Processing of procathepsin from Musca domestica eggs

Two cathepsins B are responsible for the yolk protein hydrolysis in Culex quinquefasciatus

Despite the established role of Culex quinquefasciatus as a vector of various neurotropic viruses, such as the Rift Valley and West Nile viruses, as well as lymphatic filariasis, little is known regarding the organism’s reproductive physiology. As in other oviparous animals, vitellogenin, the most important source of nutrients for the embryo development, is digested by intracellular proteases. Using mass spectrometry, we have identified two cathepsin B homologues partially purified by self-proteolysis of Cx. quinquefasciatus total egg extract. The transcriptional profile of these two cathepsin B homologues was determined by quantitative RT-PCR, and the enzymatic activity associated with the peptidase was determined in ovaries after female engorgement. According to the VectorBase (vectorbase.org) annotation, both cathepsin B homologues shared approximately 66% identity in their amino acid sequences. The two cathepsin B genes are expressed simultaneously in the fat body of the vitellogenic females, and enzymatic activity was detected within the ovaries, suggesting an extra-ovarian origin. Similar to the transcriptional profile of vitellogenin, cathepsin B transcripts were shown to accumulate post-blood meal and reached their highest expression at 36 h PBM. However, while vitellogenin expression decreased drastically at 48 h PBM, the expression of the cathepsins increased until 84 h PBM, at which time the females of our colony were ready for oviposition. The similarity between their transcriptional profiles strongly suggests a role for the cathepsin B homologues in vitellin degradation.

Sequence and function of lysosomal and digestive cathepsin D-like proteinases of Musca domestica midgut

Musca domestica larvae display in anterior and middle midgut contents, a proteolytic activity with pH optimum of 3.0-3.5 and kinetic properties like cathepsin D. Three cDNAs coding for preprocathepsin D-like proteinases (ppCAD 1, ppCAD 2, ppCAD 3) were cloned from a M. domestica midgut cDNA library. The coded protein sequences included the signal peptide, propeptide and mature enzyme that has all conserved catalytic and substrate binding residues found in bovine lysosomal cathepsin D. Nevertheless, ppCAD 2 and ppCAD 3 lack the characteristic proline loop and glycosylation sites. A comparison among the sequences of cathepsin D-like enzymes from some vertebrates and those found in M. domestica and in the genomes of Aedes aegypti, Drosophila melanogaster, Tribolium castaneum, and Bombyx mori showed that only flies have enzymes lacking the proline loop (as defined by the motif: DxPxPx(G/A)P), thus resembling vertebrate pepsin. ppCAD 3 should correspond to the digestive cathepsin D-like proteinase (CAD) found in enzyme assays because: (1) it seems to be the most expressed CAD, based on the frequency of ESTs found. (2) The mRNA for CAD 3 is expressed only in the anterior and proximal middle midgut. (3) Recombinant procathepsin D-like proteinase (pCAD 3), after auto-activation has a pH optimum of 2.5-3.0 that is close to the luminal pH of M. domestica midgut. (4) Immunoblots of proteins from different tissues revealed with anti-pCAD 3 serum were positive only in samples of anterior and middle midgut tissue and contents. (5) CAD 3 is localized with immunogold inside secretory vesicles and around microvilli in anterior and middle midgut cells. The data support the view that on adapting to deal with a bacteria-rich food in an acid midgut region, M. domestica digestive CAD resulted from the same archetypical gene as the intracellular cathepsin D, paralleling what happened with vertebrates. The lack of the proline loop may be somehow associated with the extracellular role of both pepsin and digestive CAD 3.

Embryonic diapause highlighted by differential expression of mRNAs for ecdysteroidogenesis, transcription and lipid sparing in the cricket Allonemobius socius

Embryos of the ground cricket, Allonemobius socius, enter diapause 4-5 days post-oviposition and overwinter in this dormant state that is characterized by developmental arrest. Suppressive subtractive hybridization and quantitative real-time PCR reveal eight candidate genes in pre-diapause embryos that show promise as regulators of diapause entry, when compared with embryos not destined for diapause. Identifications are based both on the magnitude/consistency of differential mRNA abundances and the predicted functions of their products when placed in context of the physiological and biochemical events of diapause characterized in our companion paper. The proteins CYP450, AKR and RACK1 (associated with ecdysteroid synthesis and signaling) are consistently upregulated in pre-diapause, followed by major downregulation later in diapause. The pattern suggests that elevated ecdysone may facilitate onset of diapause in A. socius. Upregulation seen for the transcription factors Reptin and TFDp2 may serve to depress transcription and cell cycle progression. Cathpesin B-like protease, ACLY and MSP are three downregulated genes associated with yolk mobilization and/or metabolism that we predict may promote lipid sparing. Finally, embryos that have been in diapause for 10 days show a substantially different pattern of mRNA expression compared with either pre-diapause or embryos not destined for diapause, with the majority of mRNAs examined being downregulated. These transcript levels in later diapause suggest that a number of upregulated genes in pre-diapause are transiently expressed and are less essential as diapause progresses.

