Applying microarray-based technique to study and analyze silkworm (Bombyx mori) transcriptomic response to long-term high iron diet

Effects of Dietary Iron Quantities and Sources on Lymantria dispar (Lepidoptera: Erebidae) Survival and Development

Lymantria dispar L. is a serious invasive defoliator of broadleaf trees in both North America and Eurasia. When rearing L. dispar for research, the artificial diet must have a source of iron that is bioavailable and in the quantity needed to ensure normal development and survival. The standard iron supplement in L. dispar diet, amorphous ferric phosphate, is no longer commercially available, which motivated studies on alternative iron sources and concentrations. The responses of three L. dispar populations (including an L. dispar asiatica Vnukovskij population) to seven different iron doses were determined over two generations. The response to eight iron compounds and no added iron was also assessed over two generations for an L. dispar dispar population. The optimal levels of iron were 100, 150, and 198 mg/l of available iron for the New Jersey Standard Strain, a near-wild West Virginia population, and a near-wild Russian Far East population, respectively. All three populations showed symptoms of insufficient iron when reared on the lowest dose of iron and signs of excess iron at the highest two doses. All of the alternate iron sources evaluated provided adequate available iron, although three sources had some issues that may not make them the best options. These results reveal differences in nutritional requirements among different populations of L. dispar and verify the existence of viable replacement sources of iron for the standard amorphous ferric phosphate long used in L. dispar rearing.

Molecular cloning, expression and characterization of secreted ferritin in the silkworm, Bombyx mori

Ferritin is a ubiquitous iron storage protein which plays key role in regulating iron homeostasis and metabolism. In this paper, the ferritin heavy chain homologs (HCH) and light chain homologs (LCH) from Bombyx mori (BmFerHCH and BmFerLCH) were amplified through PCR and cloned into the expression vector pET-30a(+). The recombinant BmFerHCH and BmFerLCH expressed in Escherichia coli were in the form of insoluble inclusion bodies, indicating that the two proteins were not in their natural structural conformation. In order to obtain refolded ferritin in vitro, the inclusion bodies (BmFerHCH and/or BmFerLCH) were dissolved in denaturing buffer (100 mM Tris, 50 mM Glycine, 8 M urea, 5 mM DTT, pH 8.0) and then refolded in refolding buffer (100 mM Tris, 400 mM L-arginine, 0.2 mM PMSF, 0.5 mM DTT). The result showed that it was only when both BmFerHCH and BmFerLCH were present together in the denaturing buffer that refolding was successful and resulted in the formation of heteropolymers (H-L chain dimers) over homopolymers (H-H chain or L-L chain dimers). Moreover, the molecules (NaCl, Triton and glycerol) were found to enhance protein refolding. The optimum temperature, pH and ratios of BmFerHCH/BmFerLCH required for refolding were found to be 10 °C, pH 7, 1:1 or 1:2, respectively. Finally, the refolded ferritin had the ability to store iron, exhibited ferroxidase activity, and could withstand high temperatures and pH treatment, which is consistent with ferritin in other species.