Barrier-to-autointegration factor plays crucial roles in cell cycle progression and nuclear organization inDrosophila

Abstract

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.

Barrier-to-autointegration factor is required to segregate and enclose chromosomes within the nuclear envelope and assemble the nuclear lamina

“…The genetic null phenotype for BAF was previously reported in Drosophila melanogaster, based on deletions that removed the entire D-BAF coding sequence (30). Genetic null phenotypes, even for essential genes, are not revealed in Drosophila until the larval-pupal transition, when maternally contributed mRNAs and proteins are finally depleted.…”

“…Loss of D-BAF caused defects in chromatin organization and the appearance of heterochromatin-like clumps of chromatin, similar to our findings in early C. elegans embryos down-regulated for Ce-BAF. Other structural phenotypes in BAF-null Drosophila included abnormal distribution of lamin B and abnormal nuclear shapes in interphase cells (30). In contrast, neither anaphase-bridged chroma- tin nor gapped nuclear envelopes were reported, probably because BAF-deficient Drosophila cells failed to enter mitosis.…”

Tissue-Specific Defects Are Caused by Loss of the Drosophila MAN1 LEM Domain Protein

“…Genetic studies have shown that dBAF is essential for viability, with null mutants displaying a typical mitotic phenotype (Furukawa et al 2003). That the loss of neither dMAN1 nor Otefin ( Jiang et al 2008) is lethal suggests one of two possibilities.…”

“…This domain interacts with the small, conserved protein called barrier-to-autointegration factor (BAF) that binds double-stranded DNA and histones (Zheng et al 2000;Cai et al 2001;Laguri et al 2001;Furukawa et al 2003;Liu et al 2003;Montes De Oca et al 2005).…”

“…Immunolocalization studies demonstrate that dMAN1, Bocksbeutel, and Otefin are enriched at the nuclear envelope (Padan et al 1990;Ashery-Padan et al 1997a,b;Wagner et al 2004aWagner et al , 2006Jiang et al 2008). Drosophila provides an excellent model for studies of the developmental roles of the nuclear lamina proteins, as homologs of many vertebrate lamina proteins have been identified, including A-and B-type lamins (lamin C and lamin Dm 0 , respectively) (Fisher et al 1982;Lenz-Bohme et al 1997;Osouda et al 2005;Schulze et al 2005), Drosophila (d)BAF (Furukawa et al 2003), the lamin B receptor (Wagner et al 2004b), and proteins in the linker of nucleoskeleton and cytoskeleton (LINC) complex (Starr and Fischer 2005;Stewart et al 2007).…”