64
translational inactivity, each is recruited to polyribosomes at a distinct subsequent
developmental stage (Fig. 2.3). Specifically, the mRNA encoding the Smad1
transcription factor and the mRNA encoding the BMP receptor, referred to as the
Fig. 2.3 Regulated translation of the mRNAs encoding proteins of the BMP pathway. (a) The
isolation of polyribosomes from Xenopus oocytes, eggs, and embryos (Sheets et al. 2010 ). At the
right, total (unfractionated) RNA from eggs, non-polyribosomal RNA from eggs, and polyribo-
somal RNA from eggs were analyzed with blot hybridization using probes to the cyclin B1 and
cytoskeletal actin mRNAs. (b) Polyribosome and non-polyribosome fractions were prepared from
Xenopus laevis oocytes, eggs, and stage 7 blastula embryos (Fritz and Sheets 2001 ). Total RNAs
isolated from the fractions were analyzed by blot hybridization. Filters were hybridized with
probes to detect Xenopus mRNAs encoding the Smad1 transcription factor, the BMP7 ligand,
BMPR1a receptor, and cytoskeletal actin proteins. A representative RNA blot analyzing each
mRNA is shown. Recreated from Fritz, B.R. and M.D. Sheets Developmental Biology, 2001.
236(1): p. 230–243, with permission from Elsevier
M.D. Sheets et al.