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ImpuT2T: Pangenome-Based Patching for Human Genome Assemblies.

With improvements in sequencing and assembly have come many high-quality telomere-to-telomere assemblies and reference pangenomes. However, the long-read sequencing recipes needed for high quality assemblies are expensive, and out of reach for many research groups. Here we propose ImpuT2T, a method that takes an assembly produced via inexpensive HiFi sequencing reads, and uses a panel of T2T (or near-T2T) assemblies to scaffold and fill ("patch") the gaps between the HiFi contigs. Benchmarking against reference assemblies demonstrates that ImpuT2T is highly effective at patching human HiFi assemblies, consistently outperforming existing patching approaches. Moreover, we show that including more haplotypes in the pangenome improves the quality of the patched assemblies, with the greatest gains achieved using the full HPRC Release 2 pangenome.

Journal Article

The causal relationships and potential pathways between birth weight and cardiovascular diseases: A human genomics study.

The causal relationships and potential pathways between birth weight (BW) and various cardiovascular diseases (CVDs) remain unclear, particularly when discriminating maternal and fetal contributions of BW to CVDs. Leveraging the genome-wide association studies (GWASs) of BW (N = 321,223) and a range of CVDs (ncases = 43,676-181,522), we performed a 2-sample Mendelian randomization (MR) analysis to estimate the causal effect of BW, fetal-specific BW, and maternal-specific BW on coronary artery disease (CAD), myocardial infarction (MI), heart failure (HF), atrial fibrillation (AF), and stroke. Furthermore, we applied a stepwise MR analysis approach to assess the potential involvement of childhood body mass index (CBMI) and age at menarche (AAM) in the causal pathways from BW to CVDs, while considering adult BMI. Finally, we performed colocalization analyses to justify the different biological mechanisms of maternal-specific and fetal-specific BW. The 2-sample MR analysis revealed that genetically predicted higher BW per standard deviation (SD) was associated with a decreased risk of CAD (odds ratio [OR] = 0.804, 95% confidence interval [CI]: 0.731-0.883), MI (OR = 0.720, 95% CI: 0.638-0.814), and stroke (OR = 0.900, 95% CI: 0.823-0.985), but an increased risk of AF (OR = 1.279, 95% CI: 1.160-1.410). Similar associations were observed for fetal-specific/maternal-specific BW. The stepwise MR analysis indicated that CBMI and AAM could serve as factors linking BW/fetal-specific BW and CVDs, albeit in different roles, by displaying an indirect causal effect through adult BMI. However, for maternal-specific BW, our results failed to support a causal effect on CBMI or AAM. Colocalization analyses supported the distinct biological mechanisms for maternal-specific and fetal-specific BW by showing different causal genes. The study suggested that both fetal genotype and intrauterine environmental exposure contribute to the causal associations. Additionally, AAM and CBMI may play a role in the pathways linking BW and CVDs, though the effect was only observed for fetal-specific BW.

Humans

Organization, replication and modification of the human genome: differential methylation of two classes of HeLa nuclear DNA separated on Ag+--Cs2SO4 gradients.

HeLa nuclear DNA sediments as a single peak, in neutral CsCl, while it is separated in a heavier and a lighter components, in alkaline Ag+--Cs2SO4. The heavy fraction, on the average, represents about 20% of the total DNA. CsCl analytical ultracentrifugation shows that heavy DNA bands at 1.715 g/cm3 and contains 53% GC (10% of the total GC), whereas light DNA bands at 1.703 g/cm3 and contains 40% GC (32% of the total GC). Coherently, Tm values in 0.1 x SSC are 82.5 degrees C, for heavy DNA, and 72.5 degrees C, for light DNA. After treatment with [3H-methyl-S-adenosyl-L-methionine in isolated nuclei, the concentration of labelled 5-methylcytosine was found to be highest in the more dense regions of the heavy peak and in the less dense regions of the light peak. Exposure to ultrasound modifies the quantitative relationship of the two peaks and improves the separation of supermethylated AT- and GC-rich DNAs. Four possible triplets as sites for DNA-methylase recognition are discussed.

