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Fig. 1. Enhancer trap pattern and gene structure. (A,B) 
-Galactosidase activity is demonstrated in adult testis tissue (A) and in larval testis anlagen (B). The terminal epithelium is indicated by an arrowhead in A. An arrow points to the apical expression seen at both stages (A,B). The relationship between germ cells and cyst cells is shown in the diagram with the cyst cells in red and the interconnected germ cells in grey. The situation is depicted for the premeiotic phase where the two cyst cells with their unstained nuclei are equivalent (as an example surrounding four germ cells) as well as for the postmeiotic phase (with four instead of the 64 elongated spermatids) in which the head and tail cyst cells with -galactosidase-positive nuclei surround the germ cells in a directed manner. (C) Separated spermatid bundles show two stained nuclei (arrow and arrowhead) proving that both head and tail cyst cell are active. (D) The position of the spermatid nuclei is shown by Hoechst 33258 staining (double arrow). (E) The genomic organisation of the noa gene is shown (top). Exons 1-5 are shown as white boxes. The integration sites for the three P-element lines are indicated by arrows. Restriction sites within the gene are indicated for EcoRI (E), HindIII (H), SacI (S) and XbaI (X). In head RNA an alternative form of the first exon (1') was found which extends the first exon by 60 nt in 3' direction thus leading to an alternative splice donor site. The two bars (A,A') in the 3' UTR indicate poly(A) rich regions mentioned in the RNaseH experiment (see Fig. 2B). The two transcripts are outlined below the diagram. The exons show the transcribed sequences in grey and the coding region in black. The bracketed line corresponds to a PCR fragment that was used as probe to prove the existence of the long RNA species. The sequences contained within the rescue construct are given at the bottom (see Materials and Methods).
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