Cis‐regulatory mechanisms of gene expression in an olfactory neuron type in Caenorhabditis elegans

The generation of cellular diversity is dependent on the precise spatiotemporal regulation of gene expression by both cis‐ and trans‐acting mechanisms. The developmental principles regulating expression of specific gene subsets in individual cell types are not fully understood. Here we define the cis‐regulatory mechanisms driving expression of cell‐selective and broadly expressed genes in vivo in the AWB olfactory neuron subtype in C. elegans. We identify an element that is necessary to drive expression of neuron‐selective chemoreceptor genes in the AWB neurons, and show that this element functions in a context‐dependent manner. We find that the expression of broadly expressed sensory neuronal genes in the AWB neurons is regulated by diverse cis‐ and trans‐regulatory mechanisms that act partly in parallel to the pathways governing expression of AWB‐selective genes. We further demonstrate that cis‐acting mechanisms driving gene expression in the AWB neurons appear to have diverged in related nematode species. Our results provide insights into the cis‐regulatory logic driving cell‐specific gene expression, and suggest that variations in this logic contribute to the generation of functional diversity. Developmental Dynamics 238:3080–3092, 2009. © 2009 Wiley‐Liss, Inc.     

Tschimganine and its derivatives extend the chronological life span of yeast via activation of the Sty1 pathway

Most antiaging factors or life span extenders are associated with calorie restriction (CR). Very few of these factors function independently of, or additively with, CR. In this study, we focused on tschimganine, a compound that was reported to extend chronological life span (CLS). Although tschimganine led to the extension of CLS, it also inhibited yeast cell growth. We acquired a Schizosaccharomyces pombe mutant with a tolerance for tschimganine due to the gene crm1. The resulting Crm1 protein appears to export the stress‐activated protein kinase Sty1 from the nucleus to the cytosol even under stressful conditions. Furthermore, we synthesized two derivative compounds of tschimganine, α‐hibitakanine and β‐hibitakanine; these derivatives did not inhibit cell growth, as seen with tschimganine. α‐hibitakanine extended the CLS, not only in S. pombe but also in Saccharomyces cerevisiae, indicating the possibility that life span regulation by tschimganine derivative may be conserved across various yeast species. We found that the longevity induced by tschimganine was dependent on the Sty1 pathway. Based on our results, we propose that tschimganine and its derivatives extend CLS by activating the Sty1 pathway in fission yeast, and CR extends CLS via two distinct pathways, one Sty1‐dependent and the other Sty1‐independent. These findings provide the potential for creating an additive life span extension effect when combined with CR, as well as a better understanding of the mechanism of CLS.     

H‐ficolin binds Aspergillus fumigatus leading to activation of the lectin complement pathway and modulation of lung epithelial immune responses

Aspergillus fumigatus is an opportunistic fungal pathogen that typically infects the lungs of immunocompromised patients leading to a high mortality. H‐Ficolin, an innate immune opsonin, is produced by type II alveolar epithelial cells and could participate in lung defences against infections. Here, we used the human type II alveolar epithelial cell line, A549, to determine the involvement of H‐ficolin in fungal defence. Additionally, we investigated the presence of H‐ficolin in bronchoalveolar lavage fluid from transplant patients during pneumonia. H‐Ficolin exhibited demonstrable binding to A. fumigatus conidia via l ‐fucose, d ‐mannose and N‐acetylglucosamine residues in a calcium‐ and pH‐dependent manner. Moreover, recognition led to lectin complement pathway activation and enhanced fungal association with A549 cells. Following recognition, H‐ficolin opsonization manifested an increase in interleukin‐8 production from A549 cells, which involved activation of the intracellular signalling pathways mitogen‐activated protein kinase MAPK kinase 1/2, p38 MAPK and c‐Jun N‐terminal kinase. Finally, H‐ficolin concentrations were significantly higher in bronchoalveolar lavage fluid of patients with lung infections compared with control subjects (n = 16; P = 0·00726). Receiver operating characteristics curve analysis further highlighted the potential of H‐ficolin as a diagnostic marker for lung infection (area under the curve = 0·77; P < 0·0001). Hence, H‐ficolin participates in A. fumigatus defence through the activation of the lectin complement pathway, enhanced fungus–host interactions and modulated immune responses.     

