CEACAM1 (CarcinoEmbryonic Antigen-related Cell Adhesion Molecule 1), is expressed at the surface of new blood vessels of tissues undergoing proliferation. In human tumors, CEACAM1 expression is associated with early stages of angiogenesis. CEACAM1 is a known pro-angiogenic factor, increasing VEGF activity in vivo; however, the role of CEACAM1 in angiogenesis warrants further investigation. Excisional wounds were used as an experimental model, as many of the processes that occur in healing wounds also take place in tumor growth - epithelial hyperproliferation, inflammation, and angiogenesis. 6-mm diameter skin wounds were inflicted on the dorsal side of Ceacam1-/- and wild-type mice. Upon histological examination, it was shown that wound healing in Ceacam1-/- mice is indeed delayed. In Ceacam1-/- wounds, re-epithelialization is decreased significantly at 3 and 7 days post-injury. Inflammation in Ceacam1-/- wounds is also altered: the infiltration of F4/80+ macrophages into the wound at 7 and 10 days post-injury is significantly decreased, as is the influx of mast cells at 7 days post-injury. Vascular density in Ceacam1-/- wounds is also significantly decreased at 7 and 10 days post-injury; however, VEGF expression in the wound is not altered. The results of this study not only confirm CEACAM1's role as an important factor in angiogenesis, but further expand its role as a mediator of epithelial growth and inflammation. / CEACAM1 (CarcinoEmbryonic Antigen-related Cell Adhesion Molecule 1) est exprimé à la surface de nouveaux vaisseaux sanguins de tissus en prolifération ou de tumeurs humaines, et est associé aux stades précoces de l'angiogenèse. De plus, CEACAM1 semble être un puissant facteur angiogénique en potentialisant l'activité du VEGF in vivo. Malgré de nombreuses observations, le rôle de CEACAM1 dans l'angiogenèse normale reste à définir. Dans ce contexte, nous avons réalisé des essais de cicatrisation cutanée dans des souris Ceacam1-/-. Des plaies de 6 mm ont été effectuées sur le dos des souris. La vitesse de cicatrisation a été suivie sur 10 jours, et les plaies ont été examinées en histologie 3, 7 et 10 jours après l'essai. D'un point de vue macroscopique, la délétion de CEACAM1 n'a pas d'effet sur la cicatrisation des plaies. En revanche, des analyses plus précises en histologie montrent que la cicatrisation des souris Ceacam1 -/- est différée. En effet, le mécanisme de re-épithélisation des plaies des souris Ceacam1 -/- est retardé aux points 3 et 7 jours après blessure. De plus, l'inflammation des plaies des souris Ceacam1 -/- est également affectée : l'infiltration des macrophages F4/80+ au sein des plaies 7 et 10 jours après blessure, ainsi que celle des mastocytes au point 7 jours après blessure sont significativement diminuées. Enfin, la densité vasculaire des plaies Ceacam1-/- est également réduite de façon significative. En revanche, l'expression de VEGF au sein des plaies ne semble pas altérée. Les résultats de cette étude confirment le rôle de CEACAM1 dans l'angiogenèse, mais présentent de façon plus importante CEACAM1 comme un facteur clé dans le mécanisme de cicatrisation des plaies cutanées.

