Furukawa, K. et al. Barrier-to-autointegration factor plays crucial roles in cell cycle progression and nuclear organization in Drosophila. J. Cell Sci. 116, 3811-3823

Department of Chemistry, Faculty of Science, Niigata University, Niigata 950-2181, Japan.
Journal of Cell Science (Impact Factor: 5.43). 10/2003; 116(Pt 18):3811-23. DOI: 10.1242/jcs.00682
Source: PubMed


Barrier-to-autointegration factor (BAF) is potentially a DNA-bridging protein, which directly associates with inner nuclear membrane proteins carrying LEM domains. These features point to a key role in regulation of nuclear function and organization, dependent on interactions between the nuclear envelope and chromatin. To understand the functions of BAF in vivo, Drosophila baf null mutants generated by P-element-mediated imprecise excision were analyzed. Homozygous null mutants showed a typical mitotic mutant phenotype: lethality at the larval-pupal transition with small brains and missing imaginal discs. Mitotic figures were decreased but a defined anaphase defect as reported for C. elegans RNAi experiments was not observed in these small brains, suggesting a different phase or phases of cell cycle arrest. Specific abnormalities in interphase nuclear structure were frequently found upon electron microscopic examination of baf null mutants, with partial clumping of chromatin and convolution of nuclear shape. At the light microscopic level, grossly aberrant nuclear lamina structure and B-type lamin distribution correlated well with the loss of detectable amounts of BAF protein from nuclei. Together, these data represent evidence of BAF's anticipated function in mediating interactions between the nuclear envelope and interphase chromosomes. We thus conclude that BAF plays essential roles in nuclear organization and that these BAF functions are required in both M phase and interphase of the cell cycle.

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    • "The recruitment of BAF to chromatin occurs in early anaphase and is required for post-mitotic NE assembly (Gorjanacz et al. 2007; Margalit et al. 2005; Segura-Totten et al. 2002; Furukawa et al. 2003). BAF directs the postmitotic incorporation and interphase distribution of LEMdomain containing proteins, which reciprocally modulate the distribution of BAF during interphase (Haraguchi et al. 2008; Margalit et al. 2007; Ulbert et al. 2006a; Brachner and Foisner 2011). "

    Full-text · Dataset · Dec 2014
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    • "Using these interactions, BAF is thought to act as a tethering protein to bring together chromatin DNA and LEM proteins during late stages of mitosis when the nuclear envelope (NE) is being reassembled. The importance of BAF during mitosis is underscored by evidence that misregulation of these BAF-dependent processes leads to chromosome segregation and NE defects, mislocalization of LEM proteins, and embryonic lethality in Caenorhabditis elegans and Drosophila melanogaster [52]–[55]. "
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    ABSTRACT: BAF (Barrier to Autointegration Factor) is a highly conserved DNA binding protein that senses poxviral DNA in the cytoplasm and tightly binds to the viral genome to interfere with DNA replication and transcription. To counteract BAF, a poxviral-encoded protein kinase phosphorylates BAF, which renders BAF unable to bind DNA and allows efficient viral replication to occur. Herein, we examined how BAF phosphorylation is affected by herpes simplex virus type 1 (HSV-1) infection and tested the ability of BAF to interfere with HSV-1 productive infection. Interestingly, we found that BAF phosphorylation decreases markedly following HSV-1 infection. To determine whether dephosphorylated BAF impacts HSV-1 productive infection, we employed cell lines stably expressing a constitutively unphosphorylated form of BAF (BAF-MAAAQ) and cells overexpressing wild type (wt) BAF for comparison. Although HSV-1 production in cells overexpressing wtBAF was similar to that in cells expressing no additional BAF, viral growth was reduced approximately 80% in the presence of BAF-MAAAQ. Experiments were also performed to determine the mechanism of the antiviral activity of BAF with the following results. BAF-MAAAQ was localized to the nucleus, whereas wtBAF was dispersed throughout cells prior to infection. Following infection, wtBAF becomes dephosphorylated and relocalized to the nucleus. Additionally, BAF was associated with the HSV-1 genome during infection, with BAF-MAAAQ associated to a greater extent than wtBAF. Importantly, unphosphorylated BAF inhibited both viral DNA replication and gene expression. For example, expression of two regulatory proteins, ICP0 and VP16, were substantially reduced in cells expressing BAF-MAAAQ. However, other viral genes were not dramatically affected suggesting that expression of certain viral genes can be differentially regulated by unphosphorylated BAF. Collectively, these results suggest that BAF can act in a phosphorylation-regulated manner to impair HSV-1 transcription and/or DNA replication, which is similar to the antiviral activity of BAF during vaccinia infection.
    Full-text · Article · Jun 2014 · PLoS ONE
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    • "For this reason, we postulated that the lethality caused by loss of two LEM-D proteins was linked to changes in BAF function. Loss of BAF causes a typical mitotic mutant phenotype (Furukawa et al. 2003). Lethality of baf mutants occurs at the larval–pupal transition, with larvae carrying small brains and no imaginal discs. "
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    ABSTRACT: The nuclear lamina is an extensive protein network that contributes to nuclear structure and function. LEM domain (LEM-D) proteins are components of the nuclear lamina, identified by a shared ~45 amino acid motif that binds Barrier-to-Autointegration Factor (BAF), a chromatin interacting protein. Drosophila melanogaster has three nuclear lamina LEM-D proteins, named Otefin (Ote), Bocksbeutel (Bocks) and dMAN1. Although these LEM-D proteins are globally expressed, loss of either Ote or dMAN1 causes tissue-specific defects in adult flies that differ from each other. The reason for such distinct tissue-restricted defects is unknown. Here, we generated null alleles of bocks, finding that loss of Bocks causes no overt adult phenotypes. Next, we defined phenotypes associated with lem-d double mutants. Although the absence of individual LEM-D proteins does not affect viability, loss of any two proteins causes lethality. Mutant phenotypes displayed by lem-d double mutants differ from baf mutants, indicating that BAF function is retained in animals with a single nuclear lamina LEM-D protein. Interestingly, lem-d double mutants displayed distinct developmental and cellular mutant phenotypes, suggesting that Drosophila LEM-D proteins have developmental functions that are differentially shared with other LEM-D family members. This conclusion is supported by studies showing that ectopically produced LEM-D proteins have distinct capacities to rescue the tissue-specific phenotypes found in single lem-d mutants. Our findings predict that cell-specific mutant phenotypes caused by loss of LEM-D proteins reflect both the constellation of LEM-D proteins within the nuclear lamina and the capacity of functional compensation of the remaining LEM-D proteins.
    Full-text · Article · Apr 2014 · Genetics
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