Ecdysone-dependent and ecdysone-independent programmed cell death in the developing optic lobe of Drosophila

AbstractThe adult optic lobe of Drosophila develops from the primordium during metamorphosis from mid-3rd larval stage to adult. Many cells die during development of the optic lobe with a peak of the number of dying cells at 24h after puparium formation (h APF). Dying cells were observed in spatio-temporal specific clusters. Here, we analyzed the function of a component of the insect steroid hormone receptor, EcR, in this cell death. We examined expression patterns of two EcR isoforms, EcR-A and EcR-B1, in the optic lobe. Expression of each isoform altered during development in isoform-specific manner. EcR-B1 was not expressed in optic lobe neurons from 0 to 6h APF, but was expressed between 9 and 48h APF and then disappeared by 60h APF. In each cortex, its expression was stronger in older glia-ensheathed neurons than in younger ones. EcR-B1 was also expressed in some types of glia. EcR-A was expressed in optic lobe neurons and many types of glia from 0 to 60h APF in a different pattern from EcR-B1. Then, we genetically analyzed EcR function in the optic lobe cell death. At 0h APF, the optic lobe cell death was independent of any EcR isoforms. In contrast, EcR-B1 was required for most optic lobe cell death after 24h APF. It was suggested that cell death cell-autonomously required EcR-B1 expressed after puparium formation. βFTZ-F1 was also involved in cell death in many dying-cell clusters, but not in some of them at 24h APF. Altogether, the optic lobe cell death occurred in ecdysone-independent manner at prepupal stage and ecdysone-dependent manner after 24h APF. The acquisition of ecdysone-dependence was not directly correlated with the initiation or increase of EcR-B1 expression

Integrated effects of thermal acclimation and challenge temperature on cellular immunity in the plusiine moth larvae Chrysodeixis eriosoma (Lepidoptera: Noctuidae)

Temperature is one of the most influential factors for animals. The acclimation (rearing) and challenge temperatures are often more important than the given temperature per se. These effects on physiological responses have been known, but not well understood on immune responses. Here, we investigated the integrated effects of rearing and challenge temperatures on haemocyte populations in larvae of a plusiine moth, Chrysodeixis eriosoma. We hypothesize that the haemocyte concentration is decreased (increased) at higher (lower) temperatures from rearing temperatures and that the proportions of haemocyte types exhibit directional changes at higher (lower) temperatures to compensate for immune reactions. We expect that increasing (decreasing) the challenge temperature from the rearing temperature enhances (reduces) phagocytic activity. We found that higher temperatures slightly decreased the haemocyte concentration. We detected small changes in the proportions of haemocyte types among rearing temperatures, but the changes were non‐directional and most of them were statistically insignificant. We also found the integrated effects only with increases in the challenge temperatures, which resulted in increased phagocytosis, whereas no apparent reactions were detected with decreases in the challenge temperatures. Our results show that the haemocyte concentration is significantly affected by the rearing temperature, which implies that haematopoiesis depends on the ambient temperature.We discuss some adaptive and non‐adaptive components for the positive integrated effects of increases in the challenge temperatures. We also discussed the obtained non‐responsiveness in the integrated effects with decreases in the challenge temperatures

Transcriptome Responses of Insect Fat Body Cells to Tissue Culture Environment

Tissue culture is performed to maintain isolated portions of multicellular organisms in an artificial milieu that is outside the individual organism and for considerable periods of time; cells derived from cultured explants are, in general, different from cells of the corresponding tissue in a living organism. The changes in cultured tissues that precede and often explain the subsequent cell proliferation of explant-derived cells have been partially studied, but little is known about the molecular and genomic basis of these changes. Comparative transcriptomics of intact and cultured (90 hours in MGM-450 insect medium) Bombyx mori tissues revealed that fewer genes represented a larger portion of the transcriptome of intact fat body tissues than of cultured fat body tissues. This analysis also indicated that expression of genes encoding sugar transporters and immune response proteins increased during culture and that expression of genes encoding lipoproteins and cuticle proteins decreased during culture. These results provide support for hypotheses that cultured tissues respond immunologically to surgery, adapt to the medium by accelerating sugar uptake, and terminate their identity as part of an intact organism by becoming independent of that organism