Drosophila salivary glands exhibit a regional reprogramming of gene expression during the third larval instar

A Kunitz type protease inhibitor related protein is synthesized in Drosophila prepupal salivary glands and released into the moulting fluid during pupation

From the Drosophila virilis late puff region 31C, we microcloned two neighbouring genes, Kil-1 and Kil-2, that encode putative Kunitz serine protease inhibitor like proteins. The Kil-1 gene is expressed exclusively in prepupal salivary glands. Using a size mutant of the KIL-1 protein and MALDI-TOF analysis, we demonstrate that during pupation this protein is released from the prepupal salivary glands into the pupation fluid covering the surface of the pupa. 3-D-structure predictions are consistent with the known crystal structure of the human Kunitz type protease inhibitor 2KNT. This is the first experimental proof for the extracorporal presence of a distinct Drosophila prepupal salivary gland protein. Possible functions of KIL-1 in the context of the control of proteolytic activities in the pupation fluid are discussed.

Evolution of 5S rRNA gene families in Drosophila

In Drosophila virilis, the three clusters of 5S rRNA genes on chromosome 5 comprise two different gene families (B and C), which differ profoundly in the organization of their spacer sequences. While C-type genes, which are found in two of the clusters, exhibit a true repetitive character, the B-type genes of the third cluster are each embedded in completely different genomic environments. Southern blots of genomic DNA of different D. virilis subspecies, D. hydei and D. melanogaster probed with 5S rRNA gene spacer and coding sequences demonstrate the specificity of C-type sequences for the D. virilis species group. The comparative analysis of flanking sequences of 5S rRNA genes of D. virilis, members of the D. melanogaster species subgroup and of the blowfly Calliphora erythrocephala reveals the existence of conserved sequence motifs both in the 5' upstream and 3' downstream flanking regions. Their possible roles in the control of expression and processing of the 5S rRNA precursor molecule are discussed.

Ecdysone-controlled mRNA stability in Drosophila salivary glands: deadenylation-independent degradation of larval glue protein gene message during the larval/prepupal transition

20-Hydroxyecdysone induces poly(A) shortening and the subsequent degradation of transcripts encoding the larval glue protein LGP-1 in Drosophila virilis late third larval instar salivary glands. Degradation concurs with the transient increase of ribonucleolytic activities in the gland cells. In vitro nuclease assays using crude cytoplasmic extracts of ecdysone-treated salivary glands demonstrate degradation to be deadenylation-independent and that the induced ribonucleolytic activities initiate the degradation of the Lgp-1 transcripts in putative single-stranded loop regions. The independence of degradation from deadenylation is also found in vivo in transformed D. melanogaster carrying a modified Lgp-1 gene.

In vivo functional characterization of an ecdysone response enhancer in the proximal upstream region of the Fbp1 gene of D. melanogaster

Transcription of the D. melanogaster Fat-body-protein-1 (Fbp1) gene is induced by the steroid hormone 20-hydroxyecdysone and is restricted to the fat body tissue at the end of the third larval instar. The location and functional properties of the Fbp1 cis-acting regulatory sequences contained in the region from -1386 to +80 relative to the transcription start were examined by transformation using hybrid constructs with the Adh or lacZ genes as reporters. Regulatory element(s) required for the full level of transcription of the Fbp1 gene were located between positions -1386 and -138. Sequences between -138 and -68 were able to drive transcription from a heterologous minimal promoter in the fat body of late third instar larvae. Remarkably, these sequences also conferred 20-hydroxyecdysone inducibility and behaved as an enhancer-like element. These results provide the first functional characterization, at the level of the whole organism, using a direct in vivo ecdysone induction assay, of a discrete ecdysone response element.

The salivary gland chromosomes of Drosophila virilis: a cytological map, pattern of transcription and aspects of chromosome evolution

By combining information from microscopical observation and photography a graphical map of Drosophila virilis salivary gland chromosomes was constructed. About 1,560 individual bands are shown and patterns of transcription at about 360 sites are indicated. The application of the map is demonstrated by using genetic, morphological and in situ hybridization data to identify the white-Notch regions of D. virilis and Drosophila melanogaster as homologous chromosome segments with constant and variable features.

Spatial organization of microtubules and microfilaments in larval and adult salivary glands of Drosophila melanogaster

We examined the distribution of microtubules and microfilaments by conventional fluorescence microscopy and laser scanning confocal microscopy in larval and adult salivary glands of Drosophila melanogaster. The cells of the larval salivary gland epithelium were characterized by the same spatial distribution of microfilaments, whereas microfilament localization was more complex in adult salivary glands, showing some regional differentiation. Microtubules distributed throughout the cell cytoplasm of the larval salivary glands, whereas in adult glands they were mostly observed in the basal or apical cytoplasm of the cells. These observations were related to the secretory process and the mechanism of saliva discharge.