The Abl/Enabled signaling pathway regulates Golgi architecture in Drosophila photoreceptor neurons

The Abl tyrosine kinase signaling pathway, including its key effector, the actin regulatory protein Enabled, controls the fragmentation state and subcellular localization of the Golgi compartment in Drosophila photoreceptor neurons via Abl/Enabled-dependent control of actin organization.The Golgi apparatus is optimized separately in different tissues for efficient protein trafficking, but we know little of how cell signaling shapes this organelle. We now find that the Abl tyrosine kinase signaling pathway controls the architecture of the Golgi complex in Drosophila photoreceptor (PR) neurons. The Abl effector, Enabled (Ena), selectively labels the cis-Golgi in developing PRs. Overexpression or loss of function of Ena increases the number of cis- and trans-Golgi cisternae per cell, and Ena overexpression also redistributes Golgi to the most basal portion of the cell soma. Loss of Abl or its upstream regulator, the adaptor protein Disabled, lead to the same alterations of Golgi as does overexpression of Ena. The increase in Golgi number in Abl mutants arises in part from increased frequency of Golgi fission events and a decrease in fusions, as revealed by live imaging. Finally, we demonstrate that the effects of Abl signaling on Golgi are mediated via regulation of the actin cytoskeleton. Together, these data reveal a direct link between cell signaling and Golgi architecture. Moreover, they raise the possibility that some of the effects of Abl signaling may arise, in part, from alterations of protein trafficking and secretion

A comparative biochemical and pathological evaluation of brain samples from knock-in murine models of Gaucher disease

Gaucher disease (GD) is a lysosomal storage disorder stemming from biallelic mutations i

Artificially Introduced Aneuploid Chromosomes Assume a Conserved Position in Colon Cancer Cells

BACKGROUND: Chromosomal aneuploidy is a defining feature of carcinomas. For instance, in colon cancer, an additional copy of Chromosome 7 is not only observed in early pre-malignant polyps, but is faithfully maintained throughout progression to metastasis. These copy number changes show a positive correlation with average transcript levels of resident genes. An independent line of research has also established that specific chromosomes occupy a well conserved 3D position within the interphase nucleus. METHODOLOGY/PRINCIPAL FINDINGS: We investigated whether cancer-specific aneuploid chromosomes assume a 3D-position similar to that of its endogenous homologues, which would suggest a possible correlation with transcriptional activity. Using 3D-FISH and confocal laser scanning microscopy, we show that Chromosomes 7, 18, or 19 introduced via microcell-mediated chromosome transfer into the parental diploid colon cancer cell line DLD-1 maintain their conserved position in the interphase nucleus. CONCLUSIONS: Our data is therefore consistent with the model that each chromosome has an associated zip code (possibly gene density) that determines its nuclear localization. Whether the nuclear localization determines or is determined by the transcriptional activity of resident genes has yet to be ascertained

Reticular dysgenesis-associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress.

Adenylate kinases (AKs) are phosphotransferases that regulate the cellular adenine nucleotide composition and play a critical role in the energy homeostasis of all tissues. The AK2 isoenzyme is expressed in the mitochondrial intermembrane space and is mutated in reticular dysgenesis (RD), a rare form of severe combined immunodeficiency (SCID) in humans. RD is characterized by a maturation arrest in the myeloid and lymphoid lineages, leading to early onset, recurrent, and overwhelming infections. To gain insight into the pathophysiology of RD, we studied the effects of AK2 deficiency using the zebrafish model and induced pluripotent stem cells (iPSCs) derived from fibroblasts of an RD patient. In zebrafish, Ak2 deficiency affected hematopoietic stem and progenitor cell (HSPC) development with increased oxidative stress and apoptosis. AK2-deficient iPSCs recapitulated the characteristic myeloid maturation arrest at the promyelocyte stage and demonstrated an increased AMP/ADP ratio, indicative of an energy-depleted adenine nucleotide profile. Antioxidant treatment rescued the hematopoietic phenotypes in vivo in ak2 mutant zebrafish and restored differentiation of AK2-deficient iPSCs into mature granulocytes. Our results link hematopoietic cell fate in AK2 deficiency to cellular energy depletion and increased oxidative stress. This points to the potential use of antioxidants as a supportive therapeutic modality for patients with RD

DNA damage responses by human ELG1 in S phase are important to maintain genomic integrity

Genomic integrity depends on DNA replication, recombination and repair, particularly in S phase. We demonstrate that a human homologue of yeast Elg1 plays an important role in S phase to preserve genomic stability. The level of ELG1 is induced during recovery from a variety of DNA damage. In response to DNA damage, ELG1 forms distinct foci at stalled DNA replication forks that are different from DNA double strand break foci. Targeted gene knockdown of ELG1 resulted in spontaneous foci formation of gamma-H2AX, 53BP1 and phosphorylated-ATM that mark chromosomal breaks. Abnormal chromosomes including fusions, inversions and hypersensitivity to DNA damaging agents were also observed in cells expressing low level of ELG1 by targeted gene knockdown. Knockdown of ELG1 by siRNA reduced homologous recombination frequency in the I-SceI induced double strand break-dependent assay. In contrast, spontaneous homologous recombination frequency and sister chromatin exchange rate were upregulated when ELG1 was silenced by shRNA. Taken together, we propose that ELG1 would be a new member of proteins involved in maintenance of genomic integrity

ING2 Regulates the Onset of Replicative Senescence by Induction of p300-Dependent p53 Acetylation

ING2 is a candidate tumor suppressor gene that can activate p53 by enhancing its acetylation. Here, we demonstrate that ING2 is also involved in p53-mediated replicative senescence. ING2 protein expression increased in late-passage human primary cells, and it colocalizes with serine 15-phosphorylated p53. ING2 and p53 also complexed with the histone acetyltransferase p300. ING2 enhanced the interaction between p53 and p300 and acted as a cofactor for p300-mediated p53 acetylation. The level of ING2 expression directly modulated the onset of replicative senescence. While overexpression of ING2 induced senescence in young fibroblasts in a p53-dependent manner, expression of ING2 small interfering RNA delayed the onset of senescence. Hence, ING2 can act as a cofactor of p300 for p53 acetylation and thereby plays a positive regulatory role during p53-mediated replicative senescence