
Depletion of the canonical TGFβ mediator SMAD4 in granulosa cells reduces the number and alters the morphology of transzonal projections (TZPs) that connect the somatic granulosa cells to the oocyte, suggesting SMAD4 plays a key role in stabilizing the soma-germline contact during oocyte growth.


coremsg

Development of the mammalian oocyte requires physical contact with the surrounding granulosa cells of the follicle, which provide it with essential nutrients and regulatory signals. This contact is achieved through specialized filopodia, termed transzonal projections (TZPs), that extend from the granulosa cells to the oocyte surface. Transforming growth factor (TGFβ) family ligands produced by the oocyte increase the number of TZPs, but how they do so is unknown. Using an inducible Cre recombinase strategy together with expression of green fluorescent protein to verify Cre activity in individual granulosa cells, we examined the effect of depleting the canonical TGFβ mediator, SMAD4. We observed a 20-50% decrease in the total number of TZPs in SMAD4-depleted granulosa cell-oocyte complexes, and a 50% decrease in the number of newly generated TZPs when the granulosa cells were reaggregated with granulosa cell-free wild-type oocytes. Three-dimensional image analysis revealed that TZPs of SMAD4-depleted cells were also longer than controls and more frequently oriented towards the oocyte. Strikingly, the transmembrane proteins, N-cadherin and Notch2, were reduced by 50% in these cells. SMAD4 may thus modulate a network of cell adhesion proteins that stabilize the attachment of TZPs to the oocyte, thereby amplifying signalling between the two cell types.

Impact statement Genetic deletion of SMAD4 in the granulosa cells of growing ovarian follicles reduces the number of transzonal projections that contact the oocyte, implicating TGFβ-family signaling in maintaining soma-germ line communication.

### Competing Interest Statement

The authors have declared no competing interest.

SMAD4 promotes somatic-germline contact during murine oocyte growth

smad4-depletion-reduces-transzonal-projections-connecting-granulosa-cells-and-oocyte


SMAD4 Depletion Reduces Transzonal Projections Connecting Granulosa Cells and Oocyte
