A subcellular localization of the gene product of the DNase-1 locus in Drosophila melanogaster

DNase II: genes, enzymes and function

Deoxyribonuclease (DNase) II, which was discovered more than 50 years ago, is a mammalian endonuclease that functions optimally at acid pH in the absence of divalent cations. Its lysosomal localization and ubiquitous tissue distribution suggested that this enzyme played a role in the degradation of exogenous DNA encountered by phagocytosis, although the relative importance of such a role was unknown. Subsequent investigations also suggested that DNase II was important for DNA fragmentation and degradation during cell death. Within the last few years, our work and that of others has lead to the cloning of various mammalian DNase II genes as well as the identification and characterization of highly homologous genes in the invertebrates Caenorhabditis elegans and Drosophila melanogaster. Interestingly, studies of the C. elegans DNase II homolog NUC-1 were the first to suggest that DNase II enzymes were fundamentally important in engulfment-mediated DNA degradation, particularly that associated with programmed cell death, due to the presence of persistent apoptotic-cell nuclei within phagocytic cells in nuc-1 mutants. Similarly, mutation of the Drosophila DNase II-like gene was found to result in the accumulation of low-molecular-weight DNA throughout the animals. Homozygous mutation (knockout) of the DNase II gene in mice revealed a much more complex and extensive phenotype including perinatal lethality. The lethality of DNase II-knockout mice is likely the result of multiple developmental defects, the most obvious being a loss of definitive erythropoiesis. Closer examination revealed that a defect in engulfment-mediated DNA degradation is the primary defect in DNase II-null mice. In this review, we have compiled information from studies on DNase II from various organisms to provide a consensus model for the role of DNase II enzymes in DNA degradation.

Molecular characterization of the lysosomal acid phosphatase from Drosophila melanogaster

In Drosophila, unlike humans, the lysosomal acid phosphatase (Acph-1) is a non-essential enzyme. It is also one of the most rapidly evolving gene-enzyme systems in the genus. In order to determine which parts of the enzyme are conserved and which parts are apparently under little functional constraint, we cloned the gene from Drosophila melanogaster via a chromosomal walk. Fragments from the gene were used to recover an apparently full-length cDNA. The cDNA was sub-cloned into a Drosophila transformation vector where it was under the control of the 5' promoter sequence of the hsp-70 gene. Three independent transformants were obtained; in each, Acph-1 expression from the cDNA was constitutive and not dependent on heat shock, as determined by densitometric analyses of the allozymic forms of the enzyme. The pattern of expression indicates the hsp-70 and endogenous Acph-1 promoters act together in some, but not all, tissues. The sequence of the cDNA was determined using deletions made with exonuclease III, and primers deduced from the cDNA sequence were used to sequence the genomic clone. Five introns were found, and putative 5' upstream regulatory sequences were identified. Amino acid sequence comparisons have revealed several highly conserved motifs between Drosophila Acph-1 and vertebrate lysosomal and prostatic acid phosphatases.