Myosin VI, encoded by jaguar (jar) in Drosophila melanogaster, is the only member of the myosin superfamily of actin-based motor proteins known to move towards the minus ends of actin filaments. In vitro studies demonstrate that Myosin VI has the ability to perform distinct functions as a cargo transporter and anchor in the cell, however which of these roles Myosin VI plays in the nervous system has yet to be determined. A locomotor defect, observed as sluggish movement in severe jar mutant larvae, was confirmed by behavioural assays. As this can indicate problems at the neuromuscular synapse, microscopy and electrophysiology were used to investigate neuromuscular junction (NMJ) structure and function in jar loss of function mutants of varying severity. Confocal imaging studies revealed a decrease in NMJ length, a reduction in bouton number per NMJ, alterations to the microtubule cytoskeleton and mislocalization of the synaptic vesicle protein Synaptotagmin in jar mutant boutons. FM dye labeling was consistent with the immunostaining data revealing vesicles endocytosed following electrical stimulation occupy the bouton centre in jar mutants. The data is indicative of a function for Myosin VI in maintaining proper peripheral vesicle localization. Electrophysiological experiments revealed a role for Myosin VI in basal synaptic transmission, with a reduction in low frequency nerve-evoked responses and spontaneous release in severe jar mutants. Changes in short-term synaptic plasticity were also observed in Myosin VI mutants by using both paired-pulse experiments to examine release probability and high-frequency stimulation paradigms to recruit vesicles from different functional pools. Taken together, the data suggest that Myosin VI functions as an anchor to peripherally localize vesicles within the bouton enabling their efficient release during nerve stimulation. Synaptic vesicles are mobile at the Drosophila NMJ; thus if Myosin VI is acting as a vesicle tether, it would normally be expected to restrain vesicle mobility at the synapse. FRAP analysis revealed a significant increase in synaptic vesicle mobility in jar mutant boutons. This study elucidates novel roles for Myosin VI function in the nervous system via regulation of the synaptic microtubule architecture and localization of synaptic vesicles within the nerve terminal.

Myosin VI, encoded by jaguar (jar) in Drosophila melanogaster, is the only member of the myosin superfamily of actin-based motor proteins known to move towards the minus ends of actin filaments. In vitro studies demonstrate that Myosin VI has the ability to perform distinct functions as a cargo transporter and anchor in the cell, however which of these roles Myosin VI plays in the nervous system has yet to be determined. A locomotor defect, observed as sluggish movement in severe jar mutant larvae, was confirmed by behavioural assays. As this can indicate problems at the neuromuscular synapse, microscopy and electrophysiology were used to investigate neuromuscular junction (NMJ) structure and function in jar loss of function mutants of varying severity. Confocal imaging studies revealed a decrease in NMJ length, a reduction in bouton number per NMJ, alterations to the microtubule cytoskeleton and mislocalization of the synaptic vesicle protein Synaptotagmin in jar mutant boutons. FM dye labeling was consistent with the immunostaining data revealing vesicles endocytosed following electrical stimulation occupy the bouton centre in jar mutants. The data is indicative of a function for Myosin VI in maintaining proper peripheral vesicle localization. Electrophysiological experiments revealed a role for Myosin VI in basal synaptic transmission, with a reduction in low frequency nerve-evoked responses and spontaneous release in severe jar mutants. Changes in short-term synaptic plasticity were also observed in Myosin VI mutants by using both paired-pulse experiments to examine release probability and high-frequency stimulation paradigms to recruit vesicles from different functional pools. Taken together, the data suggest that Myosin VI functions as an anchor to peripherally localize vesicles within the bouton enabling their efficient release during nerve stimulation. Synaptic vesicles are mobile at the Drosophila NMJ; thus if Myosin VI is acting as a vesicle tether, it would normally be expected to restrain vesicle mobility at the synapse. FRAP analysis revealed a significant increase in synaptic vesicle mobility in jar mutant boutons. This study elucidates novel roles for Myosin VI function in the nervous system via regulation of the synaptic microtubule architecture and localization of synaptic vesicles within the nerve terminal.

