Oogenesis in the anuran Xenopus laevis can be divided into six stages based on the anatomy of the developing oocyte. Stage I consists of small (50 to 100 μ) colorless oocytes whose cytoplasm is transparent. Their large nuclei and mitochondrial masses are clearly visible in the intact oocyte. Stage II oocytes range up to 450 μ in diameter, and appear white and opaque. Stage I and II are both previtellogenic. Pigment synthesis and yolk accumulation (vitellogenesis) begins during Stage III. Vitellogenesis continues through Stage IV (600 to 1000 μ), the oocytes grow rapidly, and the animal and vegetal hemispheres become differentiated. By Stage V (1000 to 1200 μ) the oocytes have nearly reached their maximum size and yolk accumulation gradually ceases. Stage VI oocytes are characterized by the appearance of an essentially unpigmented equatorial band. They range in size from 1200 to 1300 μ, are postivtellogenic and ready for ovulation. These stages of oocyte development have been correlated with physiological and biochemical data related to oogenesis in Xenopus.

Oogenesis in Xenopus laevis (Daudin). I. Stages of oocyte development in laboratory maintained animals.

Publisher Summary Among animal hormones, juvenile hormone (JH) is distinctive because of its unique structure and the diversity of its effects on insect development and reproduction. This chapter reviews the actions of JH on the fat body, gonads, accessory glands, muscle, and nervous system of adult insects. Whereas the epidermis is a major target of premetamorphic JH action, it has been studied little in adult insects, which generally do not moult. However, since the development of yellow pigmentation that accompanies sexual maturation in adult male locusts is clearly dependent on JH-regulation processes, in which cellular and molecular mechanism are investigated. The rapid recent progress in understanding how ecdysteroids regulate the gene activities has resulted from the opportunities afforded by drosophila melanogaster: mapped and characterized mutants, polytene chromosomes with puffs marking active genes, efficient germ-line transformation. The recognition of two aspects of JH action in the tissues of adult insects is reviewed. A model for understanding some aspects of priming by JH may be found in the action of ecdysteroids, where early genes produce factors needed for the expression of late genes. In structure, thyroxine is very different from JH, but there is considerable resemblance between thyroxine and phenoxyphenoxy carbamate, fenoxycarb. Functionally, there are marked similarities. Thyroxine governs metamorphosis in amphibians, but is remarkably pleiotropic in governing many processes ranging from the maturation of the central nervous system to thermoregulation. The chapter emphasizes the importance of selecting insect systems on the basis of their optimal features for research, rather than historical precedent or economic importance. With selection of appropriate systems and application of the cell and molecular research techniques now available, the elusive problem of JH action should soon yield to enlightenment.

Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects

Vitellogenin is the generic name for a unique group of proteins that are synthesized extraovarially and become the major egg yolk protein, vitellin. Similar proteins are found in all animals with yolky eggs. Because of their high concentration in the egg, and the relative ease with which they can be purified, these proteins are excellent material for the study of the regulation of their synthesis from the molecular, developmental, and physiological points of view. This review covers the synthesis, uptake, and physical and chemical properties of vitellogenins and vitellins in insects. The term vitellogenin was derived from vitellogenesis (102), the period of rapid oocyte growth during which yolk is deposited. Once inside the oocyte these proteins are known as vitellins, because in some cases the molecules are changed during uptake. The definition of vitellogenins has traditionally included the following criteria: (a) They usually comprise 60-90% of the soluble egg yolk proteins (13, 69); (b) they are not made the oocyte, the fat body being the site of synthesis (22, 69, 102); (c) are present in large amounts only in females and thus have been called female-specific proteins (11, 102), although rigorous techniques have revealed small amounts in males (83, 119) and so this definition is not exclusive; and (d) they are selectively taken up by the oocyte during vitellogenesis (120). Because of the dynamics of the uptake mechanism (112,

/pdf/vitellogenin-and-vitellin-in-insects-13xmoaybil.pdf

Vitellogenin and vitellin in insects

Publisher Summary This chapter describes the different aspects of vitellogenesis and oocyte assembly The major components of fish oocytes are derived from the blood-borne high-molecular-weight compound, vitellogenin, which is synthesized in the liver of oviparous vertebrates The classification of vitellogenin as a phospholipoglycoprotein indicates the crucial functional groups that are carried on the protein backbone of the molecule—namely, lipids, some carbohydrates, and phosphate groups In the rainbow trout, estrone administration leads to the induction of vitellogenin synthesis in the liver and its release into the bloodstream, but estrone displays only 5%–12% of the potency of estradiol The biochemical information concerning vitellogenin clearly indicates that a great deal of posttranslational modification must occur in the liver cell to reach the finished product seen in the serum An integral part of estradiol action is the observed hypercalcemia in vitellogenic fish, which can largely be ascribed to the calcium-binding properties of phosphorylated and highly charged, components of the native vitellogenin molecule

5 Vitellogenesis and Oocyte Assembly

Publisher Summary Vitellogenins are defined as the predominant yolk protein precursors that are produced extraovarially and taken up by the growing oocytes against a concentration gradient. One of the most exciting aspects, and one that has attracted increasing attention during the last few years, is the mechanism of control of vitellogenin biosynthesis. This chapter focuses on the known control mechanisms that are amenable to experimental manipulation. The close analogy to the control mechanisms known for avian and amphibian vitellogenins makes research on insect vitellogenin even more rewarding. The chapter tabulates the identification of vitellogenin and vitellin according to the chronological documentation, the known species, grouped by orders, for which vitellogenins have been described. The very fact that only the female of the species contains a protein that is also the predominant yolk protein may allow speculating that ovaries transplanted into males may not incorporate yolk. However, as early as 1907 Meisenheimer found for the Lepidopteran Porthetria dispar that, larval ovaries transplanted into male larvae produced fully grown and chorionated eggs after metamorphosis. Contribution of non-specific proteins to protein yolk and uptake of haemolymph proteins by the oocytes have been discussed. The chapter discusses a model for endocrine controlled vitellogenin synthesis and vitellogenesis.

Insect Vitellogenin: Identification, Biosynthesis, and Role in Vitellogenesis

The female fat body of a moth and a roach incorporated labeled amino acids in vitro into substances precipitable by antibodies formed in response to the sex-limited vitellogenic blood proteins of these species. The fat body of males failed to do so, as did that of females before the appearance of these proteins in the blood.

http://science.sciencemag.org/content/sci/165/3891/393.full.pdf

M. L. Pan

Papers

Vitellogenic Blood Protein Synthesis by Insect Fat Body