An F-Actin Mega-Cable Is Associated With the Migration of the Sperm Nucleus During the Fertilization of the Polarity-Inverted Central Cell of Agave inaequidens

Asparagaceae’s large embryo sacs display a central cell nucleus polarized toward the chalaza, which means the sperm nucleus that fuses with it during double fertilization migrates an atypical long distance before karyogamy. Because of the size and inverted polarity of the central cell in Asparagaceae, we hypothesize that the second fertilization process is supported by an F-actin machinery different from the short-range F-actin structures observed in Arabidopsis and other plant models. Here, we analyzed the F-actin dynamics of Agave inaequidens, a classical Asparagaceae, before, during, and after the central cell fertilization. Several parallel F-actin cables, spanning from the central cell nucleus to the micropylar pole, and enclosing the vacuole, were observed. As fertilization progressed, a thick F-actin mega-cable traversing the vacuole appeared, connecting the central cell nucleus with the micropylar pole near the egg cell. This mega-cable wrapped the sperm nucleus in transit to fuse with the central cell nucleus. Once karyogamy finished, and the endosperm started to develop, the mega-cable disassembled, but new F-actin structures formed. These observations suggest that Asparagaceae, and probably other plant species with similar embryo sacs, evolved an F-actin machinery specifically adapted to support the migration of the fertilizing sperm nucleus within a large-sized and polarity-inverted central cell.

Central Giant Cell Granuloma of the Mandible: Clinical Observation

The Giant central cell granuloma (GCCG) is a benign intra-osseous lesion of the neo-plastic type. It appears mainly in the mandible, but can be observed in the maxilla and small bones of the hand and foot, with a predilection for the female sex and prevalence at a young age. Its diagnosis is clinical and radiological, confirmed by histological examination. The differential diagnosis is biological because it has a wide range of morphologies and a misinterpretation with other giant cell lesions can often occur. The authors present a case of the Giant central cell granuloma in a 62-year-old woman developing for 3 years after dental extractions. The most favorable treatment for giant cell granulomas is surgical whose main objective is to prevent recurrences.

An F-actin mega-cable supports the migration of the sperm nucleus during the fertilization of the polarity-inverted central cell of Agave inaequidens

Asparagaceae's large embryo sacs display a central cell nucleus polarized toward the chalaza, which means the sperm nucleus that fuses it during double fertilization migrates a long distance before karyogamy. Because of the size and inverted polarity of the central cell in Asparagaceae, we hypothesize that the second fertilization process is supported by F-actin structures different from the short-range aster-like ones observed in Arabidopsis. Here, we analyzed the F-actin dynamics of Agave inaequidens, a typical Asparagaceae, before, during, and after central cell fertilization. Several parallel F-actin cables emerging from the nucleus within the central cell, enclosing the vacuole, and reaching the micropylar pole were observed. As fertilization progressed, a thick F-actin mega-cable traversing the vacuole appeared, connecting the central cell nucleus with the micropylar pole near the egg cell. This mega-cable wrapped the sperm nucleus in transit to fuse the central cell one. Once karyogamy finished, the mega-cable disassembled, but new F-actin structures formed during the endosperm development. These observations suggest that Asparagaceae, and probably other plant species with similar embryo sacs, evolved an F-actin machinery specifically adapted to support the migration of the fertilizing sperm nucleus within a large-sized and polarity-inverted central cell.

A New Hashing based Nearest Neighbors Selection Technique for Big Datasets

KNN has the reputation of being a simple and powerful supervised learning algorithm used for either classification or regression. Although KNN prediction performance highly depends on the size of the training dataset, when this one is large, KNN suffers from slow decision making. This is because each decision-making process requires the KNN algorithm to look for nearest neighbors within the entire dataset. To overcome this slowness problem, we propose a new technique that enables the selection of nearest neighbors directly in the neighborhood of a given data point. The proposed approach consists of dividing the data space into sub-cells of a virtual grid built on top of the dataset. The mapping between data points and sub-cells is achieved using hashing. When it comes to selecting the nearest neighbors of a new observation, we first identify the central cell where the observation is contained. Once that central cell is known, we then start looking for the nearest neighbors from it and the cells around. From our experimental performance analysis of publicly available datasets, our algorithm outperforms the original KNN with a predictive quality as good and offers competitive performance with solutions such as KDtree.

