CELL BIRTH Section 22.1 Grace Githunguri BIRTH OF CELLS Cell division Stem cells Properties Tissue maintenance Embryonic stem cells Cell Fate Cell lineage C. elegans Cell Division Symmetric The progeny do not change their properties (same). Differences arise when cells diverge by receiving distinct developmental or environmental signals. Asymmetric Size, shape, and/or composition, or genes may differ in their state of activity. Internal signals confer different fates on cells. Stem cells- properties Divides symmetrically Produce themselves indefinitely (Self renewing). 2. Asymmetric division generates an identical copy and a stem cell with restricted capabilities. 1. Pluripotent (Multipotent) – Generate a number of different cell types, but not all e.g. blood cells. Unipotent – Forms a copy of itself forms one cell type. Stem cells Stem cells Totipotent –generate all the cells types of the body e.g Zygote. Zygote and neuron-glial cell precursor are not stem cells because they are incapable of self renewing. Embryonic stem cells Human Embryonic cells can be grown in Suspension Culture and in Solid culture. Suspension Culture ES cells differentiate into multicellular aggregates (embryoid bodies). Solid Medium They grow into confluent cell sheets with differentiated cell types. ES can also be induced to differentiate into precursors for various types of blood cells. Embryonic stem cells cont… Treatment of Parkinson’s disease Culture grown neurons that produce dopamine. Other conditions like Alzheimer’s disease. Stem cells Differentiated cells have a shorter life span than that of an organism. They are replenished from nearby stem cell populations. Skin – epidermis Epithelial lining of the small intestine. Underlain by a layer of stem cells that give rise to more layers and keratinocytes. Regenerated from deep intestinal wall in pits called crypts. Plant stem cells Persist for life in the meristem. Stem cells Production of new cells is controlled. By specific signals e.g - catenin Overproduction leads to excess proliferation of the intestinal lining. Links certain cell-cell junctions to the cytoskeleton Signal transducer in the Wnt pathway. Moves cells from epidermis to hair cell fates. Cell Fate. Restricted during development. 1. Gastrulation form germ layers; Ectoderm Mesoderm Endoderm cell populations with different fates. 2. Germ line Stem cells and precursor cells that give rise to eggs and sperm. They have reduced number of replications. Cell lineage Are identical in all individual of a species because Cell are under tight genetic control. Signals can direct identical cells to different fates. C. elegans produce six different founder cells. Cell lineage Genetic control of cell linage come from heterochronic mutants. Too early (precocious development) Too late (retarded development). Too early e.g C. elegans Mutation of lin-14 leads to premature formation of PDNB neuroblast. Prevent L2-type cell division. lin-14 and lin-7 are micro RNAs that serves as timers of gene expressions. Control translation of mRNAs by hybridizing them. Summary Cell Divide Symmetrically Asymmetrically Pluripotent stem cells More than one type of cells Cultured Embryonic stem cells Stem cells Are controlled from differentiating by specific signals. Persist for life in the meristem. During development Differentiated cell types Regenerate tissue cells Plant stem cells precursor cells are restricted in number of cell type they form. Animal development Germ layers- Ectoderm, Mesoderm and Endoderm Population of stem cells C.elegans Germ line- eggs or sperm Asymmetric division of zygote Short regulatory RNAs Control timing of developmental division.