gas2 is a multifunctional gene involved in the regulation of apoptosis and chondrogenesis in the developing mouse limb

miR-520c-3p regulates IL-1β-stimulated human chondrocyte apoptosis and cartilage degradation by targeting GAS2

Background

MicroRNAs (miRNAs) have been shown to be associated with osteoarthritis (OA) progression. This study aimed to explore the role of miR-520c-3p in OA progression.

Methods

Expression levels of miR-520c-3p and Growth arrest-specific 2 (GAS2) were detected using quantitative real-time PCR. The proliferation and apoptosis of cells were measured using cell counting kit 8 (CCK8) assay and flow cytometry. Furthermore, the protein levels of apoptosis-related markers, extracellular degradation markers, inflammatory response markers, and GAS2 were tested using quantitative real-time polymerase chain reaction (RT-PCR) and western blot (WB) analysis. In addition, the interaction between miR-520c-3p and GAS2 was examined using dual luciferase reporter assay.

Results

GAS2 was highly expressed, and miR-520c-3p was lowly expressed in OA cartilage tissues. miR-520c-3p could promote the proliferation and inhibit the apoptosis and inflammation of OA chondrocytes. miR-520c-3p could be sponged by GAS2, and its inhibitor could reverse the regulation of GAS2 on the biological functions of OA chondrocytes. GAS2 was a target of miR-520c-3p, which was identified by bioinformatic analysis and dual-luciferase reporter assay. Overexpression of GAS2 could inhibit the proliferation and promoted the apoptosis and inflammation of OA chondrocytes.

Conclusion

Our data showed that miR-520c-3p might regulate the GAS2 to inhibit the progression of OA.

Growth arrest-specific 2 protein family: Structure and function

Members of the growth arrest–specific 2 (GAS2) protein family consist of a putative actin‐binding (CH) domain and a microtubule‐binding (GAR) domain and are considered miniversions of spectraplakins. There are four members in the GAS2 family, viz. GAS2, GAS2L1, GAS2L2 and GAS2L3. Although GAS2 is defined as a family of growth arrest–specific proteins, the significant differences in the expression patterns, interaction characteristics and biological issues or diseases among the different GAS2 family members have not been systemically reviewed to date. Therefore, we summarized the available evidence on the structures and functions of GAS2 family members. This review facilitates a comprehensive molecular understanding of the involvement of the GAS2 family members in an array of biological processes, including cytoskeleton reorganization, cell cycle, apoptosis and cancer development.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.

Growth arrest specific gene 2 in tilapia (Oreochromis niloticus): molecular characterization and functional analysis under low-temperature stress

BACKGROUND

Growth arrest specific 2 (gas2) gene is a component of the microfilament system that plays a major role in the cell cycle, regulation of microfilaments, and cell morphology during apoptotic processes. However, little information is available on fish gas2. In this study, the tilapia (Oreochromis niloticus) gas2 gene was cloned and characterized for the first time.

RESULTS

The open reading frame was 1020 bp, encoding 340 amino acids; the 5'-untranslated region (UTR) was 140 bp and the 3'-UTR was 70 bp, with a poly (A) tail. The highest promoter activity occurred in the regulatory region (-3000 to -2400 bp). The Gas2-GFP fusion protein was distributed within the cytoplasm. Quantitative reverse transcription-polymerase chain reaction and western blot analyses revealed that gas2 gene expression levels in the liver, muscle, and brain were clearly affected by low temperature stress. The results of gas2 RNAi showed decreased expression of the gas2 and P53 genes.

CONCLUSION

These results suggest that the tilapia gas2 gene may be involved in low temperature stress-induced apoptosis.

Growth Arrest Specific 2 (GAS2) is a Critical Mediator of Germ Cell Cyst Breakdown and Folliculogenesis in Mice

In the mouse ovary, the primordial follicle pool is established through a diverse array of signaling pathways and tissue remodeling events. Growth arrest specific gene two (GAS2) is a highly conserved cytoskeleton-associated protein whose in vivo function remains unclear. In Drosophila, loss of the GAS2 homolog, Pigs, results in infertility. We demonstrate herein that, in the mouse ovary, GAS2 is expressed in the stromal cells surrounding the oocyte cysts on 16.5 dpc, and in stromal cells surrounding growing follicles during juvenile and adult life. We have generated genetically engineered mice with inactivated Gas2. Gas2 homozygous mutant mice are viable but have severely impaired fertility in females, in which oocyte cyst breakdown is disrupted and follicle growth is impaired, with significantly reduced numbers of large antral follicles and corpora lutea. In these mutant mice, the organization of the basal lamina surrounding developing follicles is severely defective at multiple stages of folliculogenesis. We also found that Notch signaling activity was altered in ovaries from Gas2 null mice around the time of birth and during follicular development later in life. These results indicate that GAS2 is a critical and novel regulator of tissue remodeling in the ovary during oocyte cyst breakdown and folliculogenesis.

Key pathways regulated by HoxA9,10,11/HoxD9,10,11 during limb development

Background

The 39 mammalian Hox genes show problematic patterns of functional overlap. In order to more fully define the developmental roles of Hox genes it is necessary to remove multiple combinations of paralogous and flanking genes. In addition, the downstream molecular pathways regulated by Hox genes during limb development remain incompletely delineated.

Results

In this report we examine limb development in mice with frameshift mutations in six Hox genes, Hoxa9,10,11 and Hoxd9,10,11. The mice were made with a novel recombineering method that allows the simultaneous targeting of frameshift mutations into multiple flanking genes. The Hoxa9,10,11^−/−/Hoxd9,10,11^−/− mutant mice show a reduced ulna and radius that is more severe than seen in Hoxa11^−/−/Hoxd11^−/− mice, indicating a minor role for the flanking Hox9,10 genes in zeugopod development, as well as their primary function in stylopod development. The mutant mice also show severe reduction of Shh expression in the zone of polarizing activity, and decreased Fgf8 expression in the apical ectodermal ridge, thereby better defining the roles of these specific Hox genes in the regulation of critical signaling centers during limb development. Importantly, we also used laser capture microdissection coupled with RNA-Seq to characterize the gene expression programs in wild type and mutant limbs. Resting, proliferative and hypertrophic compartments of E15.5 forelimb zeugopods were examined. The results provide an RNA-Seq characterization of the progression of gene expression patterns during normal endochondral bone formation. In addition of the Hox mutants showed strongly altered expression of Pknox2, Zfp467, Gdf5, Bmpr1b, Dkk3, Igf1, Hand2, Shox2, Runx3, Bmp7 and Lef1, all of which have been previously shown to play important roles in bone formation.