Germ cell apoptosis in men with complete and incomplete spermiogenesis failure

Germ cell apoptosis was evaluated in 11 men suffering from nonobstructive azoospermia and enrolled in a spermatid conception programme. In six of these patients, round spermatids (Sa stage) were the most advanced spermatogenic cells recovered from testicular biopsy samples. This condition is referred to as complete spermiogenesis failure. In the remaining five men, a few late elongated spermatids (Sd stage) were unexpectedly found in the testicular biopsy samples on the day of treatment. This condition is referred to as incomplete spermiogenesis failure. Germ cell apoptosis in both groups of patients was examined by analysing cell smears prepared from mechanically disintegrated testicular tissues using terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL), which detects apoptosis-specific DNA fragmentation, and annexin-V binding, detecting apoptosis-related translocation of plasma membrane phosphatidylserine to the membrane's outer surface. Both methods were combined, in double- fluorescence labelling preparations, with immunocytochemical detection of proacrosin, a specific germline marker. Patients with complete spermiogenesis failure had significantly higher frequencies of primary spermatocytes and round spermatids carrying the apoptosis-specific DNA damage in comparison with patients with incomplete spermiogenesis failure. Surprisingly, apoptosis-related phosphatidylserine externalization occurs rarely until the advanced stages of spermiogenesis. Since externalized phosphatidylserine is expected to be involved in the recognition of apoptotic cells by phagocytes, apoptotic spermatocytes and round spermatids may not be removed easily by phagocytosis. The high frequency of DNA damage in round spermatids from patients with complete spermiogenesis failure explains the low success rates of spermatid conception in these cases. The evaluation of apoptosis can help predict success rates of spermatid conception.      

Ultrastructure of sperm and spermiogenesis ofPterastericola astropectinis (Platyhelminthes,Rhabdocoela, Pterastericolidae)

During development of the spermatid, two free flagella are transported distally from the main spermatid mass by elongation of the shaft. They rotate back towards the shaft and lie parallel with it prior to fusion in a distal-proximal direction. This process conforms to that found in other free-living platyhelminths that have fused or adjoined axonemes in their sperm (Acoela, Kalyptorhynchia, Polycladida). It is basically different from the process of fusion in the majority of neodermatan species (major groups of parasitic platyhelminths), where the attachment of axonemes remains near the main spermatid body, a median process grows out between them, the nucleus and mitochondria migrate into this process and axonemes then fuse with it in a proximal-distal manner.Pterastericola astropectinis also differs from the Neodermata in the presence of dense bodies in the sperm. The ultrastructure of the sperm, spermiogenesis and protonephridia does not support the view of a close affinity between Pterastericolidae and Neodermata.     

TAP‐mediated processing of exoerythrocytic antigens is essential for protection induced with radiation‐attenuated Plasmodium sporozoites

MHC class I dependent CD8⁺ T cells are essential for protection induced by radiation‐attenuated Plasmodium sporozoites (RAS) in murine malaria models. Apart from the mechanism of activation of CD8⁺ T cells specific for the circumsporozoite protein, the major sporozoite antigen (Ag), CD8⁺ T cells specific for other exoerythrocytic Ags that have been shown to mediate protection have not been thoroughly investigated. Specifically, mechanisms of processing and presentation of exoerythrocytic Ags, which includes liver stage (LS) Ags, remain poorly understood. We hypothesize that as exogenous proteins, LS Ags are processed by mechanisms involving either the TAP‐dependent phagosomal‐to‐cytosol or TAP‐independent vacuolar pathway of cross‐presentation. We used TAP‐deficient mice to investigate whether LS Ag mediated induction of naïve CD8⁺ T cells and their recall during sporozoite challenge occur by the TAP‐dependent or TAP‐independent pathways. On the basis of functional attributes, CD8⁺ T cells were activated via the TAP‐independent pathway during immunizations with Plasmodium berghei RAS; however, IFN‐γ⁺CD8⁺ T cells previously induced by P. berghei RAS in TAP‐deficient mice failed to be recalled against sporozoite challenge and the mice became parasitemic. On the basis of these observations, we propose that TAP‐associated Ag processing is indispensable for sterile protection induced with P. berghei RAS.     

