Cornelia de Lange syndrome (CdLS; OMIM 122470) is a dominantly inherited multisystem developmental disordercharacterized by growth and cognitive retardation; abnormalities of the upper limbs; gastroesophageal dysfunction; cardiac, ophthalmologic and genitourinary anomalies; hirsutism; and characteristic facial features 1-3 . Genital anomalies, pyloric stenosis, congenital diaphragmatic hernias, cardiac septal defects, hearing loss and autistic and selfinjurious tendencies also frequently occur 2 . Prevalence is estimated to be as high as 1 in 10,000 (ref. 4). We carried out genome-wide linkage exclusion analysis in 12 families with CdLS and identified four candidate regions, of which chromosome 5p13.1 gave the highest multipoint lod score of 2.7. This information, together with the previous identification of a child with CdLS with a de novo t(5;13)(p13.1;q12.1) translocation, allowed delineation of a 1.1-Mb critical region on chromosome 5 for the gene mutated in CdLS. We identified mutations in one gene in this region, which we named NIPBL, in four sporadic and two familial cases of CdLS. We characterized the genomic structure of NIPBL and found that it is widely expressed in fetal and adult tissues. The fly homolog of NIPBL, Nipped-B, facilitates enhancer-promoter communication and regulates Notch signaling and other developmental pathways in Drosophila melanogaster 5 .CdLS is a dominantly inherited disorder with characteristic facial appearance, limb defects ( Fig. 1) and growth and cognitive retardation. We carried out a genome-wide linkage analysis in nine families with CdLS with more than one affected family member. Under a model of genetic homogeneity, we used a linkage exclusion mapping approach,

Cornelia de Lange Syndrome (CdLS) is a multi-organ system birth defects disorder linked, in at least half of cases, to heterozygous mutations in the NIPBL gene. In animals and fungi, orthologs of NIPBL regulate cohesin, a complex of proteins that is essential for chromosome cohesion and is also implicated in DNA repair and transcriptional regulation. Mice heterozygous for a gene-trap mutation in Nipbl were produced and exhibited defects characteristic of CdLS, including small size, craniofacial anomalies, microbrachycephaly, heart defects, hearing abnormalities, delayed bone maturation, reduced body fat, behavioral disturbances, and high mortality (75–80%) during the first weeks of life. These phenotypes arose despite a decrease in Nipbl transcript levels of only ∼30%, implying extreme sensitivity of development to small changes in Nipbl activity. Gene expression profiling demonstrated that Nipbl deficiency leads to modest but significant transcriptional dysregulation of many genes. Expression changes at the protocadherin beta (Pcdhb) locus, as well as at other loci, support the view that NIPBL influences long-range chromosomal regulatory interactions. In addition, evidence is presented that reduced expression of genes involved in adipogenic differentiation may underlie the low amounts of body fat observed both in Nipbl+/− mice and in individuals with CdLS.

To elucidate the regulatory mechanisms underlying lens development, we searched for members of the large Maf family, which are expressed in the mouse lens, and found three, c-Maf, MafB, and Nrl. Of these, the earliest factor expressed in the lens was c-Maf. The expression of c-Maf was most prominent in lens fiber cells and persisted throughout lens development. To examine the functional contribution of c-Maf to lens development, we isolated genomic clones encompassing the murine c-maf gene and carried out its targeted disruption. Insertion of the ␤-galactosidase (lacZ) gene into the c-maf locus allowed visualization of c-Maf accumulation in heterozygous mutant mice by staining for LacZ activity. Homozygous mutant embryos and newborns lacked normal lenses. Histological examination of these mice revealed defective differentiation of lens fiber cells. The expression of crystallin genes was severely impaired in the c-maf-null mutant mouse lens. These results demonstrate that c-Maf is an indispensable regulator of lens differentiation during murine development.Lens development commences in the 9.5-day-old (e9.5) mouse embryo by invagination of the lens placode to form lens pits on either side of the prospective forebrain (1, 2). Subsequently at e10.5, the lens pit forms a lens vesicle, where embryonic ectodermal cells differentiate into primary lens fiber cells. By e13.0, the primary posterior lens fiber cells grow into the lumen to eventually fill the lens vesicle. The anterior cells of the vesicle become epithelial cells and constitute the lens germinal epithelium; secondary fiber cells then differentiate from the epithelial cells after this stage. This arrangement persists throughout the lifetime of the animal, as new lens fibers are continuously regenerated (3).Differentiation of the lens involves biosynthesis of a group of fibrous lens-specific proteins called crystallins, which constitute 80 -90% of the soluble protein of the lens (4 -6). The regulation of the crystallin genes has been characterized extensively (7-10), and an enhancer for the chicken ␣A-crystallin gene has been identified (11,12). Biochemical analyses of the core region of this enhancer revealed key interacting transcription factors (13,14). Of the cis elements identified in the enhancer, the ␣CE2 sequence, which shares high similarity with the Maf responsive element (MARE 1 (15)), is crucial for its transcriptional activity. MARE-related consensus sequences have also been found in the regulatory regions of other lensspecific genes (12).Recently a new transcription factor, L-Maf, which can interact with the ␣CE2 enhancer element, was isolated from chicken lens (13). L-Maf is a member of the large Maf oncoprotein/ transcription factor family (16 -18). The Maf family factors contain a basic leucine zipper domain and bind to MARE either as homodimers or as heterodimers with other basic leucine zipper transcription factors (19). L-Maf regulates the expression of multiple lens-specific genes, and its forced expression can convert primary chick embry...