Follicle microenvironment associated alterations in gene expression in the mouse oocyte and its polar body

Capsule:
Changes in the follicle microenvironment lead to quantifiable differences in gene expression in individual oocytes and their polar bodies.

Authors:
Ze-Xu Jiao, M.D., Ph.D. and Teresa K. Woodruff, Ph.D.

Volume 99, Issue 5, Pages 1453-1459.e1, April 2013

Abstract:

Objective:
To determine whether the follicle environment modulates oocyte-specific gene transcript levels in cultured oocytes and polar bodies (PB).

Design:
Animal study.

Setting:
Large academic research center.

Animals:
CD1 mice.

Interventions:
In vitro growth of secondary mouse follicles in 0.25% or 1.5% alginate (ALG) in a three-dimensional culture system.

Main outcome measures:
Relative RNA levels of Gdf9, Bmp15, Nlrp5, Tcl1, and Zp3 measured by real-time quantitative RT-PCR in oocytes during in vitro follicle development and oocyte maturation and in their first polar bodies after removal from MII eggs.

Results:
All transcripts decreased earlier in oocytes cultured in 1.5% ALG compared with 0.25% ALG. Transcript levels were lower in MII eggs cultured in 1.5% ALG compared with 0.25% ALG. All genes were expressed in PBs; levels were lower in follicles cultured in 1.5% ALG compared with 0.25% ALG. Abundance of all transcripts was lower in PBs than in their sibling oocytes.

Conclusions:
Local follicle environment modulates oocyte-specific gene expression in the oocyte and first PB. There is a significant difference in the transcript levels of oocyte-specific genes in PB from 1.5% vs. 0.25% ALG that correlates with ovarian environment-related decreases in oocyte competence.

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