One is Nothing without the Other: Theoretical and Empirical Analysis of Cell Growth and Cell Cycle Progression

Mid-cell migration of the chromosomal terminus is coupled to origin segregation in Escherichia coli

Bacterial chromosomes are dynamically and spatially organised within cells. In slow-growing Escherichia coli, the chromosomal terminus is initially located at the new pole and must therefore migrate to midcell during replication to reproduce the same pattern in the daughter cells. Here, we use high-throughput time-lapse microscopy to quantify this transition, its timing and its relationship to chromosome segregation. We find that terminus centralisation is a rapid discrete event that occurs ~25 min after initial separation of duplicated origins and ~50 min before the onset of bulk nucleoid segregation but with substantial variation between cells. Despite this variation, its movement is tightly coincident with the completion of origin segregation, even in the absence of its linkage to the divisome, suggesting a coupling between these two events. Indeed, we find that terminus centralisation does not occur if origin segregation away from mid-cell is disrupted, which results in daughter cells having an inverted chromosome organisation. Overall, our study quantifies the choreography of origin-terminus positioning and identifies an unexplored connection between these loci, furthering our understanding of chromosome segregation in this bacterium.

Integration of Transcriptome and Methylome Highlights the Roles of Cell Cycle and Hippo Signaling Pathway in Flatfish Sexual Size Dimorphism

Sexual size dimorphism (SSD) is the difference in segments or body size between sexes prevalent in various species. Understanding the genetic architecture of SSD has remained a significant challenge owing to the complexity of growth mechanisms and the sexual influences among species. The Chinese tongue sole (Cynoglossus semilaevis), which exhibits a female-biased SSD and sex reversal from female to pseudomale, is an ideal model for exploring SSD mechanism at the molecular level. The present study aimed to integrate transcriptome and methylome analysis to unravel the genetic and epigenetic changes in female, male, and pseudomale C. semilaevis. The somatotropic and reproductive tissues (brain, liver, gonad, and muscle) transcriptomes were characterized by RNA-seq technology. Transcriptomic analysis unravelled numerous differentially expressed genes (DEGs) involved in cell growth and death-related pathways. The gonad and muscle methylomes were further employed for screening differentially methylated genes (DMGs). Relatively higher DNA methylation levels were observed in the male and pseudomale individuals. In detail, hypermethylation of the chromosome W was pronounced in the pseudomale group than in the female group. Furthermore, weighted gene co-expression network analysis showed that turquoise and brown modules positively and negatively correlated with the female-biased SSD, respectively. A combined analysis of the module genes and DMGs revealed the female-biased mRNA transcripts and hypomethylated levels in the upstream and downstream regions across the cell cycle-related genes. Moreover, the male and pseudomale-biased gene expression in the hippo signaling pathway were positively correlated with their hypermethylation levels in the gene body. These findings implied that the activation of the cell cycle and the inhibition of the hippo signaling pathway were implicated in C. semilaevis female-biased SSD. In addition, the dynamic expression pattern of the epigenetic regulatory factors, including dnmt1, dnmt3a, dnmt3b, and uhrf1, among the different sexes correspond with their distinct DNA methylation levels. Herein, we provide valuable clues for understanding female-biased SSD in C. semilaevis.

The linkage of cell cycle and DNA replication with growth difference in female Chinese tongue sole (Cynoglossus semilaevis): Analysis from transcriptomic study and WGCNA

In addition to the typical sexual size dimorphism, considerable size differences within the female population of the Chinese tongue sole (Cynoglossus semilaevis) have become a further bottleneck of the improvement of sole aquaculture. To identify the internal mechanism, transcriptomic analysis and weighted gene co-expression network analysis (WGCNA) were employed simultaneously. Transcriptomic analyses of brain, pituitary gland, liver, gonad, and muscle tissues from two female groups with size differences identified 109, 698, 1325, 2299, and 2141 differentially expressed genes (DEGs), respectively. The results of these enrichment analyses suggest that the up-regulation of neuroactive ligand-receptor interaction, cell cycle, DNA replication, and MAPK signaling pathway in the group with larger females may be involved in the regulation of the observed growth differences. WGCNA of DEGs showed that cell cycle and DNA replication might be crucial pathways for accelerating cell growth in the groups with larger females. Finally, a series of hub genes including 6-phosphofructokinase type C (pfkp), ribosome biogenesis protein (wdr12), bleomycin hydrolase (blmh), and semaphorin-3A (sema3a) were recognized by the illustrated network map of modules. The linkage of cell cycle, DNA replication, and hub genes in the growth regulation of C. semilaevis provides further information for a better understanding of growth differences in fish.