Influence of temperature variation on gene expression and cocoon production in Bombyx mori Linnaeus, 1758 (Lepidoptera: Bombycidae).

Silkworms (Bombyx mori) are lepidopterans of economic importance for global silk production. However, factors that directly affect the yield and quality of silkworm cocoon production, such as diseases and temperature fluctuations, cause great economic losses. Knowing how they respond to rearing temperature during the most critical stage of their life cycle (i.e., fifth instar) could provide information on their adaptation and improve silk production. In the current work, we analyzed transcriptional data from two groups of B. mori that were reared at 26 °C and 34 °C throughout the fifth instar. The silkworms and cocoons were weighed. In total, 3115 transcripts were differentially expressed (DE; including 1696 down-regulated and 1419 up-regulated) among the 29,157 sequences found by transcriptome assembly. We emphasize the genes associated with immunological response, transcription factors, silk biosynthesis, and heat shock proteins, among the DE transcripts in response to the temperature conditions. Silkworms reared at 34 °C presented a reduced mean body weight (-0.944 g in comparison to the 26 °C group), which had a direct impact on the weight of cocoons formed and the silk conversion rate. These changes were statistically significant when compared to silkworms reared at 26 °C. Mortality rates (6 and 9 %, at 26 °C and 34 °C, respectively) were similar to those obtained in breeding fields. The findings provide information on the biological processes involved in the temperature response mechanism of silkworms, as well as information that may be used in future climatization processes at rearing facilities and in breeding for improved thermotolerance.

A New Approach to Chromosomal Evolution in the Giant Water Bug (Heteroptera: Belostomatidae).

The genus Belostoma, known colloquially as "giant water bugs," presents striking cytogenetic diversity and extensive chromosome variability. Notwithstanding, its karyotype evolution is not well understood. We analyzed 8 species of Belostoma (77 samples). The meiotic analysis revealed 2n = 14 + XY for Belostoma horvathi and Belostoma candidulum; 2n = 22 + XY for Belostoma cummings; 2n = 26 + X1X2Y for Belostoma dentatum, Belostoma elongatum, and Belostoma discretum; and 2n = 26 + X1X2X3Y for Belostoma testacopallidum and Belostoma dilatatum. All species showed holokinetic chromosomes. Based on heterochromatin distribution patterns and 18S rDNA, the species of the genus Belostoma were separated into four groups. The analysis of C0t-1 DNA showed that the repetitive DNA, partly composed of microsatellite DNA, was absent on the Y chromosome. Fluorescent in situ hybridization (FISH) using a microdissected X chromosome in species with simple sex system presents uniform hybridization in the nuclear region corresponding to the X chromosome. Species with multiple systems revealed discrete markings. The present data in conjunction with the existing literature led us to propose a new evolutionary hypothesis for the group, with an ancestral karyotype with a low diploid number, simple sex determination system, and nucleolus organizer regions (NORs) on the sex chromosomes. That karyotype would have originated other karyotypes through agmatoploidy, simploidy, heterochromatinization, and movement of the 18S rDNA.

Creatine does not promote hypertrophy in skeletal muscle in supplemented compared with nonsupplemented rats subjected to a similar workload.

The purpose of this study was to test the hypothesis that creatine (Cr) supplementation may promote an additional hypertrophic effect on skeletal muscle independent of a higher workload on Cr-supplemented trained muscle compared with Cr-nonsupplemented trained muscle. Male Wistar rats (2-3 months old, 250-300 g) were divided randomly into 4 groups (n = 8 per group): nontrained without Cr supplementation (CO), nontrained with Cr supplementation (CR), trained without Cr supplementation (TR), and trained with Cr supplementation (TRCR). Creatine supplementation was given at 0.5 g/kg per day. Trained groups were submitted to a 5-week resistance training program (5 d/wk). The progressive workloads were similar between the Cr-supplemented (TRCR) and Cr-nonsupplemented (TR) trained groups; the only difference between groups was the Cr treatment. After the 5-week experiment, the soleus muscle was dissected to analyze the cross-sectional area (CSA) of the muscle fibers. Resistance training promoted a significant (P < .05) increase in the muscle fibers CSA in the TR group compared with the CO group. However, no additional hypertrophic effect was found when Cr supplementation was added to training (TRCR vs TR comparison, P > .05). In addition, Cr supplementation alone did not promote significant alterations in muscle fiber CSA (CR vs CO comparison, P > .05). We conclude that Cr supplementation does not promote any additional hypertrophic effect on skeletal muscle area when Cr-supplemented trained muscles are submitted to same training regimen than Cr-nonsupplemented trained muscles. Specifically, any benefits of Cr supplementation on hypertrophy gains during resistance training may not be attributed to a direct anabolic effect on the skeletal muscle.