CHORDATENEUROGENESIS · Interplay between cell cycle control and differentiation during the formation of the central nervous system in a basal chordate, the ascidian Ciona intestinalis

Final Activity Report Summary - CHORDATENEUROGENESIS (Interplay between cell cycle control and differentiation during the formation of the central nervous system in a basal chordate)

The chordates are a group of animals that includes the vertebrates. The chordate central nervous system (CNS) is composed of neurons and glia. Each neurons and glial cells exit the cell cycle at specific developmental times before their terminal differentiation. The timing of this exit is often important for the final fate of the cell. This project focuses on the links between cell cycle exit and cellular differentiation during CNS formation in a basal chordate, the ascidian Ciona intestinalis. Until now, the project engaged two analyses using the ascidian Ciona intestinalis for obtaining basic information: 1) Establishment of a pan-genome list of general cell cycle regulators, all the protein kinases and all the protein phosphatases, 2) Characterisation the spatio-temporal transcriptional expression pattern of general CCR genes during embryogenesis. 1) Establishment of a pan-genome list of general CCRs, all the PKs and all the PPs. The project got involved in the comprehensive annotation of Ciona intestinalis CCR genes with another post-doc in the host lab, Dr. Kenji Kobayashi, based on the Gene Ontology (GO) annotation found in the Ciona database in the host lab (ANISEED). As the results, 146 CCR genes (including 43 PKs and 1 PP) were identified and classified. This includes 14 Cyclins, 15 CDKs /CDKLs, 2 Cip/Kip family CDK Inhibitors (CKIs), Cdc25 phosphatase, Wee1 kinase, Myt1 kinase, RB, E2F, etc. We found that the known repertoire of these genes is conserved in Ciona intestinalis with some exceptions. They also performed genome-wide surveys of all the PKs and all the PPs in Ciona intestinalis because many cell cycle regulatory steps occur at the post-translational level (phosphorylation, dephosphorylation and proteolysis). Finally, 337 PKs and 84 PPs were identified and classified. In this analysis, they found that several phosphoregulators have been lost in the ascidian lineage after the split of the vertebrate and ascidian lineages. 2) Characterisation the spatio-temporal transcriptional expression pattern of general cell cycle genes during embryogenesis. The cell cycle is controlled at specific checkpoints. While many regulatory steps of cell cycle regulation occur at the post-transcriptional level (phosphorylation, dephosphorylation and proteolysis), some crucial cell cycle regulators are transcriptionally regulated (e.g. cdc25, tribbles). Therefore, the project examined the spatio-temporal transcriptional expression patterns of CCR genes during embryogenesis (from late gastrula to late tailbud stage), especially in the CNS, by whole-mount in situ hybridization (WISH) method. This was also shared work with Dr Kobayashi. Until now, we examined total 155 genes (98 PKs, 22 PPs and 35 other CCRs). Although almost all genes are expressed maternally, 53 genes (34%) are expressed zygotically in the specific tisuue(s). Among them, at least 28 genes were expressed in CNS (brain and/or nerve cord). For example, 5 genes including Ci-Piwi-like1 are expressed specifically in brain. Now we are re-examining their expression patterns in detail. And a Cip/Kip family CDK inhibitor (CKI) gene, Ci-Cip/Kip CKI-b, is expressed zygotically in several tissues including brain and nerve cord. This will be the first metazoan systematic expression atlas of cell cycle regulators. Taken together the pan-genome list, the present result should enhance future research on cell cycle regulation in this model.

Data: CORDIS, © European Union