Spatio-Temporal Distribution of Cell Wall Components in the Placentas, Ovules and Female Gametophytes of Utricularia during Pollination

In most angiosperms, the female gametophyte is hidden in the mother tissues and the pollen tube enters the ovule via a micropylar canal. The mother tissues play an essential role in the pollen tube guidance. However, in Utricularia, the female gametophyte surpasses the entire micropylar canal and extends beyond the limit of the integument. The female gametophyte then invades the placenta and a part of the central cell has direct contact with the ovary chamber. To date, information about the role of the placenta and integument in pollen tube guidance in Utricularia, which have extra-ovular female gametophytes, has been lacking. The aim of this study was to evaluate the role of the placenta, central cell and integument in pollen tube pollen tube guidance in Utricularia nelumbifolia Gardner and Utricularia humboldtii R.H. Schomb. by studying the production of arabinogalactan proteins. It was also determined whether the production of the arabinogalactan proteins is dependent on pollination in Utricularia. In both of the examined species, arabinogalactan proteins (AGPs) were observed in the placenta (epidermis and nutritive tissue), ovule (integument, chalaza), and female gametophyte of both pollinated and unpollinated flowers, which means that the production of AGPs is independent of pollination; however, the production of some AGPs was lower after fertilization. There were some differences in the production of AGPs between the examined species. The occurrence of AGPs in the placental epidermis and nutritive tissue suggests that they function as an obturator. The production of some AGPs in the ovular tissues (nucellus, integument) was independent of the presence of a mature embryo sac.

Physalidiella pentagona sp. nov. from Guizhou, China

A new species, Physalidiella pentagona, collected on dead twigs of Lindera communis in Guizhou Province, China, is described and illustrated. The fungus is mainly characterized by differentiated conidiophores with opposite or verticillate short branches and monoblastic, percurrently extending conidiogenous cells that produce solitary, smooth, quasi-stellate or T-shaped conidia with an approximately pentagonal central cell and two smaller hemispherical lateral cells. A dichotomous key to Physalidiella species is provided.

Structural and Functional Peculiarities of Outer and Central Cell Layers of Yeast Colony

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Polyspermy Block in the Central Cell During Double Fertilization of Arabidopsis thaliana

During double fertilization in angiosperms, two male gametes (sperm cells), are released from a pollen tube into the receptive region between two female gametes; the egg cell and the central cell of the ovule. The sperm cells fertilize the egg cell and the central cell in a one-to-one manner to yield a zygote and an endosperm, respectively. The one-to-one distribution of the sperm cells to the two female gametes is strictly regulated, possibly via communication among the four gametes. Polyspermy block is the mechanism by which fertilized female gametes prevent fertilization by a secondary sperm cell, and has been suggested to operate in the egg cell rather than the central cell. However, whether the central cell also has the ability to avoid polyspermy during double fertilization remains unclear. Here, we assessed the one-to-one fertilization mechanism of the central cell by laser irradiation of the female gametes and live cell imaging of the fertilization process in Arabidopsis thaliana. We successfully disrupted an egg cell within the ovules by irradiation using a femtosecond pulse laser. In the egg-disrupted ovules, the central cell predominantly showed single fertilization by one sperm cell, suggesting that neither the egg cell nor its fusion with one sperm cell is necessary for one-to-one fertilization (i.e., monospermy) of the central cell. In addition, using tetraspore mutants possessing multiple sperm cell pairs in one pollen, we demonstrated that normal double fertilization was observed even when excess sperm cells were released into the receptive region between the female gametes. In ovules accepting four sperm cells, the egg cell never fused with more than one sperm cell, whereas half of the central cells fused with more than one sperm cell (i.e., polyspermy) even 1 h later. Our results suggest that the central cell can block polyspermy during double fertilization, although the central cell is more permissive to polyspermy than the egg cell. The potential contribution of polyspermy block by the central cell is discussed in terms of how it is involved in the one-to-one distribution of the sperm cells to two distinct female gametes.