Term
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Definition
Single layer of ~1000 blastomeres of different
sizes and properties
• Hollow ball-blastocoel
• Vegetal end is flattened |
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Term
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Definition
o Most of the epithelial sheet remains external, producing the ectoderm—the
future epidermis and nervous system
o Part of the internal epithelial sheet will form the endoderm—the precursor of
the gut and accessory organs
o Another group of cells / tissue migrate between the ectoderm and
endoderm, thus forming the Mesoderm—future muscles and connective tissues |
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Term
Four Basic Processes Used
During Early Development |
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Definition
cell proliferation
cell specialization
cell interaction
cell movement |
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Term
| movement of primary Mesenchyme |
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Definition
Early Gastrulation:
•Enter into the blastocoel as primary mesenchyme
•Primary mesenchyme begin to extend filopodia
•Cells move along the extracellular matrix to future ventral side
•Matrix contain fibronectin and glycoproteins |
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Term
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Definition
Early Gastrulation (Ingression):
• Large micromeres (primary
mesenchyme cells) begin to
change their shape
• Break tight junctions with
neighboring vegetal cells
and hyaline layer—a change
in adhesion
• Primary mesenchyme cells
develop a high affinity for
the basement membrane on
the inside of the blastrula—
process known as
Ingression |
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Term
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Definition
•VEGF
•Fibroblast Growth Factor |
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Term
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Definition
| Primary mesenchyme cells fuse and begin spicule formation (calcium carbonate) |
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Term
| Archenteron Formation (3 phases) |
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Definition
As the primary mesenchyme begin to migrate, the remaining cells
on the vegetal plate start to form the archenteron
•Archenteron formation occurs in different phases
Phase 1—Blastopore forms as the vegetal plate invaginates
and extends one-third into the blastocoel
•Apical Constriction Model
•Apical “Tractoring” or “Involution” Model
•Proteoglycan Model
Phase 2—Archenteron elongates by convergent extension
Phase 3-- Archenteron tip is pulled by filopodia |
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Term
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Definition
in this model, which has been proposed for many
decades, the apical ends of some cells in the vegetal plate would actively
constrict, forcing the vegetal plate to buckle |
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Term
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Definition
in this
model, cells lateral to the vegetal plate actively migrate towards the vegetal pole,
forcing the vegetal plate to indent. In this model apical surfaces of the lateral
cells would have to migrate actively. (Involution) |
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Term
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Definition
n this model, local secretion of chondroitin sulfate proteoglycan would result in
invagination if after its release the proteoglycan swells, and the swollen material
is held in place by the hyaline layer. |
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Term
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Definition
Blastopore forms as the vegetal plate invaginates and
extends one-third into the blastocoel
• Initiated by shape changes in the vegetal plate cells
• “Actomyocin Model”—Actin microfilaments collect in the
apical ends of the vegetal cells—causing the cells to constrict
and form “Bottle Cell” formation |
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Term
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Definition
| cells begin to move from the ouside to the inside, but don't break their ECM holds |
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Term
Invagination: Proteoglycan
Model |
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Definition
Vegetal plate cells (and only those cells) secrete a chondroitin
sulfate proteoglycan into the inner lamina of the hyaline layer directly
beneath them. This hygroscopic (water-absorbing) molecule swells
the inner lamina, but not the outer lamina. This causes the vegetal
region of the hyaline layer to buckle |
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Term
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Definition
| convergent extension(elongates to form archeneron) |
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Term
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Definition
Archenteron elongates by convergent extension at the same time the
archenteron tip is pulled by filopodia
•Filopodia makes contact at specific target sites on of the blastocoel wall
•Where the archenteron makes contact—mouth forms
•Blastopore forms the anus--deuterostome |
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