Embryology (Fach) / Part 1 (Lektion)
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Part 1
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- cycle of life embryonic stage (fertilization of the oocyte -> birth) juvenile stage (growth metamorphosis -> larva) adult stage (fertile individuals -> reproduction) ageing stage (growing old -> physiological death)
- animal models the principles of developmental mechanisms are highly conserved from organism to organism all models are practical (easy to breed, fast life cycle...) animal models for disease can phenocopy human diseases precisely
- developmental stages cleavage (fertilized egg -> mitosis -> blastomeres) blastulation (ordening of blastomeres -> formation of blastocoel) gastrulation (morphogenic movements of blastomeres -> formation of 3 embryonic germ layers (endoderm + ectoderm + mesoderm)) organogenesis (differentation of the the 3 embryonic germ layer -> formation of organs)
- ootypes isolecithal mesolecithal telolecithal centrolecithal
- patterns of cleavage main patterns: holoblastic or meroblastic specific patterns: radial, spiral, discoidal, superficial
- blastula hollow sphere of cells formed during an early stage of embryonic development in animals; created when the zygote undergoes the cell division process known al cleavage
- gastrulation phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layerd") structure known as the gastrula; germ layers: ectoderm, mesoderm, endoderm
- gastrulation - types of cell movement invagination (infolding of a region of cells) involution (inward movement of an expanding outer layer) ingression (migration of individual cells from the surface layer into the interior of the embryo) delamination (splitting of one cellular sheet into two more or less parallel sheets) epiboly (moveent of epithelial sheets (usually of ectodermal cells) that spread as a unit to enclose the deeper layers of the embryo)
- neurulation stage of organogenesis in vertebrate embryo's, during which the neural tube is transformed into the primitive structures that will later develop into the central nervous system neural plate -> neural fold -> neural groove -> neural folds apposing -> neural tube -> migration neural crest cells (mainly peripheral nervous system)
- function blastocoel prevents the animal cells from premature induction by underlying vegetal cells into mesoderm permits cell migration during gastrulation
- extraembryonic membranes in birds and mammals yolk sac: surrounds the yolk; mediates nutrition during development; hematopoesis (formation of blood islands); formation of germ cells amnion: surrounds the embryo with amnionic fluid; prevents dehydration; cushion for mechanical shocks; regulation of temperture (in birds) chorion: surrounds the yolk and the embryo; exchange of gases between the embryo and the surrounding air allantois: functions as disposal sac for certain metabolic waste products; functions with the corion as a respiratory organ extraembryonic membranes are supplied with blood vessels extending form the embryo
- fundamental molecular processes in development cell specification induction and cell determination fate mapping morphogenesis morphogens and positional information
- modes of cell specification autonomous specification: the blastomere inherits morphogenetic determinants which will influence the cells development. An isolated blastomere will produce the same cells that it would have made if it were still part of the embryo. Moreover, the embryo from which that cell is taken will lack only those cells that would have been produced by the missing blastomere. -> in most invertebrates conditional specification: the fate of a cell depends upon the conditions in which the cell finds itself. If such a blastomere is removed from an early embryo, the remaining embryonic cells alter their fates so that the roles of the missing cells can be taken over. The isolated blastomere can also give rise to a wide variety of cells. -> in vertebrates and a few invertebrates syncytial specification: here, interactions occur not between cells, but between parts of one cell (Drosophila) -> in most insect classes
- induction of neural tissue transplantation experiment of Spemann and Mangold -> the dorsal lip cells (called the organizer) "organize" the host cells to form a new body axis the involuting mesodermal cells of the IMZ (=involuting marginal zone) release several molecules that interfere with the BMP signals between ectodermal cells in that way, ceberus, chordin, nogging, and follistatin all interfere with the activation of the BMP receptor by the BMPs in the ectoderm and thereby block the anti-neuralizing effects of BMP4 they "induce" this region of the embryo to develop as neural tissue, utimately generating the brain, spinal chord and most of the peripheral nervous system early gastrula cells are uncomitted; late gastrula cells are determined
- fate maps tracing of cell lineages: following individual cells to follow what those cells become GFP lineage tracing to follow the cells
- molecular aspects of cell adhesion cell adhesion molecules (CAMs) - cadherines: cell-cell adhesion (Ca-dependent) - CAMs: cell-cell adhesion (Ca-independent), member of superfamily immunoglobulines integrins -> cell-extracellular matrix adhesion extracellular matrix molecules (ECMs) -> collagen, fibronectin, laminin and tenascin bind to integrin
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- morphogens and positional information the position of cells in an embryo is specified by a variety of mechanisms positional information is used by the embryonic cells to differentiate in a certain direction: first the cells acquire an identity or positional value that is related o their position in the embryo then the cells interpret this information and differentiate according to their genetic program a chemical that provides positional information is called a morphogen. It diffuses from its site of synthesis to its site degradation forming a gradient of positional information in the embryo the combination of multiple morphogen gradients defines the mode of pattern formation. The general mode of pattern formation can be illustrated by considering the patterning of a simple non-biological model, the French flag
- Drosophila antennapedia-bithorax complex consists of 8 homeobox-containing genes located in two clusters on one chromosome
- homeobox mice and human Mice and human possess at least 39 homologous homeobox genes (called Hox genes in vertebrates and HOX in humans), which are found in 4 clusters on 4 different chromosomes. The Hox genes on the 4 mammalian chromosomes are arranged in 13 paralogous groups.
- they are 3 categories of molecules that guide embryonic development: transcription factors signaling molecules receptor molecules
- transcription factors These proteins contain a highly conserved homeodomain of 60 amino acids (a helix-loop-helix region). The 180 nucleotides in the gene that encode the homeodomain are collectively called a homeobox the Pax gene family (master control genes), consisting of 9 known members, are involved in many aspects of mammalian development. They are homologous to the Drosophila pair-rule segmentation genes All pax proteins contain a paired domain of 128 amino acids, which binds to DNA. Various members of this group also contain entire or pail homeobox domains and a conserved octapeptide sequence
- signaling molecules play an important role in cell interactions during embryogenesis. They are sent from one group of cells and received another the number of signaling molecules that are needed during embryogenesis are greatly reduced because: - the same signaling molecule can be used at different times and places - their local concentration or the duration of exposure to a signaling molecule are important the sequence of a signaling molecule (ligand) -> receptor -> signaling transduction pathway is characterized by a specific signaling pathway most signaling molecules are members of several, mostly large families early inducers, TGF ß family, FGF family, Hedgehog family, Wnt family