Cloning, chromosomal organization and expression analysis of Neurl, the mouse homolog of Drosophila melanogaster neuralized gene

Clinical and Genetic Contributors to New-Onset Atrial Fibrillation in Critically Ill Adults

OBJECTIVES

New-onset atrial fibrillation during critical illness is an independent risk factor for mortality. The ability to identify patients at high risk for new-onset atrial fibrillation is limited. We hypothesized that genetic susceptibility contributes to risk of new-onset atrial fibrillation in the ICU.

DESIGN

Retrospective sub-study of a prospective observational cohort study.

SETTING

Medical and general surgical ICUs in a tertiary academic medical center.

PATIENTS

One-thousand three-hundred sixty-nine critically ill patients admitted to the ICU for at least 2 days with no known history of atrial fibrillation who had DNA available for genotyping.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We genotyped 21 single-nucleotide polymorphisms associated with atrial fibrillation in ambulatory studies using a Sequenom platform (San Diego, CA). We collected demographics, medical history, and development of new-onset atrial fibrillation during the first four days of ICU admission. New-onset atrial fibrillation occurred in 98 patients (7.2%) and was associated with age, male sex, coronary artery disease, and vasopressor use. Single-nucleotide polymorphisms associated with new-onset atrial fibrillation were rs3853445 (near PITX2, p = 0.0002), rs6838973 (near PITX2, p = 0.01), and rs12415501 (in NEURL, p = 0.03) on univariate testing. When controlling for clinical factors, rs3853445 (odds ratio, 0.47; 95% CI, 0.30-0.73; p = 0.001) and rs12415501 (odds ratio, 1.72; 95% CI, 1.27-2.59; p = 0.01) remained significantly associated with new-onset atrial fibrillation. The addition of genetic variables to clinical factors improved new-onset atrial fibrillation discrimination in a multivariable logistic regression model (C-statistic 0.82 vs 0.78; p = 0.0009).

CONCLUSIONS

We identified several single-nucleotide polymorphisms associated with new-onset atrial fibrillation in a large cohort of critically ill ICU patients, suggesting there is genetic susceptibility underlying this common clinical condition. This finding may provide new targets for future mechanistic studies and additional insight into the application of genomic information to identify patients at elevated risk for a common and important condition in the ICU.

NEURL rs6584555 and CAND2 rs4642101 contribute to postoperative atrial fibrillation: a prospective study among Chinese population

Postoperative atrial fibrillation (POAF) is a serious, common complication after coronary artery bypass grafting (CABG) surgery. Recently, 5 novel loci were identified to be associated with atrial fibrillation susceptibility using a combination of genotyping, eQTL mapping, and functional validation. In current study, we aim to evaluated the positive findings for POAF susceptibility after CABG among Chinese population, using a population-based, two-stage, nested case-control study with 1,400 patients. NEURL rs12415501 and CAND2 rs4642101 were significantly associated with POAF susceptibility after CABG among Chinese population in both stages. When pooled together, the ORs for each additional copy of minor allele was 1.29 (95% CI: 1.13-1.48, P = 1.7×10⁻⁴) for NEURL rs12415501, and 1.21 (95% CI: 1.08-1.36, P = 9.8×10⁻⁴) for CAND2 rs4642101. Functional validation experiments found the AF risk allele of NEURL rs6584555 and CAND2 rs4642101 correlated with an increased expression of its corresponding genes (P<0.001). In this independently collected cardiac surgery cohort, we replicated the previous findings, and 2 novel loci are independently associated with POAF risk in patients who undergo CABG surgery in Chinese population.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Mind bomb 1 in the lymphopoietic niches is essential for T and marginal zone B cell development

Notch signaling regulates lineage decisions at multiple stages of lymphocyte development, and Notch activation requires the endocytosis of Notch ligands in the signal-sending cells. Four E3 ubiquitin ligases, Mind bomb (Mib) 1, Mib2, Neuralized (Neur) 1, and Neur2, regulate the Notch ligands to activate Notch signaling, but their roles in lymphocyte development have not been defined. We show that Mib1 regulates T and marginal zone B (MZB) cell development in the lymphopoietic niches. Inactivation of the Mib1 gene, but not the other E3 ligases, Mib2, Neur1, and Neur2, abrogated T and MZB cell development. Reciprocal bone marrow (BM) transplantation experiments revealed that Mib1 in the thymic and splenic niches is essential for T and MZB cell development. Interestingly, when BM cells from transgenic Notch reporter mice were transplanted into Mib1-null mice, the Notch signaling was abolished in the double-negative thymocytes. In addition, the endocytosis of Dll1 was impaired in the Mib1-null microenvironment. Moreover, the block in T cell development and the failure of Dll1 endocytosis were also observed in coculture system by Mib1 knockdown. Our study reveals that Mib1 is the essential E3 ligase in T and MZB cell development, through the regulation of Notch ligands in the thymic and splenic microenvironments.

