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Developmental Biology

Defining the Program of Maternal mRNA Translation during In vitro Maturation using a Single Oocyte Reporter Assay

Published: June 16th, 2021



1Center for Reproductive Sciences, University of California at San Francisco, 2Department of Obstetrics Gynecology and Reproductive Sciences, University of California at San Francisco, 3Present affiliation: Laboratoire de Biologie du Développement-Institut de Biologie Paris Seine, LBD-IBPS, Sorbonne Université

This protocol describes a reporter assay to study the regulation of mRNA translation in single oocytes during in vitro maturation.

Events associated with oocyte nuclear maturation have been well described. However, much less is known about the molecular pathways and processes that take place in the cytoplasm in preparation for fertilization and acquisition of totipotency. During oocyte maturation, changes in gene expression depend exclusively on the translation and degradation of maternal messenger RNAs (mRNAs) rather than on transcription. Execution of the translational program, therefore, plays a key role in establishing oocyte developmental competence to sustain embryo development. This paper is part of a focus on defining the program of maternal mRNA translation that takes place during meiotic maturation and at the oocyte-to-zygote transition. In this method paper, a strategy is presented to study the regulation of translation of target mRNAs during in vitro oocyte maturation. Here, a Ypet reporter is fused to the 3' untranslated region (UTR) of the gene of interest and then micro-injected into oocytes together with polyadenylated mRNA encoding for mCherry to control for injected volume. By using time-lapse microscopy to measure reporter accumulation, translation rates are calculated at different transitions during oocyte meiotic maturation. Here, the protocols for oocyte isolation and injection, time-lapse recording, and data analysis have been described, using the Ypet/interleukin-7 (IL-7)-3' UTR reporter as an example.

A fully-grown mammalian oocyte undergoes rapid changes in preparation for fertilization and acquisition of totipotency. These changes are essential to sustain embryonic development after fertilization. Although the events associated with nuclear maturation are relatively well described, much less is known about the molecular processes and pathways in the oocyte cytoplasm. During the final stages of oocyte maturation, oocytes are transcriptionally silent, and gene expression is entirely dependent on mRNA translation and degradation1,2. The synthesis of proteins critical for developmental competence, therefore, ....

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The experimental procedures involving animals were approved by the Institutional Animal Care and Use Committee of the University of California at San Francisco (protocol AN182026).

1. Preparation of media

  1. Add all components, as described in Table 1, to make the basic oocyte collection medium and oocyte maturation medium. For the basic collection medium, set the pH to 7.4. For both collection and maturation medium, add 3 mg/mL of bovine serum albumin (BSA) and 1 .......

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Denuded prophase I-arrested oocytes of 21-day-old C57/BL6 mice were injected with a reporter mix containing mRNA encoding the Ypet reporter fused to the 3' UTR of IL-7 and mRNA encoding mCherry. YFP and mCherry expression was recorded in 39 oocytes, of which 30 were matured, and 9 were arrested in prophase I as a negative control. Three maturing oocytes were excluded for analysis because they either had a delayed GVBD (N=2) or moved in the dish during the recording (N=1). Figure 3 shows .......

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The presented method describes a strategy to study activation and repression of translation of target mRNA at different transitions during in vitro oocyte meiotic maturation. IL-7, a cytokine released by the oocyte that may be involved in oocyte-cumulus cell communication8,13, was chosen for the purpose of describing this method. IL-7 is known to be increasingly translated during oocyte maturation8 and allows for good visualizatio.......

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This work was supported by NIH R01 GM097165, GM116926 and Eunice Kennedy Shriver NICHD National Centers for Translational Research in Reproduction and Infertility P50 HD055764 to Marco Conti. Enrico M. Daldello was supported by a fellowship from the Lalor Foundation and Natasja G. J. Costermans was supported by a Rubicon fellowship from the Netherlands Organisation for Scientific Research (NWO).


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Name Company Catalog Number Comments
Preparation of media
Bovine Serum Albumin Powder Bioxtra Sigma-Aldrich SIAL-A3311
Cilostamide EMD Millipore 231085
MEM alpha Gibco 12561-056
Minimum Essential Medium Eagle  Sigma-Aldrich M2645
Penicillin-Streptomycin 100x Solution, Sterile Filtered Genesee Scientific Corporation (GenClone) 25-512
Sodium Bicarbonate  JT-Baker 3506-1
Sodium Pyruvate Gibco  11360-070
Ultrapure distilled water Invitrogen 10977-015
Preparation of mRNA encoding YFP/3' UTR and mCherry
Agarose Apex Biomedical  20-102QD
Carbenicillin disodium salt Sigma-Aldrich C1389-1G
Choo-Choo Cloning Kit McLab CCK-20
CutSmart Buffer (10x) New England Biolabs B7204
DNA loading dye (6x) Thermo Scientific R0611
dNTP Solution New England Biolabs N0447S
DpnI New England Biolabs R0176
GeneRuler 1 kb DNA ladder Thermo Fisher SM1333
LB Agar Plates with 100 µg/mL Carbenicillin, Teknova  Teknova L1010
LB Medium (Capsules) MP Biomedicals 3002-021
MEGAclear Transcription Clean-Up Kit Life Technologies AM1908
MfeI-HF restriction enzyme New England Biolabs R3589
mMESSAGE mMACHINE T7 Transcription Kit Invitrogen AM1344
Phusion High Fidelity DNA polymerase New England Biolabs M0530
Poly(A) Tailing kit Invitrogen AM1350
QIAprep Spin Miniprep Kit  Qiagen 27106
QIAquick Gel Extraction Kit Qiagen 28704
S.O.C. medium Thermo Fisher 15544034
TAE buffer  Apex Biomedical  20-193
Ultrapure Ethidium Bromide Solution Life Technologies 15585011
Oocyte collection
Aspirator tube assembly for calibrated micro-pipettes Sigma-Aldrich A5177-5EA
Calibrated micro-pipettes Drummond Scientific Company 2-000-025 
PMSG- 5000 Mybiosource MBS142665
PrecisionGlide Needle 26 G x 1/2 BD 305111
Syringe 1 ml BD 309659
Oocyte micro-injection
35 mm Dish | No. 0 Coverslip | 20 mm Glass Diameter | Uncoated MatTek P35G-0-20-C For time-lapse microscopy
Borosilicate glass with filament Sutter Instrument BF100-78-10
Oil for Embryo Culture Irvine Scientific 9305
Petri Dish Falcon 351006 For micro-injection
Tissue Culture Dish Falcon 353001 For oocyte incubation
VacuTip Holding Capillary Eppendorf 5195000036
Biorender BioRender Preparation of Figure 1S
MetaMorph, version  Molecular Devices  For time-lapse microscopy, analysis of 3' UTR translation 

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