Martin GG, Oakes CT, Tousignant HR, Crabtree H, Yamakawa R. 2007. Structure and function of haemocytes in two marine gastropods, Megathura crenulata and Aplysia californica. Journal of Molluscan Studies 73: 355-365.
These authors characterised the blood cells of two species of gastropods chosen for their importance to other areas of research. Other studies have reported either one or two types of cells in mollusc blood, either with or without granules visible as electron-dense patches in electron microscopy.
This paper found only a single, generally granule-lacking type of cell in the blood of each species. These cells show phagocytic and aggregation abilities, but the blood does not clot. These cells appear to be general-purpose circulating amoeboid cells, capable of responding to stress, wounds, shell damage, infection, and other insults to the organism. This contributes to the circumstantial and weak evidence that molluscan haemocytes are probably not endopolyploid, as they apparently must be produced rapidly in large numbers by stem cell lineages to respond to changes to both the external and internal environments.
Showing posts with label Polyploidy and Endopolyploidy. Show all posts
Showing posts with label Polyploidy and Endopolyploidy. Show all posts
Saturday, August 9, 2008
Erenpreisa et al. 2002
Erenpreisa J, Ivanov A, Cragg M, Selivanova G, Illidge T. 2002. Nuclear envelope-limited chromatin sheets are part of mitotic death. Histochemistry & Cell Biology 117: 243-255.
These authors investigated the structure and formation of nuclear envelope-limited chromatin sheets (ELCS) in two lines of mutant human cells commonly used in cancer studies. ELCS are membranous structures of unknown function; they are flat folds of inner nuclear envelope that project outwards from the nucleus, sometimes as far as the cytoplasm, and enfold chromatin. Larger projections containing chromatin are termed nuclear pockets (NP), and are strongly associated with some types of cancer such as leukaemia in mammals, but are also found less commonly in healthy tissues including spermatogonia.
Cells were treated with irradiation to induce double-stranded breaks and with a microtubule inhibitor to inhibit mitosis. Earlier investigations by these and other authors have developed the concept of “mitotic death”, which is a syndrome of cells including failed mitosis, the uncoupling of mitosis from DNA replication, delayed (but inevitable) apoptosis, and the formation of giant cells with high levels of aneuploidy and often endopolyploidy.
This paper demonstrates that mitotic death can be induced by quite different mechanisms, in this case by the failure of mitosis driven by microtubule depolymerisation and by a large number of double-stranded DNA breaks induced by radiation. In both cases, DNA repair was effected over considerable time, though apparently cells were unable to “repair” their aneuploidy.
Of particular interest to my work in this paper is their investigations of nuclear morphology. Cells were suspended in solution, then treated to prepare them for either nuclear DNA contents measures (by PI-flow cytometry and by Feulgen staining), light microscopy, or electron microscopy. For light microscopy cell- and nuclear-morphology investigation, these authors fixed cells in a 1:1 mixture of ethanol and acetone, hydrolysed the cells (and presumably freed the nuclei) in 0.1N HCl, and washed them in a poorly-described solution that may be either MacIlvain buffer (pH 5) or Toluidene blue stain in MacIlvain buffer. All of this occurred at 4°C. This was followed by a rinse in distilled water, and dehydration of slides carrying mounted cells in “warm tertiary butanol”. I have seen ethanol used as a fixative and preservative agent in histology studies before, but this represents the clearest description I have encountered of the process as applied specifically for investigations of cell nuclear morphology. There are some obvious similarities with our procedure for Feulgen staining, which helps to confirm that ethanol preservation may be reversible for whole-nuclear investigations.
These authors investigated the structure and formation of nuclear envelope-limited chromatin sheets (ELCS) in two lines of mutant human cells commonly used in cancer studies. ELCS are membranous structures of unknown function; they are flat folds of inner nuclear envelope that project outwards from the nucleus, sometimes as far as the cytoplasm, and enfold chromatin. Larger projections containing chromatin are termed nuclear pockets (NP), and are strongly associated with some types of cancer such as leukaemia in mammals, but are also found less commonly in healthy tissues including spermatogonia.
Cells were treated with irradiation to induce double-stranded breaks and with a microtubule inhibitor to inhibit mitosis. Earlier investigations by these and other authors have developed the concept of “mitotic death”, which is a syndrome of cells including failed mitosis, the uncoupling of mitosis from DNA replication, delayed (but inevitable) apoptosis, and the formation of giant cells with high levels of aneuploidy and often endopolyploidy.
