HeLa cell nucleus, a source of thymidine for Trichomonas vaginalis growing in vitro

Trichomonas vaginalis is a parasitic protist incapable of de novo purine and pyrimidine biosynthesis. The lack of these de novo syntheses of nucleotides is supplemented with purine and pyrimidine salvage pathways. Likewise, T. vaginalis is incapable of converting its ribonucleotides to deoxyribonucleotides. Therefore, the parasite must rely on the salvage of exogenous deoxyribonucleosides for DNA synthesis. It has been demonstrated that the parasite can incorporate external adenine and guanine in vitro, but no in vivo nucleotide source has been identified so far. Accordingly, we set out to determine if the parasite could incorporate 3H-thymidine from the nuclei of a cervical-derived cell line into its own DNA. By light and electron microscopy we found that the parasite was able to interact directly, both with mechanically isolated HeLa cell nuclei and with the nuclei released after the disruption of HeLa cell monolayers by the parasite. This study shows that T. vaginalis was capable of incorporating 3H-thymidine from labeled HeLa cells into its own DNA suggesting that the nuclei of this cervical cell line could be an in vivo source of nucleotides for T. vaginalis.