Conclusions

The recombineering based frameshift mutation of the six flanking and paralogous Hoxa9,10,11 and Hoxd9,10,11 genes provides a resource for the analysis of their overlapping functions. Analysis of the Hoxa9,10,11^−/−/Hoxd9,10,11^−/− mutant limbs confirms and extends the results of previous studies using mice with Hox mutations in single paralogous groups or with entire Hox cluster deletions. The RNA-Seq analysis of specific compartments of the normal and mutant limbs defines the multiple key perturbed pathways downstream of these Hox genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0078-5) contains supplementary material, which is available to authorized users.

GAS2-like proteins mediate communication between microtubules and actin through interactions with end-binding proteins

Crosstalk between the microtubule (MT) and actin cytoskeletons is fundamental to many cellular processes including cell polarisation and cell motility. Previous work has shown that members of the growth-arrest-specific 2 (GAS2) family mediate the crosstalk between filamentous actin (F-actin) and MTs, but the molecular basis of this process remained unclear. By using fluorescence microscopy, we demonstrate that three members of this family, GAS2-like 1, GAS2-like 2 and GAS2-like 3 (G2L1, G2L2 and G2L3, also known as GAS2L1, GAS2L2 and GAS2L3, respectively) are differentially involved in mediating the crosstalk between F-actin and MTs. Although all localise to actin and MTs, only the exogenous expression of G2L1 and G2L2 influenced MT stability, dynamics and guidance along actin stress fibres. Biochemical analysis and live-cell imaging revealed that their functions are largely due to the association of these proteins with MT plus-end-binding proteins that bind to SxIP or SxLP motifs located at G2L C-termini. Our findings lead to a model in which end-binding (EB) proteins play a key role in mediating actin–MT crosstalk.

Gas2l3, a novel constriction site-associated protein whose regulation is mediated by the APC/C Cdh1 complex

Growth arrest-specific 2-like protein 3 (Gas2l3) was recently identified as an Actin/Tubulin cross-linker protein that regulates cytokinesis. Using cell-free systems from both frog eggs and human cells, we show that the Gas2l3 protein is targeted for ubiquitin-mediated proteolysis by the APC/C^Cdh1 complex, but not by the APC/C^Cdc20 complex, and is phosphorylated by Cdk1 in mitosis. Moreover, late in cytokinesis, Gas2l3 is exclusively localized to the constriction sites, which are the narrowest parts of the intercellular bridge connecting the two daughter cells. Overexpression of Gas2l3 specifically interferes with cell abscission, which is the final stage of cell division, when the cutting of the intercellular bridge at the constriction sites occurs. We therefore suggest that Gas2l3 is part of the cellular mechanism that terminates cell division.

Dual role for glucocorticoids in cardiomyocyte hypertrophy and apoptosis

Glucocorticoids and their synthetic derivatives are known to alter cardiac function in vivo; however, the nature of these effects and whether glucocorticoids act directly on cardiomyocytes are poorly understood. To explore the role of glucocorticoid signaling in the heart, we used rat embryonic H9C2 cardiomyocytes and primary cardiomyocytes as model systems. Dexamethasone (100 nm) treatment of cardiomyocytes caused a significant increase in cell size and up-regulated the expression of cardiac hypertrophic markers, including atrial natriuretic factor, β-myosin heavy chain, and skeletal muscle α-actin. In contrast, serum deprivation and TNFα exposure triggered cardiomyocyte apoptosis, and these apoptotic effects were inhibited by dexamethasone. Both the hypertrophic and anti-apoptotic actions of glucocorticoids were abolished by the glucocorticoid receptor (GR) antagonist RU486 and by short hairpin RNA-mediated GR depletion. Blocking the activity of the mineralocorticoid receptor had no effect on these glucocorticoid-dependent cardiomyocyte responses. Aldosterone (1 μm) activation of GR also promoted cardiomyocyte hypertrophy and cell survival. To elucidate the mechanism of the dual glucocorticoid actions, a genome-wide microarray was performed on H9C2 cardiomyocytes treated with vehicle or dexamethasone in the absence or presence of serum. Serum dramatically influenced the transcriptome regulated by GR, revealing potential glucocorticoid signaling mediators in both cardiomyocyte hypertrophy and apoptosis. These studies reveal a direct and dynamic role for glucocorticoids and GR signaling in the modulation of cardiomyocyte function.

Necdin, a p53 target gene, regulates the quiescence and response to genotoxic stress of hematopoietic stem/progenitor cells

We recently defined a critical role for p53 in regulating the quiescence of adult hematopoietic stem cells (HSCs) and identified necdin as a candidate p53 target gene. Necdin is a growth-suppressing protein and the gene encoding it is one of several that are deleted in patients with Prader-Willi syndrome. To define the intrinsic role of necdin in adult hematopoiesis, in the present study, we transplanted necdin-null fetal liver cells into lethally irradiated recipients. We show that necdin-null adult HSCs are less quiescent and more proliferative than normal HSCs, demonstrating the similar role of necdin and p53 in promoting HSC quiescence during steady-state conditions. However, wild-type recipients repopulated with necdin-null hematopoietic stem/progenitor cells show enhanced sensitivity to irradiation and chemotherapy, with increased p53-dependent apoptosis, myelosuppression, and mortality. Necdin controls the HSC response to genotoxic stress via both cell-cycle-dependent and cell-cycle-independent mechanisms, with the latter occurring in a Gas2L3-dependent manner. We conclude that necdin functions as a molecular switch in adult hematopoiesis, acting in a p53-like manner to promote HSC quiescence in the steady state, but suppressing p53-dependent apoptosis in response to genotoxic stress.

