 |  | Cyclopamine
The normal Hedgehog signaling pathway is blocked by the receptor antagonist cyclopamine.
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 | | Hedgehog Gradient
The level of Hedgehog protein a cell binds during development can influence its fate.
View Quicktime Movie |
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 | | Hedgehog Signaling
The Hedgehog signaling pathway triggers expression of other developmentally important genes.
View Quicktime Movie |
|
 | | Homeobox
The color-shaded regions represent homeotic genes called Hox genes. The dark band within each gene represents a 180-base-pair region called the homeodomain.
View Animation Still |
|
 | | Homeodomain
A 3-D model of a protein with a homeodomain, a "helix-turn-helix" motif that acts as a transcription factor by binding directly to DNA to turn on other genes.
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|
 | | Retinoic Acid
A retinoic acid gradient controls the activation of many developmentally important genes. Disruptions in the embryo's retinoic acid levels can lead to malformation of the embryo.
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|
 | | Spatial and Temporal Colinearity
Hox genes display spatial colinearity — genes at one end of the chromosome are expressed at the head end of an embryo while genes at the other end are expressed toward the tail end. Vertebrate Hox genes also show temporal colinearity — genes at the head end are expressed before those at the tail end.
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Blastula
A photograph of an early stage blastula from the Xenopus
laevis frog. |
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Chick
embryo
A microphotograph of a chick embryo. |
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Colinearity
Genes that are expressed at the anterior end of an animal
are located at the more anterior region of the chromosome.
Likewise, posteriorly expressed genes reside on the posterior
end of the chromosome. This is referred to as spatial
colinearity. |
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Coordinate,
gap, pair-rule, and segment polarity genes
The cascade of developmental genes in segmentation in
Drosophila. Maternal effect/ coordinate genes set the
anterior-posterior axes. The embryo is subdivided into
progressively smaller regions by the actions of each class
of segmentation genes. |
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Corn
lilly
A substance found in the corn lilly plant, Californicum
veratrum, called cyclopamine, is the cause of birth defects
in lambs. |
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Cyclopic
lamb
This lamb's mother ate a poisonous plant, the corn lilly,
which contains a compound called cyclopamine. This compound
inhibits the action of the Sonic Hedgehog protein, which
is involved in the formation of the neural system. |
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Deformed
zebrafish embryo
This embryo was treated with retinoic acid, which causes
neurological damage. |
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Drosophila
embryo with bicoid protein stain
This is a 2-hour-old drosophila embryo that shows the
expression of the bicoid protein. The bicoid protein forms
a gradient with the highest expression at the anterior
end (left side in this photo) of the embryo. |
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Drosophila
eye
Electron microscope image of a fly eye (Drosophila melanogaster) |
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Drosophila
with antennapedia mutation
When Drosophila has a mutation in the antennapedia gene,
legs will grow out of its head. |
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Fate
map
Left: A photograph of an early stage blastula from the
Xenopus laevis frog. Right: A representation of a fate
map. |
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Fruit
fly with extra eyes
The head of a fruit fly, Drosophila melanogaster, viewed
by scanning electron microscope (380x magnification).
Targeted expression of the eyeless gene induced the formation
of the eye facets on the antenna (to the lower-right of
the eye), which are very similar to the facets of the
normal eye. This dentifies eyeless as the master control
gene of eye morphogenesis. |
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HEP-2
cells in culture
Hep-2 cells in culture (200x magnification, crystal violet
stain, high density) |
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Maternal
inheritance
Reciprocal F1 crosses involving maternal effect genes
can produce different phenotypes. |
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Monkey
kidney cells in culture
Monkey kidney cells in culture, showing a typical patch
of monolayer cells (100x magnification) |
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Pancreatic
islets
The endocrine portion of the pancreas takes the form of
many small clusters of cells, called islets of Langerhans,
or, simply, islets. Humans have roughly one million islets.
In standard histological sections of the pancreas, islets
are seen as relatively pale-staining groups of cells embedded
in a sea of darker-staining exocrine tissue. This image
shows three islets in the pancreas of a horse. |
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Transcription
factor
The triangle represents a transcription factor binding
to DNA in the nucleus to affect transcription and translation
of new proteins. |
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Undifferentiated
embryonic stem cells
Microscopic (5x magnification) view of a colony of undifferentiated
human embryonic stems cells. The embryonic stem cell colonies
are the rounded, dense masses of cells. The flat, elongated
cells in between the embryonic stem cell colonies are
fibroblasts that are used as a čfeeder layerî on which
the embryonic stem cells are grown. |
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Undifferentiated
embryonic stem cells
Microscopic view of a colony of undifferentiated human
embryonic stems cells. The embryonic stem cell colonies
are the rounded, dense masses of cells. The flat, elongated
cells in between the embryonic stem cell colonies are
fibroblasts that are used as a čfeeder layerî on which
the embryonic stem cells are grown. |
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Whorls
The tissues that will become floral organs are arranged
in concentric whorls of a developing flower. |
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Zebrafish
embryo
This 18-hour-old zebrafish embryo is labeled with a probe
that shows the expression of sonic hedgehog mRNA. |
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Zebrafish
embryo with Sonic Hedgehog protein stain
Zebrafish embryo with a stain that shows the gradient
of the hedgehog protein. |
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