Cell Nucleus

Organization, replication and modification of the human genome: temporal order of synthesis and methylation of two classes of HeLa nDNA separated in Ag+--Cs2-SO4 gradients.

During the HeLa S-phase, DNA was methylated, at 1-hr intervals in isolated nuclei and fractionated in Ag+-Cs2SO4 gradients providing a heavy GC-rich peak and a main light AT-rich peak. Both size and specific methylation of these peaks changed during the nDNA duplicative phase. Replication of the heavy GC-rich nDNA fraction, which contains genes for ribosomal RNA, occurred in early S; in contrast, replication of the main AT-rich nDNA fraction was maximal in late S. Concomitantly, specific methylation of the GC-rich nDNA was maximal in the first part of S, while that of the AT-rich nDNA was maximal in the second part of S. This suggested that genes are replicated and methylated with order during the S-phase.

Cell Cycle

"It just feels morally not right to Sell the data": Ethical and social perspectives on human genomic data sharing in Uganda-A phenomenological qualitative study.

While genomic data sharing enhances transparency and research efficiency, it also raises significant ethical and social challenges. This study explored stakeholders' perspectives on these issues, particularly around privacy, confidentiality, and equity in collaborative research. A phenomenological qualitative study was conducted between August and December 2023 at Makerere University College of Health Sciences, other research-intensive institutions, and national regulatory bodies. The study engaged 86 participants: 47 key informants (16 researchers, 14 ethics committee members, nine community advisory board members, and eight research regulators) and four deliberative focus group discussions with 39 participants. Interviews were transcribed verbatim, and thematic analysis was conducted using NVivo 14. Three major themes emerged: (1) stakeholders' experiences in genomic research, including their roles as participants, implementers, or overseers; (2) ethical concerns, such as informed consent, third-party data access, inequities between high-income and low- and middle-income country (LMIC) researchers and participants, and the lack of benefit-sharing frameworks; and (3) social implications, including stigma, discrimination, labeling, community perceptions of fairness, and the need for meaningful engagement. Participants emphasized the importance of protecting participant rights, promoting equity, and ensuring robust data governance and security. The theoretical frameworks of principlism and distributive justice provided a valuable lens for examining these concerns, particularly by highlighting the need to safeguard privacy and fairly distribute responsibilities and benefits in global collaborations. Participants also noted that perceptions of fairness are shaped by trust, local context, and past experiences with research factors that are critical for building equitable and respectful partnerships. This study underscores the urgent need to strengthen protections for research participants and promote fairness in genomic data sharing. Policies should, if adopted, emphasize culturally contextualized consent, active community engagement, restricted third-party data access, and strong data protection mechanisms to address existing inequities and prevent misuse.

LMICs

Pervasive cryptic selection in the human noncoding genome.

The prevailing dogma in evolutionary genetics holds that mutations within sequences that are conserved across a phylogeny are deleterious in those species, and mutations outside are neutrally evolving. Indeed, such comparative genomic approaches have estimated that mutations in approximately 5% of the human genome experience negative selection. However, sites that have biological function in certain lineages but not in others, i.e. functional turnover, may violate this assumption since these sites may be invisible to comparative genomic approaches. Thus, the extent of such cryptic, or hidden, negative selection remains elusive. Here, we developed a statistical test to detect cryptic selection in human polymorphism data. Applying our approach to simulated data shows that cryptic selection shapes the site frequency spectrum (SFS) and the statistical detection power depends on the proportion of mutations experiencing cryptic selection, the amount of sequence tested, and the sample size. We applied our method to polymorphism data from the 1000 Genomes Project, comparing variants in putatively functional noncoding regions to those in putatively neutral regions. We detected pervasive signals of cryptic selection in putatively functional regions, even after filtering out the top 70% of conserved sites. Using simulations with varying levels of cryptic selection, we estimated the extent of genome-wide constraint in the human genome. Our approximation suggests that mutations in at least 7% of the human genome are under negative selection, which is greater than the estimates from conservation-based methods, and that many of these mutations have escaped detection by comparative genomic methods. In sum, our results highlight the evolutionary dynamic nature of the noncoding genome and suggest the need to account for functional turnover when identifying putatively neutral variants for evolutionary analyses.