The Met receptor tyrosine kinase was originally identified as a rearranged oncogene, Tpr-Met. Both Met and its ligand, hepatocyte growth factor (HGF) regulate epithelial cell dispersal and morphogenesis and are deregulated in several human tumors. At the onset of this thesis, little was known about the signals that regulate these events. In this thesis I have defined the involvement of the Crk adapter protein in Met-dependent anchorage independent growth, cell spreading, cell dispersal, invasion and morphogenesis. The disruption of focal adhesion signaling in Met transformed fibroblasts is associated with the loss of Crk/p130Cas and Crk/Paxillin complexes. In contrast, Crk associates with Cbl and Gab1 in Met transformed fibroblasts. A role for Crk/Gab1 coupling in anchorage independent growth is proposed based on the retention of these complexes in Met transformed fibroblasts grown in suspension and their ability to enhance JNK activity. Using MDCK epithelial colonies, I demonstrated that mutants of Crk lacking the amino terminal SH3 domain inhibit HGF-stimulated lamellipodia formation, cell spreading and breakdown of adherens junctions. Moreover, when overexpressed, wild type Crk can promote all of these events in the absence of HGF. Consistent with the elevated Rac activity observed in cells overexpressing Crk, the ability of Crk to promote these events is Rac-dependent. The overexpression of Crk results in the formation of a molecular complex containing Crk, Paxillin, GIT2 (an ARF-GAP) and beta-PIX (a Rac exchange factor) that relocalizes to focal complexes in cells at the edge of the colony. The formation of this complex is critical for the ability of Crk to mediate lamellipodia formation and cell spreading, as mutants of Paxillin that fail to associate with Crk or GIT2, or that do not target to focal adhesions, inhibit these processes. Consistent with the involvement of Crk in HGF cell dispersal, the coupling of Gab1 with Crk is requi

Apoptosis is a genetically programmed highly regulated form of cellular suicide that plays an essential role in the development and tissue homeostasis of multicellular organisms. As a variety of pathological states such as cancer, autoimmune and neurodegenerative diseases can be ascribed to the deregulation of the apoptotic program, understanding the molecular mechanisms underlying this process is a necessary first step to therapeutic intervention. The BCL-2 family of proteins is of paramount importance in the regulation of apoptosis through their control of caspases, a family of cysteine proteases responsible for cellular demolition. The p53 tumour suppressor protein is a transcription factor that eliminates potentially dangerous cells via activation of the apoptotic program through the regulation of various genes, including those of the BCL-2 family. I found that BIK, a member of the pro-apoptotic BH3-only class of BCL-2 homologues, is upregulated by p53. Unlike all other BH3-only proteins however, BIK was found to be uniquely localized to membranes of the endoplasmic reticulum. BIK was induced in response to several stress stimuli, including genotoxic stress (radiation; doxorubicin) and over-expression of E1A or p53, but not by ER stress pathways resulting from protein misfolding. Using siRNA technology, I showed that BIK plays a critical role in p53-induced cell death by acting at the ER to trigger Ca2+ release, mitochondrial fission, BAX/BAK activation, cytochrome c release, caspase activation and apoptosis. BIK also stimulated the (BCL-2 inhibited) accumulation and oligomerization of BAK at ER membranes. Cells doubly deficient of both BAX and BAK were resistant to ER Ca2+ release and apoptosis by ectopic expression of both BIK and p20BAP31, suggesting that these multidomain pro-apoptotic BCL-2 proteins may serve as a common checkpoint at the ER for varying modes of stress stimuli. Thus, p53 appears to employ BIK as part of its apopto

Arginine methylation is a post-translational modification occurring in higher eukaryotes that results in the addition of one or two methyl group on the nitrogen in the side chain of arginines. The enzymes responsible for protein arginine methylation have been classified in three groups. Type I enzymes promote the formation of both NG-monomethylated and asymmetric o-NG,NG-dimethylated arginines (aDMA). Type II enzymes catalyze the formation of monomethylated and symmetrical o-N G,N'G-dimethylated arginines (sDMA). The type III enzyme found in yeast catalyzes the monomethylation of the delta-guanidino nitrogen atom of the arginine residue. Although some abundant proteins have been described as being substrates for