Inflated wings, tissue autolysis and early death in tissue inhibitor of metalloproteinases mutants of Drosophila

Integrin-ECM interactions and membrane-associated Catalase cooperate to promote resilience of the Drosophila intestinal epithelium

Balancing cellular demise and survival constitutes a key feature of resilience mechanisms that underlie the control of epithelial tissue damage. These resilience mechanisms often limit the burden of adaptive cellular stress responses to internal or external threats. We recently identified Diedel, a secreted protein/cytokine, as a potent antagonist of apoptosis-induced regulated cell death in the Drosophila intestinal midgut epithelium during aging. Here, we show that Diedel is a ligand for RGD-binding Integrins and is thus required for maintaining midgut epithelial cell attachment to the extracellular matrix (ECM)-derived basement membrane. Exploiting this function of Diedel, we uncovered a resilience mechanism of epithelial tissues, mediated by Integrin-ECM interactions, which shapes cell death spreading through the regulation of cell detachment and thus cell survival. Moreover, we found that resilient epithelial cells, enriched for Diedel-Integrin-ECM interactions, are characterized by membrane association of Catalase, thus preserving extracellular reactive oxygen species (ROS) balance to maintain epithelial integrity. Intracellular Catalase can relocalize to the extracellular membrane to limit cell death spreading and repair Integrin-ECM interactions induced by the amplification of extracellular ROS, which is a critical adaptive stress response. Membrane-associated Catalase, synergized with Integrin-ECM interactions, likely constitutes a resilience mechanism that helps balance cellular demise and survival within epithelial tissues.

OUP accepted manuscript

Tissue inhibitors of metalloproteinases (TIMPs) are a conserved family of proteins that were originally identified as endogenous inhibitors of matrixin and adamalysin endopeptidase activity. The matrixins and adamalysins are the major mediators of extracellular matrix (ECM) turnover, thus making TIMPs important regulators of ECM structure and composition. Despite their high sequence identity and relative redundancy in inhibitory profiles, each TIMP possesses unique biological characteristics that are independent of their regulation of metalloproteinase activity. As our understanding of TIMP biology has evolved, distinct roles have been assigned to individual TIMPs in cancer progression. In this respect, data regarding TIMP2's role in cancer have borne conflicting reports of both tumor suppressor and, to a lesser extent, tumor promoter functions. TIMP2 is the most abundant TIMP family member, prevalent in normal and diseased mammalian tissues as a constitutively expressed protein. Despite its apparent stable expression, recent work highlights how TIMP2 is a cell stress-induced gene product and that its biological activity can be dictated by extracellular posttranslational modifications. Hence an understanding of TIMP2 molecular targets, and how its biological functions evolve in the progressing tumor microenvironment may reveal new therapeutic opportunities. In this review, we discuss the continually evolving functions of TIMP proteins, future perspectives in TIMP research, and the therapeutic utility of this family, with a particular focus on TIMP2.

Construction of wound repair model and function of recombinant TIMP from Hyriopsis cumingii

Metalloproteinase tissue inhibitors (TIMPs) have the activity of inhibiting matrix metalloproteinases (MMPs), which can promote cell growth, bind to the matrix, inhibit angiogenesis, and play a key role in extracellular matrix (ECM) metabolism regulation. In this study, TIMP-1, 2 from Hyriopsis cumingii (designated as HcTIMP-1, 2) were cloned and identified. Full-length cDNA of HcTIMP-1, 2 was 1160 bp and 729 bp, encoding 235 and 150 amino acid residues, respectively. The predicted molecular weight of HcTIMP-1 and 2 protein was 27.26 and 16.58 kDa, with isoelectric points of 8.89 and 8.72, respectively. HcTIMP-2 contained only one netrin (NTR) domain at the N-terminal but lacked a C-terminal domain. The mRNA of HcTIMP-1, 2 was expressed in hepatopancreas, gills, muscles, hemocytes, and mantles, which had the highest expression in hemocytes and muscles. The expression of HcTIMP-1, 2 had increased remarkably in hemocytes after bacterial challenge. After trauma, HcTIMP-1, 2 genes had the highest expression level in the first day. This indicated that HcTIMP-1 and 2 were involved in the immune response of H. cumingii. The soluble recombinant proteins HcTIMP-1, 2 were expressed efficiently in Escherichia coli BL21 (DE3) by constructing pET32a-TIMP1, 2 recombinant plasmids. The concentration of the recombinant was 0.14 and 0.31 mg/mL, respectively. The recombinant HcTIMP-1, 2 proteins were shown to inhibit human MMP2 activity and promoted the growth of NBL-7 and HUVE cells.

Atypical laminin spots and pull-generated microtubule-actin projections mediate Drosophila wing adhesion

During Drosophila metamorphosis, dorsal and ventral wing surfaces adhere, separate, and reappose in a paradoxical process involving cell-matrix adhesion, matrix production and degradation, and long cellular projections. The identity of the intervening matrix, the logic behind the adhesion-reapposition cycle, and the role of projections are unknown. We find that laminin matrix spots devoid of other main basement membrane components mediate wing adhesion. Through live imaging, we show that long microtubule-actin cables grow from those adhesion spots because of hydrostatic pressure that pushes wing surfaces apart. Formation of cables resistant to pressure requires spectraplakin, Patronin, septins, and Sdb, a SAXO1/2 microtubule stabilizer expressed under control of wing intervein-selector SRF. Silkworms and dead-leaf butterflies display similar dorso-ventral projections and expression of Sdb in intervein SRF-like patterns. Our study supports the morphogenetic importance of atypical basement-membrane-related matrices and dissects matrix-cytoskeleton coordination in a process of great evolutionary significance.

From genes to shape during metamorphosis: a history

Metamorphosis (Greek for a state of transcending-form or change-in-shape) refers to a dramatic transformation of an animal's body structure that occurs after development of the embryo or larva in many species. The development of a fly (or butterfly) from a crawling larva (or caterpillar) that forms a pupa (or chrysalis) before eclosing as a flying adult is a classic example of metamorphosis that captures the imagination and has been immortalized in children's books. Powerful genetic experiments in the fruit fly Drosophila melanogaster have revealed how genes can instruct the behaviour of individual cells to control patterns of tissue growth, mechanical force, cell-cell adhesion and cell-matrix adhesion drive morphogenetic change in epithelial tissues. Together, the distribution of mass, force and resistance determines cell shape changes, cell-cell rearrangements, and/or the orientation of cell divisions to generate the final form of the tissue. In organising tissue shape, genes harness the power of self-organisation to determine the collective behaviour of molecules and cells, which can often be reproduced in computer simulations of cell polarity and/or tissue mechanics. This review highlights fundamental discoveries in epithelial morphogenesis made by pioneers who were fascinated by metamorphosis, including D'Arcy Thompson, Conrad Waddington, Dianne Fristrom and Antonio Garcia-Bellido.

