Gene expression of HSP90 and HSP70 in four silkworm hybrids (Bombyx mori L.) in response to severe thermal shock

Abstract

Usually silkworm egg producers provide several silkworm hybrids with different qualities of productivity and viability traits. This study was conducted to compare the expression of HSP70 and HSP90 genes among different silkworm hybrids. In the fourth day of fifth larval instar of two Japanese maternal parents (103×104 and 107×110) and two Chinese maternal parents (110×107 and 104×103), silkworm larval fat body was sampled from heat shock (45 °C for 35 min) and non-heat shock groups. Sampling was done at 0, 2, 4 and 24 h after heat shock. Gene expression of HSP70 and HSP90 (target genes) were measured by qRT-PCR using RPL27a as reference gene. The prolonged heat shock (8 h at 39 °C) was utilized to examine the thermal tolerance of larvae in comparison with control group (24°C). The results showed both HSP70 and HSP90 have been up-regulated in the treated larvae. The hybrids with Japanese female parents (107×110 and 103×104) were more sensitive than two others; moreover in these hybrids, HSP90 and HSP70 were expressed significantly more than others after heat exposure. The maximum expression was occurred in the time zero, then a decreasing trend was observed over time. Comparison of larval mortality among four hybrids revealed that (103×104) and (110×107) hybrids had the highest and the lowest mortality rate.