Regulatory mechanisms controlling the timing of developmental events are crucial for proper development to occur. ftz-f1 is expressed in a temporally regulated manner following pulses of ecdysteroid and this precise expression is necessary for the development of Drosophila melanogaster. To understand how insect hormone ecdysteroids regulate the timing of FTZ-F1 expression, we purified a DNA binding regulator of ftz-f1. Mass spectroscopy analysis revealed this protein to be a fly homolog of mammalian B lymphocyte-induced maturation protein 1 (Blimp-1). Drosophila Blimp-1 (dBlimp-1) is induced directly by 20-hydroxyecdysone, and its product exists during high-ecdysteroid periods and turns over rapidly. Forced expression of dBlimp-1 and RNA interference analysis indicate that dBlimp-1 acts as a repressor and controls the timing of FTZ-F1 expression. Furthermore, its prolonged expression results in delay of pupation timing. These results suggest that the transient transcriptional repressor dBlimp-1 is important for determining developmental timing in the ecdysone-induced pathway.The steroid hormone ecdysone and its active metabolite 20-hydroxyecdysone (20E) (hereafter referred to collectively as ecdysone) are responsible for many essential developmental processes, including insect molting, metamorphosis, oogenesis, and embryogenesis (25,40). The insect ecdysone response provides an excellent model for studying hormone function, in which temporally regulated induction of multiple genes is required to control complex developmental events. For instance, at the onset of metamorphosis in Drosophila melanogaster, a large pulse of ecdysone causes the third-instar larval-to-prepupal transition. Based on the observation of puffs on polytene chromosomes in cultured salivary glands more than 30 years ago, it has long been known that there are at least four categories of ecdysone-inducible genes (1-4, 38). The early genes are induced directly by the ecdysone-receptor complex and are repressed by their products. The early-late genes are also induced directly by ecdysone but require an ecdysone-induced gene product(s) for maximal induction. The late genes are induced by the early gene products, and the mid-prepupal genes are induced only after ecdysone levels have declined. In the last two decades, many of the genes belonging to these four groups have been cloned, and their regulated expression profile has been confirmed. These include multiple transcription factors, which constitute an ecdysone-induced gene cascade.ftz-f1 is a mid-prepupal gene (29) that encodes a nuclear receptor-type transcription factor (30). The beta isoform of the ftz-f1 gene product is expressed not only during the mid-prepupal period at the onset of metamorphosis but also during late embryogenesis, just before larval ecdysis and eclosion (45,51,54,55). All of these periods closely follow declines in ecdysone levels. The importance of timing of ftz-f1 expression has been shown by rescue of ftz-f1 mutants by temporally specific expression of ␤FTZ-F1 as well...

BackgroundSPO11 is a key protein for promoting meiotic recombination, by generating chromatin locus- and timing-specific DNA double-strand breaks (DSBs). The DSB activity of SPO11 was shown by genetic analyses, but whether SPO11 exerts DSB-forming activity by itself is still an unanswered question. DSB formation by SPO11 has not been detected by biochemical means, probably because of a lack of proper protein-folding, posttranslational modifications, and/or specific SPO11-interacting proteins required for this activity. In addition, plants have multiple SPO11-homologues.ResultsTo determine whether SPO11 can cleave DNA by itself, and to identify which plant SPO11 homologue cleaves DNA, we developed a Drosophila bioassay system that detects the DSB signals generated by a plant SPO11 homologue expressed ectopically. We cytologically and genetically demonstrated the DSB activities of Arabidopsis AtSPO11-1 and AtSPO11-2, which are required for meiosis, in the absence of other plant proteins. Using this bioassay, we further found that a novel SPO11-homologue, OsSPO11D, which has no counterpart in Arabidopsis, displays prominent DSB-forming activity. Quantitative analyses of the rice SPO11 transcripts revealed the specific increase in OsSPO11D mRNA in the anthers containing meiotic pollen mother cells.ConclusionsThe Drosophila bioassay system successfully demonstrated that some plant SPO11 orthologues have intrinsic DSB activities. Furthermore, we identified a novel SPO11 homologue, OsSPO11D, with robust DSB activity and a possible meiotic function.

This study investigated the effect of feedings taurine-enriched rotifers on the growth and development of larval red sea bream (RSB). Rotifers incubated in taurine-enriched water at a taurine concentration of 800 mg L À1 (T-800) and 0 mg L À1 (T-0) were fed to larvae from 3 to 20 days after hatching (DAH). Notochord length, body weight and specific growth rate of T-800 group were significantly greater than those of T-0 at 14, 17, 9-11 and 18-20 DAH. Taurine content of larvae in the T-800 group increased rapidly from 11 DAH and thereafter remained significantly higher than T-0. Flexion larvae firstly appeared in both groups at 8 DAH, however, at 20 DAH post-flexion larvae were significantly more abundant in T-800 than T-0. While nucleic acid and protein contents (lg mg À1 wet fish) showed remarkable changes, ontogenetic growth in RSB larvae stage was observed to switch from hyperplastic growth to hypertrophic growth with the start of the flexion stage. Although a similar change in nucleic acid contents was observed between the two groups, the protein content (lg fish À1 ) and protein/DNA ratio of T-800 remained higher than that of T-0 during the hypertrophic growth period. These results suggest that dietary taurine accelerates the growth and development in RSB larvae especially during hypertrophic growth (flexion stage) after the early hyperplastic growth. Effect of taurine on red sea bream larvae Y-S Kim et al.

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