Neuralized is expressed in the alpha/beta lobes of adult Drosophila mushroom bodies and facilitates olfactory long-term memory formation

Memory formation involves multiple molecular mechanisms, the nature and components of which are essential to understand these processes. Drosophila is a powerful model to identify genes important for the formation and storage of consolidated memories because the molecular mechanisms and dependence of these processes on particular brain regions appear to be generally conserved. We present evidence that the highly conserved ubiquitin ligase Neuralized (Neur) is expressed in the adult Drosophila mushroom body (MB) alpha/beta lobe peripheral neurons and is a limiting factor for the formation of long-term memory (LTM). We show that loss of one copy of neur gene results in significant LTM impairment, whereas overexpression of Neur in the peripheral neurons of the alpha/beta lobes of the adult MBs results in a dosage-dependent enhancement of LTM. In contrast, learning, early memories, or anesthesia-resistant memory are not affected. We also demonstrate that the role of Neuralized in LTM formation is restricted within the neurons of the periphery of the alpha/beta lobes, and we suggest that this structural subdivision of the MBs participates in the formation of LTM.

The neuralized homology repeat 1 domain of Drosophila neuralized mediates nuclear envelope association and delta-dependent inhibition of nuclear import

Signaling by the Notch (N) pathway is critical for many developmental processes and requires complex trafficking of both the N receptor and its transmembrane ligands, Delta (Dl) and Serrate. neuralized encodes an E3 ubiquitin ligase required for N ligand internalization. Neuralized (Neur) is conserved from worms to humans and comprises two Neur homology repeat (NHR) domains, NHR1 and NHR2, and a carboxyl-terminal RING domain. We have previously shown that the RING domain is required for ubiquitin ligase activity and that NHR1 mediates binding to Dl, a ubiquitination target. In Drosophila, Neur associates with the plasma membrane and hepatocyte responsive serum phosphoprotein-positive endosomes. Here we demonstrate that Neur also exhibits nuclear envelope localization. We have determined that Neur subcellular localization is regulated by nuclear trafficking and that inhibition of chromosome region maintenance 1, a nuclear export receptor, interferes with Neur nuclear export, trapping Neur in the nucleus. Moreover, we demonstrate that nuclear envelope localization is mediated by the Neur NHR1 domain. Interestingly, Dl expression in Schneider cells is sufficient to inhibit Neur nuclear import and inhibition occurs in an NHR1-dependent manner, suggesting that Neur nuclear localization occurs in contexts where Dl expression is either low or absent. Consistent with this, we found that Neur exhibits nuclear trafficking and associates with the nuclear envelope in the secretory cells of the larval salivary gland and that overexpression of Dl can reduce Neur localization to the nucleus. Altogether, our data demonstrate that Neur localizes to the nuclear envelope and that this localization can be negatively regulated by Dl, suggesting a possible nuclear function for Neur in Drosophila.

Neuralized-like 1 (Neurl1) targeted to the plasma membrane by N-myristoylation regulates the Notch ligand Jagged1

Notch signaling constitutes an evolutionarily conserved mechanism that mediates cell-cell interactions in various developmental processes. Numerous regulatory proteins interact with the Notch receptor and its ligands and control signaling at multiple levels. Ubiquitination and endocytosis followed by endosomal sorting of both the receptor and its ligands is essential for Notch-mediated signaling. The E3 ubiquitin ligases, Neuralized (Neur) and Mind Bomb (Mib1), are crucial for regulating the activity and stability of Notch ligands in Drosophila; however, biochemical evidence that the Notch ligands are directly targeted for ubiquitination by Neur and/or Mib1 has been lacking. In this report, we explore the function of Neurl1, a mouse ortholog of Drosophila Neur. We show that Neurl1 can function as an E3 ubiquitin ligase to activate monoubiquitination in vitro of Jagged1, but not other mammalian Notch ligands. Neurl1 expression decreases Jagged1 levels in cells and blocks signaling from Jagged1-expressing cells to neighboring Notch-expressing cells. We demonstrate that Neurl1 is myristoylated at its N terminus, and that myristoylation of Neurl1 targets it to the plasma membrane. Point mutations abolishing either Neurl1 myristoylation and plasma membrane localization or Neurl1 ubiquitin ligase activity impair its ability to down-regulate Jagged1 expression and to block signaling. Taken together, our results argue that Neurl1 at the plasma membrane can affect the signaling activity of Jagged1 by directly enhancing its ubiquitination and subsequent turnover.