Metalloprotease inhibitor TIMP proteins control FGF-2 bioavailability and regulate skeletal growth

Saw et al. show via the combinatorial deletion of Timp family members in mice that metalloprotease regulation of FGF-2 is a crucial event in the chondrocyte maturation program, underlying the growth plate development and bone elongation responsible for attaining proper body stature.

Regulated growth plate activity is essential for postnatal bone development and body stature, yet the systems regulating epiphyseal fusion are poorly understood. Here, we show that the tissue inhibitors of metalloprotease (TIMP) gene family is essential for normal bone growth after birth. Whole-body quadruple-knockout mice lacking all four TIMPs have growth plate closure in long bones, precipitating limb shortening, epiphyseal distortion, and widespread chondrodysplasia. We identify TIMP/FGF-2/IHH as a novel nexus underlying bone lengthening where TIMPs negatively regulate the release of FGF-2 from chondrocytes to allow IHH expression. Using a knock-in approach that combines MMP-resistant or ADAMTS-resistant aggrecans with TIMP deficiency, we uncouple growth plate activity in axial and appendicular bones. Thus, natural metalloprotease inhibitors are crucial regulators of chondrocyte maturation program, growth plate integrity, and skeletal proportionality. Furthermore, individual and combinatorial TIMP-deficient mice demonstrate the redundancy of metalloprotease inhibitor function in embryonic and postnatal development.

The Drosophila Hox gene Ultrabithorax controls appendage shape by regulating extracellular matrix dynamics

Although the specific form of an organ is frequently important for its function, the mechanisms underlying organ shape are largely unknown. In Drosophila, the wings and halteres, homologous appendages of the second and third thoracic segments, respectively, bear different forms: wings are flat, whereas halteres are globular, and yet both characteristic shapes are essential for a normal flight. The Hox gene Ultrabithorax (Ubx) governs the difference between wing and haltere development, but how Ubx function in the appendages prevents or allows flat or globular shapes is unknown. Here, we show that Ubx downregulates Matrix metalloproteinase 1 (Mmp1) expression in the haltere pouch at early pupal stage, which in turn prevents the rapid clearance of Collagen IV compared with the wing disc. This difference is instrumental in determining cell shape changes, expansion of the disc and apposition of dorsal and ventral layers, all of these phenotypic traits being characteristic of wing pouch development. Our results suggest that Ubx regulates organ shape by controlling Mmp1 expression, and the extent and timing of extracellular matrix degradation.

Apical and Basal Matrix Remodeling Control Epithelial Morphogenesis

Epithelial tissues can elongate in two dimensions by polarized cell intercalation, oriented cell division, or cell shape change, owing to local or global actomyosin contractile forces acting in the plane of the tissue. In addition, epithelia can undergo morphogenetic change in three dimensions. We show that elongation of the wings and legs of Drosophila involves a columnar-to-cuboidal cell shape change that reduces cell height and expands cell width. Remodeling of the apical extracellular matrix by the Stubble protease and basal matrix by MMP1/2 proteases induces wing and leg elongation. Matrix remodeling does not occur in the haltere, a limb that fails to elongate. Limb elongation is made anisotropic by planar polarized Myosin-II, which drives convergent extension along the proximal-distal axis. Subsequently, Myosin-II relocalizes to lateral membranes to accelerate columnar-to-cuboidal transition and isotropic tissue expansion. Thus, matrix remodeling induces dynamic changes in actomyosin contractility to drive epithelial morphogenesis in three dimensions.

Juvenile hormone and 20-hydroxyecdysone coordinately control the developmental timing of matrix metalloproteinase-induced fat body cell dissociation

Tissue remodeling is a crucial process in animal development and disease progression. Coordinately controlled by the two main insect hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E), tissues are remodeled context-specifically during insect metamorphosis. We previously discovered that two matrix metalloproteinases (Mmps) cooperatively induce fat body cell dissociation in Drosophila However, the molecular events involved in this Mmp-mediated dissociation are unclear. Here we report that JH and 20E coordinately and precisely control the developmental timing of Mmp-induced fat body cell dissociation. We found that during the larval-prepupal transition, the anti-metamorphic factor Kr-h1 transduces JH signaling, which directly inhibited Mmp expression and activated expression of tissue inhibitor of metalloproteinases (timp) and thereby suppressed Mmp-induced fat body cell dissociation. We also noted that upon a decline in the JH titer, a prepupal peak of 20E suppresses Mmp-induced fat body cell dissociation through the 20E primary-response genes, E75 and Blimp-1, which inhibited expression of the nuclear receptor and competence factor βftz-F1 Moreover, upon a decline in the 20E titer, βftz-F1 expression was induced by the 20E early-late response gene DHR3, and then βftz-F1 directly activated Mmp expression and inhibited timp expression, causing Mmp-induced fat body cell dissociation during 6-12 h after puparium formation. In conclusion, coordinated signaling via JH and 20E finely tunes the developmental timing of Mmp-induced fat body cell dissociation. Our findings shed critical light on hormonal regulation of insect metamorphosis.

Chikungunya virus dissemination from the midgut of Aedes aegypti is associated with temporal basal lamina degradation during bloodmeal digestion

