visualization-axonal-projection-pattern-embryonic-motor-neurons

Visualization of the Axonal Projection Pattern of Embryonic Motor Neurons in <em>Drosophila</em>

The establishment of functional neuromuscular circuits relies on precise connections between developing motor axons and target muscles. Motor neurons ...

Chonbuk National University

Hox genes have been implicated in the evolution of many animal body patterns, but the molecular events underlying trait modification have not been elucidated. Pigmentation of the posterior male abdomen is a recently acquired trait in the Drosophila melanogaster lineage. Here, we show that the Abdominal-B (ABD-B) Hox protein directly activates expression of the yellow pigmentation gene in posterior segments. ABD-B regulation of pigmentation evolved through the gain of ABD-B binding sites in a specific cis-regulatory element of the yellow gene of a common ancestor of sexually dimorphic species. Within the melanogaster species group, male-specific pigmentation has subsequently been lost by at least three different mechanisms, including the mutational inactivation of a key ABD-B binding site in one lineage. These results demonstrate how Hox regulation of traits and target genes is gained and lost at the species level and have general implications for the evolution of body form at higher taxonomic levels.

Regulation of body pigmentation by the Abdominal-B Hox protein and its gain and loss in Drosophila evolution.

Understanding the mechanisms underlying the morphological divergence of species is one of the central goals of evolutionary biology. Here, we analyze the genetic and molecular bases of the divergence of body pigmentation patterns between Drosophila yakuba and its sister species Drosophila santomea. We found that loss of pigmentation in D. santomea involved the selective loss of expression of the tan and yellow pigmentation genes. We demonstrate that tan gene expression was eliminated through the mutational inactivation of one specific tan cis-regulatory element (CRE) whereas the Tan protein sequence remained unchanged. Surprisingly, we identify three independent loss-of-function alleles of the tan CRE in the young D. santomea lineage. We submit that there is sufficient empirical evidence to support the general prediction that functional evolutionary changes at pleiotropic loci will most often involve mutations in their discrete, modular cis-regulatory elements.

The evolution of gene regulation underlies a morphological difference between two Drosophila sister species.

&#x6211;&#x4EEC;&#x5728;&#x6240;&#x663E;&#x793A;&#x4EE5;&#x524D;&#x7684;&#x8179;&#x90E8;&#x8272;&#x7D20;&#x6C89;&#x7740;&#x7684;&#x635F;&#x5931; D.santomea &#x4E0E;&#x7269;&#x79CD; D.&#x4E9A;&#x5E93;&#x5DF4;&#x90E8;&#x5206;&#x5730;&#x5BFC;&#x81F4;&#x4E86;&#xFF0C;&#x4ECE;&#x72EC;&#x8054;&#x4F53;&#x76D1;&#x7BA1;&#x7A81;&#x53D8; tan &#x7684;&#x8F68;&#x8FF9;&#x5728;&#x5176;&#x59D0;&#x59D0;&#x3002;&#x9A6C;&#x56FE;&#x7279;&#x4E2D;&#x5357;&#x5DE5;&#x4E1A;&#x5927;&#x5B66;&#x58F0;&#x79F0;&#xFF0C;&#x4ECE; D.santomea &#x548C; D.&#x9ED1;&#x8179;&#x679C;&#x8747;&#x9057;&#x4F20;&#x6742;&#x4EA4;&#xFF0C;&#x66F4;&#x591A;&#x4E0D;&#x540C;&#x7684;&#x7269;&#x79CD;&#xFF0C;&#x8FD9;&#x81F3;&#x5C11;&#x56DB;&#x4E2A; X &#x67D3;&#x8272;&#x4F53;&#x533A;&#x57DF;&#x5916;&#x63A8;&#x7684;&#x552F;&#x4E00;&#x4F9D;&#x636E;&#xFF0C;&#x4F46;&#x4E0D;&#x662F;&#x81BB;&#x8D1F;&#x8D23;&#x8272;&#x7D20;&#x6C89;&#x7740;&#x7684;&#x5DEE;&#x5F02;&#x3002;&#x5728;&#x8FD9;&#x91CC;&#xFF0C;&#x6211;&#x4EEC;&#x63D0;&#x4F9B;&#x66F4;&#x591A;&#x8BC1;&#x636E;&#xFF0C;&#x4ECE; introgressions D.&#x4E9A;&#x5E93;&#x5DF4;&#x57FA;&#x56E0;&#x5230; D.santomea &#x7684;&#x652F;&#x6301;&#x81F4;&#x75C5;&#x4F5C;&#x7528;&#x7684;&#x8C2D;&#x4E2D;&#x8272;&#x7D20;&#x6C89;&#x7740;&#x548C;&#x73B0;&#x72B6;&#x5206;&#x6790;&#x77DB;&#x76FE;&#x4E2D;&#x5357;&#x5DE5;&#x4E1A;&#x5927;&#x5B66;&#x9A6C;&#x56FE;&#x7279;&#x7684;&#x7D22;&#x8D54;&#x7684;&#x635F;&#x5931;&#x3002;&#x6211;&#x4EEC;&#x8BA8;&#x8BBA;&#x80B2;&#x513F;&#x7269;&#x79CD;&#x7684;&#x9009;&#x62E9;&#x548C;&#x5176;&#x4ED6;&#x56E0;&#x7D20;&#x5982;&#x4F55;&#x5F71;&#x54CD;&#x80FD;&#x591F;&#x6807;&#x8BC6;&#x8D1F;&#x8D23;&#x7269;&#x79CD;&#x5206;&#x5316;&#x7684;&#x57FA;&#x56E0;&#x4F4D;&#x70B9;&#x548C;&#x6211;&#x4EEC;&#x7533;&#x660E;&#x6211;&#x4EEC;&#x4EE5;&#x524D;&#x6240;&#x62A5;&#x544A;&#x7684;&#x7ED3;&#x679C;&#x548C;&#x7ED3;&#x8BBA;&#x90FD;&#x8981;&#x7AD9;&#x3002;