This paper demonstrates that mitotic death can be induced by quite different mechanisms, in this case by the failure of mitosis driven by microtubule depolymerisation and by a large number of double-stranded DNA breaks induced by radiation. In both cases, DNA repair was effected over considerable time, though apparently cells were unable to “repair” their aneuploidy.
Of particular interest to my work in this paper is their investigations of nuclear morphology. Cells were suspended in solution, then treated to prepare them for either nuclear DNA contents measures (by PI-flow cytometry and by Feulgen staining), light microscopy, or electron microscopy. For light microscopy cell- and nuclear-morphology investigation, these authors fixed cells in a 1:1 mixture of ethanol and acetone, hydrolysed the cells (and presumably freed the nuclei) in 0.1N HCl, and washed them in a poorly-described solution that may be either MacIlvain buffer (pH 5) or Toluidene blue stain in MacIlvain buffer. All of this occurred at 4°C. This was followed by a rinse in distilled water, and dehydration of slides carrying mounted cells in “warm tertiary butanol”. I have seen ethanol used as a fixative and preservative agent in histology studies before, but this represents the clearest description I have encountered of the process as applied specifically for investigations of cell nuclear morphology. There are some obvious similarities with our procedure for Feulgen staining, which helps to confirm that ethanol preservation may be reversible for whole-nuclear investigations.
Sunday, May 18, 2008
Baršiene et al. 1996
Baršiene J, Tapia G, Barsyte D. 1996. Chromosomes of molluscs inhabiting some mountain springs of eastern Spain. Journal of Molluscan Studies 62: 539-543.
These authors report karyotypes for four species of molluscs (three gastropods and one bivalve) collected from small, high-altitude freshwater habitats in Spain. These habitats are quite diverse, with some very small springs occupying only 3-4 m^2 of surface area. Previous studies had associated small and isolated populations with polyploidy and its effects on tolerance of environmental stress and avoiding inbreeding depression.
Collected animals were injected with (large body) or immersed in (small body) a colchicine solution before dissection. The authors do not clearly describe what tissues from which species and populations were used, though they do describe “gonal and somatic cells”; presumably the gonadal cells were sperm, and the somatic cells are loosely described as “soft tissues” that were dissociated in 45% acetic acid by pipetting.
The high fraction of “hypodiploid” cells found in some individuals of Lymnaea peregra and some instances of apparent cell degeneration was attributed to “ecological stress”, though no supporting evidence or further discussion appears. They also state that the bivalve in their study, Pisidium casertanum, was almost certainly diploid, despite different populations having chromsome numbers ranging from 150 to 180, and other, uncited studies that found high and idiosyncratic levels of polyploidy in this family (Pisidiidae) and the closely related family Sphaeriidae (e.g. Burch and Huber 1966). As a final negative criticism of this paper, I found the frequent reference of the authors’ own unpublished data in support of presumed trends to be rather annoying.
These authors report karyotypes for four species of molluscs (three gastropods and one bivalve) collected from small, high-altitude freshwater habitats in Spain. These habitats are quite diverse, with some very small springs occupying only 3-4 m^2 of surface area. Previous studies had associated small and isolated populations with polyploidy and its effects on tolerance of environmental stress and avoiding inbreeding depression.
Collected animals were injected with (large body) or immersed in (small body) a colchicine solution before dissection. The authors do not clearly describe what tissues from which species and populations were used, though they do describe “gonal and somatic cells”; presumably the gonadal cells were sperm, and the somatic cells are loosely described as “soft tissues” that were dissociated in 45% acetic acid by pipetting.
The high fraction of “hypodiploid” cells found in some individuals of Lymnaea peregra and some instances of apparent cell degeneration was attributed to “ecological stress”, though no supporting evidence or further discussion appears. They also state that the bivalve in their study, Pisidium casertanum, was almost certainly diploid, despite different populations having chromsome numbers ranging from 150 to 180, and other, uncited studies that found high and idiosyncratic levels of polyploidy in this family (Pisidiidae) and the closely related family Sphaeriidae (e.g. Burch and Huber 1966). As a final negative criticism of this paper, I found the frequent reference of the authors’ own unpublished data in support of presumed trends to be rather annoying.
Wednesday, March 19, 2008
Burch and Huber 1966
Burch JB, Huber JM. 1966. Polyploidy in mollusks. Malacologia 5: 41-43.