In the mosquito, the midgut epithelium is the initial tissue to become infected with an arthropod-borne virus (arbovirus) that has been acquired from a vertebrate host along with a viremic bloodmeal. Following its replication in midgut epithelial cells, the virus needs to exit the midgut and infect secondary tissues including the salivary glands before it can be transmitted to another vertebrate host. The viral exit mechanism from the midgut, the midgut escape barrier (MEB), is poorly understood although it is an important determinant of mosquito vector competence for arboviruses. Using chikungunya virus (CHIKV) as a model in Aedes aegypti, we demonstrate that the basal lamina (BL) of the extracellular matrix (ECM) surrounding the midgut constitutes a potential barrier for the virus. The BL, predominantly consisting of collagen IV and laminin, becomes permissive during bloodmeal digestion in the midgut lumen. Bloodmeal digestion, BL permissiveness, and CHIKV dissemination are coincident with increased collagenase activity, diminished collagen IV abundance, and BL shredding in the midgut between 24–32 h post-bloodmeal. This indicates that there may be a window-of-opportunity during which the MEB in Ae. aegypti becomes permissive for CHIKV. Matrix metalloproteinases (MMPs) are the principal extracellular endopeptidases responsible for the degradation/remodeling of the ECM including the BL. We focused on Ae. aegypti (Ae)MMP1, which is expressed in midgut epithelial cells, is inducible upon bloodfeeding, and shows collagenase (gelatinase) activity. However, attempts to inhibit AeMMP activity in general or specifically that of AeMMP1 did not seem to affect its function nor produce an altered midgut escape phenotype. As an alternative, we silenced and overexpressed the Ae. aegyptitissue inhibitor of metalloproteinases (AeTIMP) in the mosquito midgut. AeTIMP was highly upregulated in the midgut during bloodmeal digestion and was able to inhibit MMP activity in vitro. Bloodmeal-inducible, midgut-specific overexpression of AeTIMP or its expression via a recombinant CHIKV significantly increased midgut dissemination rates of the virus. Possibly, AeTIMP overexpression affected BL degradation and/or restoration thereby increasing the midgut dissemination efficiency of the virus.

The biological nature of the midgut escape barrier in insects for arthropod-borne viruses has been a mystery for decades. Here we show that the basal lamina (BL) surrounding the mosquito midgut acts as a barrier for chikungunya virus, an alphavirus, which has emerged in the New World hemisphere around three years ago. The barrier became permissive for the virus during digestion of a viremic bloodmeal inside the midgut lumen. Concurrent with BL permissiveness, we observed that collagen IV, a major component of the BL became temporally degraded while the BL was visibly damaged. Based on previous findings, we hypothesized that matrix metalloproteinases such as Ae. aegypti (Ae)MMP1 may be involved in BL degradation. We confirmed that recombinant AeMMP1 exhibited strong gelatinase activity, which was profoundly reduced when recombinant AeMMP1 interacted in vitro with the recombinant Ae. aegypti tissue inhibitor of metalloproteinases (AeTIMP). When transgenically overexpressing AeTIMP in an attempt to temporally inhibit general MMP activity in the mosquito midgut, we observed that the dissemination efficiency of chikungunya virus became significantly increased, while its midgut infection was not affected. It is possible that AeTIMP overexpression affected BL degradation/restoration permitting increased quantities of virus to escape from the midgut.

Secreted tissue inhibitor of matrix metalloproteinase restricts trans-synaptic signaling to coordinate synaptogenesis

Synaptogenesis is coordinated by trans-synaptic signals that traverse the specialized synaptomatrix between presynaptic and postsynaptic cells. Matrix metalloproteinase (Mmp) activity sculpts this environment, balanced by secreted tissue inhibitors of Mmp (Timp). Here, we use the simplified Drosophila melanogaster matrix metalloproteome to test the consequences of eliminating all Timp regulatory control of Mmp activity at the neuromuscular junction (NMJ). Using in situ zymography, we find Timp limits Mmp activity at the NMJ terminal and shapes extracellular proteolytic dynamics surrounding individual synaptic boutons. In newly generated timp null mutants, NMJs exhibit architectural overelaboration with supernumerary synaptic boutons. With cell-targeted RNAi and rescue studies, we find that postsynaptic Timp limits presynaptic architecture. Functionally, timp null mutants exhibit compromised synaptic vesicle cycling, with activity that is lower in amplitude and fidelity. NMJ defects manifest in impaired locomotor function. Mechanistically, we find that Timp limits BMP trans-synaptic signaling and the downstream synapse-to-nucleus signal transduction. Pharmacologically restoring Mmp inhibition in timp null mutants corrects bone morphogenetic protein (BMP) signaling and synaptic properties. Genetically restoring BMP signaling in timp null mutants corrects NMJ structure and motor function. Thus, Timp inhibition of Mmp proteolytic activity restricts BMP trans-synaptic signaling to coordinate synaptogenesis.

Matrix Metalloproteinases are required for membrane motility and lumenogenesis during Drosophila heart development

Matrix Metalloproteinases (Mmps) degrade glycoproteins and proteoglycans of the extracellular matrix (ECM) or cell surface and are crucial for morphogenesis. Mmps and their inhibitors are expressed during early stages of cardiac development in vertebrates and expression is altered in multiple congenital cardiomyopathies such as cardia bifida. Drosophila genome encodes two copies of Mmps, Mmp1 and Mmp2 whereas in humans up to 25 Mmps have been identified with overlapping functions. We investigated the role of Mmps during embryonic heart development in Drosophila, a process which is morphogenetically similar to early heart tube formation in vertebrates. We demonstrate that the two Mmps in Drosophila have distinct and overlapping roles in cell motility, cell adhesion and cardiac lumenogenesis. We determined that Mmp1 and Mmp2 promote Leading Edge membrane dynamics of cardioblasts during collective migration. Mmp2 is essential for cardiac lumen formation, and mutants generate a cardia bifida phenotype. Mmp1 is required for luminal expansion. Mmp1 and Mmp2 both localise to the basal domains of cardiac cells, however, occupy non-overlapping domains apically. Mmp1 and Mmp2 regulate the proteoglycan composition and size of the apical and basal ECM, yet only Mmp2 is required to restrict ECM assembly to the lumen. Mmp1 negatively regulates the size of the adhesive Cadherin cell surface domain, whereas in a complementary fashion, Mmp2 negatively regulates the size of the Integrin-ECM domain and thereby prescribes the domain to establish and restrict Slit morphogen signalling. Inhibition of Mmp activity through ectopic expression of Tissue Inhibitor of Metalloproteinase in the ectoderm blocks lumen formation. Therefore, Mmp expression and function identifies ECM differentiation and remodelling as a key element for cell polarisation and organogenesis.

