Ectoderm I: Neural Tube Formation

Elongation, folding, convergence, closure

The 4 steps of primary neurulation are...

Notochord

The process of neurulation is promoted by signals from the ______.

Folding

The second step of primary neurulation is ______. This is when the neural plate folds inward at the midline and creates a neural groove and a medial hinge point (MHP).

Convergence

The third step of primary neurulation is _____. This is when cells at the dorsolateral hinge points (DLHP) apically constrict, which causes the neural folds to come in contact with each other.

Ectoderm

This section focuses on _____ formation.

Shh

Ventrally, _____ slightly prevents noggin from expressing in cells which shouldn't apically constrict.

Craniorachischisis

_____ is a human disease that results from failure of closing of the whole neural tube. (incompatible with life).

Secondary neurulation

_____ occurs when the neural tube is formed by the hollowing out of the interior of a solid precursor. Occurs Posteriorly.

shroom

______ is another gene which is expressed at both the MHP and the DLHP and is involved in the apical contraction process. *Note: The other genes are not expressed in the MHP.*

N-cadherin, E-cadherin

______ is expressed by the neural plate prior to folding, and _____ is expressed by the presumptive epidermis prior to folding.

Cadherins

______ mediate the fusion and separation of the neural tube.

Spina bifida

_______ is a human disease resulting from failure of the neural tube to close posteriorly.

Primary neurulation

_______ is the formation of the neural tube by the folding of the neural folds, which come in contact and fuse together. Occurs Anteriorly.

Anencephaly

________ is a human disease resulting from failure of the neural tube to close anteriorly.

Neural tissue

BMP complete knockout results in complete expression of ______ throughout embryo.

Noggin

BMP inhibitors such as chordin, ______, and follistatin promote neural fates. It is required for proper hinge point formation and neural tube closure. Here, this partially inhibits BMP and therefore, the presence of this in combination with BMP makes sure the hinge points are exactly right for proper closure. (not too much, not too little).

Surface ectoderm, neural crest, neural tube

During neural tube formation, the ectoderm forms these 3 major products....

Nervous system

Ectoderm doesn't only form skin, but also the entire ______ with thousands of unique neuronal cell types.

Surface ectoderm, neural ectoderm, neural crest

Expression patterns during neurulation: High BMP = _____ Low BMP = ______ Intermediate Bmp = _______

Anterior

For the most part, neural gradient along A-P axis occurs first at the ____ end.

Posterior to anterior

In neural tube closer of larval Ciona, fusion of the neural tube occurs ______, unlike the others we've seen and occurs by actin and myosin interactions to contract to tissue and bring it together.

BMP

In the embryo, ______ signaling promotes epidermal ectoderm fates. It functions to making sure the width of the hinge point is just right (prevents tube from closing too much). These signals must be just right in order for high formation. - Too much = no formation of DLHP - Too little = exaggerated DLHP - Just right = wild type hinge formation.

Neural tissue

Knocking down Noggin and other BMP inhibitors results in almost no _______.

Zippers, buttons

Neural tube closing in mammals _____ in the hindbrain, and _____ in the midbrain. These occur at multiple sites and different directions simultaneously.

Apical constriction, hinge point formation

Neural tube closure depends essentially on _______ and ______.

Neural folds

Neurulation occurs by the _____ bringing ectoderm tissue inside. These are the thick tissue on either side of neural groove.

Filopodia

Non-neural ectodermal cells extend long _____ to contact cells of apposing neural folds and cause it to close.

Neural tube

The _____ derives form the ectoderm and forms the central nervous system consisting of the brain, neural pituitary, spinal cord, motor neurons, and retina. It also forms the skin, but we will not focus on that here.

Neural crest

The _____ derives from the ectoderm and becomes The PNS, adrenal medulla, melanocytes, facial cartilage and dentine of teeth.

Surface ectoderm

The ______ derives from the ectoderm and forms all epithelial structures such as epidermis, hair, nails, cornea, etc....

Elongation

The first step of primary neurulation is ______. This is when general ectoderm tranforms into a thickened and elongated neural plate.

Neurulation

The formation of the neural tube is referred to as ______ and begins when gastrulation begins. This occurs by neural folds bringing ectoderm tissue inside.

Closure

The fourth and last step of neurulation is _______. This is when the neural folds come together and the epidermis pinches away from the newly formed neural tube. During this process, neural crest cells lay between the neural tube and the epidermis.