There are three systems for choline transport: polyspecific organic cation transporters with low affinities for choline; high-affinity choline transporters, and intermediate-affinity choline transporter-like proteins. Hemicholinium-3 is one of the strongest CHT inhibitors and has been shown to inhibit cell proliferation in human colon cancer and lung cancer cells. It remains unclear, however, how each choline transporter is involved in proliferation. Here, we demonstrate that cows with high birth weights carry an A polymorphism in the 59 untranslated region of solute carrier family 44, member 5. This gene encodes a CTL protein, and the A polymorphism is correlated with an increased dystocia rate in the calving female. Luciferase assays and quantitative polymerase chain reaction assays reveal that the number of PF-04217903 c-Met inhibitor SLC44A5 transcripts with the A polymorphism is reduced compared to the number of transcripts with the G polymorphism. Choline uptake studies and cell viability assays in HeLa cells further indicate that SLC44A5 knockdown reduces choline efflux and increases cell proliferation. Our results therefore demonstrate an unexpected role for SLC44A5 in regulating birth weight. In this study, we identified a SNP in the 59 UTR of SLC44A5 that is correlated with birth weight in cattle and with the rate of dystocia; cows carrying the G polymorphism express this gene at higher levels. SLC44A5 encodes a choline transporter-like protein, and our results demonstrate that SLC44A5 overexpression suppresses cell proliferation. If farmers select for cows that carry the G polymorphism in the SLC44A5 59 UTR, this would results in calves with smaller birth weights, preventing difficult labors. Using 1151 microsatellite markers, we successfully identified the region associated with birth weight in cattle. We also narrowed the region of 0.1 Mb with additional 290 microsatellite markers. Now association studies using SNPs with high density are more popular than using microsatellite markers. However, typing more than one thousand microsatellite markers could still be a useful method for association studies at least in cattle. One reason is that microsatellite markers are more polymorphic than SNPs and give more information of recombination. The other reason is that the extent of LD on cattle is greater than human and less markers could be enough to identify the region in association studies for cattle. Thus it is worth typing of microsatellite markers for association studies although it is laboriousness. Recently we also identified the region associated with ovulation rate in cattle using 1154 microsatellite markers. Although SLC44A5 seems to have a major QTL effect on bovine birth weight, there are additional QTL other than this gene on chromosome 3. Heritability estimates for birth weight are 53% in a Holstein-Friesian population, whereas the SLC44A5 SNP we identified accounted for 11% of variability in our Holstein population. Maltecca et al. identified QTL for birth weight on chromosomes 2, 6, and 14 in a crossbred Holstein and Jersey population. There may be other genetic factors that are associated with birth weight on these chromosomes. Since the polymorphism in the 59UTR of SLC44A5 influences its expression level. Our results suggest that SLC44A5, which is an intermediateaffinity CTL, increases choline efflux similar to low-affinity OCTs and does not increase choline uptake to as great a degree the highaffinity CHTs. Reports have been inconsistent regarding the function of CTL1, the other member of the intermediate-affinity CTLs. Overexpression of yeast CTL1 does not increase choline uptake in yeast, whereas overexpression of mouse CTL1 increases choline uptake in Cos-7 cells.