Le trafic intracellulaire consiste en la formation et le transport de vésicules ou tubules qui acheminent des composants protéiques et lipidiques entre les différents organites ou avec la membrane plasmique. L’élaboration de ces tubulo-vésicules est initiée par le remodelage local d’une membrane, tout d’abord en générant une courbure puis un bourgeon qui, s’allongeant, forme la tubulo-vésicule. Enfin, la rupture de la membrane, ou scission, libère le transporteur nouvellement formé. Ces étapes repose sur un sculptage profond de la membrane. Ceci requière des forces générées par des moteurs moléculaires, lesquels s’associent aux cytosquelettes comme les microtubules ou les filaments d’actine. Afin de mieux comprendre comment le cytosquelette et leurs moteurs façonnent ces transporteurs, nous avons examiné le rôle de l’actine et de la myosine VI dans la formation de tubules membranaires aux mélanosomes. Les mélanosomes sont des organites apparentés aux lysosomes, générés dans les mélanocytes de la peau et de la choroïde de l’œil, et qui sont le lieu de synthèse et de stockage d’un pigment, la mélanine. Dans l’épiderme, ces compartiments spécialisés évoluent par différentes étapes de maturation qui aboutissent à leurs transferts aux cellules voisines, les kératinocytes. Les mélanosomes sont des organites dynamiques qui reçoivent et recyclent constamment des composants membranaires, comme la SNARE VAMP7. Nous résultats montrent que la myosine VI et son adapteur optineurine se localisent à un sous-domaine spécifique de la membrane des mélanosomes, ou elles contrôlent la scission de tubules. En effet, l’activité motrice de la myosine VI et le réseau d’actine branchée, dépendant des complexes Arp2/3 et WASH, permettent la constriction des membranes du tubule et son détachement du mélanosome. Un défaut de scission de ces tubes engendre des mélanosomes plus pigmentés, enrichis en cargos et au pH plus acide. L’altération de l’homéostasie du mélanosome affecte sa fonction, comme sa capacité à être sécrété et transféré aux kératinocytes. Nos résultats démontrent que la myosine VI en coopération avec le cytosquelette d’actine permet la constriction et fission de membranes aux mélanosomes. Les intermédiaires de transport ainsi formés recyclent des protéines cargos pour leur possible réutilisation, et participent ainsi au maintien de l’homéostasie et de la fonction de ces organites. / Intracellular transport among organelles and the plasma membrane occurs through the formation and transport of vesicular and tubular membrane carriers. The formation of these carriers requires first the bending of membrane and the generation of a bud, followed by its elongation to form the tubule-vesicle. Lastly, the carrier is released from the membrane source by the scission of the membrane. Importantly, all these different steps need an accurate orchestration to properly deform the membrane. The actions exerted by molecular motors onto microtubule and actin cytoskeletons provide forces onto membrane that contribute to its remodeling during the biogenesis of carrier. Actin filaments (F-actin) and myosins are thought to participate in the initiation and the fission of carriers. However, the role of actin machinery during carrier biogenesis remains elusive. We thus decided to address the role of F-actin and the actin-based motor myosin VI in the formation of tubular intermediates at melanosome. Melanosomes are lysosome-related organelles of skin melanocytes and eye pigment cells that function in the synthesis and storage of the melanin pigment. Melanosomes originate from endosomes and progressively mature into fully pigmented compartments, which fate is to be secreted and transferred to neighboring keratinocytes. Melanosomes are dynamic organelles that constantly receive, but also recycle proteins such as the SNARE VAMP7 through the formation and release of tubular intermediates. Our work reveals that myosin VI, together with Arp2/3- and WASH-mediated branched actin localize at specific melanosomal subdomains where they promote the constriction and scission of tubular intermediates. This fission event allows the export of components such as VAMP7 from melanosomes and promotes their maturation and subsequent transfer to keratinocytes. Altogether, our results uncover a new role for myosin VI and F-actin in the constriction and scission of membrane tubules at melanosome that is required for organelle homeostasis and function.

