Functional role of aspartic proteinase cathepsin D in insect metamorphosis

Abstract

BackgroundMetamorphosis is a complex, highly conserved and strictly regulated development process that involves the programmed cell death of obsolete larval organs. Here we show a novel functional role for the aspartic proteinase cathepsin D during insect metamorphosis.ResultsCathepsin D of the silkworm Bombyx mori (BmCatD) was ecdysone-induced, differentially and spatially expressed in the larval fat body of the final instar and in the larval gut of pupal stage, and its expression led to programmed cell death. Furthermore, BmCatD was highly induced in the fat body of baculovirus-infected B. mori larvae, suggesting that this gene is involved in the induction of metamorphosis of host insects infected with baculovirus. RNA interference (RNAi)-mediated BmCatD knock-down inhibited programmed cell death of the larval fat body, resulting in the arrest of larval-pupal transformation. BmCatD RNAi also inhibited the programmed cell death of larval gut during pupal stage.ConclusionBased on these results, we concluded that BmCatD is critically involved in the programmed cell death of the larval fat body and larval gut in silkworm metamorphosis.

20‐Hydroxyecdysone‐upregulated proteases involved in Bombyx larval fat body destruction

“…BmCatB had the highest expression abundances, and was highly expressed at larval-pupal transformation, which was consistent with its trends detected in haemocytes and fat body previously (Xu & Kawasaki, 2001;Lee et al, 2009). The transcriptional variation of BmCatD from fifth instar to prepupa here was similar to its overlapped detection from that of the last larval instar to pupa; both reached their expressional high peaks at wandering and then were followed by a decline (Gui et al, 2006). However, the high mRNA level of BmCatD at wandering was found to be much less than 4M stage in Bombyx fat body ( Fig.…”

“…20E is the primary hormone in the architecture of insects' moulting and metamorphosis, which is confirmed to regulate the PCD, including apoptosis, autophagy and histolysis of midgut (Rabossi et al, 2004;Tian et al, 2012Tian et al, , 2014Yang et al, 2017). BmCatB and BmCatD are previously reported to be induced by 20E in Bombyx fat body (Gui et al, 2006;Lee et al, 2009); however, other tissue-destruction-related proteases are rarely checked. So in this case, 20E was injected into day 2 of fifth instar (5L-2) larvae, when the 20E level is low and the fat body is sensitive to 20E injection (Liu et al, 2006;Tian et al, 2014).…”

“…Cathepsin D has physiological functions in PCD of the larval tissues in Bombyx, as well as in the hydrolysis of cysteine peptidase inhibitors in midguts in Dysdercus peruvianus (Wu et al, 2011;Yu et al, 2012;Pimentel et al, 2017). Additionally, cathepsin D is also involved in vitellogenin production and degradation in mosquitoes and fat body proteins histolysis in Ceratitis capitata and Bombyx (Cho & Raikhel, 1992;Rabossi et al, 2004;Gui et al, 2006).…”

Intestinal aspartate proteases TiCatD and TiCatD2 of the haematophagous bug Triatoma infestans (Reduviidae): Sequence characterisation, expression pattern and characterisation of proteolytic activity

“…Data significantly different to the previous pH value are indicated by * (P 0.05), ** (P 0.01) and *** (P 0.001). and Ixodus ricinus, and are with about 43 kDa also congruent with the molecular mass of these enzymes (Terra et al, 1988;Cho et al, 1991;Cho and Raikhel, 1992;Rabossi et al, 2004;Gui et al, 2006;Sojka et al, 2008), except for the cathepsin D from Tribolium castaneum in which the molecular mass at 22 kDa is apparently smaller. The cathepsin D-like proteases from Aedes aegypti and R. prolixus have first been detected as native enzymes with molecular masses of 80 and 88 kDa, respectively, which seem to be homodimers respectively composed of two 40 and two 44 kDa subunits (Terra et al, 1988;Cho and Raikhel, 1992).…”

Is digestive cathepsin D the rule in decapod crustaceans?

“…By hydrolyzing intracellular proteins it participates in various physiological processes involved in maintaining tissue homeostasis, regulation of apoptosis, activation of hormones and growth factors (Benes et al, 2008), to mention a few. In insects, cathepsin D-like peptidases showed specialized functions like cellular remodelling during metamorphosis (Gui et al, 2006). In humans, cathepsin D is synthesized in the rough endoplasmic reticulum as a pre-pro-enzyme but rapidly loses the signal peptide.…”