Dscam and neuronal uniqueness

In the fruit fly Drosophila the gene encoding the cell adhesion molecule Dscam generates alternatively spliced mRNAs that can be translated into thousands of different protein isoforms. Three recent papers show that isoform-specific homophilic Dscam interactions cause dendritic branches of the same neuron to avoid each other (Hughes et al., 2007; Soba et al., 2007; Matthews et al., 2007). This process ensures the correct patterning of dendrites in the peripheral nervous system.     

A two-way street: LSD1 regulates chromatin boundary formation in S. pombe and Drosophila

Two recent studies in Molecular Cell (Lan et al., 2007; Rudolph et al., 2007) implicate histone demethylation by LSD1 in the regulation of boundaries between silenced and active chromatin domains in both fission yeast and flies, but by distinct mechanisms.     

H3K27 demethylases, at long last

Methylation of lysine 27 on histone H3 (H3K27me) by the Polycomb complex (PRC2) proteins is associated with gene silencing in many developmental processes. A cluster of recent papers (Agger et al., 2007; De Santa et al., 2007; Lan et al., 2007; Lee et al., 2007) identify the JmjC-domain proteins UTX and JMJD3 as H3K27-specific demethylases that remove this methyl mark, enabling the activation of genes involved in animal body patterning and the inflammatory response.     

Cytokinetic pyrotechnics

Cytokinesis, the final step in cell division, is dependent on formation and closure of a ring of actin filaments (F-actin) and myosin-2 which is, in turn, dependent on activation of the small GTPase, RhoA, at the cell equator. Four new papers, including two in this issue of Developmental Cell (Petronczki et al., 2007; Birkenfeld et al., 2007), provide new insights into how RhoA activation at the equator is initiated and maintained.     

浙江天台盆地晚白垩世恐龙蛋新类型(英文)

浙江天台盆地上白垩统赖家组和赤城山组是我国最重要的恐龙蛋化石产出地层之一。近年来,我们对天台盆地陆相红层中的恐龙蛋化石层位进行了详细厘定,对恐龙蛋类型进行了系统描述,并对前人报道的一些属种进行了分类订正。研究显示,天台恐龙蛋化石群基本上可分为7蛋科、12蛋属和15蛋种,代表了我国晚白垩世早期的恐龙蛋化石组合。本文简要报道了主要产自天台盆地赤城山组的双塘似蜂窝蛋(新蛋属、新修订种)、木鱼山半蜂窝蛋(新蛋属、新蛋种)、国清寺副蜂窝蛋(新修订种)、天台棱柱形蛋(新修订种)和张头槽马赛克蛋(新蛋属、新修订种)等3新蛋属、5新蛋种和修订种的主要鉴定特征,并建立一新蛋科——似蜂窝蛋科。     

A backup DNA repair pathway moves to the forefront

Chromosomal translocations between antigen receptor loci and oncogenes are a hallmark of lymphoid cancers. Several new studies now reveal that programmed DNA breaks created during assembly of antigen receptor genes can be channeled into an alternative DNA end-joining pathway that is implicated in the chromosomal translocations of lymphoid cancers (Corneo et al., 2007; Soulas-Sprauel et al., 2007; Yan et al., 2007).     

Location of 64K collagen producer chondrocytes in developing chicken embryo tibiae.

The synthesis of a new low-molecular-weight collagen by cultured chicken embryo chondrocytes has been recently demonstrated (Capasso et al., Exp. Cell Res. 142:197-206, 1982; Gibson et al., J. Cell Biol. 93:767-774, 1982; Schmid and Conrad, J. Biol. Chem. 257:12444-12450, 1982). In this paper we report results on the location of chondrocytes synthesizing this new collagen (64K collagen) in the developing chicken embryo. The 64K collagen is synthesized in very large amounts by cells concentrated at the diaphysis of 9-day-old and at the epiphysis of 17-day-old embryo tibiae. These regions are characterized by a remodeling of the cartilage matrix leading to the replacement of the cartilage with bone tissue; therefore, this collagen appears to be a marker of a specific developmental stage of chondrocytes. The origin of cells competent for the synthesis of the 64K collagen is also discussed.     

