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Fertilization, cell proliferation and differentiation www.sciencepicturecompany.com Molecular Cell Gene-cs 416451 Mingkwan Nipitwa6anaphon fertilization • Fusion of 2 haploid gametes to become diploid zygote – Internal fertilization – External fertilization • Involved in many signaling process and cell division • In animals, there must be mechanisms to prevent polyspermy – in mammals, the "cortical reaction" modifies the extracellular coat of the egg (the zona pellucida), and additional mechanisms modify the egg's plasma membrane fertilization • When the sperm bind to the egg before fertilization, the egg become metabolically active – Lots of transcription, translation and protein synthesis • The fusion of the sperm to the egg continues the meiotic process resulting in the releasing of polar nuclei fertilization en.wikipedia.org fertilization Click to see fertilization video link http://www.youtube.com/watch?v=BFrVmDgh4v4 h6p://humanphysiology2011.wikispaces.com/ fertilization Proliferation • Cleavage - Rapid cell division • Gastrulation - Cell movements and 3 layers form – Ectoderm – Mesoderm – Endoderm • Organogenesis – Pattern formation – Cell differentiation • Endoderm -> digestive tract • Mesoderm -> support tissues, e.g. skeleton, muscle, connective tissues, blood, urogential system • Endoderm - > epidermis, nervous system www.stemcure.com Differentiation • A process by which individual cells become specialized and distinct from other groups of cells • Change in cell’s size, shape, membrane potential, metabolic activity, responsiveness to signals • Differentiation occurs at various stage of development but mostly after fertilization Different ways of differentiation Determination & differentiation • Determination = the process of establishing which genes will be expressed and which will not. • Cells progressively lose their genetic capacity (genes, or chromosomes) during the development à cells become determined? • In fact, determination is regulated by gene expression Control of gene activity • RNA level – Transcription regulation – RNA processing – RNA transport – Selection of mRNA for translation – mRNA degradation • Protein level – Translational control – Protein modification – Protein degradation mRNA processing apbio-‐werle.wikispaces.com mRNA degradation Specialized cells in different tissues have large amount of certain mRNAs Fraction No. Of different mRNAs Copies per cell % of total mRNAs Oviduct I 1 100,000 50 II 8 3,750 15 III 14,000 5 35 1 32,800 16 II 106 750 40 III 11,600 7 44 Liver I Fraction I = highly abundant Fraction II = moderately abundant Fraction III = rare Cell potency • Developmental potency = ability of cell to develop into different cell types – Unipotency – pluripotency – totipotency h6p://163.16.28.248/bio/ac-velearner/16/ch16c4.html Pluripotency: stem cells can differentiate into many blood cell types Regeneration • A process of renewal, restora-on, and growth to repair the damage or maintain physiological and morphological stages • Regulated by a sexual cellular process snowbio.wikispaces.com psi.wikia.com www.tutorvista.com Pattern formation • Cells need to know what they are and what they do • A local group of cells organize into a pattern of different cell types – Need communication between cells by chemical signal – The signal can vary in concentrations (gradient) resulting in different fate of cells morphogen • A special type of chemical signal that specifies development of particular pattern • There is a threshold of the morphogen – Reach the threshold -> cell become determined -> differentiate Pattern formation Pattern formation Pattern formation h6p://plantdev.bio.wzw.tum.de/index.php?id=58 Mutation of the homeobox (transcriptional factor) result in developmental abnormality: antenapedia (fly that have legs where the antena should be Eyeless is a transcription factor eyeless mutant has no eye while overexpression of this gene results in developing eyes at the legs www.gehring.biozentrum.unibas.ch www.scienceforums.net Dedifferentiation • A cellular process that differentiated cells reverts to the earlier developmental stage – Ex. worms and amphibians in which a partially or terminally differentiated cell reverts to an earlier developmental stage, usually as part of a regenerative process. Dedifferentiation also occurs in plants. • Cells in cell culture can lose properties they originally had, such as protein expression, or change shape. This process is also termed dedifferentiation. • Some believe dedifferentiation is an aberration of the normal development cycle that results in cancer, whereas others believe it to be a natural part of the immune response lost by humans at some point as a result of evolution. • A small molecule dubbed reversine, a purine analog, has been discovered that has proven to induce dedifferentiation in myotubes. These dedifferentiated cells could then redifferentiate into osteoblasts and adipocytes. Terminal differentiation • Cells specilized • Post mitotic (stop dividing) -> die • Sometimes cell dead is a part of differentiation, e.g. Progressive keratinization of skin cell, progressive lignification of xylogenic cells