Oocytes lipids

Replacement of the famesyl group by lipid analogues could be performed for full length Ras proteins in vitro by means of the enzyme famesyltrans-ferase. When such partially modified Ras constructs were applied in Xenopus oocytes the cellular machinery completed modification (endoprotease activity, carboxymethylation and palmitoylation). In these cases the H-Ras famesyl group could be stripped off most of its isoprenoid features that distinguish it from a fatty add without any apparent effect on its ability to induce oocyte maturation and activation of mitogen-activated protdn kinase In contrast, replacement by the less hydrophobic isoprenoid geranyl causes severely delayed oocyte activation. 

Replacement of the H-Ras Farnesyl Group by Lipid Analogues Implication for Downstream Processing and Effector Activation in Xenopus Oocytes, T. Dudler, M. H. Gelb, Biochemistry 1997, 36,12434-12441. 

The properties of the lipids in oocyte membranes are different from those seen in mammalian cells and this may affect the functional properties of the expressed proteins. 

De Vlaming, V., Fitzgerald, R., Delahunty, G., Cech, J., Selman, K. and Barkley, M. (1984). Dynamics of oocyte development and related changes in serum oestradiol-17(5, yolk precursor, and lipid levels in the teleostean fish Leptocottus armatus. Comparative Biochemistry and Physiology 77A, 599-610. 

Precursor of egg-yolk proteins rich in carbohydrates, lipids, phosphates and calcium. It is the principal energy reserve in oocytes. Vg expression is under the control of estradiol-17(3 receptors. This protein complex is produced in the liver by oviparous vertebrates and used as a biomarker to detect environmental estrogens. Volume 1(14). 

The eggs of B. germanica contain the same types of hydrocarbons as the hemolymph, HDLp, and cuticle of the adult female. Only 150 pg of hydrocarbons accumulate on the epicuticular surface whereas up to 450 pg accumulate within the female during the period of egg maturation (Fan et al., 2002). The internal hydrocarbons are divided primarily between the ovaries, fat body, and 150 pg of HDLp-bound hydrocarbons in the hemolymph. During oocyte maturation ovarian hydrocarbons increase by more than 65-fold - from 3.5 pg on day-1 to 232 pg on day-8 (Fan et al., 2002). However, after oviposition on day-9, ovarian hydrocarbons decline to only 8.2 pg, demonstrating that hydrocarbons were associated with the ovulated oocytes. Radiotracing results indicate that they serve as components of the cuticular lipids of the embryos and first instars (Fan and Schal, unpublished results). 

Incubated oocytes accept hydrocarbons at similar rates from hemolymph and from purified HDLp, suggest that LTP might not be required for uptake of hydrocarbons (Fan et al., 2002). However, this idea will have to await careful experiments with LTP antibodies, as detailed above. In M. sexta LTP plays a role in delivery of lipids to the developing oocytes and the conversion of adult HDLp to VHDLp in the egg (Liu and Ryan, 1991). 

Liu H. and Ryan R. O. (1991) Role of lipid transfer particle in transformation of lipophorin in insect oocytes. Biochim. Biophys. Acta 1085, 112-118. 

Atella, G.C., Silva-Neto, A.C., Golodne, D.M., Arehn, S. and Shahabuddin, M. (2006). Anopheles gambiae lipophorin Characterization and role in lipid transport to developing oocyte. Insect Biochem. Mol. Ecol., 36, 375-386. 

Transfection efficiency is dependent on mitotic activity, as cells prevented from going into mitosis after transfection express transgenes much less efficiently than proliferating cells. In search for an explanation, the transport of plasmids across the nuclear membranes has been studied. Plasmids injected into the cytoplasm of quiescent human fibroblasts are not expressed, in contrast to plasmid injected into the nucleus. This has been found to be true for the cationic lipid-based systems as plasmid injected into the cytoplasm of Xenopus oocytes is not expressed, unlike that injected into the nucleus, it must be concluded that the plasmid must dissociate from the cationic lipids before entering into the nucleus. 

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