Catalyzes the key rate-limiting step in the CDP-choline pathway for phosphatidylcholine biosynthesis (PubMed:12842190). Plays an important role in ovary maturation and the maintenance of sperm production (PubMed:15143167). Catalyzes the key rate-limiting step in the CDP-choline pathway for phosphatidylcholine biosynthesis. CTP + H(+) + phosphocholine = CDP-choline + diphosphate Phospholipid metabolism; phosphatidylcholine biosynthesis; phosphatidylcholine from phosphocholine: step 1/2. Homodimer. Highly expressed in brain (at protein level) (PubMed:12842190). Expressed in liver (at protein level) (PubMed:12842190). Expressed at lower levels in lung and gonads (PubMed:15143167). Expressed in brain (at protein level) (PubMed:12842190). Expressed at lower levels in lung and gonads (PubMed:15143167). Expression is low at 7 dpc, reaches a maximum at 15 dpc and decreases at 17 dpc. Not expressed in embryo. Expression starts at 5 weeks. Female mice lacking isoform 1 have reduced fecundity due to failure in ovary maturation. Male mice lacking isoform 1 have reduced fecundity due to testicular degeneration. Belongs to the cytidylyltransferase family.