Genome-wide analysis of hepatic gene silencing in hepatoma cell variants

Genome-wide gene expression profiling was carried out on rat hepatoma cells and compared to profiles of hepatoma "variant" cell lines derived via a stringent selection protocol that enriches for rare cells (<1 in 100,000 cells) that fail to drive liver function. Results show 132 genes that are strongly (>5-fold) repressed in each of the four variant cell lines tested. An additional 68 genes were repressed in 3 of 4 variant cell lines. Importantly, several of the repressed genes are members of transcriptional activation pathways, suggesting that they may contribute to maintaining the hepatic phenotype. Ectopic expression of the HNF1A gene in a variant cell line resulted in activation of 56 genes, 37 of which were included in the repressed data set. These data suggest that a high level of reprogramming occurs when hepatoma cells convert to a non-differentiated phenotype, a process that can be partially reversed by the introduction of transcription factors.

Characterization of G2L3 (GAS2-like 3), a new microtubule- and actin-binding protein related to spectraplakins

The microtubule (MT) and actin cytoskeletons are fundamental to cell integrity, because they control a host of cellular activities, including cell division, growth, polarization, and migration. Proteins involved in mediating the cross-talk between MT and actin cytoskeletons are key to many cellular processes and play important physiological roles. We identified a new member of the GAS2 family of MT-actin cross-linking proteins, named G2L3 (GAS2-like 3). We show that GAS2-like 3 is widely conserved throughout evolution and is ubiquitously expressed in human tissues. GAS2-like 3 interacts with filamentous actin and MTs via its single calponin homology type 3 domain and C terminus, respectively. Interestingly, the role of the putative MT-binding GAS2-related domain is to modulate the binding of GAS2-like 3 to both filamentous actin and MTs. This is in contrast to GAS2-related domains found in related proteins, where it functions as a MT-binding domain. Furthermore, we show that tubulin acetylation drives GAS2-like 3 localization to MTs and may provide functional insights into the role of GAS2-like 3.

Transcriptional profiling identifies differentially expressed genes in developing turkey skeletal muscle

Background

Skeletal muscle growth and development from embryo to adult consists of a series of carefully regulated changes in gene expression. Understanding these developmental changes in agriculturally important species is essential to the production of high quality meat products. For example, consumer demand for lean, inexpensive meat products has driven the turkey industry to unprecedented production through intensive genetic selection. However, achievements of increased body weight and muscle mass have been countered by an increased incidence of myopathies and meat quality defects. In a previous study, we developed and validated a turkey skeletal muscle-specific microarray as a tool for functional genomics studies. The goals of the current study were to utilize this microarray to elucidate functional pathways of genes responsible for key events in turkey skeletal muscle development and to compare differences in gene expression between two genetic lines of turkeys. To achieve these goals, skeletal muscle samples were collected at three critical stages in muscle development: 18d embryo (hyperplasia), 1d post-hatch (shift from myoblast-mediated growth to satellite cell-modulated growth by hypertrophy), and 16wk (market age) from two genetic lines: a randombred control line (RBC2) maintained without selection pressure, and a line (F) selected from the RBC2 line for increased 16wk body weight. Array hybridizations were performed in two experiments: Experiment 1 directly compared the developmental stages within genetic line, while Experiment 2 directly compared the two lines within each developmental stage.

Results

A total of 3474 genes were differentially expressed (false discovery rate; FDR < 0.001) by overall effect of development, while 16 genes were differentially expressed (FDR < 0.10) by overall effect of genetic line. Ingenuity Pathways Analysis was used to group annotated genes into networks, functions, and canonical pathways. The expression of 28 genes involved in extracellular matrix regulation, cell death/apoptosis, and calcium signaling/muscle function, as well as genes with miscellaneous function was confirmed by qPCR.

Conclusions

The current study identified gene pathways and uncovered novel genes important in turkey muscle growth and development. Future experiments will focus further on several of these candidate genes and the expression and mechanism of action of their protein products.

An association study on polymorphisms in the PEA15, ENTPD4, and GAS2L1 genes and schizophrenia

Our previous study examined a number of methamphetamine (METH)/phencyclidine (PCP)-reactive tags in rat brain, using a serial analysis of gene expression. Among human homologous genes, which matched METH/PCP-reactive tags, three human genes were identified: phosphoprotein enriched in astrocyte 15 (PEA15), ectonucleoside triphosphate diphosphohydrolase 4 (ENTPD4), and growth arrest-specific 2 like 1 (GAS2L1), which are localized in the chromosome 1q21.1, 8p21.3, and 22q12.2, respectively. We postulated that these genes are plausible candidate genes that play a role in pathogenesis for schizophrenia. Using tagging single-nucleotide polymorphisms (SNPs), we performed a case-control comparison for three SNPs in the PEA15 gene, and six SNPs in the GAS2L1 gene in a sample set of subjects (240 schizophrenia patients and 286 control subjects). Twelve SNPs in the ENTPD4 gene were analyzed in a subset of subjects (94 schizophrenia patients and 94 control subjects). No single SNP displayed a significant difference regarding the allelic frequency or genotypic distribution between the affected cases and controls for any of the genes examined. There was neither a significant difference in the frequency of three marker haplotype in the PEA15 gene or of six marker haplotype in the GAS2L1 gene between the cases and controls. The present study fails to provide evidence for the contribution of PEA15, ENTPD4, and GAS2L1 genes to the etiology of schizophrenia in the Japanese population.

Microarray-based analysis of cell-cycle gene expression during spermatogenesis in the mouse

Mammalian spermatogenesis is a continuum of cellular differentiation in a lineage that features three principal stages: 1) a mitotically active stage in spermatogonia, 2) a meiotic stage in spermatocytes, and 3) a postreplicative stage in spermatids. We used a microarray-based approach to identify changes in expression of cell-cycle genes that distinguish 1) mitotic type A spermatogonia from meiotic pachytene spermatocytes and 2) pachytene spermatocytes from postreplicative round spermatids. We detected expression of 550 genes related to cell-cycle function in one or more of these cell types. Although a majority of these genes were expressed during all three stages of spermatogenesis, we observed dramatic changes in levels of individual transcripts between mitotic spermatogonia and meiotic spermatocytes and between meiotic spermatocytes and postreplicative spermatids. Our results suggest that distinct cell-cycle gene regulatory networks or subnetworks are associated with each phase of the cell cycle in each spermatogenic cell type. In addition, we observed expression of different members of certain cell-cycle gene families in each of the three spermatogenic cell types investigated. Finally, we report expression of 221 cell-cycle genes that have not previously been annotated as part of the cell cycle network expressed during spermatogenesis, including eight novel genes that appear to be testis-specific.