Tan &#x8F68;&#x8FF9;&#x7684;&#x6F14;&#x53D8;&#x4F5C;&#x51FA;&#x4E86;&#x8D21;&#x732E;&#x5728;&#x679C;&#x8747; santomea &#x8272;&#x7D20;&#x635F;&#x5931;&#xFF1A; &#x5411;&#x9A6C;&#x56FE;&#x7279; et al &#x7684;&#x54CD;&#x5E94;&#x3002;

We have shown previously that the loss of abdominal pigmentation in D. santomea relative to its sister species D. yakuba resulted, in part, from cis-regulatory mutations at the tan locus. Matute et al. claim, based solely upon extrapolation from genetic crosses of D. santomea and D. melanogaster, a much more divergent species, that at least four X chromosome regions but not tan are responsible for pigmentation differences. Here, we provide additional evidence from introgressions of D. yakuba genes into D. santomea that support a causative role for tan in the loss of pigmentation and present analyses that contradict Matute et al.'s claims. We discuss how the choice of parental species and other factors affect the ability to identify loci responsible for species divergence, and we affirm that all of our previously reported results and conclusions stand.

Evolution of the tan locus contributed to pigment loss in Drosophila santomea: a response to Matute et al.

Nous avons montr&#xE9; pr&#xE9;c&#xE9;demment que la perte de la pigmentation abdominale chez D. par rapport &#xE0; sa soeur esp&#xE8;ces D. yakuba santomea entra&#xEE;n&#xE9;, en partie, &#xE0; partir de cis-r&#xE9;gulation des mutations au niveau du locus bronzage. Matute et al. revendication, fond&#xE9;e uniquement sur l&#x26;#39;extrapolation &#xE0; partir de croisements g&#xE9;n&#xE9;tiques de D. santomea et D. melanogaster, une esp&#xE8;ce beaucoup plus divergents, au moins quatre r&#xE9;gions du chromosome X, mais ne bronzent pas responsables de diff&#xE9;rences de pigmentation. Ici, nous fournissent une preuve suppl&#xE9;mentaire de introgressions de g&#xE8;nes Yakuba D. D. dans santomea qui soutiennent le r&#xF4;le causal de bronzage dans la perte de la pigmentation et des analyses qui contredisent pr&#xE9;sente Matute et al. D &#x26;#39;all&#xE9;gations. Nous discutons comment le choix des esp&#xE8;ces parentales et d&#x26;#39;autres facteurs affectent la capacit&#xE9; d&#x26;#39;identifier des loci responsables de divergence des esp&#xE8;ces, et nous affirmons que l&#x26;#39;ensemble de nos r&#xE9;sultats pr&#xE9;c&#xE9;demment rapport&#xE9;s et les conclusions se tenir debout.