A trypsin-like protease with apparent dual function in early Lepeophtheirus salmonis (Krøyer) development

BACKGROUND

Trypsin-like serine proteases are involved in a large number of processes including digestive degradation, regulation of developmental processes, yolk degradation and yolk degradome activation. Trypsin like peptidases considered to be involved in digestion have been characterized in Lepeophtheirus salmonis. During these studies a trypsin-like peptidase which differed in a number of traits were identified.

RESULTS

An intronless trypsin-like serine peptidase (LsTryp10) from L., salmonis was identified and characterized. LsTryp10 mRNA is evenly distributed in the ovaries and oocytes, but is located along the ova periphery. LsTryp10 protein is deposited in the oocytes and all embryonic cells. LsTryp10 mRNA translation and concurrent degradation after fertilization was found in the embryos demonstrating that LsTryp10 protein is produced both by the embryo and maternally. The results furthermore indicate that LsTryp10 protein of maternal origin has a distribution pattern different to that of embryonic origin.

CONCLUSION

Based on present data and previous studies of peptidases in oocytes and embryos, we hypothesize that maternally deposited LsTryp10 protein is involved in regulation of the yolk degradome. The function of LsTryp10 produced by the embryonic cells remains unknown. To our knowledge a similar expression pattern has not previously been reported for any protease.

Glucose metabolism during embryogenesis of the hard tick Boophilus microplus

Glucose metabolism plays an essential role in the physiology and development of almost all living organisms. In the present study we investigated glucose metabolism during the embryogenesis of the hard tick Boophilus microplus. An increase in glucose and glycogen content during the embryonic development of B. microplus was detected and shown to be due to the high enzyme activity of both gluconeogenesis and glycolytic pathways. Glucose 6-phosphate (G-6P), formed by hexokinase, is driven mainly to pentose-phosphate pathway, producing fundamental substrates for cellular biosynthesis. We detected an increase in glucose 6-phosphate dehydrogenase and pyruvate kinase activities after embryo cellularization. Accumulation of key metabolites such as glycogen and glucose was monitored and revealed that glycogen content decreases from day 1 up to day 6, as the early events of embryogenesis take place, and increases after the formation of embryo cellular blastoderm on day 6. Glucose and guanine (a sub-product of amino acids degradation in arachnids) accumulate almost concomitantly. The activity of phosphoenolpyruvate carboxykinase was increased after embryo cellularization. Taken together these data indicate that glycogen and glucose, formed during B. microplus embryogenesis after blastoderm formation, are produced by intense gluconeogenesis.

Analysis of fat body transcriptome from the adult tsetse fly, Glossina morsitans morsitans

Tsetse flies (Diptera: Glossinidia) are vectors of pathogenic African trypanosomes. To develop a foundation for tsetse physiology, a normalized expressed sequence tag (EST) library was constructed from fat body tissue of immune-stimulated Glossina morsitans morsitans. Analysis of 20,257 high-quality ESTs yielded 6372 unique genes comprised of 3059 tentative consensus (TC) sequences and 3313 singletons (available at http://aksoylab.yale.edu). We analysed the putative fat body transcriptome based on homology to other gene products with known functions available in the public domain. In particular, we describe the immune-related products, reproductive function related yolk proteins and milk-gland protein, iron metabolism regulating ferritins and transferrin, and tsetse's major energy source proline biosynthesis. Expression analysis of the three yolk proteins indicates that all are detected in females, while only the yolk protein with similarity to lipases, is expressed in males. Milk gland protein, apparently important for larval nutrition, however, is primarily synthesized by accessory milk gland tissue.

Cathepsin D-mediated yolk protein degradation is blocked by acid phosphatase inhibitors

Vitellin (VT) is a lipoglycophosphoprotein stored inside the eggs of every oviparous organism during oogenesis. In the blood-sucking bug Rhodnius prolixus, VT is deposited inside growing oocytes together with two acid hydrolases: acid phosphatase (AP) and cathepsin D (CD). Egg fertilization triggers AP activity and VT proteolysis in vivo [Insect Biochem. Mol. Biol. 2002 (32) 847]. Here, we show that CD is the main protease targeting VT proteolysis during egg development. CD activity in total egg homogenates is blocked by the classical aspartyl protease inhibitor, pepstatin A. Surprisingly, AP inhibitors such as NaF, Na+/K+ tartrate, and inorganic phosphate also block VT proteolysis, whereas this effect is not observed when tyrosine phosphatase inhibitors such as vanadate and phenylarsine oxide or an inhibitor of alkaline phosphatases such as levamisole are used in a VT proteolysis assay. NaF concentrations that block isolated AP activity do not affect the activity of partially purified CD. Therefore, a specific repressor of VT proteolysis must be dephosphorylated by AP in vivo. In conclusion, these results demonstrate for the first time that acid hydrolases act cooperatively to promote yolk degradation during egg development in arthropods.

