A putative digestive cysteine proteinase from Drosophila melanogaster is predominantly expressed in the embryonic and larval midgut

Plant seeds have biodefense systems for protection against insects. One of these systems may be based on the occurrence of phytocystatins, cysteine proteinase inhibitors of plant origin, that probably inhibit insect cysteine proteinases involved in digestive functions. To elucidate a molecular mechanism for this biodefense phenomenon, we isolated a gene encoding a putative digestive cysteine proteinase from Drosophila melanogaster, a suitable model species. The cloned genomic DNA fragment contained a sequence encoding a cysteine proteinase. The mature enzyme from the encoded protein, termed Drosophila cysteine proteinase-1, consisted of 218 amino acid residues. Drosophila cysteine proteinase-1 showed 67% similarity in its amino acid sequence to a lobster cysteine proteinase-3 contained in the digestive juice. This enzyme also showed significant similarities to cysteine proteinases of animal origin such as cathepsins H and L, and to proteinases of plant origin such as rice oryzains alpha and beta. In situ hybridization studies for the embryo showed that the mRNA for Drosophila cysteine proteinase-1 was predominantly expressed in the midgut. Larval alimentary organs, such as the salivary gland and the midgut including the gastric caeca, also expressed the mRNA at significant levels. These observations, suggesting that Drosophila cysteine proteinase-1 is a digestive cysteine proteinase which can be used as a model target of phytocystatins, will hopefully lead to new strategies for the regulation of pest insects.

Calpain localization changes in coordination with actin-related cytoskeletal changes during early embryonic development of Drosophila

Calpain, a calcium-dependent intracellular protease, was identified in Drosophila melanogaster. Drosophila calpain has an amino acid sequence highly homologous to those of mammalian calpains and exhibits a distinct domain structure consisting of cysteine protease and calcium-binding domains. Specific antibodies raised against a recombinant calpain fragment were used to identify the localization of calpain in developing Drosophila embryos. Calpain was first detected near the anterior pole and in posterior region of the embryo just after fertilization. The anterior calpain disappeared during the cleavage cycles. On the other hand, the posterior calpain moved to the posterior pole when polar buds were formed, and condensed just below the pole cells. At cleavage cycles 8 and 9, when nuclei reached the egg surface, calpain was localized between the nuclei at the surface beneath the precleavage furrows. Co-staining experiments with anti-actin antibody revealed that calpain condenses specifically at the edge of and between actin caps that underlie the plasma membrane immediately above each nucleus. These results indicate that calpain is involved in the dynamic changes in the embryonic cytoskeleton, especially actin-related structures, during early embryogenesis prior to cellularization.

Drosophila phospholipase C-gamma expressed predominantly in blastoderm cells at cellularization and in endodermal cells during later embryonic stages

A Drosophila gene encoding a gamma-type isozyme of phosphoinositide-specific phospholipase C (PLC) was isolated and characterized. The gene, termed plc-gamma d, was mapped at position 14B-C of the X chromosome. The encoded protein, termed PLC-gamma D, contains X and Y regions, common to all known PLC isozymes. The two regions are split by a Z region that comprises two src homology 2 and one src homology 3 domains and is characteristic of gamma-type mammalian PLC (PLC-gamma 1 and -gamma 2). The deduced amino acid sequence of PLC-gamma D shows overall similarity to mammalian PLC-gamma s; no large deletion was observed except the short C-terminal extended region. In particular, the two split catalytic domains (X and Y regions) and the regulatory Z region including the src homology 2 and src homology 3 domains are well conserved. The mRNA is expressed throughout development, but expression is relatively higher during the embryonic stage, suggesting fundamental and important roles in both cell proliferation and differentiation. Distribution of the mRNA during embryogenesis, as analyzed by whole amount in situ hybridization, revealed that the mRNA emerges and reaches maximum levels at the cellular blastoderm stage and then decreases rapidly to a lower level. In later embryonic stages, invaginated anterior and posterior midgut primordia show high levels of mRNA expression, and fused midgut also maintains a high level of expression. In other tissues and cells, the mRNA was detected at lower levels. These results indicate that Drosophila PLC-gamma may be involved in universal cellular processes mediated possibly by receptor tyrosine kinases during embryogenesis and may also play specific roles during cellularization and midgut differentiation.

