|Kim, Mijung - OHIO ST UNIV, COLUMBUS|
|Robich, Rebecca - OHIO ST UNIV, COLUMBUS|
|Denlinger, David - OHIO ST UNIV, COLUMBUS|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 11, 2006
Publication Date: November 1, 2006
Citation: Kim, M., Robich, R.M., Rinehart, J.P., Denlinger, D.L. 2006. Upregulation of two actin genes and redistribution of actin during diapause and cold stress in the northern house mosquito, Culex pipiens. Journal of Insect Physiology. 52(11-12):1226-1233. Interpretive Summary: Winter poses a major challenge for insects. To be successful in environments with distinct seasons, insects must grow and reproduce only for a few months during the summer and then survive the remainder of the year without feeding, while dealing with the stresses that winter brings to them. Most insects survive winter by entering diapause, a state that is characterized by, among other things, an increase in stress tolerance. Recently, our group searched for genes that were expressed at increased levels (upregulated) during diapause in the northern house mosquito. One of the genes we found to be upregulated was actin, a key building block of the cytoskeleton (the framework that supports a cell). This study further characterizes the role of actin during diapause in this mosquito. We have found that two different actin genes are upregulated during diapause. This is important because many different types of actin exist in any given organism, and some of them can be involved in increased cold tolerance, which is an important part of diapause in this species. Additionally, we used actin-specific stains to observe actin behavior during cold exposure in diapausing individuals. We discovered that actin behaves differently in diapausing individuals, further suggesting that the actin genes that are upregulated during diapause play a role in the increased cold tolerance seen in this species.
Technical Abstract: Two actin genes cloned from Culex pipiens L. are upregulated during adult diapause. Though actins 1 and 2 were expressed throughout diapause, both genes were most highly expressed early in diapause. These changes in gene expression were accompanied by a conspicuous redistribution of polymerized actin that was most pronounced in the midguts of diapausing mosquitoes that were exposed to low temperature. In nondiapausing mosquitoes reared at 25°C and in diapausing mosquitoes reared at 18°C, polymerized actin was clustered at high concentrations at the intersections of the muscle fibers that form the midgut musculature. When adults 7-10 days post-eclosion were exposed to low temperature (-5°C for 12 h), the polymerized actin was evenly distributed along the muscle fibers in both nondiapausing and diapausing mosquitoes. Exposure of older adults (1 month post-eclosion) to low temperature (-5 °C for 12 h) elicited an even greater distribution of polymerized actin, an effect that was especially pronounced in diapausing mosquitoes. These changes in gene expression and actin distribution suggest a role for actins in enhancing survival of diapausing adults during the low temperatures of winter by fortification of the cytoskeleton.