RISE OF THE RISE OF THE MITOCHONDRIONMITOCHONDRION

COMMUNITY OF REASONCOMMUNITY OF REASON13 OCTOBER, 201313 OCTOBER, 2013

MINDY L. WALKER, PH.D.MINDY L. WALKER, PH.D.ASSOCIATE PROFESSOR OF BIOLOGYASSOCIATE PROFESSOR OF BIOLOGYROCKHURST UNIVERSITYROCKHURST UNIVERSITY

OVERVIEW

• Prok vs. Euk

• Mitochondrial A&P

• Origin of eukaryotic cells, some 2.5 Bya, via endosymbiosis

• Consequences: separate mitochondrial and chloroplast genomes

• mtDNA/Mitochondrial Eve

GENERAL PHYLOGENY

PROK’S VS. EUK’S

MITOCHONDRIAL A

MITOCHONDRIAL P

OR, MORE SIMPLY…

EVOLUTION OF EUKARYOTES

• As early as 1.5 Bya, fossil eukaryotic cells appear

Reproduced from Schopf, J.W., Scientific American 239 (1978): 111-138. Courtesy of J. William Schopf, Professor of Paleobiology & Director of IGPP CSEOL

Microfossils of probable eukaryotic cells

ENDOSYMBIOSIS – CELLULAR INCEPTION

ENDOSYMBIOSIS EXPLAINED

WHAT ABOUT THE OTHER M-B ORGANELLES?

EVIDENCE – EXTANT ENDOSYMBIOTIC SPP.

The ciliate Paramecium bursaria houses hundreds of symbiotic green algae which can be liberated from the Protistan cell and live independently

Courtesy of Anthony L. Swinehart, Hillsdale College

EVIDENCE - PROK VS. MITO

EVIDENCE - ORGANELLE DNA DIFFERS FROM NUCLEAR DNA

1) In location: organelle vs. nucleus

2) In organization: single circular vs. multiple linear strands

3) In function: which proteins are coded for and how are they regulated

4) In mode of replication and inheritance

EVIDENCE - MTDNA

• mtDNA is a single, ds, circular DNA molecule

• There are several copies in each mitochondrion

• mtDNA is similar to prokaryotic DNA: there are no histones, and mtDNA genes contain no introns

• Because mtDNA is in a highly oxidizing environment, it has a much higher mutation rate than nuclear DNA

• mtDNA genes code for mitochondrial ribosomes and tRNAs

• mtDNA relies on nuclear gene products for replication and transcription

EVIDENCE - MTDNA

CHLOROPLAST DNA (CPDNA)

• CP DNA is a single, ds, circular DNA molecule (the smallest of the three plant genomes)

• 20-200 copies in every chloroplast

• Inherited uniparentally from the maternal parent

• CP DNA contains some 113 genes, 20 of which contain introns; most of these genes are involved with photosynthesis and plastid gene expression

• Structural rearrangements of the genome are rare (but when they occur, they are useful in establishing relationships phylogenetically)

Primary, secondary and tertiary endosymbiosis

Adapted Cracraft, J. and M. J. Donoghue (Eds). Assembling the Tree of Life. Oxford University Press, 2004.

ORIGIN OF VARIOUS PHOTOSYNTHETIC EUKARYOTES

The Origin of early Eukaryotic Ancestors leading to the lineages of animals and fungi was probably an independent event from that of the origin of plants

TRANSFER OF GENES BETWEEN ORGANELLES AND NUCLEUS

• Many genes were transferred to the eukaryotic nucleus and vice versa

• Chloroplasts synthesize only a small portion of the proteins they use

• Transfer of nuclear genes coding for symbiotic organelle proteins

• Such HGTs improve efficiency and reduce the likelihood of mutations, but complicates their use in establishing phylogenies

– mtDNA’s mutation rate is ten times faster than that of nuclear DNA– mtDNA is passed down from mother to offspring without recombination

MITOCHONDRIAL DNA IS USED TO STUDY CLOSELY RELATED SPECIES

grandparents

parents

child

Nuclear DNA is inherited from bothparents, making it more difficult totrace back through generations.

