Gastrulation. Becoming trilaminar (Week 3) Flashcards
What is gastrulation?
Gastrulation is the process where the three germ layers (ectoderm, mesoderm, and endoderm) are formed in the embryo.
Which germ layer forms the skin and nervous system?
The ectoderm.
What structure initiates gastrulation?
The primitive streak.
What germ layer gives rise to the circulatory system?
The mesoderm.
Which germ layer forms the lining of the gut and associated organs?
The endoderm.
What is the role of the primitive node?
It organizes the development of the notochord and body axis.
What signaling molecule establishes the primitive streak?
Nodal.
Where is the primitive streak located?
At the posterior end of the epiblast.
What happens to the primitive streak after gastrulation?
It regresses and disappears.
What structure does the primitive node induce?
The notochord.
What is the function of the notochord?
It serves as a signaling center for the development of the neural tube and somites.
Which germ layer forms the notochord?
The mesoderm.
What does the notochord become in adults?
The nucleus pulposus of the intervertebral discs.
Which molecular signal is secreted by the notochord?
Sonic hedgehog (Shh).
What is the fate of cells that migrate through the node during gastrulation?
They form the prechordal plate and notochord.
What structure induces neural tissue formation?
The notochord.
What molecular signal inhibits BMP to allow neural induction?
Noggin, Chordin, and Follistatin.
What does the ectoderm differentiate into without BMP signaling?
Neural tissue.
What role does FGF play in neural induction?
It promotes the transition of epiblast cells to mesoderm and ectoderm fates.
What structure forms as a precursor to the nervous system?
The neural plate.
How is left-right asymmetry established in the embryo?
By the flow of fluid created by cilia in the primitive node.
Which signaling molecule is concentrated on the left side of the embryo?
Nodal.
What is situs inversus?
A condition where the positions of internal organs are mirrored.
What causes ciliary dysfunction in left-right asymmetry disorders?
Mutations in dynein genes.
What is the role of Lefty-1 and Lefty-2 in asymmetry?
They limit the activity of Nodal to the left side of the embryo.
What allows epiblast cells to migrate during gastrulation?
Loss of cell adhesion and acquisition of migratory properties.
What molecule is involved in epiblast cell migration?
Fibronectin in the extracellular matrix
Which molecules regulate epithelial-to-mesenchymal transition (EMT)?
Snail and Slug.
What is the function of E-cadherin in gastrulation?
It maintains cell adhesion in epithelial cells, which is reduced during migration.
What happens to mesoderm cells after migration?
They differentiate into specific tissues based on their position.
What does the paraxial mesoderm form?
In head and trunk region
trunk: Somites, which give rise to skeletal muscles and vertebrae.
head: UNSEGMENTED
HEAD MESENCHYME
+ NEURAL CREST CONTRIBUTION
+ prechordal plate contribution
What does the intermediate mesoderm form?
Only in the trunk
The urogenital system, including kidneys and gonads.
What does the lateral plate mesoderm form?
Only in the trunk
splanchnic mesoderm, somatic mesoderm (lining of the body cavities, formation the serose, formation of the wall of intestinal tube…)
The circulatory system and body wall.
Which mesodermal structure forms the notochord?
The axial mesoderm.
How is the mesoderm patterned during gastrulation?
By signals such as BMP, FGF, and Wnt.
What does the definitive endoderm form?
The lining of the gut, respiratory system, and associated organs like the liver.
Which structure guides endodermal migration during gastrulation?
The hypoblast.
How is the endoderm separated from the mesoderm?
By basement membrane signaling.
What is the role of Sox17 in endoderm development?
It regulates differentiation of endodermal cells.
How does the endoderm contribute to organogenesis?
By interacting with mesodermal signals to form organs like lungs and pancreas.
What is the result of impaired BMP signaling in gastrulation?
Defects in mesodermal patterning.
What is sirenomelia, and what causes it?
A condition where lower limbs are fused, caused by defects in mesoderm formation.
AKA caudal dysgenesis
What is the prechordal plate?
A structure that contributes to forebrain development.
What is the role of Cerberus in development?
It inhibits Wnt, Nodal, and BMP to help pattern the anterior embryo.
