To test the potential usefulness of transgenic rabbits as production systems for human proteins of pharmaceutical value, we cloned the rabbit beta-casein promoter and fused it to the genomic sequence of the human interleukin-2 (hIL2) gene. Four transgenic female rabbits were tested for expression and biological activity of the foreign protein in their milk. The milk of all four females proved to contain biologically active hIL2. The results show that transgenic rabbits may represent a convenient and economic system for the rapid production of biologically active protein in milk.
Summary 1. Many insects reproduce by parthenogenesis. In one of the largest orders of the animal kingdom, the Hymenoptera, most of its members reproduce by arrhenotokous parthenogenesis. Egg activation in parthenogenetic animals obviously cannot be caused by fertilization of the egg. The question of what initiates egg development in parthenogenetically reproducing animals has been studied for a few insect species and is discussed in this article. 2. The grasshopper Melanoplus differentialis is one of several Orthoptera displaying accidental parthenogenesis. In this species, egg laying provides the stimulus to the completion of meiosis and start of embryonic development in unfertilized and probably also in fertilized eggs. The same holds true for the dipteran insect Drosophila melanogaster which exhibits rudimentary parthenogenesis, and for D. mercatorum showing accidental parthenogenesis. The precise way in which oviposition affects the egg is unknown. 3. The stick insect Carausius morosus reproduces by obligatory thelytoky. The triggering factor for removal of the meiotic block and initiation of embryonic development is oxygen from the air which penetrates to the egg through the micropyle immediately after oviposition. The oviposition act itself is not necessary for activation of the egg. 4. Comparative studies of the different types of oogenesis in the dipteran insect Heteropeza pygmaea show that in paedogenetically developing follicles meiotic arrest in prophase is of very short duration and a meiotic block at the end of oogenesis is absent. It is suggested that in this case triggering events for egg development are dispensable. On the other hand, under certain experimental conditions a meiotic block can be established in some of these follicles. 5. Investigations on the Ichneumonid wasp Pimpla turionellae have shown that unfertilized, male‐determined eggs ‐ and most likely also fertilized, femaledetermined eggs ‐ are activated by mechanical stress exerted on the eggs during natural or imitated oviposition. This mechanical stress, in addition, activates a streaming system which is independent of meiotic completion and nuclear multiplication. Egg activation by egg distortion is also found in the Pteromalid species Nasonia vitripennis and occurs presumably in many other Hymenoptera. 6. Carausius morosus, Pimpla turionellae and Nasonia vitripennis are species with parthenogenetic reproduction for which the natural factors responsible for the initiation of egg development have been identified. The cases of Pimpla turionellae and Nasonia vitripennis are of particular interest because of the feasibility of artificially imitating the natural activating mechanism. 7. It is concluded that apart from fertilization various events at oviposition may trigger egg development. In addition, the occurrence of rudimentary parthenogenesis in many sexually reproducing animal species suggests that sperm entry and fertilization may frequently be necessary for the continuation of egg development rather than for its initiation.
1. In the paedogenetic gall midgeHeteropeza pygmaea, embryonic growth is at the expense of maternal tissues. The possibility of culturing egg folliclesin vitro throughout the entire period of embryonic development allowed the filming of embryogenesis. In the present paper development, growth and degeneration of egg folliclesin vitro (at 25° C) are analysed by time-lapse film. 2. During development of the mature egg follicle up to germ band formation, the yolk globules undergo alternative periods of oscillation and rest within the yolk syncytium. During the periods of time in which the yolk globules are at rest, cleavage divisions take place. All egg follicles analysed showed 13 resting periods which corresponded to the 13 cleavage divisions. A comparison with other investigations indicates, that oscillation of the yolk globules is not required for the migration of the nuclei, but is connected with a special function of the yolk syncytium in paedogenetic gall midges. 3. From the 1st until the 6th cleavage division the average duration of the mitotic cycle decreases from 75 to 50 minutes; from the 6th until the 13th cleavage division it increases to more than 3 hours. 4. Blastokinesis, i. e. germ band extension and germ band retraction, in all probability is the consequence of autonomous movements of the germ band and not of a morphogenetic effect of the yolk syncytium. 5. Egg follicles from different preparations show varying rates of development and growth whereas egg follicles within one culture drop develop and grow with the same rate although they may not be at exactly the same stage of development. 6. In certain stages of development (cleavage, germ band retraction and dorsal closure) the increase in length of the egg follicle is discontinuous. During germ band retraction many egg follicles show up to 7 elongations and contractions, which may amount to as much as one fifth of the egg follicle length. The period of time of one elongation-contraction cycle is between 1 1/4 and 2 3/4 hours and increases by 1/4 hour with each new cycle. At the same time as the egg follicle length increases, its width decreases and vice-versa, suggesting that the increase in volume is continuous. 7. Measurements of two egg follicles at the blastoderm stage revealed rhythmic fluctuations in length which amounted to no more than one fiftieth of the total egg follicle length. There may be as many as 60 such fluctuation cycles, each of which has a constant period of about 15 minutes. The endogenous process underlying these fluctuations is obscure. 8. The egg follicles which degenerate in culture are generally the smaller and less developed ones in any given preparation; however, until their sudden degeneration, they show the same rate of growth and development as the non degenerating egg follicles. 9. The extraordinary mode of paedogenetic egg development ofHeteropeza is interpreted as a displacement of embryogenesis into oogenesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.