Unfertilized egg

The Xenopus system has proven instrumental in determining the mechanism controlling exit from mitosis at the metaphase/anaphase transition. Studies in this area have relied heavily on extracts prepared from fully mature oocytes/ unfertilized eggs that are arrested at metaphase of the second meiotic division. Upon Ca2+ addition, anaphase is initiated and the extract enters the first embryonic cell cycle to replicate DNA. The activity responsible for metaphase arrest was discovered by Masui at the same time as MPF (Masui Markert 1971), and given the name cytostatic factor (CSF). CSF has never been purified... 

Mailer Murakami and Vande Woude published a nice paper a couple of years ago where they took a Mos arrest ed blastomere and re-started the cell cycle with Ca2+, getting a new cycle of tyrosine phosphorylation equivalent to cycle one, even though the embryo was actually entering cycle two or three. This would suggest that MAP kinase sets the timer back to zero. Of course, MAP kinase is very high in the unfertilized egg, the cell in which the timer is activated. 

Haplodiploidy in N. sertifer leads to male production from unfertilized eggs, which seriously complicates the issue of mating disruption with the acetate of... 

Akberali, H.B., M.J. Earnshaw, and K.R.M. Marriott. 1985. The action of heavy metals on the gametes of the marine mussel, Mytilus edulis (L.)- II. Uptake of copper and zinc and their effect on respiration in the sperm and unfertilized egg. Mar. Environ. Res. 16 37-59. 

The dart-poison frog Dendrobatespumilio uses odors for homing. This species lives in the understory of lowland tropical forests in Central America. The eggs are laid on land, and the female carries the newly hatched tadpoles on her back to water-filled leaf axils of bromeliads. She feeds the tadpoles with unfertilized eggs, while the male defends the territory. Captive dart-poison frogs tested in a Y-olfactometer chose the odor from their own communal tank over odors from tanks planted with different plants. However, they did not distinguish between... 

Evaluate embryos for developmental stage and viability under a stereomicroscope, removing unfertilized eggs and embryos that appear nonviable, damaged, or of a developmental stage outside the desired range. 

The anterior-posterior axis in Drosophila is defined at least in part by the products of the bicoid and nanos genes. The bicoid gene product is a major anterior morphogen, and the nanos gene product is a major posterior morphogen. The mRNA from the bicoid gene is synthesized by nurse cells and deposited in the unfertilized egg near its anterior pole. 

Nuclear transplantation technique. The nucleus of an unfertilized egg is mechanically removed with a micropipette (.left), and a nucleus from a blastula cell is removed and microinjected into the enucleated egg. 

Heinze, J., Foitzik, S., Oberstadt, B., Rueppell, O. and Holldobler, B. (1999). A female caste specialized for the production of unfertilized eggs in the ant Crematogaster smithi. Naturwissenschaften, 86, 93-95. 

Fig.8. The total lipid content (% on a wet weight basis) of rainbow trout Oncorhynchus my-kiss) eggs during development. The lipid data of unfertilized egg, fertilized egg (9 days after fertilization), and just before eye stage (13 days) are from reference [100], all other data are from reference [99]...

Parthenogenesis in animals refers to reproduction in which a new individual genetically identical to the parent develops from an unfertilized egg. The analogous event in plants, which results in seed formation without fertilization, is called agamospermy. Parthenogenesis is viewed as an aberration of sexual reproduction because animals that reproduce by parthenogenesis evolved from organisms that once reproduced sexually. In sexual reproduction female sex cells (ova) must be fertilized by male sex cells (typically sperm), for development to occur. 

Parthenogen esis.—The production of an embryo from an unfertilized egg. Pathol ogy.—The study of diseases. 

Figure 1. An unfertilized egg of the red abalone Haliotis rufescens. The dark egg is 1 75 l m in diameter. The vitelline envelope is 0.6 pm in thickness and 245 pm in diameter (from Lewis et al., 1982).

Litscher, E.S., Juntunen, K., Seppo, A., Penttila, L., Niemela, R., Renkonen, O., and Wassarman, P.M. (1995). Oligosaccharide constructs with defined structures that inhibit binding of mouse sperm to unfertilized eggs in vitro. Biochem. 34 4662-4669. 

Fig. 2. Amino acid sequences of L-PSGPs isolated from fertilized eggs of salmonid fish species where indicates the 0-glycosylation sites. H-PSGPs isolated from unfertilized eggs are polymerized forms of L-PSGP.

Fig. 6. Structures of free sialoglycans accumulated in the unfertilized eggs of Otyzias talipes, Plecoglossus altiuelis, and Tribolodon hakonensis and N-Iinked glycan structures determined for glycophosphoproteins isolated from the corresponding fish species.

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