Timers in Early Development of Sea Urchin Embryos

To elucidate the timing mechanisms in the early development of sea urchin embryos, we measured the times of initiation of the first four cleavages, of ciliary movement, of primary mesenchyme cell ingression, and of gastrulation at four temperatures ranging from 11 to 20°C. The times of cleavage and of initiation of ciliary movement showed similar temperature dependency, indicating that these events may be controlled by a common timer (the first timer). Although batches of eggs often showed variation in the period between fertilization and the first cleavage, their subsequent cleavages were more regular. This indicates that the first timer may not start at fertilization. The ingression of mesenchyme cells and the onset of gastrulation showed similar temperature dependency that was higher than that of other events, suggesting the existence of a second timer. Temperature shift experiments indicate that the second timer starts at the mid-blastula (the 8–9th cleavage) stage when divisions of blastomeres become asynchronous.     

Pattern Regulation of the Leg Disc of the Fleshfly, Sarcophaga peregeina

A fate map of the hind leg disc of Sarcophaga peregrina was constructed by examining the adult structures of implanted disc fragments. The locations of presumptive adult structures in the disc were similar to those of fore leg disc of Drosophila and Sarcophaga ruficornis . However, the concentric borderlines of the segments could not be ascertained in the present case.
Pattern regulation of disc fragments was studied by culturing them either in adult females for several days or for 3 days in mature larvae placed on wet condition. Cultured disc fragments regenerated or duplicated as in Drosophila , with some exceptions. For instance, the region with a high density of positional values, the upper medial quarter, of the fore leg disc of Drosophila was not found. A characteristic difference in the rate of regeneration or duplication was observed in the implanted fragments, when cultured in larvae or adult hosts. This variable pattern regulation in larval and adult hosts could be due to different compositions of the hemolymph in which would healing of the implanted disc fragments takes place.     

Determination and Regulation Capacities of the Wing Disc of the Fleshfly, Sarcophaga peregrina

Unilateral extirpation of the wing discs was performed on mid- and late-third instar larvae of Sarcophaga peregrina to investigate the regulation capacities of the thoracic discs. Out of 636 operated larvae, 175 became adult and all of them exhibited hemithoracic structures, lacking any adult structures in the operated side, which were normally produced from a wing disc. These findings suggest that the wing disc does not possess the capacity of bicentric regulation to produce the thoracic structures of the opposite side.     

Does seed production of spring ephemerals decrease when spring comes early?

To predict the effect of global warming on plant reproductive success, seed-sets of spring ephemerals were compared between a year of extremely warm spring (2002) and normal years at cool-temperate deciduous forests in northern Japan. The spring of 2002 was the warmest in the last 40years and most spring-ephemeral plants bloomed 7–17days earlier than usual. The seed-set of bumblebee-pollinated Corydalis ambigua drastically decreased in 2002 in every population. The small bee-pollinated Gagea lutea also significantly decreased in 2002. However, the seed-sets of two fly pollinated species, Adonis ramosa and Anemone flaccida, were not influenced by early flowering. These results indicat that the effect of global warming on seed production of spring ephemerals differs between species depending on the type of pollinators, and that bee-pollinated species can have serious impacts on reproductive success as a result of climate change.     

Regenerated cell wall of carrot protoplasts isolated from suspension-cultured cells

Protoplasts of Daucus carota L. cultured in a synthetic liquid medium resumed cell division after about 4 days of cultivation. During this lag period, nucleic acid and protein showed only slight increases but the protoplasts commenced cell-wall regeneration soon after the removal of lytic enzymes. The originally spherical protoplasts became ellipsoidal before they underwent division. Radioactive glucose and myo-inositol were readily utilized by the protoplasts. Most of the radioactivity, however, appeared in extracellular polysaccharides and only a small portion was deposited in the regenerated wall. The sugar composition of new cell wall, as studies by chemical analysis and incorporation of labelled precursors, was shown to be considerably different from that of normal cell wall.     

Ecdysteroid Metabolism in Insects

SYNOPSIS. Remarkable development in ecdysone research has beenachieved during this decade in terms of organic chemistry, biochemistryand physiology, although the problems concerning the actionand behavior of ecdysteroids in target cells still remain tobe solved. To elucidate the dynamics of secretion, action andinactivation of ecdysone, the metabolic pathways for ecdysteroidshave been examined in several insect species and are summarizedhere. There may be at least three major inactivation processesfor ecdysone, namely, (i) catabolic degradation, (ii) conjugateformation and (iii) epimerization to 3-epi-ecdysteroids through3-dehydro compounds. Two means of regulation of the ecdysonetiter to ensure normal development of insects are seen in Sarcophaga:(1) Enhanced epimerization of 20-hydroxyecdysone at the prepupalstage resulting in a decreasing titer of biologically activeecdysteroids. (2) Reactivation of a conjugate at the onset ofadult development (a stage with an increasing titer of biologicallyactive ecdysteroids).