Zscan4: A novel gene expressed exclusively in late 2-cell embryos and embryonic stem cells

Abstract

The first wave of transcription, called zygotic genome activation (ZGA), begins during the 2-cell stage in mouse preimplantation development and marks a vital transition from the maternal genetic to the embryonic genetic program. Utilizing DNA microarray data, we looked for genes that are expressed only during ZGA and found Zscan4, whose expression is restricted to late 2-cell stage embryos. Sequence analysis of genomic DNA and cDNA clones revealed nine paralogous genes tightly clustered in 0.85 Mb on mouse chromosome 7. Three genes are not transcribed and are thus considered pseudogenes. Among the six expressed genes named Zscan4a-Zscan4f, three - Zscan4c, Zscan4d, and Zscan4f - encode full-length ORFs with 506 amino acids. Zscan4d is a predominant transcript at the late 2-cell stage, whereas Zscan4c is a predominant transcript in embryonic stem (ES) cells. No transcripts of any Zscan4 genes are detected in any other cell types. Reduction of Zscan4 transcript levels by siRNAs delays the progression from the 2-cell to the 4-cell stage and produces blastocysts that fail to implant or proliferate in blastocyst outgrowth culture. Zscan4 thus seems to be essential for preimplantation development.

An in situ hybridization-based screen for heterogeneously expressed genes in mouse ES cells

“…The presence of T-positive cells in ES cell colonies has also been reported (Suzuki et al, 2006). Recently, we have reported that a gene named Zscan4, which is expressed exclusively in 2-cell embryos and ES cells, shows heterogeneous expression in ES cells: only up to 10% of ES cells cultured in undifferentiated conditions express Zscan4 by in situ hybridization (Falco et al, 2007). We suspect the existence of other transcription-regulating genes that show similar expression patterns.…”

“…Zscan4, which encodes SCAN domain and four zinc-finger domains, was identified previously for the heterogeneous spot-in-colony expression pattern (Falco et al, 2007). Zscan4 is expressed exclusively in mouse 2-cell embryos and ES cells.…”

“…Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (Falco et al, 2007). We suspect the existence of other transcription-regulating genes that show similar expression patterns.…”

Zscan4 promotes genomic stability during reprogramming and dramatically improves the quality of iPS cells as demonstrated by tetraploid complementation

“…Here, we demonstrate that Zscan4, a unique gene highly expressed at the zygotic genome activation stage [23], in combination with the Yamanaka factors, not only dramatically decreases DDR but also significantly promotes iPS cell generation. Zscan4 can stabilize the genomic DNA in the process of somatic reprogramming, probably via rapid enhancement of telomere lengthening, resulting in high quality iPS cells as demonstrated by TCA analyses.…”

“…Zscan4 gene contains a SCAN domain and four zinc finger domains, and three isoforms (Zscan4c, Zscan4d and Zscan4f) encode full-length open reading frames [23]. Zscan4 is expressed specifically in two-cell embryos [23] and transiently in ES cells [28], and plays important roles in preimplantation embryonic development [23] and in the maintenance of genomic stability in ES cells [28]. γ-H2AX was detected in reprogramming cells two days after MEFs were transduced with either OSKM or OSKM plus Zscan4f (OSKMZ) (Figure 2A).…”