Evolution of the endoplasmic reticulum during rat spermiogenesis

The endoplasmic reticulum (ER) was stained selectively by a sequence of uranyl acetate, lead and copper citrate, according to the method of Thiéry and Rambourg ('76), and then investigated in 0.5 to 2.0-μm-thick sections with the transmission electron microscope. Examination of photographic stereopairs allowed a three-dimensional visualization of the ER at various steps of spermiogenesis. During the Golgi and cap phases of spermiogenesis (steps 1–7, classification of Leblond and Clermont, '52a), the ER is distributed throughout the cytoplasm as a three-dimensional network of spherical and tubular cisternae connected by narrow tubules. In addition, a close network of tubular cisternae is located along the convex surface of the Golgi apparatus and lines the plasma membrane. Where the cell membrane joins that of another spermatid to form an intercellular bridge, this network extends across the bridge. During the acrosome phase (steps 8–14), the cytoplasm contains an abundant ER that shows the following modifications: (A) Along the inside and outside of the caudal tube the cisternae form long tubes or plates which run adjacent and parallel to the microtubules. These cisternae are connected by delicate lateral anastomoses; (B) Along the flagellum the ER forms a “fenestrated sleeve” made up of a close network of tubular cisternae; (C) Similar networks are organized as “fenestrated spherules” enclosing large vesicles seen throughout the cytoplasm; (D) At a short distance from the flagellum, the ER cisternae are continuous with a stack of annulate lamellae and an aggregate of radially arranged collapsed cisternae called the “radial body”. During the last or maturation phase (steps 15–19), the ER regresses. Thus, during the final steps in the formation of the flagellum, the ER network fragments and then most of the cisternae disappear from the cytoplasm. The “radial body” is the last element of the ER to be dissolved. Thus the ER undergoes extensive structural modifications during spermiogenesis, suggesting an active contribution of this organelle to the differentiation of the spermatid into a spermatozoon.     

Potassium efflux fires the canon: Potassium efflux as a common trigger for canonical and noncanonical NLRP3 pathways

Murine caspase‐11 and its human orthologues, caspase‐4 and caspase‐5, activate an inflammatory response following cytoplasmic recognition of cell wall constituents from Gram‐negative bacteria, such as LPS. This inflammatory response involves pyroptotic cell death and the concomitant release of IL‐1α, as well as the production of IL‐1β and IL‐18 through the noncanonical NLR family, pyrin domain containing 3 (NLRP3) pathway. This commentary discusses three papers in this issue of the European Journal of Immunology that advance our understanding of the roles of caspase‐11, ‐4, and ‐5 in the noncanonical pathway. By utilizing the new gene editing technique, clustered regularly interspaced short palindromic repeats (CRISPR), as well as sensitive cell imaging techniques, these papers establish that cytoplasmic LPS‐dependent IL‐1β production requires the NLRP3 inflammasome and that its activation is dependent on K⁺ efflux, whereas IL‐1α release and pyroptotic cell death pathways are NLRP3‐independent. These findings expand on previous research implicating K⁺ efflux as the principal trigger for NLRP3 activation and suggest that canonical and noncanonical NLRP3 pathways are not as dissimilar as first thought.     