arginine methyltransferases for some time, there are still few known proteins to bear this modification. The primary goal of the work presented in this thesis was to identify new arginine methylated proteins and functionally characterize the roles of arginine methylation in new cellular processes. First, we generated four arginine methyl-specific antibodies: ASYM24 and ASYM25 are specific for aDMA whereas SYM10 and SYM11 recognize sDMA. Cell extracts were used to purify the protein complexes recognized by each of the four antibodies and the proteins were identified by microcapillary reverse-phase liquid chromatography coupled on line with electrospray ionization tandem mass spectrometry (LC/MS/MS). The analysis of 2 tandem mass spectra for each methyl-specific antibody resulted in the identification of 247 proteins, of which 197 are putatively arginine methylated. / The DNA repair MRE11/RAD50/NBS1 (MRN) complex was purified using one of the aDMA specific antibody. Since a role of protein arginine methylation in DNA damage checkpoint control and DNA repair had not been previously reported we chose to investigate the consequence of MRE11 methylation in DNA damage. Our results show that the MRE11 checkpoint protein is arginine methylated as determined by mass spectrometry and methylarginine-specific antibodies. The glycine-arginine rich (GAR) domain of MRE11 was specifically methylated by protein arginine methyltransferase 1 (PRMT1). Mutation of the arginines within MRE11 GAR domain severely impaired the exonuclease activity of MRE11. Cells treated with methyltransferase inhibitors displayed a DNA damage-resistant DNA synthesis phenotype and prevented the re-localization of the MRN complex to sites of DNA damage. Downregulation of PRMT1 with small interfering RNAs (siRNA) also yielded a damage-resistant DNA synthesis phenotype that was rescued with the methylated MRE11 complex. Taken together, the work presented in this thesis allowed the identification of many new potentially arginine methylated proteins and demonstrated a novel role for arginine methylation in the regulation of DNA repair enzymes and of the intra-S phase DNA damage checkpoint.

Telomeres are protective structures at the end of eukaryotic chromosomes essential for indefinite cell proliferation. Their disruption causes activation of DNA repair pathways, growth arrest and/or cell death. In normal cells telomere shortening during cell division has been proposed to act as a tumor suppressor mechanism to block the proliferation of cells at risk of undergoing malignant transformation. Overcoming this proliferative block by activating a mechanism to maintain telomeres is a necessary requirement for unlimited proliferation and tumor progression. Human cells have two mechanisms for telomere maintenance: a more common one based on telomerase and a rarer one based on recombination called ALT. / Here we report the isolation of an immortal human cell line that maintains short telomeres in the absence of biologically active telomerase and key features of active ALT. Our results suggest that the mechanisms of telomere maintenance in human cells may be more diverse than previously thought and have important implications for the development of anti-cancer strategies based on the inhibition of telomere maintenance. / Due to widespread distribution of telomerase in human tumors and its absence in most normal cells, telomerase is the main target of these anti-cancer strategies. However, targeting telomerase per se or in combination with anti-cancer drugs is not sufficient to trigger rapid cell death of tumor cells. On the other hand, disturbances in telomere capping do not require telomere shortening to induce growth arrest and may act more quickly. Our goal was to investigate the feasibility of a new approach based on the combination of telomere destabilization and chemotherapeutic drugs. Our results show that interfering with telomere maintenance enhances the susceptibility of human tumor cells to anti-cancer drugs independently of their telomere lengths and mechanisms to maintain them. / Finally, given the involvement of telomeres in maintaining genomic stability, we investigated the mechanism by which mutations in the telomerase RNA subunit contribute to autosomal dominant dyskeratosis congenita, a premature ageing disease associated with mutations in the telomerase holoenzyme. Our data strongly indicate that the clinical manifestations of this disease may be caused by telomere shortening due to haploinsufficiency of telomerase activity and provide a direct correlation between disturbances in telomere length maintenance and human disease.