Gas7 functions with N-WASP to regulate the neurite outgrowth of hippocampal neurons

Neuritogenesis, or neurite outgrowth, is a critical process for neuronal differentiation and maturation in which growth cones are formed from highly dynamic actin structures. Gas7 (growth arrest-specific gene 7), a new member of the PCH (Pombe Cdc15 homology) protein family, is predominantly expressed in neurons and is required for the maturation of primary cultured Purkinje neurons as well as the neuron-like differentiation of PC12 cells upon nerve growth factor stimulation. We report that Gas7 co-localizes and physically interacts with N-WASP, a key regulator of Arp2/3 complex-mediated actin polymerization, in the cortical region of Gas7-transfected Neuro-2a cells and growth cones of hippocampal neurons. The interaction between Gas7 and N-WASP is mediated by WW-Pro domains, which is unique in the PCH protein family, where most interactions are of the SH3-Pro kind. The interaction contributes to the formation of membrane protrusions and processes by recruiting the Arp2/3 complex in a Cdc42-independent manner. Importantly, specific interaction between Gas7 and N-WASP is required for regular neurite outgrowth of hippocampal neurons. The data demonstrate an essential role of Gas7 through its interaction with N-WASP during neuronal maturation/differentiation.

Comparative analysis of gene expression profiles between the normal human cartilage and the one with endemic osteoarthritis

OBJECTIVE

To investigate the differences in gene expression profiles of adult articular cartilage with endemic osteoarthritis (OA), Kashin-Beck disease (KBD), and the same regions in the normal joint.

METHODS

The messenger RNA expression profiles of articular cartilage with KBD diagnosed according to "Diagnosing Criteria of Kashin-Beck Disease in China" were compared with the normal cartilage. Total RNA isolated separately from four pairs of the KBD and normal cartilage samples were evaluated by oligonucleotide microarray analysis. The microarray data were confirmed by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) amplification and were compared with previously published experiments.

RESULTS

About 4100 transcripts, which corresponded to 35% of the expressed transcripts, showed >or=twofold differences in expression between the cartilage tissues in pairs. Approximately 2% of the expressed genes (79, 55 genes expressed in KBD>normal; 24 genes expressed in KBD<normal) were commonly expressed in the four pairs of samples. The expression of some genes related to the metabolism, apoptosis, cell proliferation and matrix degradation activity was significantly different in KBD cartilage than in the normal, similar to the findings for genes that inhibit matrix degradation. Comparisons of qRT-PCR data and the previously reported data with the result of gene chips support the validity of our microarray data.

CONCLUSION

Differences between KBD cartilage and the normal exhibited a similar pattern among the four pairs examined, indicating the presence of common mechanisms mainly including chondrocyte metabolism and apoptosis that contribute to cartilage destruction in KBD.

Genetic relationship between placental and fetal weights and markers of the metabolic syndrome in rat recombinant inbred strains

Epidemiological studies have shown a clear link between fetal growth retardation and an increased propensity for later cardiovascular disease in adults. It has been hypothesized that such early fetal deprivation “programs” individuals toward a life-long metabolical “thrifty phenotype” that predisposes adults to such diseases. Here we test this hypothesis, and its possible genetic basis, in rat recombinant inbred (RI) strains that uniquely allow the longitudinal studies necessary for its testing. Placental and fetal weights were determined on day 20 of pregnancy in (at least) 6 litters from each of 25 available BXH/HXB RI strains and from their SHR and BN-Lx progenitors and were correlated with metabolic traits determined in adult rats from the same inbred lines. Quantitative trait loci (QTLs) associated with placental and fetal weights were identified by total genome scanning of RI strains using the Map Manager QTX program. Heritabilities of placental and fetal weights were 56% and 62%, respectively, and total genome scanning of RI strains revealed QTLs near the D1Rat266 marker on chromosome 1 and near the D15Rat101 marker on chromosome 15 that were significantly associated with fetal and placental weights respectively. Placental weights correlated with fetal weights ( r = 0.60, P = 0.001), while reduced fetal weights correlated with increased insulin concentrations during glucose tolerance test ( r = −0.71, P = 0.0001) and with increased serum triglycerides ( r = −0.54, P = 0.006) in adult rats. Our results suggest that predisposition toward a thrifty phenotype associated with decreased placental weight and restricted fetal growth is in part genetically determined.

Expanding the Role of the Dynein Regulatory Complex to Non-Axonemal Functions: Association of GAS11 with the Golgi Apparatus

The mammalian GAS11 gene is a candidate tumor suppressor of unknown function that was previously identified as one of several genes upregulated upon growth arrest. Interestingly, although GAS11 homologs in Trypanosoma brucei (trypanin) and Chlamydomonas reinhardtii (PF2) are integral components of the flagellar axoneme and are necessary for regulating flagellar beat, the GAS11 gene was discovered based on its expression in cells that do not assemble a motile cilium. This suggests that GAS11 function might not be restricted to the cilium. To investigate this possibility, we generated GAS11-specific antibodies and demonstrate here that GAS11 is expressed in a variety of mammalian cells that lack a motile cilium. In COS7 cells, GAS11 is associated with the detergent-insoluble cytoskeleton and exhibits a juxtanuclear localization that overlaps with the pericentrosomal Golgi apparatus. This localization is dependent upon intact microtubules and is cell-cycle regulated, such that GAS11 is dispersed throughout the cytoplasm as cells progress through mitosis. GAS11 remains associated with Golgi fragments following depolymerization of cytoplasmic microtubules but is dispersed upon disruption of the Golgi with brefeldin A. These data suggest that GAS11 is associated with the Golgi apparatus. In support of this, recombinant GAS11 binds Golgi membranes in vitro. In growth-arrested mIMCD3 cells, GAS11 co-localizes with gamma-tubulin at the base of the primary cilium. The pericentrosomal Golgi apparatus and base of the cilium both represent convergence points for microtubule minus ends and correspond to sites where dynein regulation is required. The algal GAS11 homolog functions as part of a dynein regulatory complex (DRC) in the axoneme (Rupp and Porter. J Cell Biol 2003;162:47-57) and our findings suggest that components of this axonemal dynein regulatory system have been adapted in mammalian cells to participate in non-axonemal functions.

