卵母细胞在哺乳动物卵巢排卵过程中的决定性作用

哺乳动物卵巢排卵是一个复杂的调控过程。卵泡成熟破裂后,卵母细胞从卵巢中排出。卵泡细胞感受排卵刺激,并诱导卵母细胞减数分裂的恢复及其随后的释放。卵母细胞及其周围颗粒细胞的旁分泌在对此起关键性作用,其中卵母细胞对其释放具有决定性作用。作者先前已经阐述过颗粒细胞在哺乳动物卵巢排卵过程中的调控作用,该文将从卵母细胞的发育及其调控角度重点阐明其在排卵过程中的决定作用,旨在进一步理解哺乳动物卵巢的排卵过程,同时为不孕不育等卵巢疾病的治疗提供重要的研究方向和理论基础。     

干细胞因子在卵泡发育过程中的作用

干细胞因子(stemcellfactor,SCF)是酪氨酸激酶受体的配体。哺乳动物卵巢组织能表达SCF,它不仅能促进和诱导卵母细胞的发育,并能调控卵泡细胞间的相互作用及激素的生成,而且是卵泡发育过程中重要的旁分泌因子,可能激活蛋白激酶C(PKC)和有丝分裂原激活蛋白激酶的激酶(MEK)及PI3激酶途径信号分子等信号途径,对卵泡发育起调节作用。     

The Post-anaphase SUMO Pathway Ensures the Maintenance of Centromeric Cohesion through Meiosis I-II Transition in Mammalian Oocytes

1. Download high-res image (159KB)
2. Download full-size image

     

Environmental factors for establishment of the dormant state in oocytes

Guaranteeing the sustainability of gametogenesis is a fundamental issue for perpetuating the species. In the mammalian ovary, sustainability is accomplished by keeping a number of oocytes “stocked” in the dormant state. Despite the evident importance of this state, the mechanisms underlying the oocyte dormancy are not fully understood, although it is presumed that both intrinsic and extrinsic factors are involved. Here, we review environmental factors involved in the regulation of oocyte dormancy. Consideration of the environmental factors illustrates the nature of the ovarian compartment, in which primordial follicles reside. This should greatly improve our understanding of the mechanisms and also assist in reconstitution of the dormant state in culture. Accumulating knowledge on the dormant state of oocytes will contribute to a wide range of research in fields such as developmental biology, reproductive biology and regenerative medicine.     

Evaluation of three classification methods of antral follicle count and fertility to the timed artificial insemination in cattle

The controversial data about antral follicle count (AFC) may be partially explained by the different criteria used to determine what is high, intermediate and low AFC. This study evaluated different classification methods for AFC groups, relating them to the conception rate, dominant follicle size and body condition score (BCS) in cows submitted to timed artificial insemination (TAI). Nelore cows (Bos indicus; n = 935), received a reproductive program consisting of TAI and natural breeding. Conception rate, BCS and dominant follicle size during TAI were evaluated by three AFC methodologies: i) mean and standard deviation: low (≤ 15 follicles); intermediate (≥ 16 to ≤ 44 follicles) or high (≥ 45 follicles); ii) quartiles: low (≤ 15 follicles); intermediate (≥ 16 to ≤ 39 follicles), or high (≥ 40 follicles); and iii) AFC score: I (low; ≤ 15 follicles); II (intermediate; ≥ 16 to ≤ 30 follicles); III (high; ≥ 31 to ≤ 44 follicles) or IV (very high; ≥ 45 follicles). Data were analyzed by a GLIMMIX and Tukey test or binary logistic regression model (P ≤ 0.05). The conception rate to TAI was influenced (P < 0.05) by AFC in the three methods classification, being the highest conception rate observed in the low AFC group regardless of method utilized: Mean (low 61.73%^a, intermediate 54.02%^ab and high 49.48%^b), Quartiles (low 61.73%^a, intermediate 53.59%^ab and 51.46%^b) and Score (I 61.73%^a, II 54.80%^ab, III 53.23%^ab and IV 49.48%^b). There were variations (P < 0.05) in the conception rate within the 2.50 to 2.75 BCS range for all AFC classification methods, with the low AFC females presenting the best results, regardless of the method used. Also, females with low AFC showed larger (P < 0.05) diameters of dominant follicles at the TAI regardless of method. The different methodologies used (Mean, Quartile and Score) to AFC classification showed a consistency between the main findings, and we believe that this standardization will facilitate the interpretation of data involving AFC.     

Morphine Inhibits Calcium Influx and the Response to Acetylcholine in Xenopus Oocytes

Abstract: Incubation of intact Xenopus oocytes with the opioid radioligand [³H]diprenorphine (0.5 n M ) resulted in specific binding of 1.7 ± 0.3 fmol per oocyte. Morphine (10 μ M ) inhibited the uptake of ⁴⁵Ca²⁺ into the oocyte by 66 ± 9%. The opioid antagonist naltrexone partially blocked this effect of morphine. Preincubation of oocytes with morphine (10 μ M , 2 min) partially inhibited the fast and slow responses of the oocyte to acetylcholine by 26 and 52%, respectively. We conclude that native Xenopus oocytes possess opioid receptors that may modulate the muscarinic response by limiting calcium influx into the cell.     

