Development normally occurs similarly in all individuals within an isogenic population, but mutations often affect the fate of individual organisms differently1-4. This phenomenon, known as partial penetrance, has been observed in diverse developmental systems. However, it remains unclear how the underlying genetic network specifies the set of possible alternative fates and how the relative frequencies of these fates evolve5-8. Here, we identify a stochastic cell fate determination process that operates in Bacillus subtilis sporulation mutants and show how it allows genetic control of the penetrance of multiple fates. Mutations in an inter-compartmental signaling process generate a set of discrete alternative fates not observed in wild-type cells, including rare formation of two viable “twin” spores, rather than one within a single cell. By genetically modulating chromosome replication and septation, we could systematically tune the penetrance of each mutant fate. Furthermore, signaling and replication perturbations synergize to dramatically increase the penetrance of twin sporulation. These results suggest a potential pathway for developmental evolution between monosporulation and twin sporulation through states of intermediate twin penetrance. Furthermore, time-lapse microscopy of twin sporulation in wild-type Clostridium oceanicum showed a strong resemblance to twin sporulation in these B. subtilis mutants9,10. Together the results suggest that noise can facilitate developmental evolution by enabling the initial expression of discrete morphological traits at low penetrance, and allowing their stabilization by gradual adjustment of genetic parameters.
Formation of the asymmetrically located septum during sporulation of Bacillus subtilis results in enclosure of the origin-proximal 30% of the chromosome in the prespore compartment. The rest of the chromosome is then translocated into the prespore from the mother cell. Transcription of spoIIR is initiated in the prespore by RNA polymerase containing F soon after the septum is formed. The SpoIIR protein is required for the activation of the transcription program directed by E in the mother cell. The spoIIR locus is located at 324°, near the origin of replication (0/360°). We show here that movement of spoIIR to 28°had little effect on sporulation. However, movement to regions not in the origin-proximal part of the chromosome substantially reduced sporulation efficiency. At 283°sporulation was reduced to less than 20% of the level obtained when spoIIR was at its natural location, and movement to 190°reduced sporulation to about 6% of that level. These positional effects were also seen in the transcription of a spoIIR-lacZ fusion. In contrast, movement of other spo-lacZ fusions from 28°to 190°had little effect on their expression. These results suggest that spoIIR is the subject of "positional regulation," in the sense that the chromosomal position of spoIIR is important for its expression and function.During sporulation Bacillus subtilis undergoes an asymmetrically located cell division. This division is a modified form of the vegetative division (6, 16). However, formation of the sporulation septum results in enclosure of only about 30% of a chromosome in the smaller cell, the prespore (also called the forespore), that results from the division; the rest of the chromosome is then translocated from the larger cell, the mother cell, into the prespore by an active process requiring SpoIIIE ( Fig. 1) (23,25). A second copy of the chromosome remains in the mother cell. The prespores of SpoIIIE mutant cells contain only about 30% of a chromosome, with the other 70% remaining in the mother cell together with the whole of the mother cell chromosome (23). Formation of the asymmetrically located septum is followed by activation of two sporulationspecific transcription factors, F in the prespore and E in the mother cell, which specify different programs of gene expression in the two compartments (reviewed in reference 21). In a spoIIIE36 mutant the F -directed prespore genes that are located in the 70% of the chromosome distal to the origin of replication (for example, dacF and gpr) are not transcribed, whereas those located in the origin-proximal 30% are transcribed (for example, spoIIR and spoIIQ) (9,12,20,22,23,25). Thus, it has been known for some time that chromosome position is important for expression of F -directed genes in a spoIIIE36 mutant (22). It seemed plausible that there could be some prespore-specific gene (or genes) that needed to be expressed as soon as the septum was formed and so needed to be located at the origin-proximal part of the chromosome in the parental, spo ϩ strain. If such a gene were to be r...
During sporulation, σG becomes active in the prespore upon the completion of engulfment. We show that the inactivation of the σF-directed csfB locus resulted in premature activation of σG. CsfB exerted control distinct from but overlapping with that exerted by LonA to prevent inappropriate σG activation. The artificial induction of csfB severely compromised spore formation.
During formation of spores by Bacillus subtilis the RNA polymerase factor G ordinarily becomes active during spore formation exclusively in the prespore upon completion of engulfment of the prespore by the mother cell. Formation and activation of G ordinarily requires prior activity of F in the prespore and E in the mother cell. Here we report that in spoIIA mutants lacking both F and the anti-sigma factor SpoIIAB and in which E is not active, G nevertheless becomes active. Further, its activity is largely confined to the mother cell. Thus, there is a switch in the location of G activity from prespore to mother cell. Factors contributing to the mother cell location are inferred to be read-through of spoIIIG, the structural gene for G , from the upstream spoIIG locus and the absence of SpoIIAB, which can act in the mother cell as an anti-sigma factor to G . When the spoIIIG locus was moved away from spoIIG to the distal amyE locus, G became active earlier in sporulation in spoIIA deletion mutants, and the sporulation septum was not formed, suggesting that premature G activation can block septum formation. We report a previously unrecognized control in which SpoIIGA can prevent the appearance of G activity, and pro-E (but not E ) can counteract this effect of SpoIIGA. We find that in strains lacking F and SpoIIAB and engineered to produce active E in the mother cell without the need for SpoIIGA, G also becomes active in the mother cell.Central to cell differentiation is the establishment of distinct programs of gene expression in the different cell types involved. These programs determine the subsequent path of differentiation. Among prokaryotes, formation of spores by Bacillus subtilis has become a paradigm for the analysis of cell differentiation. Soon after the start of spore formation, bacteria divide asymmetrically to give the smaller prespore (also called the forespore) and the larger mother cell. The prespore is then engulfed by the mother cell. The prespore develops into the mature spore, whereas the mother cell ultimately lyses. The process of spore formation is characterized by the cell-specific activation of four RNA polymerase factors. Immediately after the completion of the spore division septum,
The Bacillus subtilis bex gene complemented the defect in an Escherichia coli era mutant. The Bex protein showed 39% identity and 67% similarity to the E. coli Era GTPase. In contrast to era, bex was not essential in all strains. bex mutant cells were elongated and filled with diffuse nucleoid material. They grew slowly and exhibited severely impaired spore formation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.