Procathepsin and acid phosphatase are stored in Musca domestica yolk spheres

Yolk spheres present in mature invertebrate oocytes are composed of yolk proteins and proteolytic enzymes. In the fly Musca domestica, yolk proteins are degraded during embryogenesis by a cathepsin-like proteinase that is stored as a zymogen. An acid phosphatase is also active in the yolk spheres during Musca embryogenesis. In this paper we show that procathepsin and acid phosphatase are initially stored by a different pathway from the one followed by yolk protein precursors. Both enzymes are taken up by the oocytes and transitorily stored into small vesicles (lysosomes) surrounding the early yolk spheres. Fusion of both structures, the early yolk spheres and lysosomes, creates the mature yolk spheres.

Phage display selection can differentiate insecticidal activity of soybean cystatins

Plant cysteine proteinase inhibitors (phytocystatins) have been implicated as defensive molecules against Coleopteran and Hemipteran insect pests. Two soybean cystatins, soyacystatin N (scN) and soyacystatin L (scL), have 70% sequence identity but scN is a much more potent inhibitor of papain, vicilin peptidohydrolase and insect gut proteinases. When these cystatins were displayed on phage particles, papain-binding affinity and CPI activity of scN were substantially greater than those of scL, in direct correlation with their relative CPI activity as soluble recombinant proteins. Furthermore, scN substantially delayed cowpea weevil (Callosobruchus maculatus (F.)) growth and development in insect feeding bioassays, whereas scL was essentially inactive as an insecticide. Papain biopanning selection of phage-displayed soyacystatins resulted in a 200-1000-fold greater enrichment for scN relative to scL. These results establish that binding affinity of cystatins can be used in phage display biopanning procedures to select variants with greater insecticidal activity, illustrating the potential of phage display and biopanning selection for directed molecular evolution of biological activity of these plant defensive proteins.

Localization of the proenzyme form of the vitellin-processing protease in Blattella germanica by affinity-purified antibodies

During Blattella germanica embryo development, the nutritive yolk protein vitellin is processed by a cysteine protease, which is activated proteolytically from a proprotease during acidification of yolk granules. A murine polyclonal antiserum was generated with the purified proprotease as the immunogen. The antiserum was made monospecific to proprotease by subtractive affinity chromatography using proprotease-free yolk proteins as ligand. The purified antibodies were employed to investigate the temporal and spatial expression of the proprotease during vitellogenesis and embryo development. Anti-proprotease-reactive peptides appeared in extracts of fat bodies and ovarian follicles of post-mating females, but not in fat bodies of males or the fat bodies or follicles of unmated females, suggesting that the proprotease is synthesized extraovarially. Use of the antibodies was extended to monitor the kinetics of proprotease disappearance during early embryo development.

Cysteine proteinase 1 (CP1), a cathepsin L-like enzyme expressed in the Drosophila melanogaster haemocyte cell line mbn-2

We have isolated cDNA clones encoding the full-length Drosophila melanogaster cysteine proteinase 1 (CP1). The clones were isolated from the Drosophila melanogaster haemocytic mbn-2 cell line, where the gene is relatively strongly expressed, giving a transcript of 1.6 kb in size. We present the sequence encoding the full-length protein, and deduced the genomic organization of the gene by comparison to previously published genomic partial sequence data. Immunofluorescence shows that CP1 is localized in small granules, probably lysosomes, in mbn-2 cells. The data presented suggest a role for cysteine proteinase in immune functions in insects. It is likely to participate in the degradation of internalized material in phagocytic cells.

A cysteine protease that processes insect vitellin. Purification and partial characterization of the enzyme and the proenzyme

A cysteine protease that initiates degradation of vitellin (Vt) in the orthopteran Blattella germanica, and its proprotease precursor, were purified from yolk and partially characterized. The protease, purified 300-fold, contains three peptides of Mr 27,000, 29,000, and 31,000. A comparison of the purified enzyme's action pattern on Vt in vivo and in vitro confirmed its role in Vt processing. Protease-deficient yolk (day 0 postovulation) contained peptides of Mr 35,500, 37,000, 39,000, and 41,000, which were absent from yolk with protease activity. These were replaced by three peptides of approximately Mr 29,000, at days 2-3, the same time in development that protease expression and acidification of yolk granules occur (Nordin, J. H., Beaudoin, E. L., and Liu, X. (1991) Arch. Insect Biochem. Physiol. 18, 177-192). Acidification of purified proprotease converted it to three peptides of approximately Mr 29, 000 with cysteine protease activity. This conversion also required participation of a cysteine protease. Activated proprotease had the same pH activity profile, susceptibility to inhibitors, and cathepsin classification (L) as the protease. These results indicate that the Vt-processing protease is derived from a proprotease, which is activated in vivo by a developmentally regulated decrease in intragranular pH.