A Drosophila homolog of human proto-oncogene ret transiently expressed in embryonic neuronal precursor cells including neuroblasts and CNS cells

We have identified a Drosophila gene encoding a putative receptor tyrosine kinase by screening a genomic DNA library with a DNA probe for a Drosophila homolog of fibroblast growth factor receptors. The newly isolated gene codes for a transmembrane protein most similar in sequence to a mammalian proto-oncogene ret; thus, the gene was termed Dret. Dret mRNA is transcribed in very small amounts in the embryonic, larval, and pupal stages. Whole mount in situ hybridization experiments revealed that the mRNA is transiently expressed in neuroblasts in early embryos. In late embryos, Dret mRNA was detected in subpopulations of differentiating CNS and PNS cells. In addition, Dret expression was affected in neurogenic mutants. These results suggest that Dret can be considered as a functional homolog of mammalian ret and should play important roles in neurogenesis.

Identification of a novel Drosophila gene encoding a Cdc2-related protein kinase

We have identified a novel gene encoding a putative protein kinase from a Drosophila genomic library. The gene, about 2 kbp in length, consists of four exons and codes for a protein of 349 amino acid residues. The deduced sequence shows significant similarity to various kinases, especially to a subgroup of Ser/Thr kinases related to Cdc2 kinase; thus, the gene was termed Dcdrk (Drosophila cdc2-related kinase gene). Among the kinases examined, mammalian galactosyltransferase-associated 58 kDa protein kinase showed the highest homology (about 50% identity in the kinase domain) to Dcdrk kinase. Northern blot analysis revealed that the Dcdrk mRNA is expressed throughout development in nearly constant amounts. Moreover, a whole mount in situ hybridization experiment showed that the Dcdrk mRNA is ubiquitously distributed in almost all embryonic cells and tissues, suggesting a universal function of Dcdrk, possibly in cell cycle regulation.

Molecular cloning and expression of cDNA encoding rat skeletal muscle cytosolic sialidase

We have isolated a cDNA clone encoding the cytosolic sialidase of rat skeletal muscle. Degenerate oligonucleotides, based on amino acid sequence data for the purified enzyme, were used as primers to amplify fragments of the gene from rat skeletal muscle cDNA by the polymerase chain reaction. The amplified cDNA fragment was then applied as probe to screen a rat skeletal muscle cDNA library. The longest cDNA clone thus isolated was incomplete at the 5'-end, and therefore an amplified cDNA from the 5'-end portion of the gene was further generated by polymerase chain reaction. These two cDNAs were used to construct a cDNA encoding the entire sequence of rat sialidase. The composite sequence encodes an open reading frame of 379 amino acids that include all sequenced peptides. Although the deduced amino acid sequence is not largely similar to those of bacterial and parasite sialidases, it contains two Asp blocks, the conserved sequence of the sialidases from these microorganisms. When the cDNA was inserted into an expression vector followed by transformation in Escherichia coli, sialidase activity appeared in the cell extract. The sialidase could be completely immunoprecipitated by antiserum against the cytosolic sialidase of rat skeletal muscle.

Molecular cloning of cDNAs for two Xenopus proteasome subunits and their expression in adult tissues

Proteasome, a large protein complex with ATP-dependent protease activities, is composed of non-identical but closely related multi-subunits. Using cDNAs for rat proteasome subunits as probes, we obtained three cDNA clones for two Xenopus proteasome subunits from ovary cDNA library. The primary structures of the three cDNAs showed high homology to the corresponding proteasome subunits of other mammalian species (above 90%) and also considerable homology to those of Drosophila and yeast. These results indicate that the sequences of proteasome subunits are well conserved during evolution. Northern blot hybridization revealed that RNAs for the newly isolated subunits (XC8 and XC9) and the previously isolated subunit (XC3) occur at very high levels in testis and ovary, at moderately high levels in lung, skin kidney and spleen, and at low levels in liver, stomach and muscle. It was also shown that relative amounts of the mRNAs for the three subunits are similar in all the adult tissues examined. From these results, we concluded that the expression of the genes for the three subunits (XC3 XC8 and XC9-1) takes place in a roughly coordinated manner in different adult tissues.

Distinct expression of two Drosophila homologs of fibroblast growth factor receptors in imaginal discs

The expression of two Drosophila homologs of FGF receptors (DRF1 and DRF2) in imaginal discs was studied. DFR1 mRNA was observed in several imaginal discs, whereas DFR2 mRNA was not detected. DFR1 expression in the wing and leg discs took place in probable myoblasts in a pattern similar to that of twist, a mesodermal gene. The mRNA was also detected in the morphogenetic furrow and its posterior region of the eye disc and around the proliferation center of the brain. These results suggest that DFR1 is involved in the development of mesodermal and neuronal cells constituting the adult body.

