Nonspecific effects of oligodeoxynucleotide injection in Xenopus oocytes: a reevaluation of previous D7 mRNA ablation experiments.

Microinjection of oligodeoxynucleotides (ODNs) complementary to cellular mRNAs has been advanced as an experimental approach to degrade target mRNAs in vivo and thereby obtain information as to the function of their cognate proteins. It is shown here that ODNs can induce a variety of aberrations in cell metabolism and structure when injected into Xenopus oocytes. Examination of histological sections of ODN-injected oocytes revealed the frequent abnormal accumulation of heavily staining basophilic material in the area of the germinal vesicle (gv). Ultrastructural analysis detected further abnormalities including blebbing of the plasma membrane, anomalous cytoskeletal structures, hyperorganised annulate lamellae, hyperinvagination of the gv, and formation of irregular nucleoli within the gv. Analysis of newly synthesised proteins by [35S]methionine radiolabelling of oocytes demonstrated that ODN injection can trigger a general decrease in both label uptake and protein synthesis. Qualitative effects on protein synthesis could also be observed, particularly a decrease in synthesis of high molecular weight proteins. The severity of ODN-induced effects is dose-dependent and highly variable from ODN to ODN. The previously reported delay in progesterone-induced maturation observed in oocytes depleted of the maternal mRNA D7 by ODN-directed degradation (Smith R. C., Dworkin M. B. and Dworkin-Rastl E. (1988) Genes and Devpt. 2, 1296-1306) is most likely a result of nonspecific ODN effects in the oocyte. Oocytes injected with effective antisense D7 ODNs that do not display detectable side effects matured with normal kinetics.