Entomology and Nematology Department, University of Florida, Gainesville, FL 32611, USA.
Department of Biology, Tufts University, Medford, MA 02155, USA.
J Exp Biol. 2023 Jun 1;226(11). doi: 10.1242/jeb.245244. Epub 2023 Jun 9.
Evolutionary change in diapause timing can be an adaptive response to changing seasonality, and even result in ecological speciation. However, the molecular and cellular mechanisms regulating shifts in diapause timing remain poorly understood. One of the hallmarks of diapause is a massive slowdown in the cell cycle of target organs such as the brain and primordial imaginal structures, and resumption of cell cycle proliferation is an indication of diapause termination and resumption of development. Characterizing cell cycle parameters between lineages differing in diapause life history timing may help identify molecular mechanisms associated with alterations of diapause timing. We tested the extent to which progression of the cell cycle differs across diapause between two genetically distinct European corn borer strains that differ in their seasonal diapause timing. We show the cell cycle slows down during larval diapause with a significant decrease in the proportion of cells in S phase. Brain-subesophageal complex cells slow primarily in G0/G1 phase whereas most wing disc cells are in G2 phase. Diapausing larvae of the earlier emerging, bivoltine E-strain (BE) suppressed cell cycle progression less than the later emerging, univoltine Z-strain (UZ) individuals, with a greater proportion of cells in S phase across both tissues during diapause. Additionally, resumption of cell cycle proliferation occurred earlier in the BE strain than in the UZ strain after exposure to diapause-terminating conditions. We propose that regulation of cell cycle progression rates ultimately drives differences in larval diapause termination, and adult emergence timing, between early- and late-emerging European corn borer strains.
滞育时间的进化变化可能是对季节变化的适应性反应，甚至导致生态物种形成。然而，调节滞育时间变化的分子和细胞机制仍知之甚少。滞育的一个标志是靶器官（如大脑和原始成虫结构）的细胞周期大量减慢，细胞周期增殖的恢复表明滞育终止和发育的恢复。比较滞育生活史时间不同的谱系之间的细胞周期参数，可能有助于确定与滞育时间改变相关的分子机制。我们测试了两个在季节性滞育时间上存在差异的欧洲玉米螟遗传上不同的品系之间，滞育过程中的细胞周期进展在多大程度上存在差异。我们表明，细胞周期在幼虫滞育期间减慢，S 期细胞的比例显著下降。脑-食管复合体细胞主要在 G0/G1 期减慢，而大多数翅膀盘细胞处于 G2 期。较早出现的二化型 E 品系（BE）的滞育幼虫比较晚出现的单化型 Z 品系（UZ）个体抑制细胞周期进展的程度要小，在两个组织中，S 期的细胞比例都更高。此外，在暴露于终止滞育的条件后，BE 品系的细胞周期增殖恢复比 UZ 品系更早。我们提出，细胞周期进展速度的调节最终导致了早期和晚期出现的欧洲玉米螟品系之间幼虫滞育终止和成虫出现时间的差异。