Journal Article

The genome of human coronavirus strain 229E.

The genomic RNA of human coronavirus strain 229E (HCV 229E) migrated on polyacrylamide gels as a single peak with a mol. wt. of 5.8 X 10(6). Denaturation of the genome with formaldehyde did not alter its electrophoretic mobility, which suggests that the HCV 229E genome is a single-stranded molecule. At least 30% of the genomic RNA was shown to contain covalently attached polyadenylic acid [poly(A)]sequences by binding the RNA to an oligo(dT)-cellulose column. These poly(A) tracts were shown to be about 70 nucleotides in length by measuring the resistance to digestion of HCV 229E RNA with pancreatic and T1 RNases. Finally, the genomic RNA was shown to terminate at or near the 3'-terminus on the basis of its susceptibility to polynucleotide phosphorylase.

Base Sequence

Genomic insights into natural selection in recent human history.

For over a century, scientists have debated the extent to which genetic and phenotypic variation among present-day humans is the result of natural selection - in which heritable traits influence survival or reproduction - versus neutral processes such as genetic drift or population history. The initial sequencing of the human genome and subsequent population resequencing studies enabled genome-scale searches for signatures of selection in present-day genomes. This first generation of genome-wide selection scans identified many targets but left open questions about the timing and nature of selection, making it challenging to identify environmental and biological drivers. Recent methodological advances based on reconstructing ancestral recombination graphs have increased the potential power and resolution of selection scans based on present-day genomes, while the availability of new data on ancient DNA has facilitated the direct reconstruction of genetic change through time. However, there is little consensus on how to use these data to detect and interpret signatures of selection, while avoiding confounders. Here, we review the current state of knowledge about the impact of selection on human genomic diversity and highlight conceptual advances in our understanding of human evolution over the past 10,000 years.

Journal Article

Expression of the human cytomegalovirus genome in mouse cells and in human-mouse heterokaryons.

Mouse cells with an established human cytomegalovirus (HCMV) infection were fused with susceptible human embryonic fibroblast cells. CMV-specific early antigens could be demonstrated in the cytoplasm and cell-membrane of the heterokaryons. Treatment with 5-iodo-2'-deoxyuridine (IUdR) of the heterokaryons or of the latently infected mouse cells, prior to their fusion with human cells, could induce the appearance of immunoflourescent elements, characterised as late antigens, and of infectious virus. Our data show that the mouse cells, in the latent stage of infection, contain the whole virus genome and that the replication of the virus is controlled by a genetic mechanism of the host cells both in virus-harbouring mouse cells and in heterokaryons.

Animals

Another chromosomal assignment for a simian virus 40 integration site in human cells.

Somatic cell hybrids derived from fusion of GM637, a human cell line transformed by simian virus 40, and mouse B82 cells were examined for simian virus 40 T antigen, V antigen, and viral DNA. All hybrid cell lines that contained viral DNA were T-antigen positive. Cells that did not have viral DNA were T-antigen negative. We determined that there is a single viral insertion in these hybrid cells. Correlation of T-antigen expression and viral DNA with the partial complements of the human genome retained in the hybrids shwed that the inserted viral genome is in human chromosome 8. The integrated viral DNA is stable; free viral DNA found in GM637 does not insert at other potential sites in the human genome.

Antigens, Viral

The human mitochondrial genome contains a second light strand promoter.

The human mitochondrial genome must be replicated and expressed in a timely manner to maintain energy metabolism and supply cells with adequate levels of adenosine triphosphate. Central to this process is the idea that replication primers and gene products both arise via transcription from a single light strand promoter (LSP) such that primer formation can influence gene expression, with no consensus as to how this is regulated. Here, we report the discovery of a second light strand promoter (LSP2) in humans, with features characteristic of a bona fide mitochondrial promoter. We propose that the position of LSP2 on the mitochondrial genome allows replication and gene expression to be orchestrated from two distinct sites, which expands our long-held understanding of mitochondrial gene expression in humans.

Adenosine Triphosphate