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Although some features underlying replication-origin activation in metazoan cells have been determined, little is known about their regulation during metazoan development. Using the nascent-strand purification method, here we identified replication origins throughout Caenorhabditis elegans embryonic development and found that the origin repertoire is thoroughly reorganized after gastrulation onset. During the pluripotent embryonic stages (pregastrula), potential cruciform structures and open chromatin are determining factors that establish replication origins. The observed enrichment of replication origins in transcription factor-binding sites and their presence in promoters of highly transcribed genes, particularly operons, suggest that transcriptional activity contributes to replication initiation before gastrulation. After the gastrula transition, when embryonic differentiation programs are set, new origins are selected at enhancers, close to CpG-island-like sequences, and at noncoding genes. Our findings suggest that origin selection coordinates replication initiation with transcriptional programs during metazoan development.

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On-line permittivity and optical density measurements have been used to monitor biomass concentration and sporulation status during growth of a spore-forming bacterium, Bacillus thuringiensis, in fed-batch culture. The correlation between permittivity, optical density and other observations showed three distinct phases of growth: growth itself, transition and sporulation. The permittivity variations during the transition and sporulation phases could be related to the sporulation development: the evolution pattern of the ratio of optical density to permittivity was representative of the culture state, and during the sporulation phase, a permittivity index could be build to measure the extend of spore liberation.