Abstract Background and aims: Stage and grade are the most widely used prognostic parameters for renal cell carcinoma (RCC). The clinical course of this disease is not, however, always predictable by traditional prognostic factors. In the era of new molecular targeted therapies a more accurate prognostication of RCC patient survival is important for the individualization of treatment and follow-up of patients. Despite exhaustive research there are still no prognostic biomarkers for RCC in clinical practice. In order to find novel prognostic tissue markers for RCC, we examined the expression of 14 biomarkers involved in carcinogenesis and clarified their prognostic significance in RCC. Material and methods: Out of 189 consecutive patients who underwent surgery for kidney cancer at Oulu University Hospital in the 1990s, 152 patients with histologically verified RCC were included in this study. The stage distribution was 70 (46%), 12 (8%), 51 (34%) and 19 (12%) patients with stages I-IV, respectively. The majority of the tumours (83 tumours, 55%) were nuclear grade II and 5 (3%), 40 (27%) and 22 (15%) of the tumours were grades I, III and IV, respectively. Clinical and follow-up data were obtained from patient records, the Finnish Cancer Registry and on demand from the Population Register Centre of Finland. The biomarkers studied included markers of the oxidative and neuroendocrine systems as well as proteins related to cell adhesion and migration, invasion, metastasis, inflammation and immune responses. The expression of various biomarkers was characterized via immunohistochemical tests of archival tumour material. The staining intensity was compared to clinicopathological parameters and patient RCC-specific survival. Results: The 5-year RCC-specific survival was 77%. The expression of Toll-like receptor 9 (TLR9) was an independent marker of favourable RCC-specific survival whereas cytoplasmic myosin VI expression was found to be an independent prognostic factor of poor RCC-specific survival. Cell culture experiments showed how cyclooxygenase-2 (COX-2) expression is regulated by HuR in RCC. HuR and COX-2 immunoexpression were also related to decreased RCC-specific survival. Immunostaining of Keap1 was associated with advanced RCC and a marker of a poorer RCC-specific prognosis. The expression of different neuroendocrine markers was evaluated but we could not establish any prognostic value for them. Conclusions: In particular, TLR9, HuR and myosin VI can be regarded as promising novel prognostic biomarkers in RCC. Stage, however, is the most important single prognostic factor for RCC. / Tiivistelmä Munuaissyöpä on vuosikymmenten ajan jatkuvasti yleistynyt. Vaikka se diagnosoidaan nykyisin useimmiten sattumalöydöksenä vatsan alueen kuvantamistutkimuksissa ja hoitomenetelmät ovat viime vuosikymmenten aikana kehittyneet, munuaissyöpäkuolleisuus ei ole laskenut. Munuaissyövän ennusteen määrittäminen voi olla haasteellista. Perinteiset ennustetekijät, levinneisyys ja erilaistumisaste, eivät riitä selittämään kaikkien potilaiden taudinkulkua, eikä munuaissyövälle vielä ole kliinisessä käytössä ennusteellista merkkiainetta. Munuaissyöpähoitojen kehittyessä taudinkulun ennustaminen on yhä tärkeämpää, jotta potilaiden hoito ja seuranta voidaan yksilöidä. Tämän väitöskirjatyön tarkoituksena oli etsiä uusia ennusteellisia kudosmerkkiaineita munuaissyöpäkasvaimille. Väitöskirjatutkimus perustuu 1990-luvulla Oulun yliopistollisessa sairaalassa leikatun 152 munuaissyöpäpotilaan aineistoon. Lähes puolet aineiston kasvaimista edusti levinneisyysluokkaa I, ja yli puolet munuaissyöpäkasvaimista oli hyvin erilaistuneita (tumagradus I ja II). Tutkimuspotilaista kerättiin kattavat seurantatiedot. Leikkauksessa poistettujen munuaissyöpäkasvainten arkistomateriaalista tutkittiin eri merkkiaineiden ilmenemistä. Tutkitut merkkiaineet käsittivät oksidatiivisen ja neuroendokriinisen järjestelmän merkkiaineita sekä valkuaisaineita, jotka liittyvät keskeisiin syövän ominaisuuksiin, kuten solujen välisiin liitoksiin ja solujen liikkumiseen sekä etäpesäkkeiden syntymiseen. Lisäksi tutkittiin merkkiaineita, jotka liittyvät tulehdusreaktioihin ja immuunipuolustukseen. Väitöskirjatutkimus paljasti useita uusia kudosmerkkiaineita, joiden ilmeneminen munuaissyöpäkasvaimessa on yhteydessä potilaan ennusteeseen. Näistä merkittävimpiä ovat myosiini VI, joka liittyy syöpäkasvainten metastasointiin, sekä immuunipuolustuksessa vaikuttava Tollin kaltainen reseptori 9 (Toll-like receptor 9, TLR9). Molemmat merkkiaineet osoittautuivat itsenäisiksi ennustetekijöiksi munuaissyövässä. Muita ennusteeseen vaikuttavia merkkiaineita ovat tutkimuksen mukaan oksidatiivista stressiä aistiva Keap1 sekä immunologisiin reaktioihin liittyvä syklo-oksigenaasi 2 (COX-2) ja sen ilmenemistä säätelevä HuR.