Synaptic roles for phosphomannomutase type 2 in a new Drosophila congenital disorder of glycosylation disease model

Congenital disorders of glycosylation (CDGs) constitute a rapidly growing family of human diseases resulting from heritable mutations in genes driving the production and modification of glycoproteins. The resulting symptomatic hypoglycosylation causes multisystemic defects that include severe neurological impairments, revealing a particularly critical requirement for tightly regulated glycosylation in the nervous system. The most common CDG, CDG-Ia (PMM2-CDG), arises from phosphomannomutase type 2 (PMM2) mutations. Here, we report the generation and characterization of the first Drosophila CDG-Ia model. CRISPR-generated pmm2-null Drosophila mutants display severely disrupted glycosylation and early lethality, whereas RNAi-targeted knockdown of neuronal PMM2 results in a strong shift in the abundance of pauci-mannose glycan, progressive incoordination and later lethality, closely paralleling human CDG-Ia symptoms of shortened lifespan, movement impairments and defective neural development. Analyses of the well-characterized Drosophila neuromuscular junction (NMJ) reveal synaptic glycosylation loss accompanied by defects in both structural architecture and functional neurotransmission. NMJ synaptogenesis is driven by intercellular signals that traverse an extracellular synaptomatrix and are co-regulated by glycosylation and matrix metalloproteinases (MMPs). Specifically, trans-synaptic signaling by the Wnt protein Wingless (Wg) depends on the heparan sulfate proteoglycan (HSPG) co-receptor Dally-like protein (Dlp), which is regulated by synaptic MMP activity. Loss of synaptic MMP2, Wg ligand, Dlp co-receptor and downstream trans-synaptic signaling occurs with PMM2 knockdown. Taken together, this Drosophila CDG disease model provides a new avenue for the dissection of cellular and molecular mechanisms underlying neurological impairments and is a means by which to discover and test novel therapeutic treatment strategies.

Drosophila Collection: This work generates a new Drosophila congenital disorder of glycosylation model for the most common disease category, caused by phosphomannomutase-2 mutation, and reveals a synaptic mechanism underlying associated neurological impairments.

ECM-Regulator timp Is Required for Stem Cell Niche Organization and Cyst Production in the Drosophila Ovary

The extracellular matrix (ECM) is a pivotal component adult tissues and of many tissue-specific stem cell niches. It provides structural support and regulates niche signaling during tissue maintenance and regeneration. In many tissues, ECM remodeling depends on the regulation of MMP (matrix metalloproteinase) activity by inhibitory TIMP (tissue inhibitors of metalloproteinases) proteins. Here, we report that the only Drosophila timp gene is required for maintaining the normal organization and function of the germline stem cell niche in adult females. timp mutant ovaries show reduced levels of both Drosophila Collagen IV α chains. In addition, tissue stiffness and the cellular organization of the ovarian niche are affected in timp mutants. Finally, loss of timp impairs the ability of the germline stem cell niche to generate new cysts. Our results demonstrating a crucial role for timp in tissue organization and gamete production thus provide a link between the regulation of ECM metabolism and tissue homeostasis.

The extracellular matrix (ECM) offers signals and support to stem cell niches, local microenvironments that provide these cells with necessary factors for their survival. The ECM also helps shaping and maintaining tissues and organs in adult animals. Because the repair of damaged tissue or the replenishment of cell lineages in functional organs requires significant cellular rearrangements, ECM remodeling has to be tightly coordinated with stem cell niche activity. By studying Timp, a regulator of ECM remodeling, we have discovered that the Drosophila timp gene is required to maintain ECM composition and biophysical properties and the organization of the female germline stem cell niche. Because loss of timp prevents proper gamete production in experimental ovaries, our results thus link ECM metabolism and tissue homeostasis.

Two classes of matrix metalloproteinases reciprocally regulate synaptogenesis

Synaptogenesis requires orchestrated intercellular communication between synaptic partners, with trans-synaptic signals necessarily traversing the extracellular synaptomatrix separating presynaptic and postsynaptic cells. Extracellular matrix metalloproteinases (Mmps) regulated by secreted tissue inhibitors of metalloproteinases (Timps), cleave secreted and membrane-associated targets to sculpt the extracellular environment and modulate intercellular signaling. Here, we test the roles of Mmp at the neuromuscular junction (NMJ) model synapse in the reductionist Drosophila system, which contains just two Mmps (secreted Mmp1 and GPI-anchored Mmp2) and one secreted Timp. We found that all three matrix metalloproteome components co-dependently localize in the synaptomatrix and show that both Mmp1 and Mmp2 independently restrict synapse morphogenesis and functional differentiation. Surprisingly, either dual knockdown or simultaneous inhibition of the two Mmp classes together restores normal synapse development, identifying a reciprocal suppression mechanism. The two Mmp classes co-regulate a Wnt trans-synaptic signaling pathway modulating structural and functional synaptogenesis, including the GPI-anchored heparan sulfate proteoglycan (HSPG) Wnt co-receptor Dally-like protein (Dlp), cognate receptor Frizzled-2 (Frz2) and Wingless (Wg) ligand. Loss of either Mmp1 or Mmp2 reciprocally misregulates Dlp at the synapse, with normal signaling restored by co-removal of both Mmp classes. Correcting Wnt co-receptor Dlp levels in both Mmp mutants prevents structural and functional synaptogenic defects. Taken together, these results identify an Mmp mechanism that fine-tunes HSPG co-receptor function to modulate Wnt signaling to coordinate synapse structural and functional development.

The orthologous Tbx transcription factors Omb and TBX2 induce epithelial cell migration and extrusion in vivo without involvement of matrix metalloproteinases

The transcription factors TBX2 and TBX3 are overexpressed in various human cancers. Here, we investigated the effect of overexpressing the orthologous Tbx genes Drosophila optomotor-blind (omb) and human TBX2 in the epithelium of the Drosophila wing imaginal disc and observed two types of cell motility. Omb/TBX2 overexpressing cells could move within the plane of the epithelium. Invasive cells migrated long-distance as single cells retaining or regaining normal cell shape and apico-basal polarity in spite of attenuated apical DE-cadherin concentration. Inappropriate levels of DE-cadherin were sufficient to drive cell migration in the wing disc epithelium. Omb/TBX2 overexpression and reduced DE-cadherin-dependent adhesion caused the formation of actin-rich lateral cell protrusions. Omb/TBX2 overexpressing cells could also delaminate basally, penetratingthe basal lamina, however, without degradation of extracellular matrix. Expression of Timp, an inhibitor of matrix metalloproteases, blocked neither intraepithelial motility nor basal extrusion. Our results reveal an MMP-independent mechanism of cell invasion and suggest a conserved role of Tbx2-related proteins in cell invasion and metastasis-related processes.