Evolution de la Locus Tan contribu&#xE9; &#xE0; la perte de pigment dans la drosophile Santomea: une r&#xE9;ponse &#xE0; Matute Et Al

Wir haben zuvor den Verlust von abdominal Pigmentierung in D. Santomea im Verh&auml;ltnis zu seiner Schwester gezeigt, dass Arten D. Yakuba, teilweise aus Cis-regulatorische Mutationen bei der Tan-Locus gef&uuml;hrt. Matute Et Al. behaupten, basiert ausschlie&szlig;lich auf Extrapolation von genetischen Kreuze von D. Santomea und D. Melanogaster, eine viel mehr unterschiedlichen Arten, dass mindestens vier x-Chromosom-Regionen, aber nicht br&auml;unen f&uuml;r Pigmentierung Unterschiede verantwortlich sind. Hier bieten wir zus&auml;tzliche Beweis von Introgressions D. Yakuba Gene in D. Santomea, die eine kausale Rolle f&uuml;r tan zum Verlust der Pigmentierung und vorliegenden Analysen, die Matute Et Al. Forderungen widersprechen unterst&uuml;tzen. Wir besprechen, wie die Wahl der elterlichen Arten und andere Faktoren beeinflussen Loci verantwortlich f&uuml;r Arten Divergenz zu identifizieren, und wir versichern, dass alle unsere zuvor berichteten Ergebnisse und Schlussfolgerungen stehen.

Entwicklung der Br&auml;une Locus trug zur Pigment-Verlust in Drosophila Santomea: eine Antwort auf Matute Et Al.

Abbiamo dimostrato in precedenza che la perdita di pigmentazione addominale in d. santomea rispetto alla sua sorella specie D. yakuba ha portato, in parte, da mutazioni cis-regolatori presso il locus tan. Matute et al claim, basato esclusivamente su un&#39;estrapolazione da incroci genetici di d. santomea e d. melanogaster, una specie molto pi&ugrave; divergente, quel cromosoma X almeno quattro regioni ma tan non sono responsabili per le differenze di pigmentazione. Qui, forniamo prove supplementari da introgressions di d. yakuba geni in d. santomea che supportano un ruolo causativo per tan la perdita di pigmentazione e le analisi presenti che contraddicono le affermazioni di Matute et al. Discutiamo di come la scelta della specie parentale e altri fattori possono influenzare la capacit&agrave; di identificare loci responsabili per le divergenze fra specie e affermiamo che tutti i nostri risultati precedentemente segnalati e conclusioni stand.

Evoluzione del locus tan ha contribuito alla perdita di pigmento in drosofila santomea: una risposta a Matute et al.