What is the embryonic shield in vertebrate embryos?
A structure analogous to the primitive streak.
How do BMP inhibitors regulate germ layer formation?
By promoting neural ectoderm development while suppressing mesoderm.
What is the embryonic organizer in humans?
The Hensen’s node, which patterns the body axis.
The primitive streak…
determines the major body axis
What drives the migration of epiblast cells towards the primitive streak during gastrulation?
The signaling molecule FGF8.
What is the primary movement of cells into the primitive streak called?
Ingression or invagination.
What changes occur in cell adhesion during ingression?
Cells transition from cell-to-cell adhesion to cell-to-substrate adhesion.
What cytoskeletal structures are involved in cell migration during gastrulation?
Lamellipodia and filopodia.
What molecule in the extracellular matrix facilitates cell migration during gastrulation?
Hyaluronic acid.
Which extracellular matrix protein supports cell adhesion and migration during gastrulation?
Fibronectin.
How are mesenchymal cells described morphologically?
Small spindle-shaped cells with large nuclei, prominent nucleoli, and fine chromatin.
What is the potency of mesenchymal cells?
Mesenchymal cells are multipotent stem cells.
Into what types of cells can mesenchymal cells differentiate?
Fibroblasts, osteoblasts, chondroblasts, and preadipocytes.
What is the composition of the extracellular matrix produced by mesenchymal cells?
A ground substance rich in hyaluronic acid.
What is mesenchyme?
A type of embryonic connective tissue made up of mesenchymal cells and their extracellular matrix.
What tissues arise from mesenchyme during early development?
All connective tissues of the body.
Where are mesenchymal cells found in adults?
In loose connective tissue, primarily in the umbilical cord, bone marrow, and adipose tissue
What role do adult mesenchymal stem cells play?
They give rise to fibroblasts and new blood vessels.
What is snail?
Snail is a transcription factor that regulates epithelial-to-mesenchymal transition (EMT), a critical process in cancer progression.
zinc finger transcription factor involved in EMT (Epithelio-mesenchymal transition)
What is epithelial-to-mesenchymal transition (EMT)?
EMT is a biological process where epithelial cells lose their cell-cell adhesion and gain migratory and invasive properties, becoming mesenchymal cells.
How does Snail promote EMT?
Snail represses the expression of E-cadherin, a key cell adhesion molecule, facilitating the transition to a mesenchymal phenotype.
How does Snail contribute to metastasis?
By promoting EMT, Snail enables cancer cells to invade surrounding tissues and enter the bloodstream.
In what way does Snail influence cancer cell survival?
Snail enhances resistance to apoptosis and contributes to cancer cell survival under stress.
What role does Snail play in cancer stem cells?
Snail is associated with the acquisition of stem-like properties in cancer cells, aiding in tumor recurrence and resistance.
Why is Snail considered a marker for aggressive tumors?
High levels of Snail are correlated with increased invasiveness, metastasis, and poor prognosis.
How is Snail linked to chemotherapy resistance?
Snail-mediated EMT can protect cancer cells from chemotherapeutic agents by altering their phenotype and promoting drug efflux mechanisms.
What is the earliest layer to form?
endoderm
What is the second layer to form?
mesoderm
What is mesodermal migration?
It is the movement of epiblast cells through the primitive streak to form the mesoderm during gastrulation.
What triggers mesodermal migration?
The process is triggered by signaling molecules like FGF8.
Which structural change is essential for mesodermal migration?
Epithelial-to-mesenchymal transition (EMT).
What extracellular matrix components guide migrating mesodermal cells?
Hyaluronic acid and fibronectin.
How do cells know where to migrate during mesodermal formation?
Cells follow chemotactic gradients established by signaling molecules such as FGF and BMP.
What is the sequence of mesodermal cell migration through the primitive streak?
Cells migrate medially, invaginate through the streak, and spread laterally and cranially.
What regions of the mesoderm are formed based on migration positions?
Paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm.
What role does hyaluronic acid play in mesodermal migration?
It creates a hydrated environment that facilitates cell movement.
What is the function of fibronectin during mesodermal migration?
It provides a substrate for migrating cells to adhere to and move along.
How do integrins contribute to mesodermal migration?
