Embryo cells from rabbit

Poly(A)-rich mRNA prepared from rabbit pancreas directed the synthesis of a protein (mol. wt. 5.65 X 10 ), which, using a cell-free protein synthesizing system derived from wheat embryo, appeared to represent the product of o-amylase mRNA cell-free translation.This protein, which was 1500 daltons larger than the purified rabbit pancreas a-amylase, was resolved by isoelectric focusing into discrete species similar to those observed for purified a-amylase. The protein, which on peptide analysis demonstrated considerable identity with the a-amylase, was selectively precipitated by glycogen, but with a much lower recovery than that observed for rabbit on porcine pancreatic a-amylases. 

Due to the limited applicability of in silico SAR approaches for developmental toxicity, there is more reliance on in vitro screening. From what has been publicly disclosed, it is evident that the four in vitro tests used for industrial screening are chick embryonic neural retina (CENR) micromass culture, whole embryo culture (WEC, rodent or rabbit), and mouse embryonic stem cells (EST). Recently, there has been significant interest within the pharmaceutical industry in the use of zebrafish for developmental toxicity testing,30 but because this aspect is in its infancy, there is little that has been publicly disclosed except limited abstracts and slide decks at several workshops.31 Although reviewed in considerable detail elsewhere,30-32 36 each test will be briefly compared and contrasted here. 

Figure 9-5 The sensitivity of the conceptus to a theoretical teratogen during rat gestation (modified from 161). The most susceptible window is organogenesis with low levels of vulnerability at the time of implantation and the period of functional maturation. Superimposed are the approximations of when the developmental landmarks that are represented in the four in vitro tests occur. The chick embryo neural retina model (CENR) represents events around GD 10-13. The mouse embryonic stem cell test (EST) corresponds roughly to the period of GD 6-10 in the rat, near the peak of sensitivity. Whole embryo culture (WEC) recapitulates the window at the peak of sensitivity, between GD 9-11 or GD 10-12 depending upon the window within which the culture is conducted. Rabbit cultures are also done between GD 10-12. Represented by the single ( ) and double asterisk ( ), respectively, are the initiation and termination of the dosing period in regulatory compliant preclinical embryo/fetal toxicity studies. Thus, the zebrafish is the only model that permits exposure to test article during this important period.

There is no net increase in RNA content, per embryo, however, until 72 hours postcoitum at which time there is a marked acceleration of uridine incorporation accompanying the transformation of the morula into a blastocyst as the embryo leaves the oviduct and enters the uterus (Manes, 1969). The qualitative aspects of RNA synthesis in preimplantation rabbit embryos have been investigated by the electrophoretic separation of tritium-labeled embryonic RNA on polyacrylamide gels (Manes, 1971). Labeling of RNA species having migratory properties identical with those of tRNA are detectable from the 2-cell stage onward. 

It should be noted that Foote and his associates have taken exception to the significance of blastokinin as well as uterine proteins in general. Thus, Kane and Foote (1971) starting with 1-cell rabbit embryos obtained expanded blatocysts on a defined medium supplemented with only bovine serum albumin. Furthermore, it was reported that if was possible to obtain one full term young from a rabbit embryo transferred into a recipient doe after 88 hours of culture on a medium containing only serum (Mauer et al., 1970). 

Mengovirus replicates efficiently in HeLa (human), L (mouse) and BHK (syrian hamster) cells but replicates poorly in rabbit embryo fibroblasts, PtK-1 cells (kangaroo rat), and MBBK cells (25). Restriction of viral growth is the most severe in MBBK cells with viral yields of only 10-20 PFU/cell seen. Yields in permissive L cells range from 5OO-IOOO PFU/cell. 

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