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Updated: Aug 24, 2026
Whole Ovary Immunofluorescence, Clearing, and Multiphoton Microscopy for Quantitative 3D Analysis of the Developing Ovarian Reserve in Mouse
Published on: September 3, 2021
Immunoneutralization of growth differentiation factor 9 reveals it partially accounts for mouse oocyte mitogenic
R B Gilchrist1, L J Ritter, M Cranfield
1Research Centre for Reproductive Health, Department of Obstetrics and Gynaecology, The Queen Elizabeth Hospital, University of Adelaide, Woodville, SA 5011, Australia. robert.gilchrist@adelaide.edu.au
Abstract:
Paracrine factors secreted by oocytes play a pivotal role in promoting early ovarian follicle growth and in defining a morphogenic gradient in antral follicles, yet the exact identities of these oocyte factors remain unknown. This study was conducted to determine the extent to which the mitogenic activity of mouse oocytes can be attributed to growth differentiation factor 9 (GDF9). To do this, specific anti-human GDF9 monoclonal antibodies were generated. Based on epitope mapping and bioassays, a GDF9 neutralizing antibody, mAb-GDF9-53, was characterized with very low cross-reactivity with related transforming growth factor (TGF)beta superfamily members, including BMP15 (also called GDF9B). Pep-SPOT epitope mapping showed that mAb-GDF9-53 recognizes a short 4-aa sequence, and three-dimensional peptide modeling suggested that this binding motif lies at the C-terminal fingertip of mGDF9. As predicted by sequence alignments and modeling, the antibody detected recombinant GDF9, but not BMP15 in a Western blot and GDF9 protein in oocyte extract and oocyte-conditioned medium. In a mouse mural granulosa cell (MGC) bioassay, mAb-GDF9-53 completely abolished the mitogenic effects of GDF9, but had no effect on TGFbeta1 or activin A-stimulated MGC proliferation. An unrelated IgG at the same dose had no effect on GDF9 activity. This GDF9 neutralizing antibody was then tested in an established oocyte-secreted mitogen bioassay, where denuded oocytes cocultured with granulosa cells promote cell proliferation in a dose-dependent manner. The mAb-GDF9-53 dose dependently (0-160 microg/ml) decreased the mitogenic activity of oocytes but only by approximately 45% at the maximum dose of mAb. Just 5 microg/ml of mAb-GDF9-53 neutralized 90% of recombinant mGDF9 mitogenic activity, but only 15% of oocyte activity. Unlike mAb-GDF9-53, a TGFbeta pan-specific neutralizing antibody did not affect the mitogenic capacity of the oocyte, but completely neutralized TGF beta 1-induced DNA synthesis. This study has characterized a specific GDF9 neutralizing antibody. Our data provide the first direct evidence that the endogenous GDF9 protein is an important oocyte-secreted mitogen, but also show that GDF9 accounts for only part of total oocyte bioactivity.
Insights
Growth differentiation factor 9 (GDF9) is an important oocyte-secreted mitogen that promotes ovarian follicle growth. However, this study shows GDF9 accounts for only part of the total mitogenic activity secreted by oocytes.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Molecular Endocrinology
Background:
- Oocyte-secreted factors are crucial for ovarian follicle development.
- The precise identity and contribution of these factors, particularly Growth Differentiation Factor 9 (GDF9), to oocyte bioactivity remain incompletely understood.
Purpose of the Study:
- To characterize a specific neutralizing antibody against mouse GDF9 (mAb-GDF9-53).
- To determine the extent to which endogenous GDF9 contributes to the mitogenic activity of oocyte-conditioned medium.
Main Methods:
- Generation and characterization of a GDF9-specific monoclonal antibody (mAb-GDF9-53).
- Epitope mapping and Western blot analysis to confirm antibody specificity.
- Bioassays using mural granulosa cells and oocyte-granulosa cell co-cultures to assess mitogenic activity and antibody neutralization.
Main Results:
- The characterized antibody (mAb-GDF9-53) specifically neutralizes GDF9 mitogenic activity with minimal cross-reactivity to related factors like BMP15.
- In bioassays, mAb-GDF9-53 significantly reduced the mitogenic activity of oocyte-conditioned medium by approximately 45% at maximal concentration.
- This indicates that while GDF9 is a key oocyte-secreted mitogen, it only accounts for a portion of the total bioactivity.
Conclusions:
- A specific GDF9 neutralizing antibody has been successfully characterized.
- This study provides direct evidence for the role of endogenous GDF9 as a significant oocyte-secreted mitogen.
- Oocytes secrete other factors that contribute to mitogenic activity beyond GDF9.