Development of membrane differentiations in the guinea pig spermatid during spermiogenesis

We have studied the development of membrane differentiations in guinea pig spermatids during spermiogenesis, using electron microscopy of thin sections, freeze-fracturing, and filipin labeling as an indicator of membrane cholesterol distribution. The development of the distinctive membrane specializations closely correlated with the developmental steps of spermatid differentiation. The annulus, the zipper, and the circumferential strands of particles overlying the mitochondrial gyres of the midpiece appeared in the plasma membrane over the tail during the last two steps of spermiogenesis. The outer acrosomal membrane showed trnsient crenations during the acrosome phase and serrations over the equatorial segment of the acrosome during the maturation phase. On the inner nuclear membrane, a depression appeared opposite the inner zone of the acrosome during the Golgi phase and persisted throughout spermiogenesis. The implantation fossa also appeared during this phase, as a bulging on the inner nuclear envelope covered with small membrane particles. By the cap phase, small and large 15–20-nm particles were present at the implantation-fossa site, and clusters of 9-nm particles were seen over the postacrosomal segment of the nuclear envelope. The migration of the nuclear pores began when close contacts were established between adjacent nuclear membranes. It started simultaneously at the anterior pole and the implantation fossa and later progressed over the segment of membrane between the caudal margin of the acrosome and the posterior ring. By the maturation phase, the nuclear pores had migrated to the redundant nuclear envelope. After filipin labeling, a gradient was visible in the distribution of the cholesterol-filipin complexes, decreasing from the plasma membrane to the nuclear membrane. Within the same membrane, cholesterol distribution varied from one pole of the cell to the other. On the differentiations of the plasma membrane over the tail, cholesterol-filipin complexes were absent, but they were profuse in the membrane over the head. In the acrosomal membrane, the complexes were gathered in clumps associated with the crenations. They became fewer in the rostral segment but remained moderate in the caudal equatorial segment as spermiogenesis proceeded. The nuclear membrane contained cholesterol-free regions opposite the inner acrosome and at the site of the implantation fossa. Otherwise, the acrosomal segment of the nuclear envelope demonstrated a homogeneous distribution of cholesterol-filipin complexes, while the postacrosomal segment showed small clumps of complexes adjacent to nuclear pores. We propose that each of the spermatid cell membranes is not an autonomous system, but is dependent upon its exchanges with the immediate external environment under the one side of the membrane and its close coupling to the internal environment (i.e., membrane-associated structures: annulus, zipper, etc.) under the otehr side of the membrane. We suggest that the cholesterol in spermatid cell membranes contributes to the establishment of their mosaicism and regulates the modeling of the spermatid by modulating the internal fluidity of individual membrane segments during spermiogenesis.     

Mechanism for the removal of residual cytoplasm from spermatids during mouse spermiogenesis

During spermiogenesis, cytoplasmic processes of Sertoli cells invade spermatid cytoplasm to form a canal complex (Sakai et al., 1988). Thin tubules are formed from the canal complex and intertwine with each other to give rise to the "mixed body." In the present study, analysis of the changes undergone by the intertwining thin tubules indicated that they contribute to the removal of cell organelles from spermatid cytoplasm. Intertwining thin tubules were first detected at step 13. By step 15, their number had greatly increased. In the present study, the membranes of the intertwining thin tubules were clearly observed to be continuous with the spermatid plasma membranes. Thus, the mixed body possibly may be formed as a long pit of the spermatid plasma membrane situated close to the invading Sertoli cell process. With the progress of spermiogenesis, the lumens of the intertwining thin tubules gradually became swollen, and the intertwining swollen tubules fused with each other so that the spermatid cytoplasm enclosed by the intertwining swollen tubules isolated into fragments. This fragmented cytoplasm, which contained a large amount of endoplasmic reticulum, became spherical. Small branches of the invading Sertoli cell processes entered into the lumens of the intertwining swollen tubules and occupied their interior to the point that, finally, they completely engulfed the fragmented spermatid cytoplasm. Because the invading Sertoli cell processes were continuous with Sertoli cell bodies surrounding a spermatid at this step, it is possible for the fragmented cytoplasm to be transported into the latter by way of the invading Sertoli cell processes.     

