| Cornelia de Lange Syndrome (CdLS) is a birth defects disorder that affects multiple organ systems, including the skeletal, neurological, gastrointestinal, visual, auditory and cardiovascular systems (de Lange 1933; Jackson, Kline et al. 1993; Kline, Krantz et al. 2007; Liu and Krantz 2009). CdLS is caused by heterozygous mutations in genes whose protein product is part of, or directly associated with, the cohesin complex (Krantz, McCallum et al. 2004; Tonkin, Wang et al. 2004; Musio, Selicorni et al. 2006; Deardorff, Kaur et al. 2007; Deardorff, Wilde et al. 2012). Cohesin is most notably known for its role in sister chromatid cohesion, however, surmounting evidence over recent years have shown the role of cohesin, and its associated proteins, as transcriptional regulators (Rollins, Morcillo et al. 1999; Dorsett 2007; Wendt, Yoshida et al. 2008; Chien, Zeng et al. 2011). Data from cell lines from people with CdLS, and animal models for CdLS, suggest that developmental defects result from small changes in gene expression across multiple loci.;The majority of CdLS cases are linked to heterozygous mutations in NIPBL (Liu and Krantz 2009). To facilitate the investigation of early developmental defects that occur in CdLS, we generated a mouse model for Nipbl haploinsufficiency. NipblRRS/+ mice recapitulate a majority of the phenotypes observed in CdLS, including microbrachycephaly, behavioral disturbances, growth defects, cranio-facial defects, congenital heart defects (CHDs), and high mortality rates during the first few weeks of life (Kawauchi, Calof et al. 2009). CHDs are detected at late stages of development; likely CHDs observed at late embryonic stages lead to the high mortality rates observed shortly after birth. Recent finding in the zebrafish model for CdLS showed that heart defect originate at very early stages of development, before the heart begins to form (Muto, Calof et al. 2011). Upon a detailed heart analysis, NipblRRS/+ embryos were found to misregulate the expression of an early heart-specifying gene at the inception of heart development.;To gain insight into the tissue origin of developmental abnormalities, we developed a new series of Nipbl alleles based on a "conditional /invertible" (FLEX) gene-trap strategy (Schnutgen, De-Zolt et al. 2005). Such alleles have been shown to toggle from mutant (FLEX), to wildtype (FLOX or FLRT), and back to mutant (FIN) gene conformations by sequential introduction of Cre and Flp recombinases. Using the EUCOMM EUCE313f02 ES cell line, containing the FLEX gene-trap vector (a modified pFlpROSAβgeo) in intron 1 of the Nipbl locus, NipblFLEX/+ mice were generated. Here we show that the Nipbl FLEX allele can toggle from mutant to wildtype, and then back to mutant conformations. Furthermore, by using tissuespecific Cre lines, we have begun to exam the how and in which cells heart defects originate when Nipbl is deficient. |
