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Endodermal & Mesodermal Derivatives Flashcards

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1
Q

What are the major lineages of the mesoderm of an amniotic embryo?

A

Chordamesoderm, paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm.

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2
Q

What is the notochord also known as in terms of mesodermal lineages?

A

Chordamesoderm, or axial mesoderm.

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3
Q

Describe segmentation during development.

A

Can be external or internal, and may be redundant, such as in worms, to compensate if another segment is damaged.

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4
Q

What is the chordamesoderm?

A

Also known as the axial mesoderm, it constitutes the central region of the trunk mesoderm. Forms the notochord that induces the neural tube and establishes the A/P axis.

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5
Q

What keeps the chordamesoderm rigid?

A

Its cells are hydrostatically pressurized with large vacuoles to provide a rigid rod-like structure for the developing embryo.

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6
Q

What is the fate of the chordamesoderm?

A

Most of this structure is lost via apoptosis or senescence, but the rest differentiates into the nucleus pulposus, or the jelly-like core of the intervertebral disc.

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7
Q

What is the paraxial mesoderm?

A

Also known as the somitic mesoderm, forms the back muscle and connective tissues, as well as the dermis layer. The anterior-most is unaffected by Hox genes and remains unsegmented, forming the skeleton, muscles, and connective tissues of the face.

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8
Q

What are somites?

A

Transitory epithelial blocks of mesodermal cells on either side of the neural tube.

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9
Q

From what cells are connective tissues of the face and skull derived?

A

Neural crest cells and the anterior-most paraxial mesoderm.

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10
Q

What are the somite derivatives?

A

Dermomyotome, which forms the dermatome and the myotome, and the sclerotome.

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11
Q

What is the myotome and how does it form?

A

The myotome forms skeletal muscles from the lateral edges of the dermamyotome by generating the primary myotome that forms muscles.

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12
Q

What is the dermatome and how does it form?

A

The dermatome forms the back dermis from the central region by generating the muscle, muscle stem cells, dermis, and brown fat cells.

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13
Q

What is the sclerotome and what does it form?

A

The sclerotome forms the vertebral and rib cartilage, and the smooth muscle cells of the dorsal aorta.
Its dorsal region forms tendons, or the syndetome.
The medial region forms blood vessels and meninges.
The central mesenchymal region forms joints, or the arthrotome.

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14
Q

What are the meninges? What forms them?

A

Tissues that connect the brain and skeleton, enveloping them. Formed by the medial sclerotome and neural plate.

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15
Q

What is the intermediate mesoderm?

A

Positioned directly lateral to the paraxial mesoderm. Forms the urogenital system consisting of the kidneys, the gonads, and their associated ducts, as well as the outer portion of the adrenal gland.

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16
Q

What is the lateral plate mesoderm?

A

Farthest away from the notochord, most laterally. Forms the heart, blood vessels, blood cells, lining of the body cavities, the pelvic and limb skeleton, and a series of extraembryonic membranes important in transporting nutrients to the embryo.

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17
Q

Which mesodermal derivative forms the limb muscles?

A

Limb skeletal muscles arise from the paraxial mesoderm, more precisely from the myotome portion of the somites.

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18
Q

What are the three types of lateral plate mesoderm derivatives?

A

Splanchnic, somatic, and extra-embryonic.

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19
Q

What is Hensen’s node, and how does it change with development?

A

Hensen’s node is the organizer region at the anterior tip of the primitive streak in avian and mammalian embryos, controlling gastrulation movements and secreting the signals Chordin, Noggin, and Nodal that pattern the body axis and induce notochord and neural fates. After laying down the first chordamesoderm, Hensen’s node begins to shift caudally along the streak.

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20
Q

How do BMP concentrations vary along the mediolateral axis?

A

Initially, the lateral mesoderm and non-neuronal mesoderm are subject to high levels of BMP. As the notochord develops, it begins secreting Noggin, thus inhibiting BMP in a gradient. Therefore, BMP concentration would decrease as you go from the lateral-most regions to the chordamesoderm.

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21
Q

What are Chordin, Paraxis, and Pax2 markers for?