Retinoic acid induces CDK inhibitors and growth arrest specific (Gas) genes in neural crest cells

Retinoic acid (RA), the active metabolite of vitamin A, regulates cellular growth and differentiation during embryonic development. In excess, this vitamin is also highly teratogenic to animals and humans. The neural crest is particularly sensitive to RA, and high levels adversely affect migration, proliferation and cell death. We investigated potential gene targets of RA associated with neural crest proliferation by determining RA-mediated changes in gene expression over time, using microarrays. Statistical analysis of the top ranked RA-regulated genes identified modest changes in multiple genes previously associated with cell cycle control and proliferation including the cyclin-dependent kinase inhibitors Cdkn1a (p21), Cdkn2b (p15(INK4b)), and Gas3/PMP22. The expression of p21 and p15(INK4b) contribute to decreased proliferation by blocking cell cycle progression at G1-S. This checkpoint is pivotal to decisions regulating proliferation, apoptosis, or differentiation. We have also confirmed the overexpression of Gas3/PMP22 in RA-treated neural crests, which is associated with cytoskeletal changes and increased apoptosis. Our results suggest that increases in multiple components of diverse regulatory pathways have an overall cumulative effect on cellular decisions. This heterogeneity contributes to the pleiotropic effects of RA, specifically those affecting proliferation and cell death.

Candidate downstream regulated genes of HOX group 13 transcription factors with and without monomeric DNA binding capability

Hox genes encode transcription factors that regulate the morphogenesis of developing embryos. In mammals, knowledge of the genetic pathways, including the possible direct or indirect targets, regulated by HOX proteins is extremely limited. To identify the downstream genes regulated by posterior HOX proteins, we expressed HOXA13 in mouse embryonic fibroblasts lacking paralog group 13 expression using a bicistronic HOXA13/EGFP retroviral vector. Microarray analysis identified 68 genes with significant, reproducible RNA expression changes (50 activated; 18 repressed) in stable HOXA13-expressing cells. Genes with the GO annotation terms "extracellular matrix" and "basement membrane" were greatly overrepresented, and several were shown to be regulated by HOX proteins in other studies. Among the genes strongly activated by HOXA13 were Enpp2, a bifunctional enzyme known to modulate tumor and normal cell motility and which is expressed in precartilaginous condensations; Fhl1, a transcription factor implicated in muscle cell differentiation and development; and M32486, a putative integral membrane molecule expressed in the female reproductive tract. Expression differences in the HOXA13-expressing cells were confirmed for selected downstream genes using semi-quantitative RT-PCR, and in vivo coexpression with Hoxa13 in the limb interdigital mesenchyme was demonstrated for many. For two candidates, Igfbp4 and Fstl, interdigital limb bud expression was reduced in Hoxa13 mutants. To explore whether paralogous and nonparalogous HOX proteins could regulate the same genes, we created new HOX cell lines and examined the expression of selected genes identified by the HOXA13 screen. HOXD13 similarly activated/repressed 6 tested candidates, demonstrating that multiple downstream genetic pathways may be regulated by paralog HOX proteins. In contrast, HOXA9 was only able to repress expression of some gene targets. A HOXD13 mutant, HOXD13(IQN >)(AAA), incapable of monomeric DNA-binding, activated the expression of 5 HOXA13-upregulated genes; but was incapable of repressing the expression of Ngef and Casp8ap2. Our results suggest that HOX protein-protein interactions without direct HOX DNA-binding may play a larger role in HOX transcriptional regulation than generally assumed, and DNA-binding appears critical for repression.

Programmed cell death in the embryonic vertebrate limb

The developing limb bud provides one of the best examples in which programmed cell death exerts major morphogenetic functions. In this work, we revise the distribution and the developmental significance of cell death in the embryonic vertebrate limb and its control by the BMP signalling pathway. In addition, paying special attention to the interdigital apoptotic zones, we review current data concerning the intracellular death machinery implicated in mesodermal limb apoptosis.

Comparative proteomic analysis identifies protein disulfide isomerase and peroxiredoxin 1 as new players involved in embryonic interdigital cell death

In this study, we used comparative proteomics to identify proteins that were involved in the regulation of interdigital cell death. The protein profiles of embryonic day (E) 12.5 and 13.5 mouse hindlimb interdigital tissues were compared to identify proteins that were differentially expressed. The interdigital cells are irreversibly committed to programmed cell death (PCD) at E13.5, whereas they are developmentally plastic at E12.5. We established that protein disulfide isomerase (PDI) expression was up-regulated at E13.5, while peroxiredoxin 1 (Prdx1) expression was down-regulated at this time point. Semiquantitative reverse transcriptase-polymerase chain reaction and Western blot analyses confirmed the data obtained from the two-dimensional electrophoresis gels. Furthermore, we were able to up-regulate PDI expression by manipulating the E12.5 interdigital tissues to die during culture, although this up-regulation was not possible when cell survival was promoted. In addition, we could inhibit interdigital cell death and expression of proapoptotic genes (Bmp-4 and Bambi) by treating interdigital tissues with PDI antibodies and bacitracin (a PDI enzyme inhibitor). These findings suggested that PDI was involved in the activation and maintenance of interdigital cell death. Conversely, we determined that Prdx1 expression was maintained when interdigital cultures were manipulated to survive but down-regulated when the cultures were permitted to die. The result suggested that Prdx1 was involved in maintaining interdigital cell survival. However, we were unable to induce interdigital cell death by means of RNA interference-mediated silencing of Prdx1 expression, indicating that Prdx1 down-regulation is not sufficient for PCD to occur. Proteomic analysis of the Prdx1 knock-down cells revealed that the level of NF-kappaB inhibitor epsilon (IkappaBepsilon) was dramatically reduced. Furthermore, we found an increase in NFkappaB activation and reactive oxygen species (ROS) levels in the cytoplasm as a result of Prdx1 knockdown. We also found that silencing Prdx1 made the interdigital cells more susceptible to ROS-induced cell death. Taken together, our study identifies two new players in interdigital cell death and highlights that PCD is regulated by a delicate balance of proapoptotic and survival-promoting activities.

