Cortical Granule Distribution and Expression Pattern of Genes Regulating Cellular Component Size, Morphogenesis, and Potential to Differentiation are Related to Oocyte Developmental Competence and Maturational Capacity In Vivo and In Vitro

Abstract

Polyspermia is an adverse phenomenon during mammalian fertilization when more than one sperm fuses with a single oocyte. The egg cell is prepared to prevent polyspermia by, among other ways, producing cortical granules (CGs), which are specialized intracellular structures containing enzymes that aim to harden the zona pellucida and block the fusion of subsequent sperm. This work focused on exploring the expression profile of genes that may be associated with cortical reactions, and evaluated the distribution of CGs in immature oocytes and the peripheral density of CGs in mature oocytes. Oocytes were isolated and then processed for in vitro maturation (IVM). Transcriptomic analysis of genes belonging to five ontological groups has been conducted. Six genes showed increased expression after IVM (ARHGEF2, MAP1B, CXCL12, FN1, DAB2, and SOX9), while the majority of genes decreased expression after IVM. Using CG distribution analysis in immature oocytes, movement towards the cortical zone of the oocyte during meiotic competence acquisition was observed. CGs peripheral density decreased with the rise in meiotic competence during the IVM process. The current results reveal important new insights into the in vitro maturation of oocytes. Our results may serve as a basis for further studies to investigate the cortical reaction of oocytes.

Analyses stratified by maternal age and recombination further characterize genes associated with maternal nondisjunction of chromosome 21

“…This gene is necessary for meiotic maturation of porcine oocytes, particularly for reaching MII metaphase 60 . rs62359711 near DAB2 (Figure 4, maternal MII errors locus #8), which may be involved in oocyte maturation, particularly at MII, 58,59 follows a similar pattern. rs73178888 (Figure 4, maternal MII errors locus #9), also significantly associated with nondisjunction in all three MII subgroups, is located near DLGAP2 but is not in linkage disequilibrium with rs1612273 (discussed above in the combined MI and MII analysis); therefore, these associations may represent independent signals.…”

Integrated Analysis of mRNAs and Long Non-Coding RNAs Expression of Oviduct That Provides Novel Insights into the Prolificacy Mechanism of Goat (Capra hircus)

“…Moreover, XLOC_020079, XLOC_107361, XLOC_169844, XLOC_252348, and the target genes ( ARHGEF2 and RAPGEF6 ) were mainly associated with prolificacy. In vitro, culture studies of mammalian oocytes reveal a well-developed increase in ARHGEF2 in mature oocytes, suggesting that ARHGEF2 may affect the development and maturation of oocytes [ 69 ]. In addition, RAPGEF6 is essential for the high egg-laying rate of chickens [ 70 ].…”

Knockin’ on Egg’s Door: Maternal Control of Egg Activation That Influences Cortical Granule Exocytosis in Animal Species

“…However, a constant increase in peripheral CG density following oocyte maturation has been reported in mouse oocytes (Ducibella et al, 1988a(Ducibella et al, , 1994. In contrast, in in vitro matured pig oocytes, it has been shown that the mean value of the peripheral density of CGs during mid-oogenesis was less than in early oocytes (Kulus et al, 2020). This suggests that the acquisition of meiotic competence and progression correlates with a decrease in the number of CGs per 100 µm 2 of the ooplasmic cortex (Figure 2).…”

“…Yet, during mid-oogenesis, a concentration twice higher of these secretory vesicles can be found at the cell periphery, suggesting their translocation from the central region toward the cortex. Moreover, CG translocation to the cortical area is associated with a high meiotic competence (Kulus et al, 2020). By analyzing fixed mouse oocytes, it has been shown that CG transport to the PM is a microfilament-dependent process (Connors et al, 1998;Wessel et al, 2002).…”