| 1. |
- Borodin, Pavel, et al.
(författare)
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Mendelian nightmares : the germline-restricted chromosome of songbirds
- 2022
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Ingår i: Chromosome Research. - : Springer Nature. - 0967-3849 .- 1573-6849. ; 30:2-3, s. 255-272
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Forskningsöversikt (refereegranskat)abstract
- Germline-restricted chromosomes (GRCs) are accessory chromosomes that occur only in germ cells. They are eliminated from somatic cells through programmed DNA elimination during embryo development. GRCs have been observed in several unrelated animal taxa and show peculiar modes of non-Mendelian inheritance and within-individual elimination. Recent cytogenetic and phylogenomic evidence suggests that a GRC is present across the species-rich songbirds, but absent in non-passerine birds, implying that over half of all 10,500 bird species have extensive germline/soma genome differences. Here, we review recent insights gained from genomic, transcriptomic, and cytogenetic approaches with regard to the genetic content, phylogenetic distribution, and inheritance of the songbird GRC. While many questions remain unsolved in terms of GRC inheritance, elimination, and function, we discuss plausible scenarios and future directions for understanding this widespread form of programmed DNA elimination.
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| 2. |
- Kleineidam, Luca, et al.
(författare)
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Midlife occupational cognitive requirements protect cognitive function in old age by increasing cognitive reserve
- 2022
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Ingår i: Frontiers in Psychology. - : Frontiers Media SA. - 1664-1078. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Several lifestyle factors promote protection against Alzheimer's disease (AD) throughout a person's lifespan. Although such protective effects have been described for occupational cognitive requirements (OCR) in midlife, it is currently unknown whether they are conveyed by brain maintenance (BM), brain reserve (BR), or cognitive reserve (CR) or a combination of them. Methods: We systematically derived hypotheses for these resilience concepts and tested them in the population-based AgeCoDe cohort and memory clinic-based AD high-risk DELCODE study. The OCR score (OCRS) was measured using job activities based on the O*NET occupational classification system. Four sets of analyses were conducted: (1) the interaction of OCR and APOE-ε4 with regard to cognitive decline (N = 2,369, AgeCoDe), (2) association with differentially shaped retrospective trajectories before the onset of dementia of the Alzheimer's type (DAT; N = 474, AgeCoDe), (3) cross-sectional interaction of the OCR and cerebrospinal fluid (CSF) AD biomarkers and brain structural measures regarding memory function (N = 873, DELCODE), and (4) cross-sectional and longitudinal association of OCR with CSF AD biomarkers and brain structural measures (N = 873, DELCODE). Results: Regarding (1), higher OCRS was associated with a reduced association of APOE-ε4 with cognitive decline (mean follow-up = 6.03 years), consistent with CR and BR. Regarding (2), high OCRS was associated with a later onset but subsequently stronger cognitive decline in individuals converting to DAT, consistent with CR. Regarding (3), higher OCRS was associated with a weaker association of the CSF Aβ42/40 ratio and hippocampal volume with memory function, consistent with CR. Regarding (4), OCR was not associated with the levels or changes in CSF AD biomarkers (mean follow-up = 2.61 years). We found a cross-sectional, age-independent association of OCRS with some MRI markers, but no association with 1-year-change. OCR was not associated with the intracranial volume. These results are not completely consistent with those of BR or BM. Discussion: Our results support the link between OCR and CR. Promoting and seeking complex and stimulating work conditions in midlife could therefore contribute to increased resistance to pathologies in old age and might complement prevention measures aimed at reducing pathology.
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| 3. |
- Mueller, Jakob C., et al.
(författare)
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Micro Germline-Restricted Chromosome in Blue Tits : Evidence for Meiotic Functions
- 2023
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Ingår i: Molecular biology and evolution. - : Oxford University Press. - 0737-4038 .- 1537-1719. ; 40:5
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Tidskriftsartikel (refereegranskat)abstract
- The germline-restricted chromosome (GRC) is likely present in all songbird species but differs widely in size and gene content. This extra chromosome has been described as either a microchromosome with only limited basic gene content or a macrochromosome with enriched gene functions related to female gonad and embryo development. Here, we assembled, annotated, and characterized the first micro-GRC in the blue tit (Cyanistes caeruleus) using high-fidelity long-read sequencing data. Although some genes on the blue tit GRC show signals of pseudogenization, others potentially have important functions, either currently or in the past. We highlight the GRC gene paralog BMP15, which is among the highest expressed GRC genes both in blue tits and in zebra finches (Taeniopygia guttata) and is known to play a role in oocyte and follicular maturation in other vertebrates. The GRC genes of the blue tit are further enriched for functions related to the synaptonemal complex. We found a similar functional enrichment when analyzing published data on GRC genes from two nightingale species (Luscinia spp.). We hypothesize that these genes play a role in maintaining standard maternal inheritance or in recombining maternal and paternal GRCs during potential episodes of biparental inheritance.
