Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
16 Cards in this Set
- Front
- Back
|
Echinoderms, Ascidians and Slime Mold
|
Echinoderms and ascidians simple models
more closely related to mammals than worms and fleas Slime mold more distantly related, have a primitive and unique cycle of development |
|
|
Echinoderms: Sea Urchins
|
Transparent and easy to handle
Deuterostome: radial cleavage and the primary invagination of the gut at gastrulation forms the anus |
|
|
Protostomes
|
Insects are protostomes: cleavage is not radial and the primary invagination forms the mouth.
|
|
|
Development of the Sea Urchin Embryo Cleavage
|
4th and 5th cleavages are unequal: micromeres and macromeres
Micromeres give rise to the primary mesenchyme Blastula is a ciliated hollow ball of about 1000 cells (epithelial) |
|
|
Development of the Sea Urchin embryo Gastrulation
|
Gastrulation starts with the primary mesenchyme
Primary mesenchymal cells eventually lay down the skeletal rods Endoderm (gut) invaginates from the vegetal pole and fuses with the mouth invaginating form the opposite side Secondary mesenchyme come from the tip of the invagination Gives rise to the muscles *invagination--> involution-->ingression |
|
|
Sea Urchin Development is Regulated
|
simple organism yet regulative development still occurs
|
|
|
Axis Formation in Sea Urchins
|
Animal vegetal axis determined maternally
first two planes of cleavage alongthe A/V axis Micromeres may be specified by cytoplasmic factors at the vegetal pole Second axis is the oral-aboral axis as defined by the postion of the mouth O/A axis is always 45 degrees clockwise from the first cleavage plane Nodal is critical for this axis to form. |
|
|
Micromeres act as an Organizer
|
Sea urchin regulative capacities due mainly to the organizer
micromeres can induce another body axis They set up by maternal factors Produce signals that induce adjacent macromeres to adopt an endomesodermal fate |
|
|
The Wnt Signlaing Pathway Promotes the Vegetal Fate
|
Localized activation of Dsh in the ventral region
Leads to B-catenin accumulation in the nuclei of micromeres Nuclear B-catenin promotes a vegetal fate |
|
|
The Endo-16 gene Regulatory Region
|
Binds multiple transcription factors
has a modular nature similar to Drosophilia Each module specifies gene expression in diff. regions of embryo Gene control regions play a part in integrating and interpreting developmental signals. |
|
|
Ascidian Life Cycle
|
Sea squirts are the adult form
Larvae are for dispersal only; they don't feed Larvae have a notochord Invariant cleavage pattern Mosaic-like development; cytoplasmic factors important Specification on a cell by cell basis |
|
|
Muscle is Specified by Localized Cytoplasmic Factors
|
natural yellow pigment granules (myoplasm) can be followed
Cells containing myoplasm give rise to muscle cells Macho-1 mRNA is localized in the myoplasm Depletion of macho-1 results in loss of muscle cells Injection of macho-1 in non-muscle cell lineages causes ectopic muscle differentiation. |
|
|
cellular Slime Mold Life cycle
|
about 24 hours
mature fruiting body--> myxamebae --> cell streams & aggregation --> aggregate --> slug --> Migration --> culmination --> stalk &developing fruiting body --> mature fruiting body |
|
|
cell flow and differentiation in the Slug
|
Most of the cells are prespore cells (posterior)
Remainder are different type of prestalk cells Dynamic flow and replacement of cells during migration Capacity for regulation |
|
|
Mechanisms of Cell Flow in Slug
|
1. positional information provided to cells
2. random differentiation then sorting (adhesion) |
|
|
Formation of the Fruiting body
|
Slug stands upright
pstB cells move downward to form the base Prestalk cells migrate to the top and then down throught "stalk tube" in the middle The growth of the stalk tube lifts up the prespore region |