Further evidence for BRCA1 communication with the inactive X chromosome

BRCA1, a breast and ovarian cancer-suppressor gene, exerts tumor-suppressing functions that appear to be associated, at least in part, with its DNA repair, checkpoint, and mitotic regulatory activities. Earlier work from our laboratory also suggested an ability of BRCA1 to communicate with the inactive X chromosome (Xi) in female somatic cells (Ganesan et al., 2002). Xiao et al. (2007) (this issue of Cell) have challenged this conclusion. Here we discuss recently published data from our laboratory and others and present new results that, together, provide further support for a role of BRCA1 in the regulation of XIST concentration on Xi in somatic cells.     

miRNAs play a tune

Two new studies describe functionally relevant interactions between microRNAs (miRNAs) and their targets in the immune system and the brain (Xiao et al., 2007; Karres et al., 2007). Furthermore, these studies illustrate the involvement of miRNAs in tuning the expression of target genes to physiologically relevant levels.     

After hours keeps clock researchers CRYing Overtime

Three recent reports, including one in this issue of Cell, reveal that the circadian regulator CRY is targeted for degradation by the F box E3 ubiquitin ligase FBXL3 (Siepka et al., 2007; Busino et al., 2007; Godinho et al., 2007). These studies confirm the importance of targeted protein degradation as a key design feature of the mammalian circadian clock.     

Neural surveillance of skeletal homeostasis

Endowed with sympathetic and peptidergic nerves, the vertebrate skeleton is under constant surveillance by the nervous system. In addition to pituitary hormone secretion, centrally regulated sympathetic release, as elegantly demonstrated by Karsenty and colleagues, integrate to control both components of skeletal remodeling, osteoblastic bone formation, and osteoclastic bone resorption (Elefteriou et al., 2005).     

The inflammasome: first line of the immune response to cell stress

The NALP3-inflammasome is a protein complex that stimulates caspase-1 activation to promote the processing and secretion of proinflammatory cytokines. Recent work indicates that the NALP3-inflammasome can be activated by endogenous "danger signals" as well as compounds associated with pathogens (Kanneganti et al., 2006; Mariathasan et al., 2006, Martinon et al., 2006; Sutterwala et al., 2006). Here, we discuss new insights into the regulation of caspase-1 activity in the inflammatory response.     

Mighty Piwis defend the germline against genome intruders

Piwis are a germline-specific subclass of the Argonaute family of RNA interference (RNAi) effector proteins that are associated with a recently discovered group of small RNAs (piRNAs). Recent studies in Drosophila and zebrafish directly implicate Piwi proteins in piRNA biogenesis to maintain transposon silencing in the germline genome (Brennecke et al., 2007; Gunawardane et al., 2007; Houwing et al., 2007). This function may be conserved in mice as loss of Miwi2, a mouse Piwi homolog, leads to germline stem cell and meiotic defects correlated with increased transposon activity (Carmell et al., 2007).     

Mdm2: p53's Lifesaver?

In a recent issue of Molecular Cell, Taira et al. (2007) and Rinaldo et al. (2007) provide insight into the involvement of the DYRK2 kinase and a surprising role of MDM2 in regulation of DNA damage-induced apoptosis via p53 phosphorylation.     

Jawing about TNF: new hope for cherubism

Mutations in the SH3-domain binding protein 2 (SH3BP2) are known to cause a rare childhood disorder called cherubism that is characterized by inflammation and bone loss in the jaw, but the mechanism has remained unclear. In this issue, Ueki et al. (Ueki et al., 2007) now demonstrate that a cherubism mutation activates mouse Sh3bp2 resulting in enhanced production of the cytokine TNF-alpha by myeloid cells, leading to both bone loss and inflammation.     

TXNIP links redox circuitry to glucose control

Thioredoxin-interacting protein (TXNIP) binds and inhibits the reducing activity of thioredoxin. A new study (Parikh et al., 2007) implicates this redox rheostat as a negative regulator of peripheral glucose metabolism in humans. Investigators combined human physiology, genomic screening, and cell-based genetic studies to highlight TNXIP as a potential culprit in the pathogenesis of type 2 diabetes.