Physiological polyspermy: Selection of a sperm nucleus for the development of diploid genomes in amphibians

The union between a sperm and an egg nucleus in egg fertilization is necessary to mix genetic materials to create a new diploid genome for the next generation. In most animals, only one sperm is incorporated into the egg (monospermy), but several animals exhibit physiological polyspermy in which several sperms enter the egg during normal fertilization. However, only one sperm nucleus forms the zygote nucleus with the egg nucleus, even in a polyspermic egg. The cellular and molecular mechanisms involved in the selection of sperm nuclei in the egg cytoplasm have been well investigated in urodele amphibians. The principal sperm nucleus develops a larger sperm aster and contacts the egg nucleus to form a zygote nucleus, whereas other accessory sperm nuclei are unable to approach the egg nucleus. The diploid zygote nucleus induces cleavage and participates in embryonic development, whereas the accessory sperm nuclei undergo pyknosis and degenerate. We propose several models to account for the mechanisms of the selection of one sperm nucleus and the degeneration of accessory sperm nuclei. The roles of physiological polyspermy in animal reproduction are discussed by comparison with other polyspermic species.     

Egg‐induced changes to sperm phenotypes shape patterns of multivariate selection on ejaculates

Sperm cells exhibit extraordinary phenotypic diversity and rapid rates of evolution, yet the adaptive value of most sperm traits remains equivocal. Recent findings suggest that to understand how selection targets ejaculates, we must recognize that female‐imposed physiological conditions often alter sperm phenotypes. These phenotypic changes may influence the relationships among sperm traits and their association with fitness. Here, we show that chemical substances released by eggs (known to modify sperm physiology and behaviour) alter patterns of selection on a suite of sperm traits in the mussel Mytilus galloprovincialis. We use multivariate selection analyses to characterize linear and nonlinear selection acting on sperm traits in (a) seawater alone and (b) seawater containing egg‐derived chemicals (egg water). Our analyses revealed that nonlinear selection on canonical axes of multiple traits (notably sperm velocity, sperm linearity and percentage of motile sperm) was the most important form of selection overall, but importantly these patterns were only evident when sperm phenotypes were measured in egg water. These findings reveal the subtle way that females can alter patterns of selection, with the implication that overlooking environmentally moderated changes to sperm, may result in erroneous interpretations of how selection targets phenotypic (co)variation in sperm traits.     

Rac1 is necessary for capacitation and acrosome reaction in guinea pig spermatozoa

Actin cytoskeleton remodeling is a critical process for the acquisition of fertilizing capacity by spermatozoa during capacitation. However, the molecular mechanism that regulates this process has not been fully elucidated. In somatic cells, Ras-related C3 botulinum toxin substrate 1 protein (Rac1) promotes the polymerization of actin by participating in the modeling of two structures: lamellipodia and adhesion complexes linked with the plasma membrane. Rac1 is expressed in mammalian spermatozoa; however, the role of Rac1 in sperm physiology is unknown. This study aimed to elucidate the participation of Rac1 in capacitation and acrosome reaction (AR). Rac1 was found to be dispersed throughout the acrosome and without changes in the middle piece. After 60 minutes of capacitation, Rac1 was found in the apical region of the acrosome only, which concurred with an increase in Rac1-GTP. Rac1 inhibition prevented such changes. In the middle piece, Rac1 localization remained unchanged. Besides, Rac1 inhibition blocked capacitation and AR. The present study demonstrates that Rac1 participates only in the actin cytoskeleton remodeling that occurs in the acrosomal apical region during capacitation, a region where a large amount of actin is polymerized and shaped in a diadem-like structure. Our data also show that this actin cytoskeleton organized by Rac1 interacts with filamin-1, and such interaction was blocked by the inhibition of Rac1, which led to a different organization of the actin cytoskeleton. All these outcomes imply that the formation of an F-actin cytoskeleton in the acrosomal apical region is a necessary event for capacitation and AR, and which is Rac1 driven.     

