Genetic studies of tissue-specific mitochondrial DNA segregation in mammals

Riikka Jokinen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Mitochondrial DNA (mtDNA) is a small extra-nuclear genome present in all nucleated cells of the body and important for mitochondrial function. The mtDNA is a present in hundreds to thousands of copies per cell and therefore arising mutations cause heteroplasmy: the co-existence of two or more distinct mtDNA variants in the same cell. Because of these features mtDNA variants segregate mitotically in the tissues of an individual, which can lead to time-dependent changes in the relative proportions of the mtDNA variants. Mutations in the mtDNA cause diseases and most pathogenic mtDNA mutations are heteroplasmic. In heteroplasmic situations a certain threshold proportion of the mutant mtDNA must be exceeded prior to onset of symptoms. Somatic mtDNA segregation of mtDNA mutations affect whether the threshold is exceeded, and can thus be a factor in determining disease onset and severity. Some pathogenic mtDNA mutations exhibit tissue-specific mtDNA segregation patterns, but the genes and mechanisms involved in this process are unknown. The aim of this thesis was to uncover genetic regulators of tissue-specific mtDNA segregation and study their properties to gain insight into the mechanisms involved in this process. We investigated tissue-specific mtDNA segregation in a mouse model that segregates two neutral mtDNA variants. These mtDNA variants display tissue-specific mtDNA segregation in three tissue types: the liver, kidney and hematopoietic tissues. In these tissues there is selection for one mtDNA variant over the other. Using this mouse model we identified and verified Gimap3 as a modifying gene for mtDNA segregation in the hematopoietic tissues. In a follow-up study we further studied Gimap3 and a functionally related gene Gimap5. We uncovered a novel subcellular localization to the endoplasmic reticulum for the Gimap3 protein. Moreover we established Gimap5, which encodes a lysosomal protein, as another genetic modifier of mtDNA segregation in hematopoietic tissues. Taken together these results demonstrated the involvement of other organelles in the segregation of mtDNA. To study tissue-specific mtDNA segregation from another aspect we investigated the role of mitochondrial fission in this process. Mitochondrial fission has been implicated to play a role in mtDNA segregation in yeast. We utilized a dominant-negative mouse model for Dnm1l, a master regulator of mitochondrial fission. We demonstrated that expression of the dominant-negative Dnm1l modulated the mtDNA segregation specifically in the hematopoietic tissues. In conclusion, we were able discover the first genetic modifiers for tissue-specific mtDNA segregation in mammals. These findings can be utilized to guide future research aiming to uncover the molecular mechanisms of this process, which can ultimately elucidate the genetics of pathogenic human mtDNA mutations.
Original languageEnglish
Place of PublicationHelsinki
Publisher
Print ISBNs978-951-51-1912-4
Electronic ISBNs978-951-51-1913-1
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Fields of Science

