Identification, genomic organization, chromosomal mapping and mutation analysis of the human INV gene, the ortholog of a murine gene implicated in left-right axis development and biliary atresia

Abstract

Determination of left-right axis is a precocious embryonic event, and all phenotypic anomalies resulting from disruption of the normal lateralization process are collectively referred to as the lateralization defect. A transgenic mouse with lateralization defect and hepatic, kidney, and pancreatic anomalies has resulted from disruption of the inv gene by insertion of a transgene. The human ortholog is thus a good candidate for lateralization defect in humans, in particular in cases with associated hepatic anomalies. Here, we have identified, mapped, and characterized the INV human gene and screened a series of heterotaxic patients (with or without biliary anomalies) for mutation in this gene. In a German family of Turkish origin, we have found that all available affected and unaffected individuals are heterozygous for a mutation in the splicing donor site of intron 12 in the INV gene resulting in two different aberrant splicing isoforms. This can be explained either by a randomization of lateralization defects or, as suggested earlier, di- or trigenic inheritance, although we have been unable to detect, in this family, a mutation in genes known to be involved in the human lateralization defect ( LEFTY1, LEFTY2, ACVR2B, NODAL, ZIC3, and CFC1). In contrast to the mouse, the affected individuals have no biliary anomalies, and the absence of mutation in a series of seven cases with lateralization defect and biliary anomalies demonstrates that INV is not frequently involved in such a phenotype in humans.

The Invs Gene Encodes a Microtubule-Associated Protein

“…Morgan et al (12) described alternative splicing in exon 13 of the full-length Invs sequence predicting three isoforms of 99, 104, and 118 kD. The existence of splicing isoforms is further supported by the study of Schön et al (39), who described two bands (4.2 and 3.5 kb) on Northern blots from several tissues. The inversin protein may also undergo several posttranslational modifications, including phosphorylation (50 serine, 11 threonine, and 6 tyrosine) as well as type O-glycosylation (11 serine and 2 threonine) (17).…”

Obstruction of extrahepatic bile ducts by lymphocytes is regulated by IFN-γ in experimental biliary atresia

“…Furthermore, animal-and patientbased studies implicate specific genes in the pathogenesis of a subgroup of patients with biliary atresia who also display defects in laterality (2,(25)(26)(27). The presence of mutations in laterality genes in patients with extrahepatic malformations, but not consistently in patients who also have biliary atresia (27,28), points to a modifying but not causative role for these genes in disease pathogenesis. Here, we began dissecting the molecular pathways regulating the pathogenic mechanisms responsible for the common inflammatory injury of the biliary system and identified IFN-γ as a key regulator of ductal obstruction during the progression of disease.…”

Effector Role of Neonatal Hepatic CD8+ Lymphocytes in Epithelial Injury and Autoimmunity in Experimental Biliary Atresia

“…6 To date, sequence analyses of genes that regulate biliary development have failed to identify disease-causing mutations. 7 In contrast, a comprehensive survey of the hepatic transcriptome and tissue analyses uncovered molecular signatures and cellular phenotypes consistent with a prominent Th1 response in the early phases of neonatal disease. 8, 9 A more direct cause-and-effect relationship emerged from mechanistic studies in which the constitutive loss of interferon-gamma (Ifng) prevented the inflammatory obstruction of bile ducts in a mouse model of biliary atresia induced by neonatal challenge with rhesus rotavirus (RRV).…”