Can sister chromatid intercrossings be considered as prelesions?

Abstract

In a study of the expression of folate-sensitive fragile sites in five normal individuals using RPMI medium containing methotrexate (MTX), we observed a high frequency of "sister chromatid intercrossings" (SCI) that is, the intersection of sister chromatids. The location of SCIs corresponded to fragile sites in 54.2% of the cases. Of the SCIs observed in each individual, 43%-53% were located at the same bands as their expressed fragile sites. Furthermore when RPMI + MTX medium was used instead of F-10 medium, the incidence of SCIs increased tenfold. We suggest that SCIs could indicate the existence of a pre-lesion.

Cytogenetic Study of Fragile Sites and Sister Chromatid Intercrossing.

“…According to this, the number of chromosomal lesions found in our study is less than what was found by Fuster et al (1988) when they used methotrevate. Also the frequency of SCI found in our study was inferior.…”

“…The aim of the present work is to check the suggestions of Fuster et al (1988) and also complete our preliminary results (Arrieta et al 1991). …”

“…In the present work we have used this medium which was not used by Fuster et al (1988) to check if the proposed hypothesis by them is fulfilled also with this other inductive medium of fragile sites (under conditions of low folate expression of common and rare fragile sites may be induced; Glover et al 1984, Sutherland and Hecht 1985, Green et al 1988. Staining procedures (conventional Giemsa and G-banding techniques) were performed as usual (Verma and Babu, 1989), for the localization of FS and SCI in the chromosomes.…”

“…The SCI were classified in three different types, following Fuster et al (1988). For the classification of gaps and breaks we followed ISCN (1985).…”

“…However, a study (Fuster et al 1988) described a new type of chromosomal abnormality related with FS which they called "sister chromatid intercrossing" (SCI), what in the authors opinion could represent a pre-lesion stage, which would be followed by a gap or by a chromosome break, a different type of expression of FS or could also be a precursor of sister chromatid exchanges (SCE).…”