Effects of silver nanoparticles on oxidative DNA damage–repair as a function of p38 MAPK status: A comparative approach using human Jurkat T cells and the nematode Caenorhabditis elegans

The large‐scale use of silver nanoparticles (AgNPs) has raised concerns over potential impacts on the environment and human health. We previously reported that AgNP exposure causes an increase in reactive oxygen species, DNA damage, and induction of p38 MAPK and PMK‐1 in Jurkat T cells and in Caenorhabditis elegans. To elucidate the underlying mechanisms of AgNP toxicity, here we evaluate the effects of AgNPs on oxidative DNA damage–repair (in human and C. elegans DNA glycosylases hOGG1, hNTH1, NTH‐1, and 8‐oxo‐GTPases—hMTH1, NDX‐4) and explore the role of p38 MAPK and PMK‐1 in this process. Our comparative approach examined viability, gene expression, and enzyme activities in wild type (WT) and p38 MAPK knock‐down (KD) Jurkat T cells (in vitro) and in WT and pmk‐1 loss‐of‐function mutant strains of C. elegans (in vivo). The results suggest that p38 MAPK/PMK‐1 plays protective role against AgNP‐mediated toxicity, reduced viability and greater accumulation of 8OHdG was observed in AgNP‐treated KD cells, and in pmk‐1 mutant worms compared with their WT counterparts, respectively. Furthermore, dose‐dependent alterations in hOGG1, hMTH1, and NDX‐4 expression and enzyme activity, and survival in ndx‐4 mutant worms occurred following AgNP exposure. Interestingly, the absence or depletion of p38 MAPK/PMK‐1 caused impaired and additive effects in AgNP‐induced ndx‐4(ok1003); pmk‐1(RNAi) mutant survival, and hOGG1 and NDX‐4 expression and enzyme activity, which may lead to higher accumulation of 8OHdG. Together, the results indicate that p38 MAPK/PMK‐1 plays an important protective role in AgNP‐induced oxidative DNA damage–repair which is conserved from C. elegans to humans. Environ. Mol. Mutagen. 55:122–133, 2014. © 2013 Wiley Periodicals, Inc.     

ENU‐3 functions in an UNC‐6/netrin dependent pathway parallel to UNC‐40/DCC/frazzled for outgrowth and guidance of the touch receptor neurons in C. elegans

Results: An enu‐3 mutation enhances defects in ventral guidance of the processes of the AVM and PVM touch receptor neurons, the dorsal guidance of the distal tip cell and causes additional architectural defects in axons in unc‐40 mutant strains in an UNC‐6 dependent manner. These observations suggest that ENU‐3 and UNC‐40 function in parallel pathways dependent on UNC‐6. ENU‐3 depends on the presence of UNC‐40 for its full effect on motor neuron axon outgrowth. 相似文献   

Endothelial SUR‐8 acts in an ERK‐independent pathway during atrioventricular cushion development

SUR‐8, a conserved leucine‐rich repeats protein, was first identified as a positive regulator of Ras pathway in Caenorhabditis elegans. Biochemical studies indicated that SUR‐8 interacts with Ras and Raf, leading to the elevated ERK activity. However, the physiological role of SUR‐8 during mammalian development remains unclear. Here we found that germline deletion of SUR‐8 in mice resulted in early embryonic lethality. Inactivated SUR‐8 specifically in mouse endothelial cells (ECs) revealed that SUR‐8 is essential for embryonic heart development. SUR‐8 deficiency in ECs resulted in late embryonic lethality, and the mutant mice displayed multiple cardiac defects. The reduced endothelial‐mesenchymal transformation (EMT) and the reduced mesenchyme proliferation phase were observed in the atrioventricular canal (AVC) within the mutant hearts, leading to the formation of hypoplastic endocardial cushions. However, ERK activation did not appear to be affected in mutant ECs, suggesting that SUR‐8 may act in an ERK‐independent pathway to regulate AVC development. Developmental Dynamics 239:2005–2013, 2010 © 2010 Wiley‐Liss, Inc.     

