Fertilization is the fusion of the male and female gamete. The process involves the fusion of an oocyte with a sperm, creating a single diploid cell, the zygote, from which a new individual organism will develop. The elucidation of the molecular mechanisms of fertilization has fascinated researchers for many years. In this review, we focus on this intriguing process at the molecular level. Several molecules have been identified to play a key role in each step of this intriguing process (the sperm attraction from the oocyte, the sperm maturation, the sperm and oocyte fusion and the two gamete pronuclei fusion leading to the zygote). Understanding the molecular mechanisms of the cell-cell interactions will provide a better understanding of the causes of fertility issues due to fertilization defects.
Background: Neurocan is the most abundant lectican considered to be expressed exclusively in the central nervous system. Neurocan interacts with other matrix components, with cell adhesion molecules, growth factors, enzymes and cell surface receptors. The interaction repertoire and evidence from cellular studies indicated an active role in signal transduction and major cellular programs. Relatively little is known about the neurocan tissue-specific distribution and function during embryonic development. This study examined the time of appearance and subsequent spatio-temporal expression pattern of neurocan and its functional activities during the earliest stages of development in the chick embryo. Methods: To detect the first expression and spatio-temporal distribution of neurocan in the early embryo, strand-specific reverse transcription-polymerase chain reaction (RT-PCR), immunoprecipitation and immunofluorescence were performed. An anti-neurocan blocking antibody transient pulse was applied to embryos at the onset of the neurula stage to perturb neurocan activities in the background of the current cellular signaling state of the developing embryo. Results: Neurocan was first detected in the inchoate neural plate and the extracellular matrix in embryos at the definitive streak stage (late gastrula). During early organogenesis, neurocan fluorescence was very intense in the neural tube, notochord, neural crest cells, pharyngeal arches, foregut lower wall, presumptive pronephric tubules, blood islands, dorsal mesocardium, intense in myocardium and distinct in endocardium, very intense in the presumptive cornea and intense in retina and lens, intense in somite and nephrotome. Antibody perturbation of neurocan function resulted in three predominant defects: (1) abnormal expansion of neuroepithelium in the surface ectoderm flanking the neural tube; (2) neural crest cells formed epithelial pockets located on the ectoderm apical surface; and (3) surface ectoderm cells (presumptive epidermis) acquired mesenchymal cell properties, invaded into the subectodermal space and interacted with neuroectoderm. Conclusions: Neurocan was first expressed in the inchoate neural plate at the late gastrula stage. Neurocan expression was very intense in the developing central nervous system as well as in many non-neural tissues. Neurocan seems to modulate signalling in the neural-non-neural tissue specification and the adhesive and signalling activities of epithelial-mesenchymal cells and neural crest cell motility in the early embryo.
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