&#x6211;&#x3005;&#x306F;&#x305D;&#x306E;&#x59C9;&#x59B9;&#x7A2E;D.&#x5F79;&#x5834;&#x304B;&#x3089;&#x306E;&#x76F8;&#x5BFE;D. santomea&#x306E;&#x8179;&#x90E8;&#x8272;&#x7D20;&#x306E;&#x640D;&#x5931;&#x304C;&#x65E5;&#x713C;&#x3051;&#x5EA7;&#x3067;&#x30B7;&#x30B9;&#x8ABF;&#x7BC0;&#x5909;&#x7570;&#x306B;&#x3088;&#x308B;&#x3001;&#x90E8;&#x5206;&#x7684;&#x306B;&#x751F;&#x3058;&#x308B;&#x3053;&#x3068;&#x304C;&#x4EE5;&#x524D;&#x306B;&#x793A;&#x3055;&#x308C;&#x3066;&#x3044;&#x308B;&#x3002;&#x30DE;&#x30C8;&#x30A5;&#x30FC;&#x30C6;&#x3089;&#x3002;&#x8272;&#x7D20;&#x6C88;&#x7740;&#x306E;&#x76F8;&#x9055;&#x306B;&#x8CAC;&#x4EFB;&#x304C;&#x3042;&#x308B;&#x65E5;&#x713C;&#x3051;&#x5C11;&#x306A;&#x304F;&#x3068;&#x3082;4&#x3064;&#x306E;X&#x67D3;&#x8272;&#x4F53;&#x9818;&#x57DF;&#x306E;&#x3053;&#x3068;&#x3067;&#x306F;&#x306A;&#x304F;D. santomea&#x3068;&#x30AD;&#x30A4;&#x30ED;&#x30B7;&#x30E7;&#x30A6;&#x30B8;&#x30E7;&#x30A6;&#x30D0;&#x30A8;&#x3001;&#x306F;&#x308B;&#x304B;&#x306B;&#x767A;&#x6563;&#x7A2E;&#x306E;&#x907A;&#x4F1D;&#x7684;&#x4EA4;&#x96D1;&#x304B;&#x3089;&#x5916;&#x633F;&#x306E;&#x307F;&#x306B;&#x57FA;&#x3065;&#x3044;&#x3066;&#x4E3B;&#x5F35;&#x3002;&#x3053;&#x3053;&#x3067;&#x306F;&#x3001;&#x8272;&#x7D20;&#x6C88;&#x7740;&#x306E;&#x640D;&#x5931;&#x306B;&#x65E5;&#x713C;&#x3051;&#x306E;&#x539F;&#x56E0;&#x306E;&#x5F79;&#x5272;&#x3092;&#x30B5;&#x30DD;&#x30FC;&#x30C8;&#x3059;&#x308B;D. santomea&#x306B;D.&#x5F79;&#x5834;&#x907A;&#x4F1D;&#x5B50;&#x306E;introgressions&#x3068;&#x73FE;&#x5728;&#x306E;&#x5206;&#x6790;&#x3068;&#x77DB;&#x76FE;&#x30DE;&#x30C8;&#x30A5;&#x30FC;&#x30C6;&#x3089;&#x306E;&#x7279;&#x8A31;&#x8ACB;&#x6C42;&#x306E;&#x7BC4;&#x56F2;&#x304B;&#x3089;&#x8FFD;&#x52A0;&#x306E;&#x8A3C;&#x62E0;&#x3092;&#x63D0;&#x4F9B;&#x3057;&#x3066;&#x3044;&#x307E;&#x3059;&#x3002;&#x79C1;&#x305F;&#x3061;&#x306F;&#x3001;&#x89AA;&#x306E;&#x7A2E;&#x3084;&#x4ED6;&#x306E;&#x8981;&#x56E0;&#x306E;&#x9078;&#x629E;&#x306F;&#x3001;&#x7A2E;&#x306E;&#x5206;&#x5C90;&#x306E;&#x8CAC;&#x4EFB;&#x907A;&#x4F1D;&#x5B50;&#x5EA7;&#x3092;&#x540C;&#x5B9A;&#x3059;&#x308B;&#x80FD;&#x529B;&#x306B;&#x3069;&#x306E;&#x3088;&#x3046;&#x306A;&#x5F71;&#x97FF;&#x3092;&#x4E0E;&#x3048;&#x308B;&#x304B;&#x306B;&#x3064;&#x3044;&#x3066;&#x8B70;&#x8AD6;&#x3057;&#x3001;&#x6211;&#x3005;&#x306F;&#x4EE5;&#x524D;&#x306B;&#x5831;&#x544A;&#x3055;&#x308C;&#x305F;&#x7D50;&#x679C;&#x3068;&#x7D50;&#x8AD6;&#x306E;&#x3059;&#x3079;&#x3066;&#x304C;&#x7ACB;&#x3064;&#x3053;&#x3068;&#x3092;&#x78BA;&#x8A8D;&#x3059;&#x308B;&#x3002;

&#x30BF;&#x30F3;&#x907A;&#x4F1D;&#x5B50;&#x5EA7;&#x306E;&#x9032;&#x5316;&#x306F;&#x3001;&#x30B7;&#x30E7;&#x30A6;&#x30B8;&#x30E7;&#x30A6;&#x30D0;&#x30A8;Santomea&#x306E;&#x8272;&#x7D20;&#x306E;&#x640D;&#x5931;&#x306B;&#x8CA2;&#x732E;&#xFF1A;&#x3089;&#x30DE;&#x30C8;&#x30A5;&#x30FC;&#x30C6;&#x3078;&#x306E;&#x5FDC;&#x7B54;&#x3092;

