PARENT SESSION
SLIDE SESSION 22: OOCYTE DEVELOPMENT
Chairs: Hugh Clarke, David Albertini, Maria Viveiros (Trainee)
Univ Ottawa-Morisset 218
1:30 PM-3:30 PM

DEVELOPMENTAL REGULATION OF OOCYTE-GRANULOSA CONNECTIVITY DURING FOLLICULOGENESIS IN THE MOUSE.

Combelles, Catherine^1,2, Carabatsos, Mary Jo¹, Albertini, David¹, ^{1 2}

ABSTRACT- Bidirectional communication between oocytes and surrounding granulosa cells mediates differential gene expression in gametic and somatic compartments as follicle development proceeds or fails (atresia). For some, and perhaps, all forms of intercellular communication, the zona pellucida must be breached by transzonal projections (TZPs) from granulosa cells that extend into the perivitelline space. In this study, we asked whether the density of TZPs was related to oocyte transcriptional activity during follicle development in the mouse. Oocytes from 19-21 day old CF-1 mice, untreated or primed with eCG, were isolated, sorted into cumulus-enclosed or cumulus-lacking populations and fixed within 15 minutes. Samples were stained with anti-tubulin for immunofluorescence detection of TZP microtubules (MT) and oocyte MT status, and Hoechst 33258 to establish germinal vesicle chromatin patterns. Naked oocytes retrieved from unprimed animals exhibit a high density of TZPs (10-30/zona) and uniformly display diffuse chromatin patterns indicative of active transcription. In contrast, oocytes that retain cumulus have fewer TZPs (2-8/zona) and condensed GV chromatin patterns consistent with transcriptional inactivation. In response to eCG priming, a higher percentage of oocytes exhibit condensed GV chromatin patterns that coincides with a dramatic reduction in TZP density. These results support a model for gonadotropin regulation of bidirectional communication in the ovarian follicle where the stability and adhesion of TZPs is differentially modulated by growth factor or FSH-elicited signaling responses in granulosa cells. Supported by NIH Training Program in Developmental Biology HD07403.

KEY WORDS: oocyte, granulosa, transzonal projections, regulation