TABLE 4.
Summary of Xist transgenic experiments
| Study | Transgene | Integrationa | Copy no. | Studied in: | Findingsb |
|---|---|---|---|---|---|
| Lee et al. (86) | 450-kb YAC | Autosome in male ES cells | 3–24 | ES cells and fibroblasts | Tg Xist is expressed exclusively (53–76% of cells) or mutually (24–44% of cells) with endogenous Xist upon differentiation. Expression of Tg Xist represses the downstream reporter gene. Tg Xist RNA coats an autosomal region flanking the Tg Xist in cis. |
| Lee and Jaenisch (87) | 450-kb YAC | Chromosome 12 in male ES cells | 24 | ES cells and fibroblasts | Tg Xist RNA coats the autosomal region in cis. Tg Xist inactivates a region of 50 cM around the integration site and causes the Ch.12 Tg to be late replicated and hypoacetylated. |
| Herzing et al. (61) | 35-kb YAC | Autosome in male ES cells | 2–8 | ES cells | Endogenous Xist expression is induced in 30% of male differentiating ES cells. Expression of Tg Xist represses the downstream reporter gene. |
| Heard et al. (57) | 460-kb YAC | Autosome by pronuclear injection | 1–2 | Transgenic mice | Tg Xist is not expressed in males and females. Tg Xist is methylated. Reporter gene downstream of Tg Xist is expressed. |
| Matsuura et al. (99) | 350-kb YAC | Autosome or Y by pronuclear injection | 3–4 | Transgenic mice | Autosomal: Tg Xist is not expressed in males (female not tested) and is methylated. |
| Y-linked: Tg Xist is expressed, and some copies are hypomethylated. Mice are phenotypically normal. | |||||
| Hendrich et al. (60) (human XIST) | 0.2–1.2-kb promoter | Autosome by pronuclear injection | NRc | Transgenic mice | Tg Xist promoter is active in 9.5–13.5-dpc embryos in 9 of 11 lines to variable extents. DNA methylation was not investigated. |
| Goto et al. (51) | 233-bp promoter | Autosome by pronuclear injection | 1–71 | Transgenic mice | Tg Xist promoter is inactive and methylated in somatic tissues but active and hypomethylated in the testis. Activity of Tg Xist promoter in preimplantation embryos is correlated with the extent of methylation in sperm. |
a
In all studies, transgenes were integrated at a single site.
b
cM, centimorgan; Tg Xist, transgene Xist; Ch.12 Tg, chromosome 12 with the Xist transgene integrated.
c
NR, not reported.