&#xC6B0;&#xB9AC; &#xD45C;&#xC2DC;&#xAC00; &#xC774;&#xC804;&#xC5D0; &#xBCF5; &#xBD80; &#xCC29; &#xC0C9; &#xC190;&#xC2E4; &#xC885; &#xB514; yakuba &#xACB0;&#xACFC;, &#xBD80;&#xBD84;&#xC801;&#xC73C;&#xB85C;, cis &#xADDC;&#xC815; &#xB3CC;&#xC5F0;&#xBCC0;&#xC774; &#xD669;&#xAC08;&#xC0C9; &#xB85C;&#xCEE4; &#xC2A4;&#xC5D0;&#xC11C;&#xC5D0;&#xC11C; &#xC790;&#xB9E4;&#xB97C; &#xAE30;&#xC900;&#xC73C;&#xB85C; &#xB514; santomea&#xC5D0;&#xC11C;. Matute &#xC678;. &#xC8FC;&#xC7A5;, &#xC804;&#xC801;&#xC73C;&#xB85C; &#xB514; santomea&#xC640; D. melanogaster&#xC758; &#xC720;&#xC804; &#xC2ED;&#xC790;&#xAC00;, &#xD6E8;&#xC52C; &#xB354; &#xBD84;&#xAE30; &#xC885;, &#xADF8; &#xC774;&#xC0C1;&#xC758; 4 &#xAC1C;&#xC758; X &#xC5FC;&#xC0C9;&#xCCB4; &#xC601;&#xC5ED;&#xC5D0;&#xC11C; &#xC678;&#xC0BD; &#xBC95;&#xC5D0; &#xB530;&#xB77C;&#xB9CC; &#xD558;&#xC9C0; &#xD669;&#xAC08;&#xC0C9; &#xCC29; &#xC0C9; &#xCC28;&#xC774; &#xB300; &#xD55C; &#xCC45;&#xC784;&#xC774; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xC5EC;&#xAE30;, &#xC6B0;&#xB9AC;&#xAC00; &#xD0C4; &#xCC29; &#xC0C9; &#xBC0F; Matute &#xC678; &#xC5EC;&#xB7EC;&#xBD84;&#xC758; &#xC8FC;&#xC7A5;&#xC744; &#xBC18;&#xBC15; &#xD558;&#xB294; &#xD604;&#xC7AC; &#xBD84;&#xC11D;&#xC758; &#xC190;&#xC2E4;&#xC5D0;&#xC11C;&#xC5D0; &#xB300; &#xD55C; &#xC6D0;&#xC778;&#xC774; &#xC5ED;&#xD560;&#xC744; &#xC9C0; &#xC6D0;&#xD558;&#xB294; &#xB514; santomea&#xC5D0; &#xB514; yakuba &#xC720;&#xC804;&#xC790;&#xC758; introgressions&#xC5D0;&#xC11C; &#xCD94;&#xAC00; &#xC99D;&#xAC70;&#xB97C; &#xC81C;&#xACF5; &#xD569;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC; &#xBD80;&#xBAA8;&#xC758; &#xC885; &#xC120;&#xD0DD; &#xBC0F; &#xB2E4;&#xB978; &#xC694;&#xC778; loci &#xC885; &#xBC1C;&#xC0B0;&#xC5D0; &#xB300; &#xD55C; &#xCC45;&#xC784;&#xC744; &#xC2DD;&#xBCC4; &#xD558;&#xB294; &#xAE30;&#xB2A5;&#xC5D0; &#xBBF8;&#xCE58;&#xB294; &#xC601;&#xD5A5;&#xC5D0; &#xB300;&#xD574; &#xC124;&#xBA85; &#xD558; &#xACE0; &#xC6B0;&#xB9AC;&#xB294; &#xBAA8;&#xB450; &#xC6B0;&#xB9AC;&#xAC00; &#xC774;&#xC804;&#xC5D0; &#xBCF4;&#xACE0; &#xB41C; &#xACB0;&#xACFC; &#xACB0;&#xB860;&#xC758; &#xC11C; &#xB9F9;&#xC138;.