Newly synthesized soluble lysosomal proteins are transported from the Golgi apparatus to the lysosomes by two mannose 6-phosphate receptors. However, the sphingolipid activator protein prosaposin is targeted by the alternative trafficking receptor, sortilin. Prosaposin is the precursor of four lysosomal saposins required for the hydrolysis of sphingolipids. A previous study demonstrated that the removal of its C-terminus abolished the trafficking of prosaposin to the lysosomes. / To identify the sequences and amino acids involved in the interaction of prosaposin to sortilin and its transport to the lysosomes, we generated six prosaposin deletion constructs and examined the effect of truncation by co-immunoprecipitation and confocal microscopy. The experiments revealed that a 17 amino acid stretch in the first half of the C-terminus (aa524-540) was necessary for the binding of prosaposin to sortilin and essential for its transport to the lysosomes. / Since the pH is able to induce conformational changes in the four saposin domains, we performed a pH-dependent binding assay to test whether or not the binding of prosaposin to sortilin was affected by different pHs. The experiments demonstrated that binding of prosaposin to sortilin occurred at 6.0 or higher. A substantial decrease in binding was detected at pH 5.5, and at pH 5.0 both proteins did not form complexes. This result indicated that the binding of prosaposin to sortilin is pH-dependent. / Since hydrophilic residues usually modulate pH-dependent protein interactions we introduced six site-directed point mutations in hydrophilic residues within the first half of the C-terminus. The results showed that the mutation of single hydrophilic amino acids did not affect the binding of prosaposin to sortilin. / Considering that tryptophan, cysteine and proline residues are important in protein structure and function, we also introduced eight site-directed point mutations to these residues within the 17 amino acid stretch in the C-terminus. The experiments revealed that two tryptophans (W530 and W535), and two cysteines (C528 and C536) were essential for the transport of prosaposin to the lysosomes. In addition, one proline residue (P532) was critical for the proper folding of prosaposin during its synthesis, which was demonstrated by the MG132 Proteasome Inhibition Assay. / In conclusion, we have narrowed down the sortilin recognition site on the prosaposin molecule to a specific 17-residue stretch in the first half of the C-terminus and discovered the essential residues in this region for the lysosomal trafficking of prosaposin. / Les protéines lysosomiales solubles récemment identifiées et synthétisées sont transférées de l'appareil de Golgi des cellules vers les lysosomes par deux récepteurs, des mannoses 6-phosphates. Cependant l'activateur sphingolipidique de la prosaposine est ciblé sur la lysosomes par un récepteur alternatif, la sortiline. La prosaposine est le précurseur de quatre saposines lysosomiales requises pour l'hydrolyse des sphingolipides. Une étude récente a déjà démontré que l'élimination de la terminaison-C de la sphingolipide empêche le transport de la prosaposine vers les lysosomes. / Pour identifier les séquences d'acides aminés impliqués dans l'interaction de la prosaposine avec la sortiline et ainsi clarifier le mode de transport de ces séquences vers les lysosomes, nous avons procédé, par co-immunoprécipitation et immunomicroscopie confocale et à l'élimination de six séquences distinctes de la saposine. Ces expériences ont montré que la première moitié de la terminaison-C (aa524-540) la séquence des 17 résidus peptidiques est nécessaire pour permettre la liaison de la sortiline à la prosaposine et le transport de la prosaposine vers les lysosomes. fr / Le pH du milieu agit sur l'interaction d'un ligand à son récepteur. Nous avons donc analysé la liaison de la prosaposine à la sortiline à différents pH. Les résultats on montré que la liaison de la prosaposine à la sortiline se fait à un pH de 6.0 ou plus. Par contre la prosaposine ne forme pas de complexes avec la sortiline à des pH de 5.0 et 5.5. fr / Puisque les résidus hydrophiles modulent normalement l'interaction des protéines nous avons introduit des mutations focales (point mutations) sur six sites de tels résidus hydrophiles de la terminaison-C de la prosaposine. Les résultats ont montré que de telles mutations n'ont aucun effet sur la liaison de la sortiline à la prosaposine. fr / Considérant que le tryptophane, la cystéine et la proline forment des séquences importantes