A new role for BMP5 during limb development acting through the synergic activation of Smad and MAPK pathways

In an attempt to identify new genes implicated in the control of programmed cell death during limb development, we have generated a cDNA library from the regressing interdigital tissue of chicken embryos. We have analyzed 804 sequences from this library and identified 23 genes involved in apoptosis in different models. One of the genes that came up in the screening was the Bone Morphogenetic Protein family member, Bmp5, that has not been previously involved in the control of apoptosis during limb development. In agreement with a possible role in the control of cell death, Bmp5 exhibited a regulated pattern of expression in the interdigital tissue. Transcripts of Bmp5 and BMP5 protein were abundant within the cytoplasm of the fragmenting apoptotic interdigital cells in a way suggesting that delivery of BMPs into the tissue is potentiated during apoptosis. Gain-of-function experiments demonstrated that BMP5 has the same effect as other interdigital BMPs inducing apoptosis in the undifferentiated mesoderm and growth in the prechondrogenic mesenchyme. We have characterized both Smad proteins and MAPK p38 as intracellular effectors for the action of BMPs in the developing limb autopod. Activation of Smad signaling involves the receptor-regulated genes Smad1 and -8, and the inhibitory Smad6, and results in both the upregulation of gene transcription and protein phosphorylation with subsequent nuclear translocation. MAPK p38 is also quickly phosphorylated after BMP stimulation in the limb mesoderm. Treatment with the inhibitor of p38, SB203580, revealed that there are interdigital genes induced by BMPs in a p38-dependent manner (DKK, Snail and FGFr3), and genes induced in a p38-independent manner (BAMBI, Msx2 and Smads). Together, our results suggest that Smad and MAPK pathways act synergistically in the BMP pathway controlling limb development.

Hypoglycemia induced changes in cell death and cell proliferation in the organogenesis stage embryonic mouse heart

BACKGROUND

Hypoglycemia is a side effect of diabetes therapy and causes abnormal heart development. Embryonic heart cells are largely resistant to teratogen-induced apoptosis.

METHODS

Hypoglycemia was tested for effects on cell death and cell proliferation in embryonic heart cells by exposing mouse embryos on embryonic day (E) 9.5 (plug = E0.5) to hypoglycemia (30-50 mg/dl glucose) in vivo or in vitro for 24 hr. Long-term effects of in vivo exposure on conceptus viability were evaluated at E18.5. Cell death was evaluated on E10.5 by: 1) two TUNEL assays in sectioned embryos to demonstrate DNA fragmentation; 2) confocal microscopy in whole embryos stained with Lysotracker; 3) flow cytometry in dispersed heart cells stained for TUNEL and myosin heavy chain (MHC) to quantify and characterize cell type susceptibility; and 4) immunohistochemistry (IHC) and Western analysis in sectioned embryos to evaluate potential involvement of caspase-3 active subunit and p53. Effects on cell proliferation were evaluated by IHC and Western analysis of proliferating cell nuclear antigen (PCNA).

RESULTS

In vivo hypoglycemic exposure on E9.5 reduced viability in conceptuses examined on E18.5. Hearts examined on E10.5 demonstrated increased TUNEL and Lysotracker staining. In hearts of embryos exposed to hypoglycemia, flow cytometry demonstrated increased TUNEL-positive cells and cells dual-labeled for TUNEL and MHC. Protein expression of caspase-3 active subunit and p53 was increased and PCNA was markedly reduced in hearts of embryos exposed to hypoglycemia.

CONCLUSIONS

Hypoglycemia reduces embryonic viability, induces significant cell death, and reduces cell proliferation in the E9.5 mouse heart, and these processes may involve active caspase-3 and p53.

Growth arrest-specific 2 gene expression during patellar tendon healing

We examined the cellular and molecular processes involved in patellar tendon healing following induced injury. A wound was surgically created at the center of the patellar tendon of adult rats. The wound site was examined at selected time intervals by immunohistochemical and in situ hybridization techniques. It was found that, between the 2nd and 7th day postoperation, fibroblast-like cells invaded the wound site. DiI-labelling experiments suggested that the majority of cells that occupied the wound originated from the edges of the wound. Furthermore, immunohistochemical studies revealed that at the wound site a meshwork of fibronectin developed that can support the migration of the DiI-labelled cells. We also examined the spatial and temporal expression patterns of the growth arrest specific 2 (GAS2) gene during patellar tendon healing. GAS2 was found strongly expressed in the tenocytes of unoperated patellar tendons. The gene was also expressed in the intact regions of operated tendons but not in the fibroblast-like cells that occupied the wound site, when examined 2 days postoperation. In addition the strip of intact tendon directly opposite the wound site also did not express GAS2. Examination of the experimental tendon at the 3rd month, when cells had completely occupied the wound site, revealed that Gas2 was expressed by all cells found in the wound. Bromodeoxyuridine (BrdU) incorporation analysis revealed that the presence of Brdu-positive cells in the wound indirectly correlated with the absence of Gas2 expression. We speculate that the GAS2 gene might play a role in regulating tenocyte proliferation during tendon healing.

Elucidating the molecular mechanism of cardiac remodeling using a comparative genomic approach

It is proposed that analysis of global gene expression would provide an understanding of the molecular mechanisms of cardiac remodeling. However, previous studies have only provided "snapshots" of differential gene expression. Furthermore, the differences in gene expression between regions of the heart that can result in sampling variability have not been characterized. In this study, we employed the Affymetrix GeneChip technology to evaluate the patterns of expression in two different in vivo models of cardiac remodeling and in two different regions (left ventricle free wall and intraventricular septum) of the heart. Mice underwent transverse aortic constriction (TAC), myocardial infarction (MI), or sham operation, and RNA from the left ventricle free wall and the septum was isolated 1 wk later. Histological analysis showed profound myocyte hypertrophy and fibrosis in both the septum and the left ventricle free wall of the TAC model, whereas, in the MI model, only the left ventricle exhibited hypertrophy. These differences were also reflected in the expression analysis. In conclusion, our analysis shows that regional differences in gene expression exist in the heart. Moreover, common pathways that are coregulated in both models exist, and these might be central to the hypertrophic phenotype regardless of the initial hypertrophic stimuli.