A Drosophila Model of Epidermolysis Bullosa Simplex

The blistering skin disorder Epidermolysis bullosa simplex (EBS) results from dominant mutations in K5 or K14 genes, encoding the intermediate filament network of basal epidermal keratinocytes. The mechanisms governing keratin network formation and collapse due to EBS mutations remain incompletely understood. Drosophila lacks cytoplasmic intermediate filaments, providing a ‚null’ environment to examine the formation of keratin networks and determine mechanisms by which mutant keratins cause pathology. Here, we report that ubiquitous co-expression of transgenes encoding wild-type human K14 and K5 resulted in the formation of extensive keratin networks in Drosophila epithelial and non-epithelial tissues, causing no overt phenotype. Similar to mammalian cells, treatment of transgenic fly tissues with phosphatase inhibitors caused keratin network collapse, validating Drosophila as a genetic model system to investigate keratin dynamics. Co-expression of K5 and a K14^R125C mutant that causes the most severe form of EBS resulted in widespread formation of EBS-like cytoplasmic keratin aggregates in epithelial and non-epithelial fly tissues. Expression of K14^R125C/K5 caused semi-lethality; adult survivors developed wing blisters and were flightless due to lack of intercellular adhesion during wing heart development. This Drosophila model of EBS is valuable for the identification of pathways altered by mutant keratins and for development of EBS therapies.

Identification of novel elements of the Drosophila blisterome sheds light on potential pathological mechanisms of several human diseases

Main developmental programs are highly conserved among species of the animal kingdom. Improper execution of these programs often leads to progression of various diseases and disorders. Here we focused on Drosophila wing tissue morphogenesis, a fairly complex developmental program, one of the steps of which – apposition of the dorsal and ventral wing sheets during metamorphosis – is mediated by integrins. Disruption of this apposition leads to wing blistering which serves as an easily screenable phenotype for components regulating this process. By means of RNAi-silencing technique and the blister phenotype as readout, we identify numerous novel proteins potentially involved in wing sheet adhesion. Remarkably, our results reveal not only participants of the integrin-mediated machinery, but also components of other cellular processes, e.g. cell cycle, RNA splicing, and vesicular trafficking. With the use of bioinformatics tools, these data are assembled into a large blisterome network. Analysis of human orthologues of the Drosophila blisterome components shows that many disease-related genes may contribute to cell adhesion implementation, providing hints on possible mechanisms of these human pathologies.

Tissue inhibitor of metalloproteinase gene from pearl oyster Pinctada martensii participates in nacre formation

Tissue inhibitors of metalloproteinases (TIMPs) are nature inhibitors of matrix metalloproteinases and play a vital role in the regulation of extracellular matrix turnover, tissue remodeling and bone formation. In this study, the molecular characterization of TIMP and its potential function in nacre formation was described in pearl oyster Pinctada martensii. The cDNA of TIMP gene in P. martensii (Pm-TIMP) was 901 bp long, containing a 5' untranslated region (UTR) of 51 bp, a 3' UTR of 169 bp, and an open reading fragment (ORF) of 681 bp encoding 226 amino acids with an estimated molecular mass of 23.37 kDa and a theoretical isoelectric point of 5.42; The predicted amino acid sequence had a signal peptide, 13 cysteine residues, a N-terminal domain and a C-terminal domain, similar to that from other species. Amino acid multiple alignment showed Pm-TIMP had the highest (41%) identity to that from Crassostrea gigas. Tissue expression analysis indicated Pm-TIMP was highly expressed in nacre formation related-tissues, including mantle and pearl sac. After decreasing Pm-TIMP gene expression by RNA interference (RNAi) technology in the mantle pallium, the inner nacreous layer of the shells showed a disordered growth. These results indicated that the obtained Pm-TIMP in this study participated in nacre formation.

The Dorsocross T-box transcription factors promote tissue morphogenesis in the Drosophila wing imaginal disc

The Drosophila wing imaginal disc is subdivided into notum, hinge and blade territories during the third larval instar by formation of several deep apical folds. The molecular mechanisms of these subdivisions and the subsequent initiation of morphogenic processes during metamorphosis are poorly understood. Here, we demonstrate that the Dorsocross (Doc) T-box genes promote the progression of epithelial folds that not only separate the hinge and blade regions of the wing disc but also contribute to metamorphic development by changing cell shapes and bending the wing disc. We found that Doc expression was restricted by two inhibitors, Vestigial and Homothorax, leading to two narrow Doc stripes where the folds separating hinge and blade are forming. Doc mutant clones prevented the lateral extension and deepening of these folds at the larval stage and delayed wing disc bending in the early pupal stage. Ectopic Doc expression was sufficient to generate deep apical folds by causing a basolateral redistribution of the apical microtubule web and a shortening of cells. Cells of both the endogenous blade/hinge folds and of folds elicited by ectopic Doc expression expressed Matrix metalloproteinase 2 (Mmp2). In these folds, integrins and extracellular matrix proteins were depleted. Overexpression of Doc along the blade/hinge folds caused precocious wing disc bending, which could be suppressed by co-expressing MMP2RNAi.

Dissection of Drosophila MTF-1 reveals a domain for differential target gene activation upon copper overload vs. copper starvation

Metal-responsive transcription factor-1 (MTF-1) is a zinc finger protein conserved from mammals to insects. It mediates protection against heavy metal load by activating the expression of metallothionein and other genes. In Drosophila, MTF-1 serves a dual function in that it not only helps to protect against heavy metal load but also induces the expression of Ctr1B, the gene for an intestinal copper importer, upon copper starvation. By dissecting Drosophila MTF-1 function, we have identified determinants for nuclear import and export, and characterized a phosphorylation site mutant (T127A) that differentially affects MTF-1 target genes. Further, by generating a series of fusion proteins with the heterologous DNA binding domain of Gal4 we identified a strong, constitutive activation domain in the central region of MTF-1 (aa 352-540). By contrast, an extended fusion protein that includes MTF-1's C-terminus (aa 352-791) is not active in standard conditions but induced by copper load. The paramount regulatory importance of the C-terminal part, that harbors a cysteine-rich "metallothionein-like" domain, was corroborated by different experiments. Transgenic flies expressing C-terminally truncated MTF-1 variants displayed high constitutive transcription of both, the genes for metallothioneins and the copper importer Ctr1B. The indiscriminate activation of these genes that are normally induced under opposite conditions of copper load and copper starvation manifested itself in a shortened lifespan, crippled wings, and female sterility.

A secreted MMP is required for reepithelialization during wound healing

Matrix metalloproteinases (MMPs) are extracellular proteases highly expressed at wound sites. However, the precise function of MMPs during reepithelialization in vivo has been elusive in mammalian models because of the high level of redundancy among the 24 mammalian MMPs. For this reason we used Drosophila melanogaster, whose genome encodes only two MMPs-one secreted type (Mmp1) and one membrane-anchored type (Mmp2)-to study the function and regulation of the secreted class of MMPs in vivo. In the absence of redundancy, we found that the Drosophila secreted MMP, Mmp1, is required in the epidermis to facilitate reepithelialization by remodeling the basement membrane, promoting cell elongation and actin cytoskeletal reorganization, and activating extracellular signal-regulated kinase signaling. In addition, we report that the jun N-terminal kinase (JNK) pathway upregulates Mmp1 expression after wounding, but that Mmp1 is expressed independent of the JNK pathway in unwounded epidermis. When the JNK pathway is ectopically activated to overexpress Mmp1, the rate of healing is accelerated in an Mmp1-dependent manner. A primary function of Mmp1, under the control of the JNK pathway, is to promote basement membrane repair, which in turn may permit cell migration and the restoration of a continuous tissue.

