The 3'-untranslated regions of c-mos and cyclin mRNAs stimulate translation by regulating cytoplasmic polyadenylation.

Abstract

Early in the development of many animals, before transcription begins, any change in the pattern of protein synthesis is attributable to a change in the translational activity or stability of an mRNA in the egg. As a result, translational control is critical for a variety of developmental decisions, including axis formation in Drosophila and sex determination in Caenorhabditis elegans. Previous work demonstrated that increases in poly(A) length can activate translation, whereas removal of poly(A) can prevent it. In this report we focus on the control of c-mos and cyclin A1, B1, and B2 mRNAs during meiotic maturation and after fertilization of frog eggs. We show that addition and removal of poly(A) from these mRNAs is extensively regulated: The time at which each mRNA receives or loses poly(A), as well as the number of adenosines it gains or loses, differ substantially. Signals in the 3'-untranslated region (UTR) of each mRNA are sufficient to reconstitute both the temporal and quantitative control of poly(A) addition: Chimeric mRNAs in which a luciferase-coding region is joined to the 3' UTRs of cyclin A1, cyclin B1, or c-mos mRNA, receive poly(A) of the same length and at the same time as do the endogenous mRNAs. Moreover, each 3' UTR also regulates translation of the chimeric mRNAs, determining when and how much translation of the luciferase reporter is stimulated during maturation. The magnitude of stimulation in luciferase activity varies from 5-to 100-fold, depending on the 3' UTR. Translational stimulation by each 3' UTR requires poly(A) lengthening, as it is prevented by mutations that prevent that process. These results suggest that the 3' UTRs of cyclin and c-mos mRNAs control not only whether or not an mRNA is turned on during maturation, but when that activation occurs and to what extent. Translational control of c-mos mRNA, which may be achieved through regulation of poly(A) length, may be critical in the activation of maturation, and in the onset of cleavage divisions. Our findings, as well as those of others, suggest that even quite complex patterns of translational activation in the early embryo can be attained through the differential control of a common mechanism.[Key Words: 3' UTR; poly(A); maternal mRNAs; translational control; cyclin; c-mos; oocyte maturation; development; Xenopus]Received December 28, 1993; revised version accepted March 2, 1994. In the earliest period of an animal's life, transcriptional control is irrelevant because the zygotic genome is inactive. Instead, any change in the pattern of protein synthesis during the earliest postfertilization period is attributable to regulation of mRNAs that were already present in the egg before fertilization--so-called maternal mRNAs. As a result, key decisions made during early development often rely on control of the translation, stability, or location of these mRNAs. For example, axis formation in Drosophila depends on proper localization This paper is dedicated to Howard M. Temin.

Inactivation of protein kinase A is not required for c-mos translation during meiotic maturation of Xenopus oocytes

“…After maturation (in the absence of IBMX), RNA was extracted from the oocytes and the increase in the length of the probe was estimated by electrophoresis and autoradiography. This increase has been shown previously to correspond to the length of the poly(A) + tail added within the oocyte to the microinjected RNA (Sheets et al, 1994). As shown in Figure 3, the scattered distribution of poly (A) + tails was found to peak between 40 and 50 nucleotides in progesterone-treated oocytes, in good agreement with previous results (Sheets et al, 1994) and even slightly higher (between 60 and 70 nucleotides) in oocytes induced to mature through microinjection of recombinant c-mos.…”

“…Polyadenylation of c-mos mRNA is known to be essential for c-mos translation and meiotic maturation in progesterone-treated oocytes (Sheets et al, 1994(Sheets et al, , 1995Gebauer et al, 1994). Thus, the above results suggested that PKA activation may have di erential e ects on polyadenylation of c-mos RNA in oocytes treated with progesterone or microinjected with recombinant c-mos.…”

“…Onset of c-mos translation has been shown to depend on increased polyadenylation of its mRNA during maturation of Xenopus oocytes (Sheets et al, 1994(Sheets et al, , 1995. Although the precise mechanism by which polyadenylation at the 3' end stimulates translation initiation at the 5' end of the message is unclear, recent studies have shown that in maturing oocytes, 3' poly(A) + addition induces 5' cap ribose methylation, and that prevention of cap ribose methylation dramatically reduces translational activation (Kuge and Richter, 1995).…”

“…However, how PKA negatively controls c-mos translation has still not been elucidated, even though control of c-mos translation in oocytes has been the subject of several recent investigations (Sheets et al, 1994(Sheets et al, , 1995Gebauer et al, 1994). The aim of the present work was to investigate the mechanism that allows PKA to suppress c-mos translation.…”

Cloning and Characterization of a Novel Oocyte-Specific Gene Encoding an F-Box Protein in Rainbow Trout (Oncorhynchus mykiss).

“…During oocyte maturation, cytoplasmic polyadenylation extends the poly (A) tail of these transcripts, a process associated with their timely translation [20,21]. The presence of a typical U-rich cytoplasmic polyadenylation element (UUUUUAA) in the 3′UTR of fbxoo mRNA indicates that this gene may have controlled translation during oocyte maturation.…”