623E |s2cid=4396543 |url=https://zenodo.org/record/897869 }}</ref>