Bishop A J, Kosaras B, Carls N, Sidman R L, Schiestl R H
Department of Cancer Cell Biology, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
Carcinogenesis. 2001 Apr;22(4):641-9. doi: 10.1093/carcin/22.4.641.
The pink-eyed unstable mutation, p(un), is the result of a 70 kb tandem duplication within the murine pink-eyed, p, gene. Deletion of one copy of the duplicated region by homologous deletion/recombination occurs spontaneously in embryos and results in pigmented spots in the fur and eye. Such deletion events are inducible by a variety of DNA damaging agents, as we have observed previously with both fur- and eye-spot assays. Here we describe a study of the effect of exposure to benzo[a]pyrene (B[a]P) at different times of development on reversion induction in the eye. Previously we, among others, have reported that the retinal pigment epithelium (RPE) displays a position effect variegation phenotype in the pattern of pink-eyed unstable reversions. Following an acute exposure to B[a]P or X-rays on the tenth day of gestation an increased frequency of reversion events was detected in a distinct region of the adult RPE. Examining exposure at different times of eye development reveals that both B[a]P and X-rays result in an increased frequency of reversion events, though the increase was only significant following B[a]P exposure, similar to our previous report limited to exposure on the tenth day of gestation. Examination of B[a]P-exposed RPE in the present study revealed distinct regions where the induced events lie and that the positions of these regions are found at increasing distances from the optic nerve the later the time of exposure. This position effect directly reflects the previously observed developmental pattern of the RPE, namely that cells in the regions most distal from the optic nerve are proliferating most vigorously. The numbers and positions of RPE cells displaying the transformed (pigmented) phenotype strongly advocate the proposal that dividing cells are at highest risk to deletions induced by carcinogens.
粉红眼不稳定突变体p(un)是小鼠粉红眼基因p内70 kb串联重复的结果。胚胎中通过同源缺失/重组自发发生重复区域一个拷贝的缺失，导致皮毛和眼睛出现色素沉着斑点。正如我们之前在皮毛和眼斑试验中所观察到的，这种缺失事件可由多种DNA损伤剂诱导。在此，我们描述了一项关于在发育的不同时间暴露于苯并[a]芘（B[a]P）对眼睛回复突变诱导作用影响的研究。此前我们（以及其他研究人员）报道过，视网膜色素上皮（RPE）在粉红眼不稳定回复突变模式中表现出位置效应斑驳表型。在妊娠第10天急性暴露于B[a]P或X射线后，在成年RPE的一个特定区域检测到回复突变事件的频率增加。在眼睛发育的不同时间检查暴露情况发现，B[a]P和X射线都导致回复突变事件的频率增加，不过只有在暴露于B[a]P后增加才显著，这与我们之前仅限于妊娠第10天暴露的报告相似。在本研究中检查暴露于B[a]P的RPE发现了诱导事件所在的不同区域，并且暴露时间越晚，这些区域离视神经的距离就越远。这种位置效应直接反映了之前观察到的RPE的发育模式，即离视神经最远区域的细胞增殖最为活跃。显示转化（色素沉着）表型的RPE细胞的数量和位置有力地支持了这样一种观点，即分裂细胞最易受到致癌物诱导的缺失影响。