Voltage‐dependent anion channel (VDAC‐1) is required for olfactory sensing in Caenorhabditis elegans

The Ras–MAP kinase signaling pathway plays important roles for the olfactory reception in olfactory neurons in Caenorhabditis elegans. However, given the absence of phosphorylation targets of MAPK in the olfactory neurons, the mechanism by which this pathway regulates olfactory function is unknown. Here, we used proteomic screening to identify the mitochondrial voltage‐dependent anion channel VDAC‐1 as a candidate target molecule of MAPK in the olfactory system of C. elegans. We found that Amphid Wing “C” (AWC) olfactory neuron‐specific knockdown of vdac‐1 caused severe defects in chemotaxis toward AWC‐sensed odorants. We generated a new vdac‐1 mutant using the CRISPR‐Cas9 system, with this mutant also showing decreased chemotaxis toward odorants. This defect was rescued by AWC‐specific expression of vdac‐1, indicating that functions of VDAC‐1 in AWC neurons are essential for normal olfactory reception in C. elegans. We observed that AWC‐specific RNAi of vdac‐1 reduced AWC calcium responses to odorant stimuli and caused a decrease in the quantity of mitochondria in the sensory cilia. Behavioral abnormalities in vdac‐1 knockdown animals might therefore be due to reduction of AWC response, which might be caused by loss of mitochondria in the cilia. Here, we showed that the function of VDAC‐1 is regulated by phosphorylation and identified Thr175 as the potential phosphorylation site of MAP kinase.     

Occurrence of class 1 integrons in uropathogenic fluoroquinolone‐resistant clinical Escherichia coli isolates from Jamaica

Quinolone resistance is generally caused by chromosomal mutations, but has been more recently found associated with the plasmid‐mediated qnr genes. The objective of this study was to screen and analyse polymorphisms of integrons in clinical isolates of Escherichia coli in Jamaica. Previous studies in Jamaica identified fluoroquinolone resistance in predominantly uropathogenic E. coli clinical isolates: 45% harbouring qnrA, qnrB and/or qnrS, and 17% were (Extended‐spectrum beta‐lactamase) ESBL‐producers. These isolates were analysed for the presence and variation of class 1 and 2 integrase genes, 5′‐ and 3′‐ conserved segments and the Orf513 recombinase gene by primer‐specific polymerase chain reaction (PCR) and restriction fragment‐length polymorphism (RFLP). Results indicated integron‐encoded integrases in 93% of isolates primarily harbouring class 1 integrase genes; four of 58 isolates carried both classes. The Orf513 and 5′‐ and 3′‐conserved segment (CS) regions were identified in 83% and 55% of the isolates respectively. RFLP evaluation of the 5′‐ and 3′‐CS regions in int1‐positive strains yielded two main types. The reduced diversity, but wide dispersion of class 1 integrons harbouring qnr genes may give rise to the conservation of the mobile genetic elements in which they are carried.     

CTLA4‐Ig inhibits allergic airway inflammation by a novel CD28‐independent,nitric oxide synthase‐dependent mechanism

The T‐cell response to antigen depends on coordinate signaling between costimulatory and inhibitory receptors. The altered function of either may underlie the pathophysiology of autoimmune and/or chronic inflammatory diseases and manipulation of these pathways is an important emerging area of therapeutics. We report here that the immunosuppressant drug CTLA4‐Ig inhibits the effector phase of allergic airway inflammation through a CD28‐independent, nitric oxide synthase (NOS)‐dependent mechanism. Using mice deficient in both B‐ and T‐lymphocyte attenuator (BTLA) and CD28, we demonstrate that simultaneous deficiency of an inhibitory receptor can rescue the in vivo but not the in vitro CD28‐deficient phenotype. Furthermore, we demonstrate that inflammation in CD28/BTLA‐double‐deficient mice is suppressed by CTLA4‐Ig. This suppression is reversed by treatment with the NOS inhibitor, N⁶‐methyl‐L ‐arginine acetate (L‐NMMA). In addition, CTLA4‐Ig is ineffective at inhibiting inflammation in NOS2‐deficient mice when given at the effector phase. Thus, CD28 and BTLA coordinately regulate the in vivo response to inhaled allergen, and CTLA4‐Ig binding to B7‐proteins inhibits the effector phase of inflammation by a CD28‐independent, NOS‐dependent mechanism.     