Effect of caspase cleavage-site phosphorylation on proteolysis

Caspases are important mediators of apoptotic cell death. Several cellular protein substrates of caspases contain potential phosphorylation site(s) at the cleavage-site region, and some of these sites have been verified to be phosphorylated. Since phosphorylation may affect substantially the substrate susceptibility towards proteolysis, phosphorylated, non-phosphorylated and substituted oligopeptides representing such cleavage sites were studied as substrates of apoptotic caspases 3, 7 and 8. Peptides containing phosphorylated serine residues at P4 and P1' positions were found to be substantially less susceptible towards proteolysis as compared with the serine-containing analogues, while phosphoserine at P3 did not have a substantial effect. P1 serine as well as P1-phosphorylated, serine-containing analogues of an oligopeptide representing the poly(ADP-ribose) polymerase cleavage site of caspase-3 were not hydrolysed by any of these enzymes, whereas the P1 aspartate-containing peptides were efficiently hydrolysed. These findings were interpreted with the aid of molecular modelling. Our results suggest that cleavage-site phosphorylation in certain positions could be disadvantageous or detrimental with respect to cleavability by caspases. Cleavage-site phosphorylation may therefore provide a regulatory mechanism to protect substrates from caspase-mediated degradation.

Protein products of human Gas2-related genes on chromosomes 17 and 22 (hGAR17 and hGAR22) associate with both microfilaments and microtubules

The human Gas2-related gene on chromosome 22 (hGAR22) encodes two alternatively spliced mRNA species. The longer mRNA encodes a protein with a deduced molecular mass of 36.3 kDa (GAR22alpha), whereas the shorter mRNA encodes a larger protein with a deduced molecular mass of 72.6 kDa (GAR22beta). We show that both hGAR22 proteins contain a calponin homology actin-binding domain and a Gas2-related microtubule-binding domain. Using rapid amplification of cDNA ends, we have cloned the mouse orthologue of hGAR22, mGAR22, and found its protein products to be extremely well conserved. We also report the cDNA cloning of a human Gas2-related gene on chromosome 17 (hGAR17). hGAR17 also encodes two protein isoforms. The overall cytoskeletal binding properties of the hGAR17 and hGAR22 proteins are remarkably similar. hGAR17 mRNA expression is limited to skeletal muscle. Although hGAR22 and mGAR22 mRNAs are expressed nearly ubiquitously, mGAR22 protein can only be detected in testis and brain. Furthermore, only the beta isoform is present in these tissues. GAR22beta expression is induced in a variety of cultured cells by growth arrest. The absolute amounts of GAR22beta protein expressed are low. The beta isoforms of hGAR17 and hGAR22 appear to be able to crosslink microtubules and microfilaments in transfected cells. This finding suggests that the physiological functions of these proteins may involve integration of these two components of the cytoskeleton.

Caspase inhibition supports proper gene expression in ex vivo mouse limb cultures

We standardized conditions for ex vivo mouse limb culture to study cartilage maturation and joint formation. We compared 12.5 d.p.c. mouse forelimbs that were cultured either mounted or freely rotating for up to 72 h. Limb outgrowth progressed ex vivo at a variable rate as compared to its development in vivo, spanning approximately 48 h. Although cartilage maturation and joint formation developed grossly normal, aberrant expression of skeletal marker genes was seen. Interestingly, no regression of the interdigital webs took place in mounted cultures, in contrast to limited webbing under freely rotating conditions. Caspase inhibition, by addition of zVAD-fmk to the culture medium of freely rotating limbs, supported proper gene expression associated with skeletal development, and prevented interdigital web regression. Taken together, a freely rotating ex vivo culture for mouse limb outgrowth that is combined with caspase inhibition provides a good model to study cartilage maturation and joint formation.

Functions of the Growth Arrest Specific 1 Gene in the Development of the Mouse Embryo

The growth arrest specific 1 (gas1) gene is highly expressed in quiescent mammalian cells (Schneider et al., 1988, Cell 54, 787-793). Overexpression of gas1 in normal and some cancer cell lines could inhibit G(0)/G(1) transition. Presently, we have examined the functions of this gene in the developing mouse embryo. The spatial-temporal expression patterns for gas1 were established in 8.5- to 14.5-day-old embryos by immunohistochemical staining and in situ hybridization. Gas1 was found heterogeneously expressed in most organ systems including the brain, heart, kidney, limb, lung, and gonad. The antiproliferative effects of gas1 on 10.5 and 12.5 day limb cells were investigated by flow cytometry. In 10.5 day limbs cells, gas1 overexpression could not prevent G(0)/G(1) progression. It was determined that gas1 could only induce growth arrest if p53 was also coexpressed. In contrast, gas1 overexpression alone was able to induce growth arrest in 12.5 day limb cells. We also examined the cell cycle profile of gas1-expressing and nonexpressing cells by immunochemistry and flow cytometry. For 10.5 day Gas1-expressing heart and limb cells, we did not find these cells preferentially distributed at G0/G1, as compared with Gas1-negative cells. However, in the 12.5 day heart and limb, we did find significantly more Gas1-expressing cells distributed at G0/G1 phase than Gas1-negative cells. These results implied that Gas1 alone, during the early stages of development, could not inhibit cell growth. This inhibition was only established when the embryo grew older. We have overexpressed gas1 in subconfluent embryonic limb cells to determine the ability of gas1 to cross-talk with various response elements of important transduction pathways. Specifically, we have examined the interaction of gas1 with Ap-1, NFkappaB, and c-myc responsive elements tagged with a SEAP reporter. In 10.5 day limb cells, gas1 overexpression had little effect on Ap-1, NFkappaB, and c-myc activities. In contrast, gas1 overexpression in 12.5 day limb cells enhanced AP-1 response while it inhibited NFkappaB and c-myc activities. These responses were directly associated with the ability of gas1 to induce growth arrest in embryonic limb cells. In the 12.5 day hindlimb, gas1 was found strongly expressed in the interdigital tissues. We overexpressed gas1 in these tissues and discovered that it promoted interdigital cell death. Our in situ hybridization studies of limb sections and micromass cultures revealed that, during the early stages of chondrogenesis, only cells surrounding the chondrogenic condensations expressed gas1. The gene was only expressed by chondrocytes after the cartilage started to differentiate. To understand the function of gas1 in chondrogenesis, we overexpressed the gene in limb micromass cultures. It was found that cells overexpressing gas1/GFP could not participate in cartilage formation, unlike cells that just express the GFP reporter. We speculated that the reason gas1 was expressed outside the chondrogenic nodules was to restrict cells from being recruited into the nodules and thereby defining the boundary between chondrogenic and nonchondrogenic forming regions.