These authors present a very brief summary of examples of polyploidy discovered to date among molluscs. The conditions promoting or presumed necessary for polyploidy in animals are first presented; of chief importance is the ability to physiologically and developmentally tolerate increased chromosome numbers and the ability to either self-fertilize or reproduce parthenogenically.
Among known selfing-capable hermaphroditic molluscs, the family Lymnaeidae has no examples of polyploids among the 40 species studied. There are unconfirmed reports of polyploidy in other families, including the land snails Succineidae and the freshwater clams Sphaeriidae (see also the much more recent Lee and O Foighil, 2002). The authors suggest that most of the observed variation in molluscan chromosome numbers can be attributed to aneuploidy, an hypothesis I find unlikely in light of more recent understanding of genome organization, especially the role of chromosome fissions, fusions, and translocations in structuring genomes.
These authors present a very brief summary of examples of polyploidy discovered to date among molluscs. The conditions promoting or presumed necessary for polyploidy in animals are first presented; of chief importance is the ability to physiologically and developmentally tolerate increased chromosome numbers and the ability to either self-fertilize or reproduce parthenogenically.
Among known selfing-capable hermaphroditic molluscs, the family Lymnaeidae has no examples of polyploids among the 40 species studied. There are unconfirmed reports of polyploidy in other families, including the land snails Succineidae and the freshwater clams Sphaeriidae (see also the much more recent Lee and O Foighil, 2002). The authors suggest that most of the observed variation in molluscan chromosome numbers can be attributed to aneuploidy, an hypothesis I find unlikely in light of more recent understanding of genome organization, especially the role of chromosome fissions, fusions, and translocations in structuring genomes.
Monday, March 17, 2008
Lee and Ó Foighil 2002
Lee T, Ó Foighil D. 2002. 6-Phosphogluconate dehydrogenase (PGD) allele phylogeny is incongruent with a recent origin of polyploidization in some North American Sphaeriidae (Mollusca, Bivalvia). Molecular Phylogenetics and Evolution 25: 112-124.
These authors produced a phylogeny for seven species in three genera in the freshwater clam family Sphaeriidae. These clams have high and variable chromosome numbers, with previous studies suggesting a majority of species polyploid up to 13n (e.g. Lee, 1999). The earliest fossils from the family are found in Cretaceous freshwater deposits, with some genera appearing in the Miocene.
Allopolyploids, derived by hybridization between relatively interfertile (segmental allopolyploidy) or nearly intersterile (genomic allopolyploidy) cause reticulations in phylogenies. Phylogenies based on mtDNA (as exist for this family: Cooley and Ó Foighil, 2000) will not capture such reticulations because of the uniparental inheritance of mtDNA. Nuclear markers, on the other hand, may show a wide range of fates after a duplication event, including gene silencing, homogenization, or independent evolution and differentiation. This variation makes some nuclear markers difficult to analyze in the context of ancient polyploidy.
These authors chose to construct a phylogeny based on a single nuclear gene, using c-DNA to examine only expressed alleles. They found many alleles for this gene in two major clades in the three genera examined. Clade A was widespread and common, while Clade B was not found at all in several species and had fewer alleles in fewer individuals where it was found. Why this imbalance should appear is difficult to state with great certainty. The authors suggest the most likely explanation is that more Clade B alleles have been lost through psuedogenization and / or recombination, though they also acknowledge the possibility, considered by them less likely, that their primer set was biased towards amplification of Clade A alleles. This is considered less likely because some B alleles were detected, such that any bias must be considerably less than 100% effective.
Overall, while the family-level tree does provide evidence of an allopolyploidization event predating the divergence of the three genera, at least some of the more recently-derived lineages experienced duplication events not reflected in this phylogeny. Further examination of the alleles of this gene in more members of this ecologically important family are required to elucidate the history of genomic and genetic events.
One outgroup species came from Cuba, and was preserved and shipped in a solution containing “TRI Reagent (Molecular Research Center)”. This reagent was also used in RNA extraction procedures for all species. I am unfamiliar with this reagent, though its possible use as a tissue preservative that appears to preserve chromatin as well as RNA is very interesting.
These authors produced a phylogeny for seven species in three genera in the freshwater clam family Sphaeriidae. These clams have high and variable chromosome numbers, with previous studies suggesting a majority of species polyploid up to 13n (e.g. Lee, 1999). The earliest fossils from the family are found in Cretaceous freshwater deposits, with some genera appearing in the Miocene.