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| 4. |
- Pei, Yifan, et al.
(författare)
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Occasional paternal inheritance of the germline-restricted chromosome in songbirds
- 2022
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 119:4
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Tidskriftsartikel (refereegranskat)abstract
- Songbirds have one special accessory chromosome, the so-called germline-restricted chromosome (GRC), which is only present in germline cells and absent from all somatic tissues. Earlier work on the zebra finch (Taeniopygia guttata castanotis) showed that the GRC is inherited only through the female line-like the mitochondria-and is eliminated from the sperm during spermatogenesis. Here, we show that the GRC has the potential to be paternally inherited. Confocal microscopy using GRC-specific fluorescent in situ hybridization probes indicated that a considerable fraction of sperm heads (1 to 19%) in zebra finch ejaculates still contained the GRC. In line with these cytogenetic data, sequencing of ejaculates revealed that individual males from two families differed strongly and consistently in the number of GRCs in their ejaculates. Examining a captive-bred male hybrid of the two zebra finch subspecies (T. g. guttata and T. g. castanotis) revealed that the mitochondria originated from a castanotis mother, whereas the GRC came from a guttata father. Moreover, analyzing GRC haplotypes across nine castanotis matrilines, estimated to have diverged for up to 250,000 y, showed surprisingly little variability among GRCs. This suggests that a single GRC haplotype has spread relatively recently across all examined matrilines. A few diagnostic GRC mutations that arose since this inferred spreading suggest that the GRC has continued to jump across matriline boundaries. Our findings raise the possibility that certain GRC haplotypes could selfishly spread through the population via occasional paternal transmission, thereby out-competing other GRC haplotypes that were limited to strict maternal inheritance, even if this was partly detrimental to organismal fitness.
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| 5. |
- Pei, Yifan, et al.
(författare)
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Weak antagonistic fitness effects can maintain an inversion polymorphism
- 2023
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Ingår i: Molecular Ecology. - : John Wiley & Sons. - 0962-1083 .- 1365-294X. ; 32:13, s. 3575-3585
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Tidskriftsartikel (refereegranskat)abstract
- The study of chromosomal inversion polymorphisms has received much recent attention, particularly in cases where inversions have drastic effects on phenotypes and fitness (e.g. lethality of homozygotes). Less attention has been paid to the question of the maintenance of inversion polymorphisms that show only weak effects. Here, we study the maintenance of such an inversion polymorphism that links 250 genes on chromosome Tgu11 in the zebra finch (Taeniopygia guttata). Based on data from over 6000 captive birds, we estimated the effects of this inversion on a wide range of fitness-related traits. We found that, compared with the ancestral allele A, the inverted allele D had small additive beneficial effects on male siring success and on female fecundity. These fitness-enhancing effects may explain the initial spread of the derived D allele (allele frequency 53%). However, individuals that were homozygous for D had a slightly lower survival rate, which may explain why the D allele has not spread to fixation. We used individual-based simulations to examine how an inversion polymorphism with such antagonistic fitness effects behaves over time. Our results indicate that polymorphisms become stabilized at an intermediate allele frequency if the inversion links an additively beneficial allele of small effect size to a recessive weakly deleterious mutation, overall resulting in weak net heterosis. Importantly, this conclusion remains valid over a wide range of selection coefficients against the homozygous DD (up to lethality), suggesting that the conditions needed to maintain the polymorphism may frequently be met. However, the simulations also suggest that in our zebra finch populations, the estimated recessive deleterious effect of the D allele (on survival in captivity) is not quite large enough to prevent fixation of the D allele in the long run. Estimates of fitness effects from free-living populations are needed to validate these results.
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| 6. |
- Voelkl, Bernhard, et al.
(författare)
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Reproducibility of animal research in light of biological variation
- 2020
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Ingår i: Nature Reviews Neuroscience. - : Nature Publishing Group. - 1471-003X .- 1471-0048. ; 21, s. 384-393
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Tidskriftsartikel (refereegranskat)abstract
- In this Perspective, Hanno Wurbel and colleagues argue that a disregard for incorporating biological variation in study design is an important cause of poor reproducibility in animal research. They put the case for the use of systematic heterogenization of study samples and conditions in studies to improve reproducibility.Context-dependent biological variation presents a unique challenge to the reproducibility of results in experimental animal research, because organisms' responses to experimental treatments can vary with both genotype and environmental conditions. In March 2019, experts in animal biology, experimental design and statistics convened in Blonay, Switzerland, to discuss strategies addressing this challenge. In contrast to the current gold standard of rigorous standardization in experimental animal research, we recommend the use of systematic heterogenization of study samples and conditions by actively incorporating biological variation into study design through diversifying study samples and conditions. Here we provide the scientific rationale for this approach in the hope that researchers, regulators, funders and editors can embrace this paradigm shift. We also present a road map towards better practices in view of improving the reproducibility of animal research.
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