Chapter 13 Part 2: Hinge Point Regulation Continued

Question 1

At a cellular level, hinge points and buckling of neural plate to form a neural tube are formed by these 3 factors. What regulates these three steps?

Answer 1

hinge points are formed by 1) apical constriction 2) basal thickening with retension of nucleus 3) cell packing in the neural folds (proliferation) these three steps are regulated by BMP.

Question 2

to induce buckling, the ____ induces MHP cells to become wedge shaped

Answer 2

notochord.

Question 3

the notochord induces MHP cells to become wedge shaped. How?

Answer 3

the notochord expresses SHH to induce floor plate cells in the neural plate to form the MHP.

Question 4

the notochord expresses ____ to induce ___ ___ cells in the neural plate to form the MHP.

Answer 4

the notochord expresses SHH to induce floor plate cells in the neural plate to form the MHP.

Question 5

____ is critical for hinge formation of the DORSOLATERAL HINGES. this is a BMP ___.

Answer 5

Noggin is critical for hinge formation of the DORSOLATERAL HINGES. this is a BMP inhibitor. No noggin = no neural tube closure.

Question 6

What dictates noggin expression at the DLHP for proper neural tube closure?

Answer 6

DLHPs only express Noggin when they are far enough away from SHH-secreting MHP-notochord region. SHH from the notochord inhibits noggin. DLHPs must be far enough away from the MHP-notochord if noggin can be expressed enough to induce closure.

Question 7

in terms of hinge point regulation, a complete loss of BMP would result in:

Answer 7

extra hinges. Intermediate amounts of BMP signalling in the neural plate are required for normal hinge point size and location. Intermed BMP facilitate apical constriction and basal thickening via the modiciation of functional complexes holding the cells together.

Question 8

Intermed BMP facilitate ____ constriction and ___ ___ via the modiciation of functional complexes holding the cells together.

Answer 8

Intermed BMP facilitate apical constriction and basal thickening via the modiciation of functional (actinomyosin) complexes holding the cells together. Therefore, you need some BMP for proper hinge formation, but you can’t have too much or else you get extopic hinges.

Question 9

Summary of hinge point regulation:

BMP regulates apical constriction, basal thickening with nucleus being in basal region of wedge shaped cell, and cell proliferation and packing in the neural folds.

Hinge point formation is dependent on precise amounts of BMP. BMP inhibits MHP and DLHP formation, whereas DLHP secretes ___ to prevent BMP, allowing for DLHP formation. ___ from the notochord ___ BMP, preventing hinge point formation in random places of the neural plate.

Answer 9

Summary of hinge point regulation:

BMP regulates apical constriction, basal thickening with nucleus being in basal region of wedge shaped cell, and cell proliferation and packing in the neural folds.

Hinge point formation is dependent on precise amounts of BMP. BMP inhibits MHP and DLHP formation, whereas DLHP secretes noggin to prevent BMP, allowing for DLHP formation. SHH from the notochord induces BMP, preventing hinge point formation in random places of the neural plate.

*SHH inhibits BMP inhibitor Noggin, effectively inducing CMP to prevent extra hinge point formation

Question 10

The neural tube is open at both ends, constituting the anterior and posterior ____. In chicks, the neural tube closure begins at the site of the future ___, and zips in both direction.s But in mammals, the neural tube closure is initiated at several places along the anterior and posterior axis.

Answer 10

The neural tube is open at both ends, constituting the anterior and posterior NEUROPORE. In chicks, the neural tube closure begins at the site of the future MIDBRAIN, and zips in both direction.s But in mammals, the neural tube closure is initiated at several places along the anterior and posterior axis.

Question 11

____ FORMS DURING GASTRULATION AND INDUCES THE FORMATION OF THE ECTODERMAL ___ ___

Answer 11

NOTOCHORD FORMS DURING GASTRULATION AND INDUCES THE FORMATION OF THE ECTODERMAL NEURAL PLATE

Question 12

Where is the closure site 1? 2? 3? How does each close?

Answer 12

closure site 1 = junction of spinal cord and hind brain

closure site 2: midbrain and forebrain junction

closure site three: fore brain.

closure site 1 an 2 close via zipper action. clsure site three is entirely depednent on the dorsal lateral hinge points.

Question 13

How do cells zip?

Answer 13

as DLHPs bend, bringing the two lips together, filopodia extend from tips of non-neural surfaces ectoderm cells on the tips of the neural folds. The filopodia extend towards opposing fold forming temporary cellular bridge..

the driving force for zipper may be the localized activation of actomyosin contraction in the apical membranes of epidermal (non-neural surface) cells lying immediately ahead of the zipper point. This causes epidermal-epidermal cell adhesion, resultin in neural tube closure.

Question 14

the driving force for zipper may be the localized activation of ___ contraction in the ___ membranes of ____ (non-neural surface) cells lying immediately ahead of the zipper point. This causes ___-____ cell adhesion, resultin in neural tube closure.

Answer 14

the driving force for zipper may be the localized activation of actomyosin contraction in the apical membranes of epidermal (non-neural surface) cells lying immediately ahead of the zipper point. This causes epidermal-epidermal cell adhesion, resultin in neural tube closure.