A

Chordin: Neural Tube.
Paraxis: Paraxial Mesoderm.
Pax2: Intermediate Mesoderm.

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22
Q

What happens if you knock-out BMP in the paraxial-intermediate region?

A

More somites would be generated.

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23
Q

What are Sox2 and Pax6 markers of?

A

The neural tube.

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24
Q

What is the role of Tbx6? What would be observed in a Tbx6 -/- embryo?

A

Required for somite formation. A Tbx6 -/- embryo would exhibit an ectopic neural-tube-like morphology adjacent to the actual neural tube in place of the expected somites.

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25
How are somites numbered?
... SIII SII SI S0 S-I S-II S-III ... The most recently formed somite is SI, its predecessors are SII, SIII, [...], the next-to-form somites are S0, S-I, S-2, [...]
26
How does somite formation occur?
Forms via a unique MET/EMT transition. Mesp-a is restricted to the anterior half of the S–I somitomere, which upregulates Eph-A4 in this same anterior region. In turn, Eph-A4 upregulates its binding partner Ephrin-B2 in the cells of the presumptive posterior S0 somitomere, which triggers epithelialization and formation of a boundary.
27
During somite formation, which cells adopt a mesenchymal state, and which adopt an epithelial state?
Mesenchymal: Posterior S0 and Anterior S-I. Epithelial: Fully formed somites.
28
Which signal triggers MET in somitic development?
Mesp-a.
29
T/F: The S0 somite is completely epithelial.
False.
30
Which part of the S0 somite is epithelial, and which is mesenchymal?
Anterior: Epithelial. Posterior: Mesenchymal.
31
What signals are involved in dermatome specification?
Pax3, Pax7, BMP, and MyoD.
32
What signals are involved in sclerotome specification?
Pax1 due to upregulated Shh from notochord, and the lack of BMP due to upregulated Noggin from notochord.
33
What are Foxc1 and Foxc2?
Foxc1 and Foxc2 are expressed in the paraxial mesoderm that will form the somites. If Foxc1 and Foxc2 are both deleted from the mouse genome, the paraxial mesoderm is re-specified as the intermediate mesoderm and initiates expression of the Pax2 gene.
34
What is a nephron?
A nephron is the functional unit of the kidney.
35
How is kidney formation first induced?
The paraxial mesoderm induces pronephros formation in the intermediate mesoderm. The PM is necessary and sufficient for this induction. This is coupled with intermediate mesoderm Pax2 expression.
36
What happens after the pronephric duct is formed?
It elongates caudally and degenerates rostrally, with its anterior region inducing the formation of the pronephros from the mesenchyme. As the pronephros degenerates, it induces the formation of the mesonephros. As the mesonephros degenerates, it yields the hematopoietic stem cells and induces the formation of the metanephros.
37
What is the first stable precursor of the permanent kidney?
The metanephros.
38
How is the permanent kidney formed?
The metanephros secretes GDNF, inducing the outgrowth of the ureteric buds which become collecting ducts of the urinary system. The ureteric buds then secrete FGF2 and BMP7 to prevent mesenchymal apoptosis. The buds then secrete Wnt9b, Wnt6, and Wnt4, inducing the aggregation of mesenchyme cells to form the nephron.
39
What does does the mesonephric duct further differentiate into?
The Wolffian duct in males.
40
What happens when a Wnt9b -/- embryo develops?
The permanent kidneys do not form.
41
How is the lateral plate mesoderm divided?
Anterior: Forms cardiogenic mesoderm. Posterior: Forms hemangiogenic mesoderm.
42
What signals are involved in lateral plate mesoderm specification?
Neural tube Wnt specifies the posterior LPM and induces the formation of hemangiogenic mesoderm alongside BMP. The anterior endoderm adjacent to the LPM secretes Wnt inhibitors such as Dickkopf (DKK), Crescent, and Cerberus, thus specifying the anterior LPM and inducing the formation of cardiogenic mesoderm alongside BMP and Fgf8.
43
Why is there no LPM at the center of the embryo's D/V axis?
Chordin and Noggin from the chordamesoderm inhibit BMP at the central LPM, thus inhibiting the formation of any tissues.
44
What is the endocardium?
