Schematic representation of eukaryotic cell cycle and key regulatory proteins which allow the transition from one cell cycle phase to another. CDKs inhibitors, such as p15, p16, p18, p19 (INK4 group), p21, p27 and p57 (CIP/KIP class) and proliferative markers are also showed. The arrows in red indicate increased or decreased expression of some trophoblast key regulatory proteins, CDKs inhibitors and proliferative markers in maternal diabetes. G1: Gap 1 phase; S: synthesis phase; G2: Gap 2 phase; M: Mitosis; CDKs: Cyclin-dependent kinases; PCNA: Proliferating cell nuclear antigen; p53: Tumor protein p53.