Mitochondrial DNA ispassed down only from the mother of each generation, so it is not subject to recombination.

mitochondrialDNA

nuclear DNA

MITOCHONDRIAL EVE

ANCIENT DNA STUDIES

• (Science: 22 September 2011)

• Aboriginal Australians are the direct descendants of the first people who arrived on the continent some 50,000 years ago; those ancestors left Africa earlier than their European and Asian counterparts

• Evidence that Aboriginal Australians are descendants of the earliest modern explorers, leaving Africa around 24,000 years before their Asian and European counterparts

• Contrary to the widely accepted hypothesis that all modern humans derive from a single out-of-Africa migration wave into Europe, Asia, and Australia

DNA REVEALS THE ABORIGINAL AUSTRALIANS ARE THE FIRST HUMANS TO LEAVE AFRICA

The study derived from a lock of hair collected by a British anthropologist one hundred years ago from an Aboriginal man from the Goldfields region of Western Australia

OUT-OF-AFRICA MIGRATION

STUDY OF MITOCHONDRIAL DNA TIES ANCIENT REMAINS TO LIVING DESCENDANTS• Compared the complete mitogenomes of 4 ancient and 3 living

individuals from the north coast of British Columbia

• Nothing definitively tied current inhabitants to ancient remains (5,000 to 6,000 years old) until this direct genetic link

• "Having a DNA link showing direct maternal ancestry dating back at least 5,000 years is huge as far as helping the Metlakatla prove that this territory was theirs over the millennia." – Petzelt

• Problem with using nuclear DNA?

Cui et. al., PLoS ONE 8(7): e66948. doi:10.1371/journal.pone.0066948

THE GENETIC IMPACT OF AZTEC IMPERIALISM: ANCIENTMITOCHONDRIAL DNA EVIDENCE FROM XALTOCAN, MEXICO

• Indicates that residents of houses before and after the Aztec conquest have distinct haplotypes that are not closely related

• mt compositions of the temporal groups are statistically different

• Matrilines present in the households were replaced following the Aztec conquest.

• Indicates that the Aztec expansion may have been associated with significant demographic and genetic changes within Xaltocan

Mata-Miguez et al., Am J Phys Anthropol 000:000–000, 2012.

OTHER APPLICATIONS OF ANCIENT MTDNA• Ancient DNA Suggests Dwarf and ‘Giant’ Emu Are Conspecific

• Ancient DNA Analysis Affirms the Canid from Altai as a Primitive Dog

• Highly Informative Ancient DNA ‘Snippets’ for New Zealand Moa

• Investigating the Global Dispersal of Chickens in Prehistory Using Ancient Mitochondrial DNA Signatures

• Ancient DNA Assessment of Tiger Salamander Population in Yellowstone National Park

• Mitochondrial Phylogenomics of Modern and Ancient Equids

• Mitochondrial DNA Variation, but Not Nuclear DNA, Sharply Divides Morphologically Identical Chameleons along an Ancient Geographic Barrier

• Origins and Evolution of the Etruscans’ mtDNA

• Multiplexed SNP Typing of Ancient DNA Clarifies the Origin of Andaman mtDNA Haplogroups amongst South Asian Tribal Populations

• Ancient mtDNA Analysis of Early 16th Century Caribbean Cattle Provides Insight into Founding Populations of New World Creole Cattle Breeds

• The Phylogeny of the Four Pan-American MtDNA Haplogroups: Implications for Evolutionary and Disease Studies

• mtDNA from the Early Bronze Age to the Roman Period Suggests a Genetic Link between the Indian Subcontinent and Mesopotamian Cradle of Civilization

• A Reevaluation of the Native American MtDNA Genome Diversity and Its Bearing on the Models of Early Colonization of Beringia

• A Mitogenomic Phylogeny of Living Primates

• Mitochondrial DNA Evidence for a Diversified Origin of Workers Building Mausoleum for First Emperor of China

QUESTIONS?

*CHIEFS CHECK**