👤 Xueli Fan

137 Russians living in Estonia was screened by isoelectric focusing and immunoblotting procedures to determine the distribution of genetic variations in apolipoprotein E (apoE) and apolipoprotein A-IV (apoA-IV) genes. The apoA-IV-2 allele and epsilon4 allele frequency of the Russians tended to be lower than in most other European populations. Show less

Prior work in our laboratory established a connection between the PALS1/PATJ/CRB3 and Par6/Par3/aPKC protein complexes at the tight junction of mammalian epithelial cells. Utilizing a stable small interfering RNA expression system, we have markedly reduced expression of the tight junction-associated protein PALS1 in MDCKII cells. The loss of PALS1 resulted in a corresponding loss of expression of PATJ, a known binding partner of PALS1, but had no effect on the expression of CRB3. However, the absence of PALS1 and PATJ expression did result in the decreased association of CRB3 with members of the Par6/Par3/aPKC protein complex. The consequences of the loss of PALS1 and PATJ were exhibited by a delay in the polarization of MDCKII monolayers after calcium switch, a decrease in the transepithelial electrical resistance, and by the inability of these cells to form lumenal cysts when grown in a collagen gel matrix. These defects in polarity determination may be the result of the lack of recruitment of aPKC to the tight junction in PALS1-deficient cells, as observed by confocal microscopy, and subsequent alterations in downstream signaling events. Show less

In Drosophila, the Crumbs-Stardust-Discs-lost complex is required during the establishment of polarized epithelia. Embryos that lack a component of this complex or overexpress Crumbs exhibit defects in epithelial morphogenesis. We recently cloned a novel mammalian epithelial Crumbs isoform, Crumbs3 (CRB3). CRB3 exists in a complex at tight junctions (TJs) with Pals1 and PATJ, the mammalian homologues of Stardust and Discs lost, respectively. Here, we observe that overexpression of CRB3 leads to delayed TJ formation in MDCK epithelial cell monolayers and disruption of polarity in MDCK cysts cultured in collagen. Both phenomena require the last four residues of CRB3. Next, we expressed, in MDCK cells, a dominant-negative Myc-Lin-2-Pals1 chimeric protein, where the PDZ domain of Lin-2 was replaced with that of Pals1. TJ and apical polarity defects were also observed in these cells. Collectively, this suggests that the CRB-Pals1 interaction is important for formation of TJs and polarized epithelia. These results provide insight into the function of the mammalian Crumbs complex during TJ formation and epithelial polarization. Show less

Hereditary multiple exostoses (EXT; MIM 133700) is an autosomal dominant bone disorder. It is genetically heterogeneous with at least three chromosomal loci: EXT1 on 8q24.1, EXT2 on 11p11, and EXT3 on 19p. EXT1 and EXT2, the two genes responsible for EXT1 and EXT2, respectively, have been cloned. Recently, three other members of the EXT gene family, named the EXT-like genes (EXTL: EXTL1, EXTL2, and EXTL3), have been isolated. EXT1, EXT2, and the three EXTLs are homologous with one another. We have identified the intron-exon boundaries of EXTL1 and EXTL3 and analyzed EXT1, EXT2, EXTL1, and EXTL3, in 36 Chinese families with EXT, to identify underlying disease-related mutations in the Chinese population. Of the 36 families, five and 12 family groups have mutations in EXT1 and EXT2, respectively. No disease-related mutation has been found in either EXTL1 or EXTL2, although one polymorphism has been detected in EXTL1. Of the 15 different mutations (three families share a common mutation in EXT2), 12 are novel. Most of the mutations are either frameshift or nonsense mutations (12/15). These mutations lead directly or indirectly to premature stop codons, and the mutations generate truncated proteins. This finding is consistent with the hypothesis that the development of EXT is mainly attributable to loss of gene function. Missense mutations are rare in our families, but these mutations may reflect some functionally crucial regions of these proteins. EXT1 is the most frequent single cause of EXT in the Caucasian population in Europe and North America. It accounts for about 40% of cases of EXT. Our study of 36 EXT Chinese families has found that EXT1 seems much less common in the Chinese population, although the frequency of the EXT2 mutation is similar in the Caucasian and Chinese populations. Our findings suggest a possibly different genetic spectrum of this disease in different populations. Show less