Calpastatin has two distinct sites for interaction with calpain--effect of calpastatin fragments on the binding of calpain to membranes

Calpain, a ubiquitously distributed intracellular cysteine protease in animals, is thought to be activated at the cell membrane in the presence of micromolar levels of calcium ions. Calpastatin, the sole specific proteinaceous inhibitor for calpain, inhibits not only proteolytic activity, but also the binding of calpain to cell membranes. The inhibition of calpain binding to membranes by calpastatin fragments was analyzed. A calpastatin peptide containing the inhibitory sequence did not inhibit the binding of calpain to membranes. On the other hand, binding was prevented by a fragment without the activity to inhibit proteolytic activity. These data indicate that calpain binds to cell membranes through a site (regulatory site) other than the active site and that calpastatin inhibits the binding of calpain to cell membranes via a site (regulatory inhibition site) other than the inhibitory sequence. Calpain and calpastatin can undergo independent interactions: interaction between the catalytic site of calpain and the inhibitory sequence of calpastatin, and interaction between the regulatory site of calpain and the regulatory inhibition site of calpastatin. The interaction between the regulatory site of calpain and the regulatory inhibition site of calpastatin is essential for the regulation of calpain activity.

Expression of oryzacystatin cDNA using yeast artificial chromosome under ADH promoter in baker's yeast

We constructed an expression vector into a yeast artificial chromosome (YAC) harboring the cDNA for oryzacystatin, a cysteine proteinase inhibitor from rice, under the control of the yeast ADH promoter. When the expression vector was introduced into Saccharomyces cerevisiae in the form of either an artificial chromosome or a circular plasmid, transformants carrying the DNA grew well in a selective medium. However, the content of the introduced DNA decreased significantly during passages in non-selective YPD medium. The stability of the introduced DNA was enhanced in selected clones obtained as colonies viable in selective medium after many passages in YPD medium. The stable transformants thus obtained expressed the mRNA for oryzacystatin at levels as high as those of intrinsic yeast ADH.

Primary structure and cell-type specific expression of a gustatory G protein-coupled receptor related to olfactory receptors

We have reported on the partial structures of a multigene family encoding GTP-binding protein (G protein)-coupled, seven-transmembrane receptors expressed in the tongue (Abe, K., Kusakabe, Y., Tanemura, K., Emori, Y., and Arai, S. (1993) FEBS Lett. 316, 253-256). Here we describe a full-length cDNA clone encoding a tongue cell-type specific receptor. The encoded protein consists of 312 amino acid residues. In overall structure, the protein is similar to known G protein-coupled, seven-transmembrane receptors such as an olfactory receptor (56% identity) but is significantly different in part, particularly in NH2-terminal extracellular and COOH-terminal cytoplasmic domain structures. Northern analysis showed that the mRNA for this protein is expressed only in the epithelium of the tongue, not in other organs. In situ hybridization experiments clearly indicated that the mRNA is expressed exclusively on the tongue apical surface, not on the reverse side of the tongue nor in its muscle layer. Expression was also detected in the taste buds and surrounding cellular tissues of the fungiform and circumvallate papillae. It is suggested that this gustatory receptor structurally related to olfactory receptors may be a candidate for a taste receptor.

Large-scale production and purification of an Erwinia ananas ice nucleation protein and evaluation of its ice nucleation activity

The ice nucleation-active protein of Erwinia ananas IN-10 (inaA protein) was over-expressed as inclusion bodies in Escherichia coli in a yield of 15.3 mg of inaA protein from 60 mg of bacterial cells on a dry-matter basis. The inaA protein was purified from the inclusion bodies by solubilization with detergents to obtain a protein preparation free from sugar and lipid. This preparation had a distinct ice nucleation activity, indicating that the inaA protein per se is able to act as a nucleus.

The effect of combination therapy of radiation and Z-100, an arabinomannan on tumor growth in mice

The effect of radiation combined with intraperitoneal administration of Z-100, an immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis, was studied using Meth A fibrosarcoma in BALB/c mice and metastasis of Lewis lung carcinoma, 3LL, in C57BL/6 mice. In mice bearing Meth A fibrosarcoma, a moderate degree of growth inhibition was observed in the group of single therapy with Z-100 or radiation (10 Gy). When radiation was combined with Z-100, the tumor growth was significantly inhibited. In mice bearing 3LL, slight inhibition of pulmonary metastasis was observed in the group of single therapy, while significant degrees of inhibition of primary tumor growth and pulmonary metastasis were observed in the combination group. This suggests the usefulness of combined use of Z-100 in radiation therapy.