The innermost layer of tissue that lines the chambers of the heart.
45
How is the endocardium formed?
Cells detach from the splanchnopleure to form the endocardial primordia, later forming the endocardium at the innermost heart layer. The rest of the splanchnopleure forms the myocardium.
46
What are the endocardial primordia, and what are their roles?
They are formed at both anterior LPM regions as two tubes and are then brought together, pinching off a portion of the endoderm to form the foregut cavity. When the two tubes combine, they form the endocardium and are coated by the rest of the splanchnopleure which form the myocardium.
47
What are the splanchnopleure and somatopleure?
Splanchnopleure: LPM and Endoderm. Somatopleure: LPM and ectoderm.
48
What induces the pacemaker cells? What are they derived from?
Tbx3 induces the formation of pacemaker cells from the cardiac myocytes.
49
What is cardia bifida?
The embryo develops two hearts, one on each side of the body. This is caused by a failure of endocardial primordia to fuse.
50
What are three causes of cardia bifida?
Surgically cutting along the embryo's ventral midline to prevent fusion, miles apart gene mutant in zebrafish, and Foxp4 deficiency in mice.
51
What day does cardiac looping occur?
Day 21-23. Begins during the fourth week and ends during the fifth week.
52
What is unique about the endoderm in terms of its transcription factors?
It is the only germ layer that does not require any BMP expression to form.
53
How is Nodal involved in specifying germ cell fates?
High Nodal concentrations inhibit BMP and lead to definitive endodermal cells whereas high BMP concentrations inhibit Nodal and lead to mesodermal cells alongside FGF and Brachyury.
54
What is Sox17?
Associated with the endoderm in many species. Activates in some cells that leave the primitive streak. It is induced by high levels of Nodal and forms the definitive endoderm.
55
What happens to embryos lacking Sox17?
Their definitive endoderm does not form.
56
After the definitive endoderm is specified, what regulates its patterning and differentiation?
The A/P axis exhibits a gradient of BMP, FGF, and Wnt that increases posteriorly.
57
What do high BMP/FGF/Wnt endodermal cells form?
Intestinal cells.
58
What do moderate BMP/FGF/Wnt endodermal cells form?
The liver and pancreas precursor.
59
What do low BMP/FGF/Wnt endodermal cells form?
The lung and thyroid precursor.
60
How does endodermal folding occur?
The intermediate mesoderm folds inwards to internalize the endoderm, forming the foregut cavity. The adjacent mesoderm induces this folding.
61
What are the factors associated with the ventral endoderm? What about the liver and pancreatic bud?
Ventral Endoderm: Nodal, Sox17. Liver: Foxa1, Foxa2. Pancreatic Bud: Pdx1, Retinoic Acid.
62
What does retinoic acid suppress in ventral endoderm specification?
RA suppresses Wnt and Shh, inducing the formation of the pancreatic bud alongside Pdx1.
63
After the pancreatic bud is formed, what are its fates? How are they related?
In the presence of Ptf1a, it forms the exocrine progenitor. In the presence of Ngn3, it forms the endocrine progenitor. Each of these fates inhibits the formation of the other, as they are mutually exclusive.
64
What are the precursors of the pancreatic bud? How do they differ in fates?
The ventral endoderm, expressing Pdx1 and retinoic acid. Usually forms the endocrine progenitors alongside Ngn3, Fgf10, and Pax6. The dorsal endoderm, expressing Pdx1, retinoic acid, and Ptf1a. Usually forms the exocrine progenitors.
65
What are the factors associated with specific endocrine progenitor fates?
Endocrine progenitors lead to Beta/Delta and Alpha/PP cell lines, both expressing Pax6. When the Beta/Delta line expresses MafA, it differentiates into Beta cells.
66
What are the Beta cells of the pancreas?
Produce insulin.
67
What would happen in an embryo deficient in the Maf factors?
Without MafA, the pancreatic Beta cells could form due to the presence of MafB which compensates for MafA during development, but these cells would not properly produce insulin post-birth. Without any Maf factors, the Beta cells do not form, and the islet structure is disrupted.

BIO401 (3 decks)

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