Reproduction systems of representatives of the genus Rosa L. under conditions of continental climate

The features of reproductive biology of rose plants from the sections Caninae Crep., Indocae Thory, Cinnamomae DC., Synstylae DC. were studied by cytological methods and with the help of scanning electron microscopy for many years. The results obtained are reported.     

室温下保存的小鼠屠体卵巢GV卵的发育能力

将ICR系雌性小鼠处死并在10℃、15℃、20℃和25℃下依次保存8、14、24和48 h后,采集其体内的卵巢GV期卵,采用常规方法进行体外成熟和体外受精,获得的2细胞期胚经体外培养或胚胎移植观察其发育能力.其结果,在10℃下保存24 h、15℃下保存14 h、20℃下保存8h和25℃下保存4 h后,其体内附有卵丘细胞的GV卵的体外成熟-体外受精后的2细胞率分别为14%、9%、10%和10%,随着保存温度的提高和保存时间的延长,带有颗粒细胞GV期卵的比率明显降低,同时其GV期卵经体外成熟及体外受精后的2细胞率明显降低.在20℃下保存24 h和25℃下保存14 h时,难以获得形态正常的GV期卵;体外受精获得的2细胞期胚经体外培养,总体上有64%的胚胎发育至扩张囊胚,未见有保存温度和保存时间的显著影响,且利用在15℃保存8 h后的GV卵获得2细胞期胚的移植获得正常新生小鼠.上述结果表明,雌性动物室温条件下死亡后,若能短时间及时采集其体内GV期卵并体外成熟、体外受精,体外培养及胚胎移植技术,就有可能获得新生后代.     

唇精子早期入卵观察

用扫描电镜对唇成熟卵子及早期精子入卵过程进行观察.结果 显示,唇成熟卵子在动物极中央有一深凹陷的表面光滑的精孔器,其外径2.512 μm,内径2.330 μm,精子直径1.567 μm.混匀的精卵刚遇水时,没有精子进入精孔器.受精后1 s,精孔器内出现精子.受精后5 s,组织切片显示,精子已经进入卵子内,并形成具有强烈抑制多精入卵作用的受精锥.受精后10 s,精子在精孔器前庭集结,尚未形成受精塞.受精后20 s,在精孔器内形成受精塞.受精塞没有阻塞精孔管,经分析它不是来源于皮层反应产物.受精塞形成后,可以吸附入卵的精子,这对多精入卵有积极的抑制作用;精子尾部在入卵过程中相互缠绕,这也是减少多精入卵的重要机制.受精后30 s, 受精塞和吸附的精子向精孔器外移动.受精后50 s, 受精塞和吸附的精子堵塞精孔器.受精后60 s, 受精塞吸附的精子开始解体,但是由于精孔管未封闭,还有精子通过精孔管进入到质膜.在人工受精过程中,卵子的单精受精屏障会因其周围精子密度大、精子与卵子距离短、精子运动速度快而被打破,从而导致这些卵子出现多精入卵的现象.受精后80 s, 精孔管仍然没有封闭,精孔器附近的精子明显出现活动能力的差异:精孔器外面的精子活动能力最强,精孔管旁边的精子活动能力较弱;精孔管外堆积的精子活性消失,受精塞吸附的精子已开始解体,经初步分析,这可能是进入其内的精子耗能有所差异的结果.受精后100 s,受精塞吸附的精子解体.     

四倍体青花菜低稔性胚胎学研究

以二、四倍体青花菜为材料,在现蕾期分别套袋自交,对四倍体与二倍体的胚囊结构、受精以及受精后胚胎发育过程进行比较研究.结果表明:四倍体青花菜胚囊发育完整,与二倍体相似.四倍体花粉萌发率较二倍体低,花粉管生长较慢且不整齐.四倍体和二倍体青花菜自交均能正常受精,四倍体青花菜在受精后胚胎发育的进程上均较其二倍体滞后约2 d,且胚胎发育在进度上不一致,并存在胚胎败育现象,正常胚胎只占25.8%,导致四倍体结实率比二倍体降低22.6%.     

