Decoupling of DNA methylation and activity of intergenic LINE-1 promoters in colorectal cancer.

Hypomethylation of LINE-1 repeats in cancer has been proposed as the main mechanism behind their activation; this assumption, however, was based on findings from early studies that were biased toward young and transpositionally active elements. Here, we investigate the relationship between methylation of 2 intergenic, transpositionally inactive LINE-1 elements and expression of the LINE-1 chimeric transcript (LCT) 13 and LCT14 driven by their antisense promoters (L1-ASP). Our data from DNA modification, expression, and 5'RACE analyses suggest that colorectal cancer methylation in the regions analyzed is not always associated with LCT repression. Consistent with this, in HCT116 colorectal cancer cells lacking DNA methyltransferases DNMT1 or DNMT3B, LCT13 expression decreases, while cells lacking both DNMTs or treated with the DNMT inhibitor 5-azacytidine (5-aza) show no change in LCT13 expression. Interestingly, levels of the H4K20me3 histone modification are inversely associated with LCT13 and LCT14 expression. Moreover, at these LINE-1s, H4K20me3 levels rather than DNA methylation seem to be good predictor of their sensitivity to 5-aza treatment. Therefore, by studying individual LINE-1 promoters we have shown that in some cases these promoters can be active without losing methylation; in addition, we provide evidence that other factors (e.g., H4K20me3 levels) play prominent roles in their regulation.

Acute corticosterone administration during meiotic segregation stimulates females to produce more male offspring.

Birds have demonstrated a remarkable ability to manipulate offspring sex. Previous studies suggest that treatment with hormones can stimulate females to manipulate offspring sex before ovulation. For example, chronic treatments with corticosterone, the primary stress hormone produced by birds, stimulated significant skews toward female offspring. It has been suggested that corticosterone acts by influencing which sex chromosome is donated by the heterogametic female bird into the ovulated ovarian follicle. However, it is difficult to pinpoint when in developmental time corticosterone affects offspring sex, because in previous studies corticosterone treatment was given over a long period of time. We treated laying hens with acute high-dose corticosterone injections 5 h before the predicted time of ovulation and quantified the sexes of the subsequently ovulated eggs to determine whether mechanisms exist by which corticosterone can skew offspring sex ratios just before ovulation. We hypothesized that an injection of corticosterone coincident with segregation of the sex chromosomes would stimulate hens to produce more female than male offspring. Contrary to our predictions, hens injected with corticosterone produced a significant bias toward male offspring, nearly 83%. These results suggest that acute corticosterone treatment during meiosis I can influence primary sex ratios in birds, potentially through nonrandom chromosome segregation. Furthermore, acute corticosterone exposure, compared with chronic exposure, may act through different mechanisms to skew offspring sex.