The recent immunocytochemical identification of type II activin receptors on mouse oocytes further supports this concept. buy flovent inhaler
In our experiments, the PCR product from activin receptors appeared to vary significantly across oocyte meiotic maturational stages. ActRIIB and ActRIB mRNA levels were significantly lower at Ml compared to either GV or M2. ActRIIA mRNA, on the other hand, was lower at Ml but remained reduced at M2. To examine these potentially quantitative relationships more closely, we repeated these experiments on a smaller group of human oocytes using a semiquantitative RT-PCR protocol with amplification in the exponential range for each target.
We observed a similar receptor mRNA pattern across maturational stages, although it did not reach significance due to the limited number of available oocytes (data not shown). Initially, this increase in mRNA at M2 seemed paradoxical, since RNA transcription ends with oocyte nuclear maturation. However, our RT procedure utilized oligo(dT) to prime cDNA synthesis and therefore presumably detected only polyadenylated transcripts. Moreover, ActRIIA mRNA has been previously demonstrated to undergo cytoplasmic po-lyadenylation during oocyte maturation and early embryonic development. Therefore, one explanation for higher mRNA levels at M2 is the cytoplasmic polyadeny-lation of ActRIIB and ActRIB late in oocyte nuclear maturation, resulting in increased detection by our RT method. These observations suggest that an increase in mRNA for both receptor subtypes at M2 might help prepare the oocyte for detection of activin signals during early embryonic development.