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

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

Animal study.

Large academic research center.

CD1 mice.

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

Relative transcript levels of Gdf9, Bmp15, Nlrp5, Tcl1, and Zp3 were measured by real-time quantitative reverse transcriptase-polymerase chain reaction in oocytes during in vitro follicle development and oocyte maturation and in their first PBs after removal from metaphase II (MII) eggs.

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 in 0.25% ALG. All genes were expressed in PBs, and transcript levels were lower in PBs cultured in 1.5% ALG compared with in 0.25% ALG. Abundance of all transcripts was lower in PBs than in their sibling oocytes.

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 PBs of 1.5% versus 0.25% ALG that correlates with ovarian environment-related decreases in oocyte competence.