Influence of arylamine n‐acetyltransferase,sex, and age on 4‐aminobiphenyl‐induced in vivo mutant frequencies and spectra in mouse liver

One model for cancer initiation by 4‐aminobiphenyl (ABP) involves N‐oxidation by cytochrome P450 CYP1A2 followed by O‐conjugation by N‐acetyltransferase(s) NAT1 and/or NAT2 and decomposition to a DNA‐binding nitrenium ion. We recently observed that neonatal ABP exposure produced liver tumors in male but not in female mice, and that NAT deficiency reduced liver tumor incidence. However, ABP‐induced liver tumor incidence did not correlate with liver levels of N‐(deoxyguanosin‐8‐yl)‐ABP adducts 24 hr after exposure. In this study, we compared in vivo ABP‐induced DNA mutant frequencies and spectra between male and female wild‐type and NAT‐deficient Muta?Mouse using both the tumor‐inducing neonatal exposure protocol and a 28‐day repetitive dosing adult exposure protocol. ABP produced an increase in liver DNA mutant frequencies in both neonates and adults. However, we observed no sex or strain differences in mutant frequencies in neonatally exposed mice, and higher frequencies in adult females than males. Neonatal ABP exposure of wild‐type mice increased the proportion of G‐T transversions in both males and females, while exposure of Nat1/2(‐/‐) mice produced increased G‐T transversions in males and a decrease in females, even though females had higher levels of N‐(deoxyguanosin‐8‐yl)‐4‐ABP adducts. There was no correlation of mutant frequencies or spectra between mice dosed as neonates or as adults. These results suggest that observed sex‐ and NAT‐dependent differences in ABP‐induced liver tumor incidence in mice are not due to differences in either mutation rates or mutational spectra, and that mechanisms independent of carcinogen bioactivation, covalent DNA binding and mutation may be responsible for these differences. Environ. Mol. Mutagen., 2012. © 2012 Wiley Periodicals, Inc.     

TEG-1 CD2BP2 regulates stem cell proliferation and sex determination in the C. elegans germ line and physically interacts with the UAF-1 U2AF65 splicing factor

Background : For a stem cell population to exist over an extended period, a balance must be maintained between self‐renewing (proliferating) and differentiating daughter cells. Within the Caenorhabditis elegans germ line, this balance is controlled by a genetic regulatory pathway, which includes the canonical Notch signaling pathway. Results : Genetic screens identified the gene teg‐1 as being involved in regulating the proliferation versus differentiation decision in the C. elegans germ line. Cloning of TEG‐1 revealed that it is a homolog of mammalian CD2BP2, which has been implicated in a number of cellular processes, including in U4/U6.U5 tri‐snRNP formation in the pre‐mRNA splicing reaction. The position of teg‐1 in the genetic pathway regulating the proliferation versus differentiation decision, its single mutant phenotype, and its enrichment in nuclei, all suggest TEG‐1 also functions as a splicing factor. TEG‐1, as well as its human homolog, CD2BP2, directly bind to UAF‐1 U2AF65, a component of the U2 auxiliary factor. Conclusions : TEG‐1 functions as a splicing factor and acts to regulate the proliferation versus meiosis decision. The interaction of TEG‐1 CD2BP2 with UAF‐1 U2AF65, combined with its previously described function in U4/U6.U5 tri‐snRNP, suggests that TEG‐1 CD2BP2 functions in two distinct locations in the splicing cascade. Developmental Dynamics 241:505–521, 2012.© 2012 Wiley Periodicals, Inc.