Developmental genetics of the essential Drosophila nucleoporin nup154: Allelic differences due to an outward-directed promoter in the P-element 3 ' end

Drosophila nup154 encodes a predicted nucleoporin homologous to yeast Nup17 0p, Nup157p, and vertebrate Nup155, all of which are major components of th e nuclear pore complex (NPC). Unlike its yeast homologs, nup154 is essentia l for viability. Animals with strong loss-of-function nup154 mutations caus ed by P-element insertion in the 5'-UTR of the gene died as larvae with sma ll discs, brains, and testes. nup154 mRNA expression appeared developmental ly regulated in tissues of wild-type embryos, larvae, and adults, suggestin g that new nup154 synthesis is required when assembly of new;NPCs is requir ed, as in proliferating or growing tissues. Two additional nup154 alleles a lso associated with different P-element inserts in the 5'-UTR were viable b ut had strong loss-of-function sterile phenotypes, including failure to mai ntain spermatogenic stem cells and failure to progress into vitellogenic st ages of oogenesis. Lethality vs, viability correlated with orientation of t he P-element inserts in the different alleles. Transcript analysis by 5'-RA CE suggested a mechanism for allelic differences: an outward-directed promo ter internal to the P-element 3' end able to drive sufficient expression of the nup154 transcript for viability but not for fertility.