de la structure et de la fonction des protéines, nous avons inséré huit mutations focales additionnelles sur la séquence de 17 résidus de la terminaison-C de la prosaposine. Les résultats ont révélé que deux molécules de tryptophane (W530 etW535) et deux molécules de cystéine (C528 et C536) sont essentielles au transport de la prosaposine vers les lysosomes. Par ailleurs, une molécule de proline (P532) provoque la dégradation de la prosaposine par des protéosomes. fr / En conclusion nous avons circonscrit certains aspects moléculaires de la relation de la sortiline à la prosaposine. Nous avons montré en particulier que la liaison de la sortiline à la prosaposine se situe au niveau d'un site précis du segment de la terminaison-C de la prosaposine dont certains éléments jouent un rôle essentiel dans le transport de la prosaposine vers les lysosomes. fr

Autophagy and apoptosis are two major signaling pathways employed by the cell in response to various stress-induced signals in order to manage such stress and ultimately to determine cellular survival or death. Central to the regulation of both pathways is the BCL-2 protein family. At the endoplasmic reticulum (ER) the pro-survival BCL-2 protein targets multiple protein complexes, which influence Ca2+ homeostasis, as well as the outcome of apoptosis and autophagy pathways. To understand how BCL-2 is partitioned between these complexes, we sought to identify BCL-2-interacting proteins at this site. Here I present the identification and characterization of NAF-1, a novel ER BCL-2-interacting partner. Interestingly, NAF-1 is required for BCL-2 antagonism of autophagy, but is not required by BCL-2 to antagonize apoptosis initiated at the ER by the BH3-only protein BIK. NAF-1 contributes to the physical interaction between BCL-2 and the autophagy effector Beclin 1, which is essential for functional inhibition of autophagy by BCL-2. Thus, NAF-1 targets BCL-2 to the autophagy pathway at the ER. Furthermore, NAF-1 is found in association with the IP3R ER Ca2+ efflux channel, and mediates BCL-2 regulation of ER Ca2+ stores. Ectopic expression of ER-targeted BCL-2 reduces ER Ca2+ content and NAF-1 is required for this process. In response to nutrient deprivation, autophagy induction is accompanied by an early release of ER Ca2+ stores. Cytosolic Ca2+ is required for autophagy in response to starvation, suggesting that the release of Ca2+ from the ER may be an essential signal for autophagy induction and, in addition to direct sequestration of Beclin 1, a mechanism of inhibition by BCL-2/NAF-1. To study the physiological contribution of the Naf-1 gene, we generated Naf-1 knockout mice. These mice begin to manifest signs of severe muscle degeneration between 2-3 months of age, and exhibit increasingly poor performance status until mortality at 6-9 months. Immortalized MEF cell lines were generated and will be utilized in conjunction with the Naf-1 knockout mice for future elucidation of NAF-1 function.In summary, this thesis provides a thorough analysis of a novel ER BCL-2-interacting partner, NAF-1, and provides further insight into the mechanism of autophagy regulation by BCL-2. / L'autophagie et l'apoptose sont les deux voies principales de signalisation employées par les cellules afin de répondre à des signaux de stress et de sélectionner la survie ou la mort cellulaire. La famille de protéines BCL-2 est l'un des éléments essentiels à la régulation de ces deux voies de signalisation. La protéine anti-apoptotique BCL-2 du réticulum endoplasmique (RE) cible plusieurs complexes de protéines, ce qui influence l'homéostasie du Ca2+, l'autophagie et l'apoptose. Afin de comprendre comme BCL-2 interagit avec ces complexes protéiques, nous avons cherché à identifier de nouvelles protéines qui interagissent avec BCL-2 dans le RE. Dans ce travail, nous montrons l'identification et la caractérisation de la protéine NAF-1, une nouvelle protéine qui interagit avec BCL-2 du RE. BCL-2 requiert la protéine NAF-1 pour antagoniser l'autophagie, mais NAF-1 n'est pas requise pour antagoniser le processus apoptotique qui est initié au RE par la protéine BIK. En outre, NAF-1 contribue à l'interaction physique entre BCL-2 et l'effecteur de l'autophagie Beclin 1. Cette interaction est essentielle à la régulation négative du processus autophagique par BCL-2. En conséquence, NAF-1 cible BCL-2 vers la voie autophagique au RE. En outre, NAF-1 s'associe au canal calcique IP3R du RE et sert également d'intermédiaire à la régulation de la réserve de calcium au RE par BCL-2. L'expression cellulaire