不同有机肥影响菠萝生长的生理生化机制

以菠萝品种'澳大利亚卡因'为材料,研究了施用不同有机肥对菠萝长叶期和抽蕾期植株生长量、生理生化指标以及土壤酶活性、微生物等的影响,以探讨不同有机肥对菠萝生长的影响机理.结果显示:(1)在花生麸处理中菠萝株高、青叶数、地上部和根鲜重较对照(施用化肥)提高,而在鸡粪和水肥处理中株高、青叶数、地上部鲜重较对照降低.(2)花生麸处理的菠萝叶片细胞膜透性较对照降低,而叶绿素含量、根系活力以及叶片和根系的可溶性糖、可溶性蛋白含量、SOD活性均较对照提高;鸡粪和水肥处理的叶片细胞膜透性和根系SOD酶活性较对照提高,而叶绿素含量、根系活力、长叶期叶片和根系的可溶性糖含量、长叶期和抽蕾期叶片的可溶性蛋白含量、叶片SOD酶活性均比对照降低.(3)花生麸能提高土壤脲酶、转化酶和过氧化氢酶的活性及土壤微生物数量;鸡粪和水肥能降低土壤脲酶、蛋白酶活性,却能增强土壤转化酶、过氧化氢酶活性,鸡粪使土壤微生物数量增加,水肥使长叶期土壤微生物数量增加,但使抽蕾期的减少.研究表明,施用花生麸能提高菠萝叶绿素含量、根系活力以及叶片和根系的可溶性糖、可溶性蛋白含量,并增强根和叶的SOD活性,同时增加了土壤相关酶活性和微生物数量,从而有效促进菠萝植株生长.     

Trampling and Spatial Heterogeneity Explain Decomposer Abundances in a Sub-Arctic Grassland Subjected to Simulated Reindeer Grazing

Mammal grazing is composed of three mechanisms—removal of foliar tissue (defoliation), return of nutrients via dung and urine (fertilization), and trampling. To evaluate the relative role of these mechanisms in the effect of reindeer grazing on soil biota in northern grasslands, we subjected experimental plots in a sub-arctic alpine meadow to defoliation, fertilization (using NPK-solution), simulated trampling, and their factorial combinations once a year from 2002 to 2004 and measured the response of plants and decomposers (including microbes, nematodes, collembolans, and enchytraeids) in 2004. Trampling affected both plant and decomposer communities: the coverage of the moss Pleurozium schreberi and the sedge Carex vaginata, as well as the abundance of collembolans and enchytraeids were reduced in trampled plots. Trampling and fertilization also interacted significantly, with fertilization increasing the abundance of bacteria and bacterial-feeding and omnivorous nematodes in trampled plots only, and trampling decreasing fungal biomass in non-fertilized plots only. Defoliation had no overall effects on plants or decomposers. Nematode genera were not affected by the experimental treatments, but nematode and plant communities were significantly associated, and all decomposer biota, except collembolans, were strongly affected by the spatial heterogeneity of the study site. Our results indicate that trampling may have larger and defoliation and fertilization smaller roles than anticipated in explaining reindeer grazing effects in sub-arctic grasslands. However, even the effects of trampling seem to be outweighed by the spatial heterogeneity of decomposer abundances. This suggests that in sub-arctic grasslands spatial variation in abiotic factors can be a more important factor than grazing in controlling soil biota abundances. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author contributions  LIS was involved in planning of the study, fieldwork, lab work, analysis, and wrote the article with contributions from all other authors; JM and MMK conceived the study and contributed to the data analyses; MMK further contributed to the field work and JM refined the final appearance of the text; JO started and was responsible for managing the field experiment, collecting the plant data and gave advice on statistical analysis.