&#xAC08;&#xC0C9; &#xB85C;&#xCEE4; &#xC2A4;&#xC758; &#xC9C4;&#xD654; Drosophila santomea&#xC5D0;&#xC11C; &#xC548;&#xB8CC; &#xC190;&#xC2E4;&#xC5D0; &#xAE30;&#xC5EC;: &#xC751;&#xB2F5; Matute &#xC678;.

Hemos demostrado anteriormente que la p&#xE9;rdida de la pigmentaci&#xF3;n abdominal en D. en relaci&#xF3;n a su especie hermana yakuba D. santomea resultado, en parte, a partir de cis-reguladoras mutaciones en el locus de bronceado. Matute et al. reclamaci&#xF3;n, basada &#xFA;nicamente en la extrapolaci&#xF3;n de los cruces gen&#xE9;ticos de D. santomea y D. melanogaster, una especie mucho m&#xE1;s divergentes, que por lo menos cuatro regiones del cromosoma X, pero tan no son responsables de las diferencias de pigmentaci&#xF3;n. En este sentido, proporcionan evidencia adicional de la introgresiones de D. genes yakuba en D. santomea que apoyan un papel causal para broncearse en la p&#xE9;rdida de la pigmentaci&#xF3;n y el presente an&#xE1;lisis que contradicen Matute et al. &#x26;#39;S reclamaciones. Se discute c&#xF3;mo la elecci&#xF3;n de las especies parentales y otros factores afectan la capacidad de identificar loci responsables de la divergencia de las especies, y afirmamos que todos los resultados y conclusiones de informes anteriores de pie.

Evoluci&#xF3;n de la Locus Tan contribuido a la p&#xE9;rdida de pigmento en la Drosophila Santomea: una respuesta a Matute et al

Transmembrane semaphorins (Semas) serve evolutionarily conserved guidance roles, and some function as both ligands and receptors. However, the molecular mechanisms underlying the transduction of these signals to the cytoskeleton remain largely unknown. We have identified two direct regulators of Rho family small GTPases, pebble (a Rho guanine nucleotide exchange factor [GEF]) and RhoGAPp190 (a GTPase activating protein [GAP]), that show robust interactions with the cytoplasmic domain of the Drosophila Sema-1a protein. Neuronal pebble and RhoGAPp190 are required to control motor axon defasciculation at specific pathway choice points and also for target recognition during Drosophila neuromuscular development. Sema-1a-mediated motor axon defasciculation is promoted by pebble and inhibited by RhoGAPp190. Genetic analyses show that opposing pebble and RhoGAPp190 functions mediate Sema-1a reverse signaling through the regulation of Rho1 activity. Therefore, pebble and RhoGAPp190 transduce transmembrane semaphorin-mediated guidance cue information that regulates the establishment of neuronal connectivity during Drosophila development.

The Control of semaphorin-1a-mediated reverse signaling by opposing pebble and RhoGAPp190 functions in drosophila.

Plexins (Plexs) comprise a large family of cell surface receptors for semaphorins (Semas) that function as evolutionarily conserved guidance molecules. GTPase activating protein (GAP) activity for Ras family small GTPases has been implicated in plexin signaling cascades through its RasGAP domain. However, little is known about how Ras family GTPases are controlled in vivo by plexin signaling. Here, we found that Drosophila Rap1, a member of the Ras family of GTPases, plays an important role controlling intersegmental nerve b motor axon guidance during neural development. Gain-of-function studies using dominant-negative and constitutively active forms of Rap1 indicate that Rap1 contributes to axonal growth and guidance. Genetic interaction analyses demonstrate that the Sema-1a/PlexA-mediated repulsive guidance function is regulated positively by Rap1. Furthermore, neuronal expression of mutant PlexA robustly restored defasciculation defects in PlexA null mutants when the catalytic arginine fingers of the PlexA RasGAP domain critical for GAP activity were disrupted. However, deleting the RasGAP domain abolished the ability of PlexA to rescue the PlexA guidance phenotypes. These findings suggest that PlexA-mediated motor axon guidance is dependent on the presence of the PlexA RasGAP domain, but not on its GAP activity toward Ras family small GTPases.

The axon guidance function of Rap1 small GTPase is independent of PlexA RasGAP activity in Drosophila.