excessive de BCL-2 au RE réduit les réserves de calcium et NAF-1 est requise pour ce processus. Pendant une carence de nutriments, l'induction autophagique est accompagnée d'une libération rapide des réserves de Ca2+ du RE. Puisque le calcium cytosolique est requis pour initier l'autophagie induite par la famine, nos travaux suggèrent que la libération de Ca2+ à partir du RE peut agir comme signal à l'initiation de l'autophagie. Alors, le complexe BCL-2/NAF-1 peut servir, en plus de la séquestration directe de Beclin 1, comme mécanisme d'inhibition de ce signal calcique. Afin d'étudier la contribution physiologique du gène Naf-1, nous avons produit de souris KO du gène Naf-1. Ces souris manifestent des signes de dégénérescence musculaire sévère entre 2-3 mois d'âge. Elles démontrent une détérioration croissante de leurs performances au cours de leur vie, et ce, jusqu'à leur mort à 6-9 mois d'âge. Afin d'éclaircir le rôle de NAF-1, des lignées cellulaires immortalisées MEF ont été générées et elles seront utilisées en combinaison avec les souris KO du gène Naf-1. En résumé, d'une part, cette mémoire fournit une analyse approfondie d'un nouveau partenaire du BCL-2 au RE, NAF-1. D'autre part, elle permet de mieux cerner le mécanisme de régulation de l'autophagie par BCL-2.

Aging is characterized by an imbalance in cellular redox status due to an increase in the production of reactive oxygen species (ROS) and a decreased activity of the cellular antioxidant defenses. Spermatozoa are highly susceptible to oxidative stress and hence this mechanism likely plays a causal role in the deficiencies associated with aging and male reproduction. The goal of this study was to determine the effect of age on antioxidant enzymatic activity, ROS production, and lipid peroxidation in spermatozoa along the epididymis of the Brown Norway rat. Aging significantly decreased glutathione peroxidase (Gpx)-1, Gpx4 and superoxide dismutase (SOD) activities and also significantly increased the production of hydrogen peroxide (H2O2) and superoxide (O2•-). Further, lipid peroxidation was found to be significantly increased in aged spermatozoa. These results indicate that aged spermatozoa are less capable of dealing with oxidative stress and provide a basis for the understanding of decreased spermatozoal quality in aging.

Articular cartilage reduces friction and absorbs shock protecting the moving ends of bones from damage during normal physical activity. These mechanical properties of cartilage result from the physiological activities of chondrocytes, the phenotypically unique cells that produce and maintain the cartilage matrix. The behaviour of these cells is controlled by extracellular milieu components including: matrix molecules, growth factors, calcium and phosphorus. The interaction of these signals maintains the homeostatic balance between anabolism and catabolism in healthy articular cartilage. Unimpeded imbalances between these processes result in disease states such as Osteoarthritis. In this thesis work the specific and combined effects of PTHrP, FGF, calcium and phosphate signalling on cartilage metabolism were studied. PTHrP was shown to localize to the cell nucleus and under conditions of stress prevented cells from progressing in the cell cycle by inhibiting ribosome biogenesis. Furthermore, it was shown that the expression of the phosphate transporter GLVR-1 was inhibited by the presence of PTHrP in a high stress growth environment. Inhibiting the expression of this receptor effectively prevented intracellular accumulation of phosphate and as a result inhibited chondrocyte differentiation processes. Observation of PTHrP -/-/FGFR3-/- double knockout mice showed a dominant role for PTHrP in promoting chondrocyte proliferation, preventing apoptosis and inhibiting terminal differentiation. In contrast, FGFR3 promoted terminal differentiation and apoptosis in the absence of PTHrP. Additionally, studies of primary chondrocyte cultures generated from FGFR3-/- and FGFR3+/+ mice demonstrated impaired mitogenic response and decreased production of collagen II and proteoglycan in response to FGF18 stimulation in the presence of FGFR3, thus, identifying FGF18 as a selective ligand for FGFR3 in chondrogenic cells. / The various studies presented in this thesis show that signals from growth factors, the extracellular matrix and mineral ion components of the extracellular milieu interact to regulate the process of chondrogenesis and identify PTHrP and FGFR3 as potential molecular targets for the bioengineering of cartilage tissue.