  • 3111 Biomedicine

Cite this

Jokinen, R. (2016). Genetic studies of tissue-specific mitochondrial DNA segregation in mammals. Helsinki: University of Helsinki.
Jokinen, Riikka. / Genetic studies of tissue-specific mitochondrial DNA segregation in mammals. Helsinki : University of Helsinki, 2016. 108 p.
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title = "Genetic studies of tissue-specific mitochondrial DNA segregation in mammals",
abstract = "Mitochondrial DNA (mtDNA) is a small extra-nuclear genome present in all nucleated cells of the body and important for mitochondrial function. The mtDNA is a present in hundreds to thousands of copies per cell and therefore arising mutations cause heteroplasmy: the co-existence of two or more distinct mtDNA variants in the same cell. Because of these features mtDNA variants segregate mitotically in the tissues of an individual, which can lead to time-dependent changes in the relative proportions of the mtDNA variants. Mutations in the mtDNA cause diseases and most pathogenic mtDNA mutations are heteroplasmic. In heteroplasmic situations a certain threshold proportion of the mutant mtDNA must be exceeded prior to onset of symptoms. Somatic mtDNA segregation of mtDNA mutations affect whether the threshold is exceeded, and can thus be a factor in determining disease onset and severity. Some pathogenic mtDNA mutations exhibit tissue-specific mtDNA segregation patterns, but the genes and mechanisms involved in this process are unknown. The aim of this thesis was to uncover genetic regulators of tissue-specific mtDNA segregation and study their properties to gain insight into the mechanisms involved in this process. We investigated tissue-specific mtDNA segregation in a mouse model that segregates two neutral mtDNA variants. These mtDNA variants display tissue-specific mtDNA segregation in three tissue types: the liver, kidney and hematopoietic tissues. In these tissues there is selection for one mtDNA variant over the other. Using this mouse model we identified and verified Gimap3 as a modifying gene for mtDNA segregation in the hematopoietic tissues. In a follow-up study we further studied Gimap3 and a functionally related gene Gimap5. We uncovered a novel subcellular localization to the endoplasmic reticulum for the Gimap3 protein. Moreover we established Gimap5, which encodes a lysosomal protein, as another genetic modifier of mtDNA segregation in hematopoietic tissues. Taken together these results demonstrated the involvement of other organelles in the segregation of mtDNA. To study tissue-specific mtDNA segregation from another aspect we investigated the role of mitochondrial fission in this process. Mitochondrial fission has been implicated to play a role in mtDNA segregation in yeast. We utilized a dominant-negative mouse model for Dnm1l, a master regulator of mitochondrial fission. We demonstrated that expression of the dominant-negative Dnm1l modulated the mtDNA segregation specifically in the hematopoietic tissues. In conclusion, we were able discover the first genetic modifiers for tissue-specific mtDNA segregation in mammals. These findings can be utilized to guide future research aiming to uncover the molecular mechanisms of this process, which can ultimately elucidate the genetics of pathogenic human mtDNA mutations.",
keywords = "Amino Acid Sequence, Chromosome Segregation, DNA, Mitochondrial, +genetics, Fibroblasts, Genetic Heterogeneity, GTP Phosphohydrolases, GTP-Binding Proteins, Haplotypes, Leukocytes, Lymphocytes, Membrane Proteins, Mice, Inbred Strains, Mitochondria, Mitochondrial Proteins, Molecular Sequence Data, 3111 Biomedicine",
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year = "2016",
language = "English",
isbn = "978-951-51-1912-4",
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Genetic studies of tissue-specific mitochondrial DNA segregation in mammals. / Jokinen, Riikka.

Helsinki : University of Helsinki, 2016. 108 p.

Research output: ThesisDoctoral ThesisCollection of Articles

TY - THES

T1 - Genetic studies of tissue-specific mitochondrial DNA segregation in mammals

AU - Jokinen, Riikka

N1 - M1 - 108 s. + liitteet Helsingin yliopisto Volume: Proceeding volume:

PY - 2016

Y1 - 2016

N2 - Mitochondrial DNA (mtDNA) is a small extra-nuclear genome present in all nucleated cells of the body and important for mitochondrial function. The mtDNA is a present in hundreds to thousands of copies per cell and therefore arising mutations cause heteroplasmy: the co-existence of two or more distinct mtDNA variants in the same cell. Because of these features mtDNA variants segregate mitotically in the tissues of an individual, which can lead to time-dependent changes in the relative proportions of the mtDNA variants. Mutations in the mtDNA cause diseases and most pathogenic mtDNA mutations are heteroplasmic. In heteroplasmic situations a certain threshold proportion of the mutant mtDNA must be exceeded prior to onset of symptoms. Somatic mtDNA segregation of mtDNA mutations affect whether the threshold is exceeded, and can thus be a factor in determining disease onset and severity. Some pathogenic mtDNA mutations exhibit tissue-specific mtDNA segregation patterns, but the genes and mechanisms involved in this process are unknown. The aim of this thesis was to uncover genetic regulators of tissue-specific mtDNA segregation and study their properties to gain insight into the mechanisms involved in this process. We investigated tissue-specific mtDNA segregation in a mouse model that segregates two neutral mtDNA variants. These mtDNA variants display tissue-specific mtDNA segregation in three tissue types: the liver, kidney and hematopoietic tissues. In these tissues there is selection for one mtDNA variant over the other. Using this mouse model we identified and verified Gimap3 as a modifying gene for mtDNA segregation in the hematopoietic tissues. In a follow-up study we further studied Gimap3 and a functionally related gene Gimap5. We uncovered a novel subcellular localization to the endoplasmic reticulum for the Gimap3 protein. Moreover we established Gimap5, which encodes a lysosomal protein, as another genetic modifier of mtDNA segregation in hematopoietic tissues. Taken together these results demonstrated the involvement of other organelles in the segregation of mtDNA. To study tissue-specific mtDNA segregation from another aspect we investigated the role of mitochondrial fission in this process. Mitochondrial fission has been implicated to play a role in mtDNA segregation in yeast. We utilized a dominant-negative mouse model for Dnm1l, a master regulator of mitochondrial fission. We demonstrated that expression of the dominant-negative Dnm1l modulated the mtDNA segregation specifically in the hematopoietic tissues. In conclusion, we were able discover the first genetic modifiers for tissue-specific mtDNA segregation in mammals. These findings can be utilized to guide future research aiming to uncover the molecular mechanisms of this process, which can ultimately elucidate the genetics of pathogenic human mtDNA mutations.