Integrins on mesodermal cells bind to ECM components, enabling adhesion and traction for movement.
what are the different subdivisions of the mesoderm?
- Prechordale plate: a mesoendodermal structure
- Notochord
- Paraxial mesoderm
- Intermediate mesoderm
- Lateral plate mesoderm
- Extraembryonic mesoderm
- Primitive heart field
What is the notochord?
Tubular structure elongating in front of the primitive node
What are prechordal cells?
group of cells that associate with the anterior visceral endoderm
What are chordomas?
Malignant cancers that develop from remnants of the notochord
base of the skull vertebral column
Slow growth
large when discovered: compression of brain and spinal structures
symptoms develop and worsen over time (most common: headache, double vision)
The intraembryonic mesoderm of the lateral plate is … with the extraembryonic mesoderm
in continuity
Where do the cells that will form the different portions of the heart migrate during development?
They migrate in the splanchnic mesoderm, rostral to the oropharyngeal membrane.
What germ layer gives rise to the neural plate?
The ectoderm.
What induces the formation of the neural plate?
Signals from the notochord and prechordal plate.
What role does BMP play in neural plate formation?
BMP signaling must be inhibited to allow ectodermal cells to differentiate into neural tissue.
What is the neural plate?
A thickened region of the ectoderm that will fold to form the neural tube.
What process transforms the neural plate into the neural tube?
Neurulation.
What structures are formed from the neural tube?
The brain and spinal cord.
What structures form adjacent to the neural tube?
Neural crest cells, which give rise to peripheral nervous system components and other structures.
In which direction does the neural tube close?
It closes bidirectionally, starting at the cervical region.
What happens if the neural tube fails to close at the cranial end?
Anencephaly, a fatal condition where the brain does not fully form.
What happens if the neural tube fails to close at the caudal end?
Spina bifida, which can cause varying degrees of disability.
When does neural tube closure typically complete in humans?
Cranial 24 days
Caudal 26 days
What structures do neural crest cells give rise to?
Peripheral nervous system, craniofacial structures, melanocytes, and adrenal medulla.
In what direction does gastrulation occur?
Gastrulation takes place in a rostro-to-caudal manner.
When does differentiation of the caudal region begin?
At the end of the 4th week.
How can ethanol act as a teratogen?
By altering the expression of genes along the midline.
It kills cells in the anterior midline.
What key developmental pathway can be disrupted by ethanol?
The Sonic Hedgehog (SHH) signaling pathway.
What are two congenital defects linked to ethanol-induced SHH pathway deficiency?
Cyclopia and holoprosencephaly.
What is the role of the Hedgehog (Hh) signaling pathway in development?
It is used for intercellular communication and is essential for the organogenesis of almost all organs in mammals, as well as for regeneration and homeostasis.
It is not entirely dependent on the primary cilium (PC), unlike many other essential developmental pathways.
How is the Hh signaling pathway implicated in cancer?
Disruption of Hh signaling is associated with diverse types of cancer.
What are the three mammalian Hedgehog proteins?
Sonic Hedgehog (Shh), Indian Hedgehog (Ihh), and Desert Hedgehog (Dhh).
What are the key roles of Shh in development?
Shh is critical for nervous system cell type specification and limb patterning.
What is the primary function of Ihh?
Ihh plays an important role in skeletal development, especially endochondral ossification.
Where is Desert Hedgehog (Dhh) primarily active?
Dhh is restricted to the gonads, including granulosa cells of the ovaries and Sertoli cells of the testes.
What common characteristics do embryogenesis and tumorigenesis share?
Both processes rely on coordinated mechanisms of proliferation, differentiation, and migration.
What is a primary cilium?
a single non motile cilium present in most cells of our body
fundamentally important for normal cell signaling during development and homeostasis: Cell’s antenna
Where does most activity of SH- signaling pathways take place?
at the level of the primary cilium
How does gastrulation end?
with the formation of the tail bud/caudal eminence -> forms form remnants of the primitive streak
What is secondary neurulation, and what structures does it form?
Secondary neurulation is the process where the tail bud forms the caudal portion of the neural tube, neural crest cells (spinal cord caudal to S2, filum terminale), and caudal somites.
