Wnt-5a inhibits the canonical Wnt pathway by promoting GSK-3–independent β-catenin degradation

Wnts are secreted signaling molecules that can transduce their signals through several different pathways. Wnt-5a is considered a noncanonical Wnt as it does not signal by stabilizing β-catenin in many biological systems. We have uncovered a new noncanonical pathway through which Wnt-5a antagonizes the canonical Wnt pathway by promoting the degradation of β-catenin. This pathway is Siah2 and APC dependent, but GSK-3 and β-TrCP independent. Furthermore, we provide evidence that Wnt-5a also acts in vivo to promote β-catenin degradation in regulating mammalian limb development and possibly in suppressing tumor formation

A dinucleotide deletion in the ankyrin promoter alters gene expression, transcription initiation and TFIID complex formation in hereditary spherocytosis

Ankyrin defects are the most common cause of hereditary spherocytosis (HS). In some HS patients, mutations in the ankyrin promoter have been hypothesized to lead to decreased ankyrin mRNA synthesis. The ankyrin erythroid promoter is a member of the most common class of mammalian promoters which lack conserved TATA, initiator or other promoter cis elements and have high G+C content, functional Sp1 binding sites and multiple transcription initiation sites. We identified a novel ankyrin gene promoter mutation, a TG deletion adjacent to a transcription initiation site, in a patient with ankyrin-linked HS and analyzed its effects on ankyrin expression. In vitro, the mutant promoter directed decreased levels of gene expression, altered transcription initiation site utilization and exhibited defective binding of TATA-binding protein (TBP) and TFIID complex formation. In a transgenic mouse model, the mutant ankyrin promoter led to abnormalities in gene expression, including decreased expression of a reporter gene and altered transcription initiation site utilization. These data indicate that the mutation alters ankyrin gene transcription and contributes to the HS phenotype by decreasing ankyrin gene synthesis via disruption of TFIID complex interactions with the ankyrin core promoter. These studies support the model that in promoters that lack conserved cis elements, the TFIID complex directs preinitiation complex formation at specific sites in core promoter DNA and provide the first evidence that disruption of TBP binding and TFIID complex formation in this type of promoter leads to alterations in start site utilization, decreased gene expression and a disease phenotype in viv

A dinucleotide deletion in the ankyrin promoter alters gene expression, transcription initiation and TFIID complex formation in hereditary spherocytosis

Ankyrin defects are the most common cause of hereditary spherocytosis (HS). In some HS patients, mutations in the ankyrin promoter have been hypothesized to lead to decreased ankyrin mRNA synthesis. The ankyrin erythroid promoter is a member of the most common class of mammalian promoters which lack conserved TATA, initiator or other promoter cis elements and have high G+C content, functional Sp1 binding sites and multiple transcription initiation sites. We identified a novel ankyrin gene promoter mutation, a TG deletion adjacent to a transcription initiation site, in a patient with ankyrin-linked HS and analyzed its effects on ankyrin expression. In vitro, the mutant promoter directed decreased levels of gene expression, altered transcription initiation site utilization and exhibited defective binding of TATA-binding protein (TBP) and TFIID complex formation. In a transgenic mouse model, the mutant ankyrin promoter led to abnormalities in gene expression, including decreased expression of a reporter gene and altered transcription initiation site utilization. These data indicate that the mutation alters ankyrin gene transcription and contributes to the HS phenotype by decreasing ankyrin gene synthesis via disruption of TFIID complex interactions with the ankyrin core promoter. These studies support the model that in promoters that lack conserved cis elements, the TFIID complex directs preinitiation complex formation at specific sites in core promoter DNA and provide the first evidence that disruption of TBP binding and TFIID complex formation in this type of promoter leads to alterations in start site utilization, decreased gene expression and a disease phenotype in viv

Of Mice and MEN1: Insulinomas in a Conditional Mouse Knockout

Patients with multiple endocrine neoplasia type 1 (MEN1) develop multiple endocrine tumors, primarily affecting the parathyroid, pituitary, and endocrine pancreas, due to the inactivation of the MEN1 gene. A conditional mouse model was developed to evaluate the loss of the mouse homolog, Men1, in the pancreatic beta cell. Men1 in these mice contains exons 3 to 8 flanked by loxP sites, such that, when the mice are crossed to transgenic mice expressing cre from the rat insulin promoter (RIP-cre), exons 3 to 8 are deleted in beta cells. By 60 weeks of age, >80% of mice homozygous for the floxed Men1 gene and expressing RIP-cre develop multiple pancreatic islet adenomas. The formation of adenomas results in elevated serum insulin levels and decreased blood glucose levels. The delay in tumor appearance, even with early loss of both copies of Men1, implies that additional somatic events are required for adenoma formation in beta cells. Comparative genomic hybridization of beta cell tumor DNA from these mice reveals duplication of chromosome 11, potentially revealing regions of interest with respect to tumorigenesis