Drosophila Lasp is the only member of the nebulin family in Drosophila. Lasp has an amino-terminal LIM domain, two actin-binding nebulin repeats and a carboxyl-terminal SH3 domain and exhibits very high homology to human Lasp. To assess Lasp function in vivo, we generated a null mutant in Drosophila Lasp, named Lasp1. Lasp1 mutants are homozygous viable, but male sterile. Lasp localizes to cyst cells, early germ cells, hub cells and actin cones. In Lasp1 mutants, the stem cell niche is no longer anchored to the apical tip of the testis, and actin cone migration is perturbed resulting in improper spermatid individualization. Lasp colocalizes with βPS integrin and genetically interact with βPS integrin resulting in complete hub cell mislocalization, which indicates that Lasp modulates integrin adhesion in this context. Lasp1 mutant larvae and flies also have impaired crawling, climbing and flying ability. Lasp localizes to Z lines of third instar larval body wall muscles. In Lasp1 mutant indirect flight muscle, thin filament and sarcomere length is reduced while sarcomere ultrastructure is not significantly affected. The same applies to larval body wall muscles, where we observe a misregulation of sarcomere length in both absence and overexpression of Lasp. This phenotype is very similar to nebulin mutant knock-out mice indicating that Lasp plays a role in regulating thin filament lengths, but with only two nebulin repeats. / Chez la drosophile, Lasp est la seule protéine représentante de la famille des Nébuline. Lasp contient un domaine LIM, deux répétitions de type Nébuline et un domaine SH3, et présente une forte homologie avec la famille Lasp des mammifères. Afin identifier le rôle de Lasp, nous avons généré une mutation nulle, nommée Lasp1. Les mutants Lasp1 sont homozygotes viables, mais les mâles stériles. Lasp se localise dans cellules kyste, dans les cellules germinales, les cellules hub et au niveau des cônes d'actine. Chez les mutants Lasp1, les cellules souches ne sont plus ancré à l'extrémité apicale du testicule, et la migration des cônes d'actine est perturbée, conduisant à une individualisation irrégulière des spermatides. Lasp est colocalisée avec l'intégrine βPS et interagit génétiquement avec l'intégrine βPS, amenant une délocalization des cellules hub, indiquant que Lasp module adhésion intégrine dans ce contexte. Les larves mutantes pour Lasp se déplacent avec difficulté et les adultes ont avec une capacité d'escalade et de vols réduite. Lasp se localise aux lignes Z dans les muscles des larves du troisième stade. Chez les adultes Lasp1, les muscles des ailes présentent une longueur réduite des filaments minces ainsi que des sarcomères, alors que l'ultrastructure du sarcomère ne semble pas être significativement affectée. Les muscles larvaires présentent le phenotype. De plus, on observe un dérèglement de la longueur du sarcomère en surexprimant Lasp dans un contexte sauvage. Ce phénotype est très similaire à celui des souris mutantes pour la nébuline, indiquant que Lasp joue un rôle dans la régulation de la longueur du filament mince, mais avec seulement deux répétitions nébuline.