The tissue inhibitors of metalloproteinases (TIMPs): an ancient family with structural and functional diversity

Tissue inhibitors of metalloproteinases (TIMPs) are widely distributed in the animal kingdom and the human genome contains four paralogous genes encoding TIMPs 1 to 4. TIMPs were originally characterized as inhibitors of matrix metalloproteinases (MMPs), but their range of activities has now been found to be broader as it includes the inhibition of several of the disintegrin-metalloproteinases, ADAMs and ADAMTSs. TIMPs are therefore key regulators of the metalloproteinases that degrade the extracellular matrix and shed cell surface molecules. Structural studies of TIMP-MMP complexes have elucidated the inhibition mechanism of TIMPs and the multiple sites through which they interact with target enzymes, allowing the generation of TIMP variants that selectively inhibit different groups of metalloproteinases. Engineering such variants is complicated by the fact that TIMPs can undergo changes in molecular dynamics induced by their interactions with proteases. TIMPs also have biological activities that are independent of metalloproteinases; these include effects on cell growth and differentiation, cell migration, anti-angiogenesis, anti- and pro-apoptosis, and synaptic plasticity. Receptors responsible for some of these activities have been identified and their signaling pathways have been investigated. A series of studies using mice with specific TIMP gene deletions has illuminated the importance of these molecules in biology and pathology.

Tissue inhibitors of metalloproteinases in cell signaling: metalloproteinase-independent biological activities

Over the past 20 years, the tissue inhibitors of metalloproteinases (TIMPs) have been implicated in direct regulation of cell growth and apoptosis. However, the mechanisms of these effects have been controversial. Recent work by several laboratories has identified specific signaling pathways and cell surface binding partners for members of the TIMP family. TIMP-2 binding to the integrin alpha(3)beta(1) is the first description of a cell surface receptor for a TIMP family member. TIMP-2 has been shown to induce gene expression, to promote G(1) cell cycle arrest, and to inhibit cell migration. TIMP-1 binding to CD63 inhibits cell growth and apoptosis. These new findings suggest that TIMPs are multifunctional and can act either directly through cell surface receptors or indirectly through modulation of protease activity to direct cell fate. The emerging concept is that TIMPs function in a contextual fashion so that the mechanism of action depends on the tissue microenvironment.

The tumor microenvironment: regulation by MMP-independent effects of tissue inhibitor of metalloproteinases-2

Proteolytic remodeling of the extracellular matrix is an important component of disease progression in many chronic disease states and is the initiating event in the formation of the tumor microenvironment in cancer. It is the balance of extracellular matrix degrading enzymes, the matrix metalloproteinases (MMPs) and their endogenous inhibitors that determine the extent of tissue remodeling. Unchecked MMP activity can result in significant tissue damage, facilitate disease progression and is associated with host responses to pathologic injury such as angiogenesis and inflammation. The tissue inhibitors of metalloproteinases (TIMPs) have been shown to regulate MMP activity. However, recent findings demonstrate that the tissue inhibitor of metalloproteinases-2 (TIMP-2) inhibits the mitogenic response of human microvascular endothelial cells to growth factors, such as VEGF-A and FGF-2 in vitro and angiogenesis in vivo. The mechanism of this effect is independent of metalloproteinase inhibition. Our lab is the first to demonstrate a cell-surface signaling receptor for a member of the TIMP family and suggest that TIMP-2 functions to regulate cellular responses to growth factors. These new findings are discussed in terms of a model of TIMP-2 regulation of cellular functions in the tumor microenvironment.

Remodeling the model organism: matrix metalloproteinase functions in invertebrates

The matrix metalloproteinase (MMP) family of extracellular proteases is conserved throughout the animal kingdom. Studies of invertebrate MMPs have demonstrated they are involved in tissue remodeling. In Drosophila, MMPs are required for histolysis, tracheal growth, tissue invasion, axon guidance, and dendritic remodeling. Recent work demonstrates that MMPs also participate in Drosophila tumor invasion. In Caenorhabditis elegans an MMP is involved in anchor cell invasion; a Hydra MMP is important for regeneration and maintaining cell identity; and a sea urchin MMP degrades matrix to allow hatching. In worms and in flies, MMPs are regulated by the JNK pathway.

Matrix metalloproteinases and the regulation of tissue remodelling

Matrix metalloproteinases (MMPs) were discovered because of their role in amphibian metamorphosis, yet they have attracted more attention because of their roles in disease. Despite intensive scrutiny in vitro, in cell culture and in animal models, the normal physiological roles of these extracellular proteases have been elusive. Recent studies in mice and flies point to essential roles of MMPs as mediators of change and physical adaptation in tissues, whether developmentally regulated, environmentally induced or disease associated.

Integrin-ECM interactions regulate the changes in cell shape driving the morphogenesis of the Drosophila wing epithelium

During development, morphogenesis involves migration and changes in the shape of epithelial sheets, both of which require coordination of cell adhesion. Thus, while modulation of integrin-mediated adhesion to the ECM regulates epithelial motility, cell-cell adhesion via cadherins controls the remodelling of epithelial sheets. We have used the Drosophila wing epithelium to demonstrate that cell-ECM interactions mediated by integrins also regulate the changes in cell shape that underly epithelial morphogenesis. We show that integrins control the transitions from columnar to cuboidal cell shape underlying wing formation, and we demonstrate that eliminating the ECM has the same effect on cell shape as inhibiting integrin function. Furthermore, lack of integrin activity also induces detachment of the basal lamina and failure to assemble the basal matrix. Hence, we propose that integrins control epithelial cell shape by mediating adherence of these cells to the ECM. Finally, we show that the ECM has an instructive rather than a structural role, because inhibition of Raf reverses the cell shape changes caused by perturbing integrins.