Follicular development in the volcano mouse (Neotomodon alstoni alstoni, Rodentia: Muridae) from birth to maturity: A morphological approach

The present study describes the morphology and ultrastructural features of postnatal follicular development in the volcano mouse ( Neotomodon alstoni alstoni ), an endemic Mexican rodent. By the first week of age, germ cells were organized in clusters within the ovigerous cords, and only 51.8% of them were associated with somatic cells. At the ultrastructural level, pairing chromosomes and cellular junctions between germ and pregranulosa cells, such as desmosomes, were observed. At this time, the zona pellucida could not be detected in the formed follicles. From 15 to 28 days postpartum, growing follicles were located at the medulla and inner cortex of the ovary, but most were atretic. The first preovulatory follicles were seen at 40 days. Likewise, corpora lutea were observed at this stage of development, which shows that the volcano mouse is a spontaneous ovulator. The follicular development of the volcano mouse shows strong similarities with that of the golden hamster, particularly during the first week. The morphological changes observed during postnatal follicular development of the volcano mouse follow the same general histological pattern as reported for other mammals, although the timing of these events is species-specific.     

SACY-1 DEAD-Box Helicase Links the Somatic Control of Oocyte Meiotic Maturation to the Sperm-to-Oocyte Switch and Gamete Maintenance in Caenorhabditis elegans

In sexually reproducing animals, oocytes arrest at diplotene or diakinesis and resume meiosis (meiotic maturation) in response to hormones. In Caenorhabditis elegans, major sperm protein triggers meiotic resumption through a mechanism involving somatic Gα_s–adenylate cyclase signaling and soma-to-germline gap-junctional communication. Using genetic mosaic analysis, we show that the major effector of Gα_s–adenylate cyclase signaling, protein kinase A (PKA), is required in gonadal sheath cells for oocyte meiotic maturation and dispensable in the germ line. This result rules out a model in which cyclic nucleotides must transit through sheath-oocyte gap junctions to activate PKA in the germ line, as proposed in vertebrate systems. We conducted a genetic screen to identify regulators of oocyte meiotic maturation functioning downstream of Gα_s–adenylate cyclase–PKA signaling. We molecularly identified 10 regulatory loci, which include essential and nonessential factors. sacy-1, which encodes a highly conserved DEAD-box helicase, is an essential germline factor that negatively regulates meiotic maturation. SACY-1 is a multifunctional protein that establishes a mechanistic link connecting the somatic control of meiotic maturation to germline sex determination and gamete maintenance. Modulatory factors include multiple subunits of a CoREST-like complex and the TWK-1 two-pore potassium channel. These factors are not absolutely required for meiotic maturation or its negative regulation in the absence of sperm, but function cumulatively to enable somatic control of meiotic maturation. This work provides insights into the genetic control of meiotic maturation signaling in C. elegans, and the conserved factors identified here might inform analysis in other systems through either homology or analogy.     

Genetic Interactions between the Aurora Kinases Reveal New Requirements for AURKB and AURKC during Oocyte Meiosis

1. Download high-res image (189KB)
2. Download full-size image

     

Gatekeeper function for Short stop at the ring canals of the Drosophila ovary

Download : Download video (7MB)     

Electrophysiological Studies in Xenopus Oocytes for the Opening of Escherichia coli SecA-Dependent Protein-Conducting Channels

Protein translocation in Escherichia coli requires protein-conducting channels in cytoplasmic membranes to allow precursor peptides to pass through with adenosine triphosphate (ATP) hydrolysis. Here, we report a novel, sensitive method that detects the opening of the SecA-dependent protein-conducting channels at the nanogram level. E. coli inverted membrane vesicles were injected into Xenopus oocytes, and ionic currents were recorded using the two-electrode voltage clamp. Currents were observed only in the presence of E. coli SecA in conjunction with E. coli membranes. Observed currents showed outward rectification in the presence of KCl as permeable ions and were significantly enhanced by coinjection with the precursor protein proOmpA or active LamB signal peptide. Channel activity was blockable with sodium azide or adenylyl 5′-(β,γ-methylene)-diphosphonate, a nonhydrolyzable ATP analogue, both of which are known to inhibit SecA protein activity. Endogenous oocyte precursor proteins also stimulated ion current activity and can be inhibited by puromycin. In the presence of puromycin, exogenous proOmpA or LamB signal peptides continued to enhance ionic currents. Thus, the requirement of signal peptides and ATP hydrolysis for the SecA-dependent currents resembles biochemical protein translocation assay with E. coli membrane vesicles, indicating that the Xenopus oocyte system provides a sensitive assay to study the role of Sec and precursor proteins in the formation of protein-conducting channels using electrophysiological methods.