P185(NEU) IS EXPRESSED IN YOLK-SAC DURING RAT POSTIMPLANTATION DEVELOPMENT

We have shown that the neu oncogene product (p185(neu)) is not present in the rat embryo before organogenesis. However, coincident with the onset of organogenesis, p185(neu) was detected in neural and connectiv e tissue as well as in the secretory epithelium as was described by Ko kai et al. (1987). In addition, p185(neu) is also expressed in the rat visceral yolk sac (VYS) endodermal cells but not in the mesenchymal a nd mesothelial layers of the same structure nor in the amnion. The fir st detectable sign of p185(neu) expression in VYS was found at d 11 of gestation and the levels of protein increased towards the end of preg nancy. In the yolk sac carcinoma (YSC), which is considered to be the malignant counterpart of the rat yolk sac, p185(neu) was observed only within columnar epithelial cells (the visceral component of the neopl asm) while parietal endoderm-like cells were devoid of detectable prot ein. From d 9 of pregnancy up to delivery some of the trophoblastic gi ant cells also showed a faint to moderate immunoreactivity. Results ar e presented which would indicate a possible role of p185(neu) in rat e mbryogenesis.