Basement membrane remodeling is essential for Drosophila disc eversion and tumor invasion

Organ and tissue integrity is often maintained in animals by a specialized extracellular matrix structure called the basement membrane (BM). Accumulated evidence indicates that BM remodeling occurs during development and tumor invasion. Although the BM organizes and functions at the organ level, most past studies have explored its biochemical and in vitro properties. In this study, we monitor the BM in vivo during developmental tissue invasion for disc eversion and tumor invasion in Drosophila and modulate BM integrity with genetic alterations affecting either the whole organism or the targeted discs or tumors. We observe that the degradation of BM by the discs or the tumors is an early event during invasion processes and that preventing BM degradation completely blocks both tissue and tumor invasion, indicating that modulation of BM is essential for developmental and tumor invasion. Furthermore, elements of the invasion machinery, including JNK-induced matrix metalloproteinase (MMP) expression, are shared by both disc eversion and tumor invasion processes. Moreover, we show that although expression of MMP inhibitor, TIMP, is sufficient to halt developmental invasion, inhibition of proteases by both TIMP and RECK are required to block tumor invasion. These data suggest that tumor cells have a more robust invasion mechanism and could acquire metastatic behavior by co-opting developmental invasion programs. This type of co-option may be a general feature contributing to the progression of tumors. Finally, although past efforts using MMP inhibitors have not yielded much success, our results strongly argue that BM modulation could be a critical target for cancer therapy.

Tissue remodeling during maturation of the Drosophila wing

The final step in morphogenesis of the adult fly is wing maturation, a process not well understood at the cellular level due to the impermeable and refractive nature of cuticle synthesized some 30 h prior to eclosion from the pupal case. Advances in GFP technology now make it possible to visualize cells using fluorescence after cuticle synthesis is complete. We find that, between eclosion and wing expansion, the epithelia within the folded wing begin to delaminate from the cuticle and that delamination is complete when the wing has fully expanded. After expansion, epithelial cells lose contact with each other, adherens junctions are disrupted, and nuclei become pycnotic. The cells then change shape, elongate, and migrate from the wing into the thorax. During wing maturation, the Timp gene product, tissue inhibitor of metalloproteinases, and probably other components of an extracellular matrix are expressed that bond the dorsal and ventral cuticular surfaces of the wing following migration of the cells. These steps are dissected using the batone and Timp genes and ectopic expression of alphaPS integrin, inhibitors of Armadillo/beta-catenin nuclear activity and baculovirus caspase inhibitor p35. We conclude that an epithelial-mesenchymal transition is responsible for epithelial delamination and dissolution.

An MMP liberates the Ninjurin A ectodomain to signal a loss of cell adhesion

Matrix metalloproteinases (MMPs) are important for developmental tissue remodeling and for the inflammatory response. Although the vertebrate MMP family is large and functionally redundant, the fruitfly Drosophila melanogaster has only two MMPs, both essential genes. Our previous work demonstrated that Mmp1 is required for growth of the tracheal system, and we suggested that the mutant phenotype resulted from aberrant persistence of cell adhesion to the extracellular matrix. Here we report the identification of NijA, a transmembrane protein whose vertebrate homologs regulate cell adhesion, as a two-hybrid binding partner for Mmp1. The binding of Mmp1 and NijA was confirmed by coimmunoprecipitation of endogenous proteins from flies, and the endogenous proteins were found to colocalize at the tracheal cell surface in larvae. When NijA is expressed in S2 cells, they lose adhesion to surfaces; this adhesion-loss phenotype is dependent on the expression and catalytic activity of Mmp1. Our data indicate that Mmp1 releases the N-terminal extracellular domain of NijA. This liberated ectodomain promotes the loss of cell adhesion in a cell-nonautonomous manner. We suggest that tracheal cell adhesion is regulated by a novel mechanism utilizing an MMP and a ninjurin family member.

Cutting Edge: Tissue Inhibitor of Metalloproteinase 3 Regulates TNF-Dependent Systemic Inflammation

Host response to infectious agents must be rapid and powerful. One mechanism is the release of presynthesized membrane-bound TNF. TNF shedding is mediated by TNF-alpha converting enzyme, which is selectively inhibited by the tissue inhibitor of metalloproteinase 3 (TIMP3). We show that loss of TIMP3 impacts innate immunity by dysregulating cleavage of TNF and its receptors. Cultured timp3-/- macrophages release more TNF in response to LPS than wild-type macrophages. In timp3-/- mice, LPS causes serum levels of TNF and its receptors to rise more rapidly and remain higher compared with wild-type mice. The altered kinetics of ligand and receptor shedding enhances TNF signaling in timp3-/- mice, indicated by elevated serum IL-6. Physiologically, timp3-/- mice are more susceptible to LPS-induced mortality. Ablation of the TNF receptor gene p55 (Tnfrsf1a) or treatment with a synthetic metalloproteinase inhibitor rescues timp3-/- mice. Thus, TIMP3 is essential for normal innate immune function.

TIMP-2: an endogenous inhibitor of angiogenesis

Remodeling of the extracellular matrix--regulated by the matrix metalloproteinases (MMPs) and their endogenous inhibitors--is an important component of disease progression in many chronic disease states. Unchecked MMP activity can result in significant tissue damage, facilitate disease progression and is associated with host responses to pathologic injury, such as angiogenesis. The tissue inhibitors of metalloproteinases (TIMPs) have been shown to regulate MMP activity. However, recent findings demonstrate that an MMP-independent effect of TIMP-2 inhibits the mitogenic response of human microvascular endothelial cells to growth factors. This is the first demonstration of a cell-surface signaling receptor for a member of the TIMP family and suggests that TIMP-2 functions to regulate cellular responses to growth factors. These new findings are integrated in a comprehensive model of TIMP-2 function in tissue homeostasis.

Flies lacking all synapsins are unexpectedly healthy but are impaired in complex behaviour

Vertebrate synapsins are abundant synaptic vesicle phosphoproteins that have been proposed to fine-regulate neurotransmitter release by phosphorylation-dependent control of synaptic vesicle motility. However, the consequences of a total lack of all synapsin isoforms due to a knock-out of all three mouse synapsin genes have not yet been investigated. In Drosophila a single synapsin gene encodes several isoforms and is expressed in most synaptic terminals. Thus the targeted deletion of the synapsin gene of Drosophila eliminates the possibility of functional knock-out complementation by other isoforms. Unexpectedly, synapsin null mutant flies show no obvious defects in brain morphology, and no striking qualitative changes in behaviour are observed. Ultrastructural analysis of an identified 'model' synapse of the larval nerve muscle preparation revealed no difference between wild-type and mutant, and spontaneous or evoked excitatory junction potentials at this synapse were normal up to a stimulus frequency of 5 Hz. However, when several behavioural responses were analysed quantitatively, specific differences between mutant and wild-type flies are noted. Adult locomotor activity, optomotor responses at high pattern velocities, wing beat frequency, and visual pattern preference are modified. Synapsin mutant flies show faster habituation of an olfactory jump response, enhanced ethanol tolerance, and significant defects in learning and memory as measured using three different paradigms. Larval behavioural defects are described in a separate paper. We conclude that Drosophila synapsins play a significant role in nervous system function, which is subtle at the cellular level but manifests itself in complex behaviour.