Two FGF-receptor homologues of Drosophila: one is expressed in mesodermal primordium in early embryos

The fibroblast growth factor (FGF)/receptor system is thought to mediate various developmental events in vertebrates. We examined molecular structures and expression of DFR1 and DFR2, two Drosophila genes closely related to vertebrate FGF-receptor genes. DFR1 and DFR2 proteins contain two and five immunoglobulin-like domains, respectively, in the extracellular region, and a split tyrosine kinase domain in the intracellular region. In early embryos, DFR1 RNA expression, requiring both twist and snail proteins, is specific to mesodermal primordium and invaginated mesodermal cells. At later stages, putative muscle precursor cells and cells in the central nervous system (CNS) express DFR1. DFR2 expression occurs in endodermal precursor cells, CNS midline cells and certain ectodermal cells such as those of trachea and salivary duct. FGF-receptor homologues in Drosophila would thus appear essential for generation of mesodermal and endodermal layers, invaginations of various types of cells, and CNS formation.

Multiple genes for G protein-coupled receptors and their expression in lingual epithelia

Using the polymerase chain reaction (PCR), we identified a gene family including more than 60 members which encoded similar G protein-coupled seven-transmembrane receptors. Sequence analyses of six representatives out of the 60 PCR clones showed that they had significant structural similarity to olfactory and optic receptors. Their expression is restricted in the surface of lingual epithelia.

Identification of four FGF receptor genes in Medaka fish (Oryzias latipes)

Four types of cDNA clones encoding tyrosine kinases highly homologous to mammalian fibroblast growth factor receptors (FGF-R) were isolated from Medaka fish (Oryzias latipes) by the reverse transcription-polymerase chain reaction. Comparison of the four deduced amino acid sequences with four known mammalian FGF-Rs indicated that four FGF-R species corresponding to mammalian FGF-Rs exist universally in vertebrates including fishes, although FGF-R4 might have diverged sequences between fishes and mammals. Each of four FGF-R genes is transcribed to various extents as multiple mRNAs possibly by alternative splicing in adult fishes.

Subtype determination of Drosophila embryonic external sensory organs by redundant homeo box genes BarH1 and BarH2

BarH1 and BarH2 are two closely related homeo box genes that form a small complex at the Bar locus on the X chromosome of Drosophila. By immunostaining, we showed that BarH1 and BarH2 proteins are coexpressed in cells belonging to the central and peripheral nervous systems in embryos. In external sensory (es) organs, their expression was particularly apparent in thecogens (glial cells) and neurons at late development. Although deletion of BarH2 caused no appreciable morphological change in es organs, the simultaneous deletion of BarH1 and BarH2 led to a homeotic change in these organs with consequent conversion from campaniform-like sensilla to trichoid sensilla. In contrast, the overexpression of either BarH1 or BarH2 resulted in opposite morphological change. It would thus follow that BarH1 and BarH2 are a pair of redundant homeo box genes required for the subtype specification of es organs.

Isolation and characterization of a Xenopus cDNA which encodes a homeodomain highly homologous to Drosophila Distal-less

A novel homeobox gene of Xenopus was isolated from the ovary cDNA library. The homeodomain of the encoded protein was homologous to that of Drosophila Distal-less (Dll), and the gene was termed Xdll. The mRNA exists in a large amount in ovary, and in a small amount in testis, but was not detected in muscle, kidney, gut, and liver. The mRNA also occurs in a large amount in oocytes and is maintained in unfertilized eggs and cleavage stage embryos as a maternal mRNA at a low but distinctly detectable level. The amount of the mRNA per embryo increases gradually in later stages by zygotic expression. Embryo dissection experiment revealed that the transcript is abundant in the anterior region at the neurula stage, suggesting that Xdll may play a role in the establishment of the structures in the anterior part of the embryo.

Isolation and characterization of rat 3Y1 fibroblast clones overexpressing the src homology region of phospholipase C-gamma 2

To examine the regulatory function of the src-related SH2 and SH3 (SH2/SH3) region of phospholipase C-gamma 2 (PLC-gamma 2), we expressed this region of rat PLC-gamma 2 cDNA in rat 3Y1 fibroblasts and isolated and characterized a number of clones (approximately 20 clones). An increase of endogenous tyrosine kinase activity was observed in all cell clones that highly expressed a translational product of the SH2/SH3 domain. Moreover, endogenous phosphatidylinositol 4,5-bisphosphate hydrolyzing activity was also enhanced in these clones, and PLC-gamma 1 seemed to be preferentially activated among endogenous PLC isozymes. Genistein, an inhibitor of tyrosine kinase, inhibited this activation of PLC-gamma 1, and tyrosine phosphorylation was observed on PLC-gamma 1 molecules, indicating the involvement of tyrosine kinases in the PLC-gamma 1 activation. These results suggest that the SH2/SH3 region of PLC-gamma would function as a multidirectional regulator which controls at least two major signaling pathways: tyrosine kinase and phosphatidylinositol 4,5-bisphosphate hydrolysis.