بایگانی برچسب برای: Cell cycle

The rice FLATTENED SHOOT MERISTEM, encoding CAF-1[taliem.ir]

The rice FLATTENED SHOOT MERISTEM, encoding CAF-1 p150 subunit, is required for meristem maintenance by regulating the cell-cycle period

We isolated flattened shoot meristem (fsm) mutants in rice that showed defective seedling growth and died in the vegetative phase. Since most fsm plants had flat and small shoot apical meristems (SAMs), we suggest thatFSM is required for proper SAM maintenance. FSM encodes a putative ortholog of Arabidopsis FASCIATA1 (FAS1) that corresponds to the p150 subunit of chromatin assembly factor-1 (CAF-1). FSM is expressed patchily in tissues with actively dividing cells, suggesting a tight association of FSM with specific cell-cycle phases. Double-target in situ hybridization counterstained with cell-cycle marker genes revealed that FSM is expressed mainly in the G1 phase. In fsm, expressions of the two marker genes representing S- and G2- to M-phases were enhanced in SAM, despite a reduced number of cells in SAM, suggesting that S- and G2- phases are prolonged in fsm. In addition, developmental events in fsm leaves took place at the proper time, indicating that the temporal regulation of development occurs independently of the cell-cycle period. In contrast to the fasciated phenotype of Arabidopsis fas1, fsm showed size reduction of SAM. The opposite phenotypes between fsm and fas1 indicate that the SAM maintenance is regulated differently between rice and Arabidopsis.
The D-Type Cyclins A Historical Perspective[taliem.ir]

The D-Type Cyclins: A Historical Perspective

D-type cyclins integrate mitogen-dependent signals to enforce progression through the frst gap phase (G1) of the cell division cycle. In simplest terms, three mammalian D-type cyclins (D1, D2, and D3), induced in a cell lineage-specifc fashion in response to extracellular signals, interact with two cyclin-dependent kinases (CDK4 and CDK6) to form holoenzyme complexes that phosphorylate the retinoblastoma protein (RB). In turn, RB phosphorylation, reinforced by other CDKs expressed later in G1 phase, inactivates the suppressive effects of RB on transcription factors that induce genes required for DNA replication. All steps in the life history of individual D-type cyclins, including their transcriptional induction, translation, assembly with CDK4 and CDK6, and their rapid turnover via ubiquitinmediated proteolysis, are governed by mitogen signaling. Hence, progression through the G1 phase of the mammalian cell cycle is tied to extracellular signals that ultimately influence cell division. Analysis of phenotypes of mice lacking D cyclins has highlighted their individual and combinatorial lineage-specifc activities during mammalian development. The genes encoding D-type cyclins and their dependent kinases, CDK4 and CDK6, are proto-oncogenes implicated in many forms of cancer. Genetic or biochemical disruption of cyclin D-dependent CDK signaling can restrain cancer development and progression. Here, we highlight the founding discoveries.