Question 15

how is the neural tube fully separated from the surface ectoderm?

Answer 15

via the expression of different cell adhesion molecules.

Question 16

the different expression cell adhesion molecules is what mediates complete neural tube separation from the surface ectoderm.

-normally, neural tube cells express ___ cadherin. They stop producing this protein as neural tube fully forms and instead synthesizes ___ cadherin.

Answer 16

normally, neural tube cells express E-cadherin. They stop producing this protein as neural tube fully forms and instead synthesizes N-cadherin. THIS CAUSES SURFACE ECTODERM TO RELEASE EACH OTHER.

Question 17

As the neural tube forms, it stops expressing E cadherin and expresses N cadherin instead. How is down regulation of Ecadherin induced?

Answer 17

it’s induced by GRAINYHEAD transcription factor. Without grainy head, ecadherin will still be expressed and the neural tube will not be formed, becuase the epithelium will still be bound to the nueral tissue, rather than the nerual tissure fusing to itself.

Question 18

in mammals, if the neural tube doesn’t close at 5 what happens? what about 2?

Answer 18

failure of closure 5 = spinabifida

failure of closure 2 (midbrain and forebrain junction)= anencephaly.

Question 19

characteristics of anencephaly

Answer 19

fatal condition caused by failure of closure site 2 + 3. Forebrain remains in contact with amniotic fluid, causing ti to degernate. Fetal forebrain stops developing, and the vault of skull does not develop.

Question 20

What is craniorachischis? What supplement can help with proper neural tube formation?

Answer 20

failure of the entire neural tube to close: will die in utero. Folic acid has been demonstrated to play a role in proper DNA synthesis during cell division in the brain. Folic Acid regulates DNA expression and methylation. Without proper DNA expression, mutation can occur.

Question 21

secondary neurulation takes place in the most ___ region of the mebryo during tail elongation

Answer 21

most posterior region

Question 22

secondary neurulation involves ___-___ transition

Answer 22

mesenchymal-epithelial transition: production of mesenchymal cells from prospective ectoderm and mesoderm. These mesenchyme cells then condense to form medullary cord under the ectoderm layer. This medullary cord undergoes cavitation to form several lumens that will coalesce to form a single central cavity.

Question 23

The mesenchyme cells formed from M-E-T during secondary neurulation condense to form ____ ____ under the ectoderm layer. This ___ ___ undergoes ____ to form several ____ that will coalesce to form a single central cavity.

Answer 23

These mesenchyme cells then condense to form medullary cord under the ectoderm layer. This medullary cord undergoes cavitation to form several lumens that will coalesce to form a single central cavity.

Question 24

difference between surface ectoderm and neural ectoderm relationship in secondary neurulation compared to primary neurulation

Answer 24

in secondary neurulation, the surface ectoderm and neural ectoderm are uncoupled and develop indepedently. They do not come into contact through fusion like they do in primary neurulation.

Question 25

recall: after hensen’s node has migrated to the posterior end of the embryo, the caudal region of the epiblast contains a precursor cell population that gives rise to both neural ectoderm and somite mesoderm as the embryo’s trunk elongates. How do these get separated?

Answer 25

the neural ectoderm cells that will form the posterior neural tube through secondary neurulation expresses Sox2, whereas the somite mesoderm will ingress and not express sox2; the mesoderm is not being exposed to the BMP levels seen on the surface of the epiblast.

• when the mesoderm cells ingress through gastrulation, they express tbx6 to form somites, suppressing neural induction by sox2.

Question 26

recall: after hensen’s node has migrated to the posterior end of the embryo, the caudal region of the epiblast contains a precursor cell population that gives rise to both neural ectoderm and somite mesoderm as the embryo’s trunk elongates.

the neural ectoderm cells that will form the posterior neural tube through ____ neurulation expresses ___, whereas the somite mesoderm will ingress and not express____; the mesoderm is not being exposed to the ____ levels seen on the surface of the epiblast. (so it won’t turn into epidermis; the neural ectoderm is expressing this repressor, so it can stay where it is without forming epidermis)

• when the mesoderm cells ingress through ____, they express ____ to form somites, suppressing neural induction by ___.

Answer 26

the neural ectoderm cells that will form the posterior neural tube through secondary neurulation expresses Sox2, whereas the somite mesoderm will ingress and not express sox2; the mesoderm is not being exposed to the BMP levels seen on the surface of the epiblast.

• when the mesoderm cells ingress through gastrulation, they express tbx6 to form somites, suppressing neural induction by sox2.

Question 27

in humans and chicks, there is a transition region at the ___ of the anterior and posterior neural tubes. This is where the cavities ___. Neural tube also forms by the bending of the neural plate cells, resulting in ____ neurulation.

Answer 27

in humans and chicks, there is a transition region at the JUNCTION of the anterior and posterior neural tubes. This is where the cavities COALESCE . Neural tube also forms by the bending of the neural plate cells, resulting in JUNCTIONAL neurulation.