The Splicing Factor Crooked Neck Associates with the RNA-Binding Protein HOW to Control Glial Cell Maturation in Drosophila

Abstract

In both vertebrates and invertebrates, glial cells wrap axonal processes to ensure electrical conductance. Here we report that Crooked neck (Crn), the Drosophila homolog of the yeast Clf1p splicing factor, is directing peripheral glial cell maturation. We show that crooked neck is expressed and required in glial cells to control migration and axonal wrapping. Within the cytoplasm, Crn interacts with the RNA-binding protein HOW and then translocates to the nucleus where the Crn/HOW complex controls glial differentiation by facilitating splicing of specific target genes. By using a GFP-exon trap approach, we identified some of the in vivo target genes that encode proteins localized in autocellular septate junctions. In conclusion, here we show that glial cell differentiation is controlled by a cytoplasmic assembly of splicing components, which upon translocation to the nucleus promote the splicing of genes involved in the assembly of cellular junctions.

Organization and Function of the Blood–Brain Barrier inDrosophila

“…Indeed, the subperineurial cell are formed early in development and these cells are connected by septate junctions from late embryonic stages onwards . Using Gal4 driver strains specific to the subperineurial cells as well as in vivo septate junction markers (Edenfeld et al, 2006), we confirm that during larval life the subperineurial cells do not divide but grow enormously large in size (Sepp et al, 2000;Silies et al, 2007). Septate junctions formed by the subperineurial cells are mostly found in interdigitated zones of cell-cell contact.…”

“…The following fly strains were used in this study: gcm N7-4 (Vincent et al, 1996); moody ⌬17 ; nrxIV 4304 (Baumgartner et al, 1996); nrxIV EP604 ; nrg 14 (Bloomington Stock Center, Bloomington, IN); nrv2 k13315 (Genova and Fehon, 2003); coracle 5 (Lamb et al, 1998); Df(3R)ED5020 to remove contactin (Faivre-Sarrailh et al, 2004); sinu NWU7 (Wu et al, 2004); Df(1)RR79 to remove the Claudin CG6398; Df(2R)M60E to remove the Claudin CG3770; Df(2R)nap2 to remove the Claudin CG1298; Df(3R)Excel6192 to remove the Claudin CG6982; pck EA97 (megatrachea) (Behr et al, 2003); 454 NeurexinIV:GFP, 125 Lachesin:GFP (Edenfeld et al, 2006); 173 nervana2:GFP (U. Lammel, unpublished observations); UAS:GFP; UAS:laminGFP; UAS:flp, nervana2Gal4 (Bloomington stock center); pvr 7.1 Viking:GFP (Olofsson and Page, 2005); 43Gal4 (Bloomington stock center); c527Gal4 (Hummel et al, 2002); FasIIGal4 (Mz507 ) (B. Altenhein, personal communication); chaGal4 (Salvaterra and Kitamoto, 2001);and SPG:Gal4 (Bainton et al, 2005). All deficiencies were obtained from the Bloomington stock collection.…”

“…Mutations in the splicing regulator Quaking lead to a dysmyelination phenotype in mice (Sidman et al, 1964;Ebersole et al, 1996). Similarly, mutations in the Drosophila ortholog how disrupt glial differentiation by affecting splicing (Edenfeld et al, 2006). One of the splicing targets of the HOW complex is neurexinIV, which encodes a septate junction component homologous to the mammalian Caspr protein.…”

Glial Cell Migration in the Eye Disc

“…For lineage analysis and cell ablation experiments, we used c527 and Mz97 (Hummel et al, 2002) and a Gal4 driver using regulatory sequences of the moody gene , UASfzr (Sigrist and Lehner, 1997) and UAShid (kindly provided by R. Lehmann, Skirball Institute, New York, NY) tubGal80 ts (McGuire et al, 2003). Additional fly stocks used were w 1118 and Nrx::GFP #454 (Edenfeld et al, 2006).…”

“…To fulfill this function, the subperineurial glial cells establish septate junctions, which can be visualized by the expression of the NeurexinIV protein (Baumgartner et al, 1996;Bainton et al, 2005;Schwabe et al, 2005). NeurexinIV expression can be faithfully detected using the GFP exon trap line 454 (Edenfeld et al, 2006). Using this gene trap insertion we detected two lines of NeurexinIV expression in the optic stalk apical to the axon bundle (Fig.…”