Download Developmental Biology 8/e - Florida International University

11.8 The embryonic shield as organizer in the fish embryo
Shield tissue:
-can convert lateral and
ventral mesoderm (blood and
connective tissue precursors)
into dorsal mesoderm.
- can cause the ectoderm to
become neural rather than
epidermis.
11.9 Axis formation in the zebrafish embryo
11.14 Discoidal meroblastic cleavage in a chick egg
11.15 Formation of the three-layered blastoderm of the chick embryo (Part 1)
- Most of the cells of the area pelucida remain at the surface, forming a
epiblast.
- Other area pelucida cells have delaminated and migrated individually
into the subgerminal cavity to form the polyinvagination islands
(primary hypoblast), an archipelago of disconnected clusters containing
5-20 cells each.
11.15 Formation of the three-layered blastoderm of the chick embryo (Part 2)
-A sheet of cells from the posterior margin of the blastoderm migrates
anteriorly and pushes the primary hypoblast cells anteriorly, therefore
forming the secondary hypoblast (endoblast).
- Epiblast and hypoblast are joined together at the marginal zone of the
area opaca, and the space between the layers forms a blastocoel.
11.15 Formation of the three-layered blastoderm of the chick embryo (Part 3)
-The primitive streak cells form a layer between the hypoblast and
epiblast cells.
- The primitive streak become a definitive region of the epiblast, with
cells migrating through it to become the mesoderm and the endoderm.
11.16 Cell movements of the primitive streak and fate map of the chick embryo (Part 1)
11.16 Cell movements of the primitive streak and fate map of the chick embryo (Part 2)
11.16 Cell movements of the primitive streak and fate map of the chick embryo (Part 3)
11.16 Cell movements of the primitive streak and fate map of the chick embryo (Part 4)
11.17 Migration of endodermal and mesodermal cells through the primitive streak
As soon as the primitive streak has formed, epiblast cells begin
to migrate through it and into the blastocoel.
11.19 Specification of the chick anterior-posterior axis by gravity
11.20 Formation of Hensen’s node from Koller’s sickle
11.21 Induction of a new embryo by transplantation of Hensen’s node (Part 1)
11.21 Induction of a new embryo by transplantation of Hensen’s node (Part 2)
11.22 Gene expression in the primitive streak
11.24 Model by which FGFs regulate mesoderm formation and neurulation (Part 1)
A) Fgf8 induces pre-neural
genes and Nodal is being
blocked by Cerberus
B) The hypoblast is displaced by
the endoblast allowing Nodal to
function. Nodal and Fgf8
induced Bra and Tbx6 to specify
the mesoderm and initiate the
ingression of mesoderm cells
through the primitive streak.
11.24 Model by which FGFs regulate mesoderm formation and neurulation (Part 2)
C) Continued Fgf8 expression
activates Churchill.
Churchill can activate the SIP1
which probably blocks the Smad1
signal and prevents further
ingression of cells through the
primitive streak.
11.26 Pathway for left-right asymmetry in the chick embryo (Part 1)
11.26 Pathway for left-right asymmetry in the chick embryo (Part 2)
Cerberus
R
Nodal
Pitx2
L
L
R