Novel roles of Celf1 and Tia1 during vegetal RNA localization in Xenopus laevis oocytes
Diana Bauermeister
Doctoral thesis
Date of Examination:
2015-01-22
Date of issue:
2015-10-29
Advisor:
Pieler, Tomas Prof. Dr.
Referee:
Pieler, Tomas Prof. Dr.
Referee:
Wimmer, Ernst A. Prof. Dr.
Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0023-9664-3
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Abstract
English
The localization of certain mRNAs to the vegetal cortex of Xenopus oocytes is of crucial importance for germ cell development and germ layer formation of the future embryo. Vegetal RNA localization is mediated by signal sequences within the RNA. These so-called localization elements recruit certain proteins that direct transport to the vegetal cortex. Although numerous localization ribonucleoprotein (RNP) components have been identified, their full composition is yet unknown. The Xenopus RNA binding proteins Celf1 (CUGBP, Elav-like family) and Tia1 (T-cell internal antigen 1) are novel components of vegetal localization RNPs that we identified in an RNA affinity purification approach, using the dead end 1 (dnd1) RNA localization element. Both Celf1 and Tia1 are detected as parts of an RNP complex together with other known vegetal localization proteins and show specific interactions with localization elements from several vegetally localizing RNAs. Immunostaining experiments reveal co-localization of Celf1 and Tia1 with vegetally localizing RNA and with known localization factors. Inhibition of Celf1 protein binding by localization element mutagenesis as well as Celf1 overexpression interfere with vegetal RNA localization, suggesting an active role for Celf1 during vegetal RNA transport in Xenopus oocytes. Ectopic expression of Celf1 and Tia1 in Xenopus embryos counteracts somatic degradation of dnd1 localization element reporter RNAs. Furthermore, Tia1 protects several other localizing and germ cell specific mRNAs from somatic degradation and synergizes with the germ cell specific protein Dnd1. These results suggest that Celf1 and Tia1 are components of vegetal localization RNPs in oocytes that could have additional functions in the protection of germ cell specific RNAs in early embryos. Furthermore, Celf1 is enriched at the vegetal cortex in zebrafish oocytes and thus may play a conserved role in vegetal RNP complexes of fish and frogs. Celf1 loss of function approaches in zebrafish result in the primary development of males, indicating a role of Celf1 during zebrafish sex determination or female viability. Our results reveal Xenopus Celf1 and Tia1 as novel components of vegetal localization complexes. While Celf1 actively participates in vegetal RNA localization in oocytes, both Celf1 and Tia1 seem to act in germ cell specific RNA protection in embryos. These findings support the idea that both mechanisms share the same proteins and they highlight the functional link between RNA localization and germ cell formation.
Keywords: RNA localization; Xenopus; oocyte; vegetal cortex
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GGNB - Göttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften [899]
GGNB - Göttingen Graduate School for Neurosciences, Biophysics and Molecular Biosciences