Allopolyploids, derived by hybridization between relatively interfertile (segmental allopolyploidy) or nearly intersterile (genomic allopolyploidy) cause reticulations in phylogenies. Phylogenies based on mtDNA (as exist for this family: Cooley and Ó Foighil, 2000) will not capture such reticulations because of the uniparental inheritance of mtDNA. Nuclear markers, on the other hand, may show a wide range of fates after a duplication event, including gene silencing, homogenization, or independent evolution and differentiation. This variation makes some nuclear markers difficult to analyze in the context of ancient polyploidy.
These authors chose to construct a phylogeny based on a single nuclear gene, using c-DNA to examine only expressed alleles. They found many alleles for this gene in two major clades in the three genera examined. Clade A was widespread and common, while Clade B was not found at all in several species and had fewer alleles in fewer individuals where it was found. Why this imbalance should appear is difficult to state with great certainty. The authors suggest the most likely explanation is that more Clade B alleles have been lost through psuedogenization and / or recombination, though they also acknowledge the possibility, considered by them less likely, that their primer set was biased towards amplification of Clade A alleles. This is considered less likely because some B alleles were detected, such that any bias must be considerably less than 100% effective.
Overall, while the family-level tree does provide evidence of an allopolyploidization event predating the divergence of the three genera, at least some of the more recently-derived lineages experienced duplication events not reflected in this phylogeny. Further examination of the alleles of this gene in more members of this ecologically important family are required to elucidate the history of genomic and genetic events.
One outgroup species came from Cuba, and was preserved and shipped in a solution containing “TRI Reagent (Molecular Research Center)”. This reagent was also used in RNA extraction procedures for all species. I am unfamiliar with this reagent, though its possible use as a tissue preservative that appears to preserve chromatin as well as RNA is very interesting.
Friday, March 14, 2008
Leitch and Bennett 1997
Leitch IJ, Bennett MD. 1997. Polyploidy in angiosperms. Trends in Plant Science 2: 470-476.
These authors reviewed the occurrence and patterns of polyploidy in angiosperms. The majority of “higher plants” apparently have polyploid ancestry, some quite recently reverted to diploid. Most polyploid plants appear to be allopolyploids, derived by hybridization. Allopolyploidy presents the possibility of multiple origins of hybrid polyploid taxa, which has been identified in a few species.
The evolution of duplicated genes is discussed, with an interesting section on homology-dependent gene silencing. This is a phenomenon possibly mediated by repeat-induced changes to chromatin structure, in which some copies within a gene family are silenced or their expression altered.
These authors reviewed the occurrence and patterns of polyploidy in angiosperms. The majority of “higher plants” apparently have polyploid ancestry, some quite recently reverted to diploid. Most polyploid plants appear to be allopolyploids, derived by hybridization. Allopolyploidy presents the possibility of multiple origins of hybrid polyploid taxa, which has been identified in a few species.
The evolution of duplicated genes is discussed, with an interesting section on homology-dependent gene silencing. This is a phenomenon possibly mediated by repeat-induced changes to chromatin structure, in which some copies within a gene family are silenced or their expression altered.
Friday, February 22, 2008
Salemaa 1984
Salemaa H. 1984. Polyploidy in the evolution of the glacial relict Pontoporeia spp. (Amphipoda, Crustacea). Hereditas 100: 53-60.
This author examined the karyotypes of two closely related species of amphipods found in the Baltic sea and other locations in northern Europe. One species is considered to have descended from the other, speciating about 100 000 years ago during a glacial maximum. The more recent species is tetraploid, but shows normal meiosis and evidence of crossing-over. The two species occur in sympatry, despite apparent ecological congruence.
The tetraploid species shows several differences from the diploid that may or may not relate to its increased chromosome number. They use greater habitat diversity, including a microhabitat difference that exposes them to increased predation from fish. The tetraploids show higher but more variable productivity in some locations where both species are found. Population density of the tetraploids varies greatly; some locations included up to 10 000 individuals per square meter of muddy benthos. The life history of the tetraploid includes more, smaller eggs (contrary to my expectations) and may be better at seasonal synchronization for breeding, based on improved visual sensitivity that allows deeper-dwelling populations to react to season variation in light levels.
All of these differences may have evolved after the speciation event that split this lineage. In particular, greater DNA content per cell should, all else being equal, lead to larger cells including embryos. The opposite difference suggests adaptations of life history to either unmeasured different environmental factors or to the larger cell nuclei of the tetraploids.
This is the first report of a dioecious tetraploid amphipod; no sex chromosomes were detected, removing the obstacle to polyploidy inherent in chromosomal sex determination.
