Transcriptional regulation of IER3IP1 gene by tumor necrosis factor-alpha and Sp family proteins

Functional characterization of zebrafish orthologs of the human Beta 3-Glucosyltransferase B3GLCT gene mutated in Peters Plus Syndrome

Peters Plus Syndrome (PPS) is a rare autosomal recessive disease characterized by ocular defects, short stature, brachydactyly, characteristic facial features, developmental delay and other highly variable systemic defects. Classic PPS is caused by loss-of-function mutations in the B3GLCT gene encoding for a β3-glucosyltransferase that catalyzes the attachment of glucose via a β1–3 glycosidic linkage to O-linked fucose on thrombospondin type 1 repeats (TSRs). B3GLCT was shown to participate in a non-canonical ER quality control mechanism; however, the exact molecular processes affected in PPS are not well understood. Here we report the identification and characterization of two zebrafish orthologs of the human B3GLCT gene, b3glcta and b3glctb. The b3glcta and b3glctb genes encode for 496-aa and 493-aa proteins with 65% and 57% identity to human B3GLCT, respectively. Expression studies demonstrate that both orthologs are widely expressed with strong presence in embryonic tissues affected in PPS. In vitro glucosylation assays demonstrated that extracts from wildtype embryos contain active b3glct enzyme capable of transferring glucose from UDP-glucose to an O-fucosylated TSR, indicating functional conservation with human B3GLCT. To determine the developmental role of the zebrafish genes, single and double b3glct knockouts were generated using TALEN-induced genome editing. Extracts from double homozygous b3glct^-/- embryos demonstrated complete loss of in vitro b3glct activity. Surprisingly, b3glct^-/- homozygous fish developed normally. Transcriptome analyses of head and trunk tissues of b3glct^-/- 24-hpf embryos identified 483 shared differentially regulated transcripts that may be involved in compensation for b3glct function in these embryos. The presented data show that both sequence and function of B3GLCT/b3glct genes is conserved in vertebrates. At the same time, complete b3glct deficiency in zebrafish appears to be inconsequential and possibly compensated for by a yet unknown mechanism.

Microcephaly with simplified gyration, epilepsy, and infantile diabetes linked to inappropriate apoptosis of neural progenitors

We describe a syndrome of primary microcephaly with simplified gyral pattern in combination with severe infantile epileptic encephalopathy and early-onset permanent diabetes in two unrelated consanguineous families with at least three affected children. Linkage analysis revealed a region on chromosome 18 with a significant LOD score of 4.3. In this area, two homozygous nonconserved missense mutations in immediate early response 3 interacting protein 1 (IER3IP1) were found in patients from both families. IER3IP1 is highly expressed in the fetal brain cortex and fetal pancreas and is thought to be involved in endoplasmic reticulum stress response. We reported one of these families previously in a paper on Wolcott-Rallison syndrome (WRS). WRS is characterized by increased apoptotic cell death as part of an uncontrolled unfolded protein response. Increased apoptosis has been shown to be a cause of microcephaly in animal models. An autopsy specimen from one patient showed increased apoptosis in the cerebral cortex and pancreas beta cells, implicating premature cell death as the pathogenetic mechanism. Both patient fibroblasts and control fibroblasts treated with siRNA specific for IER3IP1 showed an increased susceptibility to apoptotic cell death under stress conditions in comparison to controls. This directly implicates IER3IP1 in the regulation of cell survival. Identification of IER3IP1 mutations sheds light on the mechanisms of brain development and on the pathogenesis of infantile epilepsy and early-onset permanent diabetes.