The death substrate Gas2 binds m-calpain and increases susceptibility to p53-dependent apoptosis

Gas2 is a caspase-3 substrate that plays a role in regulating microfilament and cell shape changes during apoptosis. Here we provide evidence that overexpression of Gas2 efficiently increases cell susceptibility to apoptosis following UV irradiation, etoposide and methyl methanesulfonate treatments, and that these effects are dependent on increased p53 stability and transcription activity. To investigate possible pathways linking Gas2 to p53, a yeast two-hybrid screen swas performed, indicating m-calpain as a strong Gas2- interacting protein. Moreover, we demonstrate that Gas2 physically interacts with m-calpain in vivo and that recombinant Gas2 inhibits calpain-dependent processing of p53. Importantly, the Gas2 dominant-negative form (Gas2171-314) that binds calpain but is unable to inhibit its activity abrogates Gas2's ability to stabilize p53, to enhance p53 transcriptional activity and to induce p53-dependent apoptosis. Finally, we show that Gas2 is able to regulate the levels of p53 independently of Mdm2 status, suggesting that, like calpastatin, it may enhance p53 stability by inhibiting calpain activity.

Co-localization of active caspase-3 and DNA fragmentation (TUNEL) in normal and hyperthermia-induced abnormal mouse development

BACKGROUND

Previous work has shown that caspase-3 activation and DNA fragmentation, two hallmarks of apoptosis, are induced in day 9 mouse embryos exposed to hyperthermia (43 degrees C); however, the methods used to assess caspase-3 activation (Western blot) and DNA fragmentation (gel electrophoresis) did not allow these apoptotic events to be localized to specific cells within the embryo.

METHODS

To co-localize active caspase-3 and DNA fragmentation to specific cells, we used paraffin sections of day 13 mouse limb buds, sections of control and hyperthermia-treated day 9 mouse embryos, and sequential immunohistochemical staining for caspase-3 and TUNEL staining for DNA fragmentation. We used a primary rabbit antibody specific for the active, p17 subunit of caspase-3 and a goat anti-rabbit secondary antibody conjugated to Alexa 594 fluorochrome (red fluorescence) to localize active caspase-3. To co-localize DNA fragmentation, we subsequently processed the same sections by the TUNEL method using fluorescein-labeled dUTP (green fluorescence).

RESULTS

Using this dual labeling approach, we show that active caspase-3 (caspase-3 positive) and DNA fragmentation (TUNEL positive) occur in a sub-population of interdigital mesenchyme cells of day 13 mouse limb buds. Using the same approach, we detected a small number of caspase-3 positive and TUNEL-positive cells in the central nervous system and in the mesenchyme of the first branchial arch of untreated day 9 mouse embryos. The number of caspase-3 and TUNEL-positive cells are greatly increased 5 hr after a brief exposure to hyperthermia (43 degrees C, 13 min). Caspase-3 and TUNEL-positive cells were most abundant in the neuroepithelium of the developing central nervous system, mesenchyme of the first pharyngeal arch, and somitic mesoderm. In contrast, the heart, mesencephalic mesenchyme, and the visceral yolk sac contained few, if any, caspase-3 and TUNEL-positive cells.

CONCLUSIONS

This is the first demonstration that activation of caspase-3 and DNA fragmentation co-localize in cells programmed to die in the interdigital mesenchyme of day 13 limb buds and in the neuroepithelium and branchial arch mesenchyme of day 9 mouse embryos. Similarly, our results represent the first co-localization of teratogen-induced activation of caspase-3 and DNA fragmentation in specific cells of early postimplantation mouse embryos, and confirm that cells of the developing central nervous system are acutely sensitive to the cell death-inducing potential of hyperthermia, whereas cells of the heart are resistant. Finally, we show for the first time that, like cells of the heart, cells of the mesencephalic mesenchyme and the visceral yolk sac are also resistant to hyperthermia-induced apoptosis.

Bmp-4 requires the presence of the digits to initiate programmed cell death in limb interdigital tissues

The effects of Bmp-4 on interdigital cell death were investigated in the mouse. Affi-Gel beads, loaded with recombinant Bmp-4 protein, were transplanted into the interdigital tissues of day 12.5 hindlimb, ex utero. It was established that Bmp-4 could induce precocious interdigital cell death. Using in situ hybridization, the expression patterns of bmp-4 and alk-6 receptor were established. Both genes were found coexpressed in the interdigital region of 12.5- and 13. 5-day hindlimbs. This suggests that Bmp-4 may act in an autocrine fashion. We have also studied the effects of Bmp-4 on 12.5-day interdigital tissue cultures. In all specimens examined, the interdigital tissues produced cartilage instead of participating in cell death. The addition of exogenous Bmp-4 to the interdigital cultures did not induce apoptosis but instead enhanced chondrogenesis. The discrepancy between the effects of Bmp-4 in vitro and ex utero was attributed to the presence of digits. When a flanking digit was left attached to the interdigital tissues, in vitro, Bmp-4 promoted apoptosis instead of chondrogenesis. In sum, the results suggest that Bmp-4 is a multifunctional protein and its effect on the interdigital tissues is dependent on the modulating influence of the digits.

Caspase-3 and caspase-7 but not caspase-6 cleave Gas2 in vitro: implications for microfilament reorganization during apoptosis

Apoptosis is characterized by proteolysis of specific cellular proteins by a family of cystein proteases known as caspases. Gas2, a component of the microfilament system, is cleaved during apoptosis and the cleaved form specifically regulates microfilaments and cell shape changes. We now demonstrate that Gas2 is a substrate of caspase-3 but not of caspase-6. Proteolytic processing both in vitro and in vivo is dependent on aspartic residue 279. Gas2 cleavage was only partially impaired in apoptotic MCF-7 cells which lack caspase-3, thus indicating that different caspases can process Gas2 in vivo. In vitro Gas2 was processed, albeit with low affinity, by caspase-7 thus suggesting that this caspase could be responsible for the incomplete Gas2 processing observed in UV treated MCF-7 cells. In vivo proteolysis of Gas2 was detected at an early stage of the apoptotic process when the cells are still adherent on the substrate and it was coupled to the specific rearrangement of the microfilament characterizing cell death. Finally we also demonstrated that Gas2 in vitro binds to F-actin, but this interaction was unaffected by the caspase-3 dependent proteolytic processing.