While the karyotype is strongly suggestive of a polyploid recent ancestor followed by some centric fusions (the chromosome number is not exactly double), the illustrations of karyotype do not appear to show longer total chromatin. Genome size, as opposed to karyotype, is not reported here for either species; a doubling of cellular DNA contents would be more convincing to me for an argument of recent polyploidy.
This author examined the karyotypes of two closely related species of amphipods found in the Baltic sea and other locations in northern Europe. One species is considered to have descended from the other, speciating about 100 000 years ago during a glacial maximum. The more recent species is tetraploid, but shows normal meiosis and evidence of crossing-over. The two species occur in sympatry, despite apparent ecological congruence.
The tetraploid species shows several differences from the diploid that may or may not relate to its increased chromosome number. They use greater habitat diversity, including a microhabitat difference that exposes them to increased predation from fish. The tetraploids show higher but more variable productivity in some locations where both species are found. Population density of the tetraploids varies greatly; some locations included up to 10 000 individuals per square meter of muddy benthos. The life history of the tetraploid includes more, smaller eggs (contrary to my expectations) and may be better at seasonal synchronization for breeding, based on improved visual sensitivity that allows deeper-dwelling populations to react to season variation in light levels.
All of these differences may have evolved after the speciation event that split this lineage. In particular, greater DNA content per cell should, all else being equal, lead to larger cells including embryos. The opposite difference suggests adaptations of life history to either unmeasured different environmental factors or to the larger cell nuclei of the tetraploids.
This is the first report of a dioecious tetraploid amphipod; no sex chromosomes were detected, removing the obstacle to polyploidy inherent in chromosomal sex determination.
While the karyotype is strongly suggestive of a polyploid recent ancestor followed by some centric fusions (the chromosome number is not exactly double), the illustrations of karyotype do not appear to show longer total chromatin. Genome size, as opposed to karyotype, is not reported here for either species; a doubling of cellular DNA contents would be more convincing to me for an argument of recent polyploidy.
Thursday, January 17, 2008
Matlock and Dornfeld 1981
Matlock DB, Dornfeld EJ. 1981. Somatic polyploidy in the marine isopod Idothea wasnesenskii. Comparative Biochemistry and Physiology 69A: 777-781.
These authors examined polyploid somatic tissues in an intertidal isopod with a fun name, using a combination of Feuglen cytophotometry (DNA contents) and Autoradiography (DNA synthesis). They were able to examine three tissues (hepatic cecum, midgut, testis sheath) in adult, juvenile, and “emerger” isopods, except testis tissue in emergers.
Endopolyploidy was found to start first in hepatic cecum, as emergers had very few polyploid cells in their midguts. The pattern of cell ploidy distribution varied between tissues: midgut and cecum cells showed a continuous series of larger cells up to 256C, while testis sheath cells did not exceed 32C, and were distributed discontinuously.
Four hypotheses regarding the intercell synchronisation and duration of DNA synthesis were proposed in the Discussion section, though none of the four could be conclusively rejected based on these data. However, the authors suggest that hypothesis 2, that DNA synthesis is confined to a definite S phase in each cell, but there is no synchrony between cells, is probably correct for the studied tissues in this species. Finally, the authors tentatively suggest that moulting hormones may play a role in stimulating DNA synthesis, a phenomenon that has been partly demonstrated in other contexts in arthropods.
These authors examined polyploid somatic tissues in an intertidal isopod with a fun name, using a combination of Feuglen cytophotometry (DNA contents) and Autoradiography (DNA synthesis). They were able to examine three tissues (hepatic cecum, midgut, testis sheath) in adult, juvenile, and “emerger” isopods, except testis tissue in emergers.
Endopolyploidy was found to start first in hepatic cecum, as emergers had very few polyploid cells in their midguts. The pattern of cell ploidy distribution varied between tissues: midgut and cecum cells showed a continuous series of larger cells up to 256C, while testis sheath cells did not exceed 32C, and were distributed discontinuously.
Four hypotheses regarding the intercell synchronisation and duration of DNA synthesis were proposed in the Discussion section, though none of the four could be conclusively rejected based on these data. However, the authors suggest that hypothesis 2, that DNA synthesis is confined to a definite S phase in each cell, but there is no synchrony between cells, is probably correct for the studied tissues in this species. Finally, the authors tentatively suggest that moulting hormones may play a role in stimulating DNA synthesis, a phenomenon that has been partly demonstrated in other contexts in arthropods.
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