AB - Mitochondrial DNA (mtDNA) is a small extra-nuclear genome present in all nucleated cells of the body and important for mitochondrial function. The mtDNA is a present in hundreds to thousands of copies per cell and therefore arising mutations cause heteroplasmy: the co-existence of two or more distinct mtDNA variants in the same cell. Because of these features mtDNA variants segregate mitotically in the tissues of an individual, which can lead to time-dependent changes in the relative proportions of the mtDNA variants. Mutations in the mtDNA cause diseases and most pathogenic mtDNA mutations are heteroplasmic. In heteroplasmic situations a certain threshold proportion of the mutant mtDNA must be exceeded prior to onset of symptoms. Somatic mtDNA segregation of mtDNA mutations affect whether the threshold is exceeded, and can thus be a factor in determining disease onset and severity. Some pathogenic mtDNA mutations exhibit tissue-specific mtDNA segregation patterns, but the genes and mechanisms involved in this process are unknown. The aim of this thesis was to uncover genetic regulators of tissue-specific mtDNA segregation and study their properties to gain insight into the mechanisms involved in this process. We investigated tissue-specific mtDNA segregation in a mouse model that segregates two neutral mtDNA variants. These mtDNA variants display tissue-specific mtDNA segregation in three tissue types: the liver, kidney and hematopoietic tissues. In these tissues there is selection for one mtDNA variant over the other. Using this mouse model we identified and verified Gimap3 as a modifying gene for mtDNA segregation in the hematopoietic tissues. In a follow-up study we further studied Gimap3 and a functionally related gene Gimap5. We uncovered a novel subcellular localization to the endoplasmic reticulum for the Gimap3 protein. Moreover we established Gimap5, which encodes a lysosomal protein, as another genetic modifier of mtDNA segregation in hematopoietic tissues. Taken together these results demonstrated the involvement of other organelles in the segregation of mtDNA. To study tissue-specific mtDNA segregation from another aspect we investigated the role of mitochondrial fission in this process. Mitochondrial fission has been implicated to play a role in mtDNA segregation in yeast. We utilized a dominant-negative mouse model for Dnm1l, a master regulator of mitochondrial fission. We demonstrated that expression of the dominant-negative Dnm1l modulated the mtDNA segregation specifically in the hematopoietic tissues. In conclusion, we were able discover the first genetic modifiers for tissue-specific mtDNA segregation in mammals. These findings can be utilized to guide future research aiming to uncover the molecular mechanisms of this process, which can ultimately elucidate the genetics of pathogenic human mtDNA mutations.

KW - Amino Acid Sequence

KW - Chromosome Segregation

KW - DNA, Mitochondrial

KW - +genetics

KW - Fibroblasts

KW - Genetic Heterogeneity

KW - GTP Phosphohydrolases

KW - GTP-Binding Proteins

KW - Haplotypes

KW - Leukocytes

KW - Lymphocytes

KW - Membrane Proteins

KW - Mice, Inbred Strains

KW - Mitochondria

KW - Mitochondrial Proteins

KW - Molecular Sequence Data

KW - 3111 Biomedicine

M3 - Doctoral Thesis

SN - 978-951-51-1912-4

T3 - Dissertationes Scholae Doctoralis Ad Sanitatem Investigandam Universitatis Helsinkiensis

PB - University of Helsinki

CY - Helsinki

ER -

Jokinen R. Genetic studies of tissue-specific mitochondrial DNA segregation in mammals. Helsinki: University of Helsinki, 2016. 108 p. (Dissertationes Scholae Doctoralis Ad Sanitatem Investigandam Universitatis Helsinkiensis; 13/2016).