Neuralized-2 regulates a Notch ligand in cooperation with Mind bomb-1

Mutations in Drosophila neuralized (Dneur) result in a variety of developmental defects that closely resemble those of Notch mutants and other Notch pathway mutants. However, mice with disrupted neur1 do not show any aberrant cell fate specifications in neurogenesis and somitogenesis. Thus, we speculated that other vertebrate neur homolog(s) might compensate for loss of the neur gene. Here, we report the paralog of mouse Neur1, named Neuralized-2 (Neur2), which is a ubiquitin-protein isopeptide ligase (E3) that interacts with and ubiquitinates Delta. Both murine Neur1 and Neur2 have similar degrees of homology to DNeur, and neur2 is expressed in patterns similar to those of neur1 in embryos, suggesting potential functional redundancy. Interestingly, two distinct classes of E3 ligases, Mind bomb-1 (Mib1) and Neur2, have cooperative but distinct roles in Delta endocytosis to Hrs-positive vesicles, i.e. Mib1 functions in the initial step of Delta endocytosis, and Neur2 is required for targeting endocytosed Delta to Hrs-positive vesicles. Thus, our study provides a new insight into how distinct E3 ligases work together in the endocytic pathways for Notch signaling.

A novel inflammation-induced ubiquitin E3 ligase in alveolar type II cells

LINCR was identified as a glucocorticoid-attenuated response gene induced in the lung during endotoxemia. The LINCR protein has structural similarities to Drosophila Neuralized, which regulates the developmentally important Notch signaling pathway. Endotoxemia-induced LINCR expression in vivo was localized by in situ hybridization to alveolar epithelial type II cells, and shown to be induced by LPS and inflammatory cytokines in the T7 alveolar epithelial type II cell line. RING domain-dependent ubiquitin E3 ligase activity of LINCR was demonstrated using full-length FLAG-LINCR or a deletion mutant lacking the RING domain expressed in 293T cells, and using a GST-LINCR RING fusion protein expressed in Escherichia coli. LINCR preferentially interacted with the ubiquitin-conjugating enzyme UbcH6 and preferentially generated polyubiquitin chains linked via non-canonical lysine residues. We conclude that LINCR is a novel inflammation-induced ubiquitin E3 ligase expressed in alveolar epithelial type II cells, and discuss its potential role in the lung response to inflammation.

Asymmetric localization and function of cell-fate determinants: a fly's view

One mechanism to generate daughter cells with distinct fates is the asymmetric inheritance of regulatory proteins, leading to differential gene regulation in the daughter cells. This mode of cell division is termed 'asymmetric cell division.' The nervous system of the fly employs asymmetric cell division, both in the central nervous system, to generate neural precursors, neurons and glial cells; and in the peripheral nervous system, to create sensory organs that are composed of multiple cell types. These cell lineages are excellent models to examine the gene expression program that leads to fate acquisition, the cell-fate determinants that control these programs and how these determinants, in turn, are distributed through cell polarity machinery.

Split hand foot malformation is associated with a reduced level of Dactylin gene expression

Split hand foot malformation (SHFM) is a congenital limb malformation presenting with a median cleft of the hand and/or foot, syndactyly and polydactyly. SHFM is genetically heterogeneous with four loci mapped to date. Murine Dactylaplasia (Dac) is phenotypically similar, and it has been mapped to a syntenic region of 10q24, where SHFM3 has been localized. Structural alterations of the gene-encoding dactylin, a constituent of the ubiquitinization pathway, leading to reduced levels of transcript have been identified in Dac. Here, we report a significant decrease of Dactylin transcript in several individuals affected by SHFM. This observation supports a central role for dactylin in the pathogenesis of SHFM.