Drosophila TIMP is a potent inhibitor of MMPs and TACE: similarities in structure and function to TIMP-3

The four tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors that regulate the activity of matrix metalloproteinases (MMPs) and certain disintegrin and metalloproteinase (ADAM) family proteases in mammals. The protease inhibitory activity is present in the N-terminal domains of TIMPs (N-TIMPs). In this work, the N-terminal inhibitory domain of the only TIMP produced by Drosophila (dN-TIMP) was expressed in Escherichia coli and folded in vitro. The purified recombinant protein is a potent inhibitor of human MMPs, including membrane-type 1-MMP, although it lacks a disulfide bond that is conserved in all other known N-TIMPs. Titration with the catalytic domain of human MMP-3 [MMP-3(DeltaC)] showed that dN-TIMP prepared by this method is correctly folded and fully active. dN-TIMP also inhibits, in vitro, the activity of the only two MMPs of Drosophila, dm1- and dm2-MMPs, indicating that the Drosophila TIMP is an endogenous inhibitor of the Drosophila MMPs. dN-TIMP resembles mammalian N-TIMP-3 in strongly inhibiting human tumor necrosis factor-alpha-converting enzyme (TACE/ADAM17) but is a weak inhibitor of human ADAM10. Models of the structures of dN-TIMP and N-TIMP-3 are strikingly similar in surface charge distribution, which may explain their functional similarity. Although the gene duplication events that led to the evolutionary development of the four mammalian TIMPs might be expected to be associated with functional specialization, Timp-3 appears to have conserved most of the functions of the ancestral TIMP gene.

Drosophila matrix metalloproteinases are required for tissue remodeling, but not embryonic development

The matrix metalloproteinase (MMP) family is heavily implicated in many diseases, including cancer. The developmental functions of these genes are not clear, however, because the >20 mammalian MMPs can be functionally redundant. Drosophila melanogaster has only two MMPs, which are expressed in embryos in distinct patterns. We created mutations in both genes: Mmp1 mutants have defects in larval tracheal growth and pupal head eversion, and Mmp2 mutants have defects in larval tissue histolysis and epithelial fusion during metamorphosis; neither is required for embryonic development. Double mutants also complete embryogenesis, and these represent the first time, to our knowledge, that all MMPs have been disrupted in any organism. Thus, MMPs are not required for Drosophila embryonic development, but, rather, for tissue remodeling.

Compartmentalization of central neurons in Drosophila: a new strategy of mosaic analysis reveals localization of presynaptic sites to specific segments of neurites

Synaptogenesis in the CNS has received far less attention than the development of neuromuscular synapses, although only central synapses allow the study of neuronal postsynaptic mechanisms and display a greater variety of structural and functional features. This neglect is attributable mainly to the enormous complexity of the CNS, which makes the visualization of individual synapses on defined neuronal processes very difficult. We overcome this obstacle and demonstrate by confocal microscopy the specific arrangement of output synapses on individual neurites. These studies are performed via genetic mosaic strategies in the CNS of the fruitfly Drosophila melanogaster. First, we use targeted expression of synaptic proteins by the UAS/Gal4 system. Second, we apply a newly developed transplantation-based mosaic strategy that takes advantage of the intrinsic regulation and localization of synaptic proteins in single-cell clones. We propose the existence of three distinct neuritic compartments: (1) primary neurites that appear to form the main transport pathways and are mostly void of output synapses, (2) neuritic compartments that contain output synapses, and (3) neuritic compartments that are postsynaptic in nature. In addition we show that mutations of the kakapo gene have no obvious effect on the distribution of output synapses in the CNS, whereas neuromuscular synapses are severely reduced. This suggests that synaptogenic mechanisms in the CNS might differ from those at neuromuscular junctions.

Metalloproteinase inhibitors: biological actions and therapeutic opportunities

Tissue inhibitors of metalloproteinases (TIMPs) are the major cellular inhibitors of the matrix metalloproteinase (MMP) sub-family, exhibiting varying efficacy against different members, as well as different tissue expression patterns and modes of regulation. Other proteins have modest inhibitory activity against some of the MMPs, including domains of netrins, the procollagen C-terminal proteinase enhancer (PCPE), the reversion-inducing cysteine-rich protein with Kazal motifs (RECK), and tissue factor pathway inhibitor (TFPI-2), but their physiological significance is not at all clear. Alpha2-macroglobulin, thrombospondin-1 and thrombospondin-2 can bind to some MMPs and act as agents for their removal from the extracellular environment. In contrast, few effective inhibitors of other members of the metzincin family, the astacins or the distintegrin metalloproteinases, ADAMs have been identified. Many of these MMP inhibitors, including the TIMPs, possess other biological activities which may not be related to their inhibitory capacities. These need to be thoroughly characterized in order to allow informed development of MMP inhibitors as potential therapeutic agents. Over activity of MMPs has been implicated in many diseases, including those of the cardiovascular system, arthritis and cancer. The development of synthetic small molecule inhibitors has been actively pursued for some time, but the concept of the use of the natural inhibitors, such as the TIMPs, in gene based therapies is being assessed in animal models and should provide useful insights into the cell biology of degradative diseases.

Cg-TIMP, an inducible tissue inhibitor of metalloproteinase from the Pacific oyster Crassostrea gigas with a potential role in wound healing and defense mechanisms(1)

We have cloned and characterized a cDNA encoding Cg-TIMP, the first tissue inhibitor of metalloproteinase identified in mollusks. The isolated cDNA encodes a protein of 221 residues that has a domain organization similar to that of vertebrate TIMPs including a signal sequence, and the 12 cysteines characteristic of the TIMP signature. Analysis of Cg-TIMP expression in adult oyster tissues, by Northern blot and in situ hybridization, indicates that Cg-TIMP was only expressed in hemocytes which are the key components of defense mechanisms in mollusks. We also observed that Cg-TIMP mRNA accumulated during shell damage and bacterial challenge. This pattern of expression suggests that Cg-TIMP may be an important factor in wound healing and defense mechanisms.