Clark Zaramasina L, Heath Derek A, O'Connell Anne R, Juengel Jennifer L, McNatty Kenneth P, Pitman Janet L
School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
AgResearch, Invermay Agricultural Centre, Mosgiel, New Zealand.
Reproduction. 2020 May;159(5):585-599. doi: 10.1530/REP-19-0613.
Ewes with single copy mutations in GDF9, BMP15 or BMPR1B have smaller preovulatory follicles containing fewer granulosa cells (GC), while developmental competency of the oocyte appears to be maintained. We hypothesised that similarities and/or differences in follicular maturation events between WT (++) ewes and mutant ewes with single copy mutations in BMP15 and BMPR1B (I+B+) are key to the attainment of oocyte developmental competency and for increasing ovulation rate (OR) without compromising oocyte quality. Developmental competency of oocytes from I+B+ animals was confirmed following embryo transfer to recipient ewes. The microenvironment of both growing and presumptive preovulatory (PPOV) follicles from ++ and I+B+ ewes was investigated. When grouped according to gonadotropin-responsiveness, PPOV follicles from I+B+ ewes had smaller mean diameters with fewer GC than equivalent follicles in ++ ewes (OR = 4.4 ± 0.7 and 1.7 ± 0.2, respectively; P < 0.001). Functional differences between these genotypes included differential gonadotropin-responsiveness of GC, follicular fluid composition and expression levels of cumulus cell-derived VCAN, PGR, EREG and BMPR2 genes. A unique microenvironment was characterised in I+B+ follicles as they underwent maturation. Our evidence suggests that GC were less metabolically active, resulting in increased follicular fluid concentrations of amino acids and metabolic substrates, potentially protecting the oocyte from ROS. Normal expression levels of key genes linked to oocyte quality and embryo survival in I+B+ follicles support the successful lambing percentage of transferred I+B+ oocytes. In conclusion, these I+B+ oocytes develop normally, despite radical changes in follicular size and GC number induced by these combined heterozygous mutations.
在生长分化因子9（GDF9）、骨形态发生蛋白15（BMP15）或骨形态发生蛋白受体1B（BMPR1B）中存在单拷贝突变的母羊，其排卵前卵泡较小，颗粒细胞（GC）数量较少，而卵母细胞的发育能力似乎得以维持。我们推测，野生型（++）母羊与在BMP15和BMPR1B中存在单拷贝突变的突变母羊（I+B+）之间卵泡成熟事件的异同是实现卵母细胞发育能力以及在不影响卵母细胞质量的情况下提高排卵率（OR）的关键。将I+B+动物的卵母细胞移植到受体母羊后，证实了其发育能力。研究了++和I+B+母羊生长卵泡和假定排卵前（PPOV）卵泡的微环境。根据促性腺激素反应性分组时，I+B+母羊的PPOV卵泡平均直径较小，GC数量比++母羊的同等卵泡少（OR分别为4.4±0.7和1.7±0.2；P<0.001）。这些基因型之间的功能差异包括GC的促性腺激素反应性差异、卵泡液成分以及卵丘细胞衍生的多功能蛋白聚糖（VCAN）、孕激素受体（PGR）、表皮调节素（EREG）和骨形态发生蛋白受体2（BMPR2）基因的表达水平。I+B+卵泡在成熟过程中具有独特的微环境特征。我们的证据表明，GC的代谢活性较低，导致卵泡液中氨基酸和代谢底物浓度增加，可能保护卵母细胞免受活性氧的影响。I+B+卵泡中与卵母细胞质量和胚胎存活相关的关键基因表达水平正常，支持了移植的I+B+卵母细胞的成功产羔率。总之，尽管这些复合杂合突变导致卵泡大小和GC数量发生了根本性变化，但这些I+B+卵母细胞仍能正常发育。