Plexins (Plexs) are a large family of phylogenetically conserved guidance receptors that bind specifically to semaphorins (Semas), another large family of guidance molecules. In the Drosophila embryonic central nervous system (CNS), the secreted semaphorins Sema-2a and Sema-2b both act as ligands for PlexB, but mediate mutually independent and opposite functions (repulsive and attractive guidance, respectively). PlexB is also known to regulate motor axon guidance in the embryonic peripheral nervous system (PNS). However, it is unclear whether the mechanisms of ligand regulation of PlexB seen in the CNS are similar or the same as those that exist in PNS motor axon guidance. Here, we find that two distinct modes of ligand regulation underlie differential roles of PlexB in PNS motor axon pathfinding during embryonic development. Epistasis analyses in the intersegmental nerve b (ISNb) pathway suggest that PlexB serves as a receptor for both Sema-2a and Sema-2b and integrates their mutually dependent but opposite guidance functions. Furthermore, we present evidence that PlexB mediates not only Sema-2a/2b-dependent guidance functions, but also Sema-2a/2b-independent target recognition in establishing the segmental nerve a (SNa) motor axon pathway. These results demonstrate that a single guidance receptor can elicit diverse effects on the establishment of neuronal connectivity via regulation of its ligands themselves.

Differential ligand regulation of PlexB signaling in motor neuron axon guidance in Drosophila.

The γ-secretase complex represents an evolutionarily conserved family of transmembrane aspartyl proteases that cleave numerous type-I membrane proteins, including the β-amyloid precursor protein (APP) and the receptor Notch. All known rare mutations in APP and the γ-secretase catalytic component, presenilin, which lead to increased amyloid βpeptide production, are responsible for early-onset familial Alzheimer's disease. β-amyloid protein precursor-like (APPL) is the Drosophila ortholog of human APP. Here, we created Notch- and APPL-based Drosophila reporter systems for in vivo monitoring of γ-secretase activity. Ectopic expression of the Notch- and APPL-based chimeric reporters in wings results in vein truncation phenotypes. Reporter-mediated vein truncation phenotypes are enhanced by the Notch gain-of-function allele and suppressed by RNAi-mediated knockdown of presenilin. Furthermore, we find that apoptosis partly contributes to the vein truncation phenotypes of the APPL-based reporter, but not to the vein truncation phenotypes of the Notch-based reporter. Taken together, these results suggest that both in vivo reporter systems provide a powerful genetic tool to identify genes that modulate γ-secretase activity and/or APPL metabolism.

Development of a Reporter System for In Vivo Monitoring of γ-Secretase Activity in Drosophila.

The blood-brain barrier (BBB) exhibits a highly selective permeability to support the homeostasis of the central nervous system (CNS). The tight junctions in the BBB microvascular endothelial cells seal the paracellular space to prevent diffusion. Thus, disruption of tight junctions results in harmful effects in CNS diseases and injuries. It has recently been demonstrated that glucocorticoids have beneficial effects on maintaining tight junctions in both in vitro cell and in vivo animal models. In the present study, we found that dexamethasone suppresses the expression of JMJD3, a histone H3K27 demethylase, via the recruitment of glucocorticoid receptor α (GRα) and nuclear receptor co-repressor (N-CoR) to the negative glucocorticoid response element (nGRE) in the upstream region of JMJD3 gene in brain microvascular endothelial cells subjected to TNFα treatment. The decreased JMJD3 gene expression resulted in the suppression of MMP-2, MMP-3, and MMP-9 gene activation. Dexamethasone also activated the expression of the claudin 5 and occludin genes. Collectively, dexamethasone attenuated the disruption of the tight junctions in the brain microvascular endothelial cells subjected to TNFα treatment. Therefore, glucocorticoids may help to preserve the integrity of the tight junctions in the BBB via transcriptional and post-translational regulation following CNS diseases and injuries.

Dexamethasone suppresses JMJD3 gene activation via a putative negative glucocorticoid response element and maintains integrity of tight junctions in brain microvascular endothelial cells.

Sangyun Jeong

Department of Molecular Biology

Chonbuk National University

Visualization of the Axonal Projection Pattern of Embryonic Motor Neurons in Drosophila