CLUSTERIN EXPRESSION DURING PROGRAMMED AND TERATOGEN-INDUCED CELL-DEATH IN THE POSTIMPLANTATION RAT EMBRYO

Clusterin appears to play a role in multiple cellular processes includ ing reproductive cell function, lipid transport, complement regulation , and endocrine secretion. In addition, clusterin has been shown to be associated with both developmental and induced cell death. We have us ed immunohistochemistry and in situ hybridization to study the relatio nship between clusterin expression, normal programmed cell death (PCD) in the developing rat limb bud, and abnormal cell death induced by hy perthermia in day 11 rat embryos. Immunohistochemical localization of clusterin in day 14-16 limb buds showed that the most intense immunost aining was associated with the condensing mesenchyme of the developing digit, a tissue exhibiting low levels of PCD. Moreover, areas of digi tal cell death, confined to future interphalangeal spaces, were devoid of clusterin immunostaining. Clusterin immunostaining was also observ ed in the interdigital mesenchyme and partially overlapped the cell de ath that occurs in this tissue during the early development of the dig its. Although clusterin immunostaining overlaps areas of interdigital cell death, most apoptotic cells in the interdigital mesenchyme and un derlying the surface ectoderm were not associated with clusterin immun ostaining. We also examined the expression of clusterin in day 11 rat embryos exposed to 43 degrees C, an exposure that induces extensive ce ll death primarily in the developing neuroepithelium. In control embry os cultured at 37 degrees C, clusterin mRNA and protein were expressed at high revels in the heart, a tissue that is completely resistant to the cytotoxic effects of hyperthermia. Within 2.5 hr after an exposur e of 43 degrees C, clusterin mRNA showed a dramatic induction in the p rosencephalic mesenchyme and only a modest induction in the prosenceph alic neuroepithelium. Although less dramatic, clusterin immunostaining was also induced in the prosencephalic mesenchyme, a tissue that is r elatively resistant to the cytotoxic effects of hyperthermia. Our resu lts suggest that clusterin is not associated with either PCD or hypert hermia-induced cell death. Nonetheless, our results suggest that clust erin plays some role in the differentiation of digital cartilage/bone and possibly in the protection of specific embryonic cell types (heart , mesenchyme) from hyperyhermia-induced cell death. (C) 1995 Wiley-Lis s, Inc.