Mechanisms Of Development Flashcards
Genome equivalence
All cells contain the same set of genes but different cells express different sets of genes
Homologous gene
Similar in structure and evolutionary origin and function to gene I’m another species
Many human genes are found in invertebrates, use similar mechanisms and genes during development
Somatic nuclear transfer (cloning)
Mammary gland cell nucleus from donor was fused with an enucleated oocyte->dolly
Evidence that all cells contain same genes
Differentiated gene expression
Only a small percentage of genome is expressed in each cell type
Regulated by differential gene transcription, selective nuclear RNA processing, selective mRNA translation, differential protein modification
Controls fundamental cellular processes like cell proliferation, cell movement, cell specialization, cell interaction
Induction
One group of cells changes the behavior of an adjacent set of cells
Inducer provides signal to responder, competence if responder is able to respond to signal
Induction signal transmission
Paracrine signaling: protein secreted into extra cellular space to neighbors
Juxtacrine signaling: contact between cells
Optic vesicle inducer in frog embryo
Able to induce lens formation in anterior head portion of ectoderm not in the trunk or abdomen
Competence is actively acquired, Pax6 transcription factor makes ectoderm competent to respond to inductive signals from optic vesicle
Aniridia
Caused by autosomal dominant mutations in PAX6
Affects iris, intraocular pressure, lens, cornea, optic nerve
Morphogens
Paracrine signaling molecules that causes concentration-dependent effects
Can specify more than one cell type by forming a concentration gradient, direct into different developmental pathways
Signal transduction cascades
Many inductive molecules and morphogens transmit their signals through cell membrane and to cell nucleus via signal transduction pathway
Examples:
Transformating growth factor beta (TGFB) signaling pathway
Hedgehog signaling pathway (sonic hedgehog signaling molecule binds Patched protein which alleviates inhibition of SMO such that GLI-mediated transcription is activated)
Morphogen gradients pattern the neural tube
Formation of left-right body axis
Internal organs are asymmetrical along left-right axis
Left-right asymmetry defects
Situs invertus totalis: compete mirror reversal of organ LR symmetry
Heterotaxy: perturbed asymmetry only on subset of organs (results km congenital heart defects, asplenia or polysplenia, malrotation of intestine)
Cardiac looping
Heart development that aligns chambers and vascular connections
Conserved asymmetrical gene expression
Nodel gene expressed asymmetrically in organizer/node region, signal for expression along left side of body=differential gene expression
Kartagener’s syndrome
Bronchiectasis, infertility, sinus inversus
Ciliary beating controls which way left-right axis is oriented by driving fluid towards left side to establish a morphogen gradient
Nodal signaling cascade activates Pitx2 and Nodel inhibitor Lefty (restricts asymmetric domain of Nodel signaling)
