title: HGPRT mutation induction by N-ethyl-N-nitrosourea as measured by 6-thioguanine resistance is higher in male than in female Syrian hamster fetuses.
abstract: BACKGROUND
  The consequences of mutations in embryonic and fetal cells are serious and contribute to high prenatal sensitivity to mutagenic agents. An understanding of the factors that influence the yield of such mutations is important for management of adverse effects of perinatal exposures. Resistance to 6-thioguanine (6-TG) can be utilized to study mutational events at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus. HGPRT is X-linked and recessive. According to the Lyon hypothesis, male cells have only one X-chromosome and female cells randomly inactivate the second X-chromosome. This leads to the prediction that X-linked genes should be equally sensitive to the mutagenic effects of toxicants in male and female fetuses.
  
  
  METHODS
  We tested this supposition by in utero exposure of Syrian hamster fetuses to N-ethyl-N-nitrosourea (ENU) at day 12 of gestation. ENU is a strong carcinogen and mutagen. HGPRT mutations were detected by selection with 6-TG.
  
  
  RESULTS
  Surprisingly. the male cells had 4 to 5 times more 6-TG mutants than female cells, in two separate experiments (p<0.001). Ouabain resistance, reflecting a co-dominant autosomal locus, was used as a control, and we found that there was no significant difference between male and female cells (p=0.549).
  
  
  CONCLUSIONS
  Possible reasons for the sex difference in mutations include escape of the second X-chromosome from inactivation in some of the female cells, or higher mutability in male cells. In any event, there is a gender difference in vulnerability to mutation of an X-linked gene that has previously not been appreciated, and that may be relevant to toxicological studies of such genes. HGPRT is frequently used to monitor mutagenic events in human fetuses.
authors.affiliation: Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, Room 205, NCI-Frederick, Frederick, Maryland 21702-1201, USA. donovapa@mail.ncifcrf.gov
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Donovan
authors.forename: George T
authors.initials: GT
authors.lastname: Smith
authors.forename: Lee F
authors.initials: LF
authors.lastname: Dove
authors.forename: John
authors.initials: J
authors.lastname: Klose
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Powell
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D005038:Ethylnitrosourea / Q000633:toxicity*; D005260:Female; D005333:Fetus / Q000187:drug effects* / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008297:Male; D008647:Mesocricetus; D016296:Mutagenesis / Q000187:drug effects*; D011247:Pregnancy; D012727:Sex Characteristics; D013866:Thioguanine / Q000494:pharmacology*
chemical_list: D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine; D005038:Ethylnitrosourea