Translational control of maskin mRNA by its 3′ untranslated region

Abstract

Background information. Maskin is a member of the TACC (transforming acidic coiled-coil) domain proteins found in Xenopus laevis oocytes and embryos. It has been implicated in the co-ordination of the spindle and has been reported to mediate translational repression of cyclin B1 mRNA.Results. In the present study, we report that maskin mRNA is translationally repressed at the level of initiation in stage 4 oocytes and becomes activated in stage 6 oocytes. The translational repression of maskin mRNA correlates with the presence of a short poly(A) tail on this mRNA in stage 4 oocytes. The 3 -UTR (untranslated region) of maskin can confer the translational regulation to a reporter mRNA, and so can the 3 -UTR of human TACC3. A conserved GUCU repeat element was found to repress translation in both stage 4 and stage 6 oocytes, but deletion of this element did not abrogate repression in stage 4 oocytes. UV cross-linking experiments indicated that overlapping sets of proteins bind efficiently to both the maskin and the cyclin B1 3 -UTRs. As reported previously, CPEB [CPE (cytoplasmic polyadenylation element)-binding protein] binds to the cyclin B1 3 -UTR, but its binding to the maskin 3 -UTR is minimal. By RNA affinity chromatography and MS, we identified the EDEN-BP [EDEN (embryonic deadenylation element)-binding protein] as one of the proteins binding to both the maskin and the cyclin B1 3 -UTRs.Conclusions. Maskin mRNA is translationally regulated by at least two repressor elements and an activation element. One of the repessor elements is the evolutionarily conserved GUCU repeat. EDEN-BP binds to both the maskin and cyclin B1 3 -UTRs, indicating it may be involved in the deadenylation of these mRNAs.

Spatially Restricted Translation of the xCR1 mRNA in Xenopus Embryos

“…It is interesting to note that the 3Ј UTR of cyclin B1 contains both a PBE and a CUG-BP1 site and yet its translation is not repressed in vegetal cells (28,32,33). Perhaps efficient vegetal cell translation repression exhibited by the xCR1 mRNA requires the actions of the multiple PBEs and CUG-BP1 sites present in the xCR1 mRNA's 3Ј UTR.…”

“…Another possibility is that the CPEs in the 3Ј UTR of the cyclin B1 are optimized for polyadenylation and translational activation, while the CPEs in the 3Ј UTR of the xCR1 mRNA are not. Such optimal CPEs in the cyclin B1 3Ј UTR and/or the polyadenylation that they direct may counteract the repressive effects of the adjacent PBE and CUG-BP1 site (28,32,33). Systematic and comprehensive mutational analyses are necessary to sort out the balances between translational activation and repression signals that achieve remarkably different modes of mRNA behavior while presumably using similar sequence elements.…”

Faulty old ideas about translational regulation paved the way for current confusion about how microRNAs function

“…(iii) The most important new finding is that maskin is not produced until late in oogenesis. Maskin mRNA is present in earlier stages, but maskin protein does not accumulate until stage 6 (Meijer et al, 2007). Some other mechanism is obviously needed to silence translation of cyclin B1 in stages 1 through 5.…”

Structural insights into the targeting of mRNA GU-rich elements by the three RRMs of CELF1

“…In Xenopus , CELF1 induces deadenylation and appears to play a key role in regulating poly(A) shortening (27–29). Recent studies, using in vitro assays for assessing mRNA decay in AU-rich mRNAs, have shown that CELF1 binds specifically to mRNAs and stimulates poly(A) shortening in the 3′ untranslated region (3′ UTR) by recruiting the poly(A) deadenylase ribonuclease (PARN) (13,30).…”