Prepared by: Wilson R. Jacinto

Accomplishmentsof ectoderm into three distinct groups of cells Formation of somites on either side of notochord Separation

Period

of development starting with the first traces of formation of neural plate and ending with the closure of neural tube

FISH

Mammalian, Avian

and Reptilian

chordal tissue induce the overlaying ectodermal cells, causing them to thicken and form neural plate. In the absence, what will happen to the ectoderm? The reaction is primary neural induction. The

Primary

Neurulation

Stages: Formation and Shaping of Neural Plate

Primary Induction Median Hinge points and Dorsolateral Hinge points

Bending of Neural Plate to Form Groove

Closure of Neural Groove

Secondary

Neurulation

Neural tube forms, and hollows out

Similar

in amphibians, birds, reptiles, mammalsEctoderm

Neural tube

Epidermis

Neural crest

Effect

of one embryonic tissue (inductor) on another so that the development of the responding tissue is qualitatively changed. Chordamesoderm inductor Ectoderm competent responding tissue Noggin protein inductor in Xenopus

Expressed in chordamesoderm.

Not

simultaneous as seen in elongated embryos Junction cells form neural crest

Migrates prior to or after closing of the tube

Forms

anterior and posterior neuropores

Pax3,

sonic hedgehog and openbrain gene required in mammalian neural tube

E-cadherin (L-cam) originally in neural plate N-cadherin and N-cam detaches neural tube from ectoderm

Components to Induction Inductive

signal Acquisition of competence of dorsal ectodermIncreased protein kinase C in dorsal ectoderm Vertical induction (transinduction) Planar induction (homeogenetic)

Components Regional

specification of the neural plate into craniocaudal regions from brain to spinal cordArchencephalic - induction of anterior head struc. Deuterencephalic posterior head structures Spinocaudal induction trunk and tails formed Heteroinductors - different tissues

making of medullary cord and hollowing out Seen in lumbar and caudal vertebrae In frog and chick, occurs in the neural tube and lumbar vertebra.

Secondary Steps

Condensation of mesenchyme beneath the dorsal ectoderm of tail bud Cavitation to form central canal Canal becomes continuous with the primary neural tube.

Secondary Fishes Birds

- exclusively secondary

anterior portions of the neural tube - primary neurulation, neural tube caudal to the twenty-seventh somite pair (i.e., everything posterior to the hindlimbs) secondary neurulation

Secondary Amphibians

such as Xenopus, most of the tadpole neural tube- 1st neurulation, but the tail neural tube is derived from 2nd neurulation.

Mice

(and probably humans, too), 2nd neurulation begins at or around the level of somite 35.

Formation

of chambers of brain and spinal

cord Re-arrangement of cell population along the wall of the tube Neuroepithelial cells differentiate

Growing

region of the tip of the dorsal blastophore lip - chordoneural hinge Growth converts the spherical gastrula to linear tadpole some 9-mm long.

Folic acid can prevent 50% of human neural tube defects.

Primary

mesenchyme mesodermal precursors migrating from primitive streak Mesenchyme aggregates of spindle-shaped cells in the extracellular matrix, regardless of germ layer origin.

becomes organized as epithelium (like a somite). A somite has central cavity, surface of cells face the cavit. Mesoderm

Division of Mesoderm Paraxial

mesoderm (segmental plate)

Paraxial is organized into somites

Intermediate

mesoderm Lateral mesoderm

Lateral mesoderm splits to somatic (upper) and splanchnic (lower).

(ecto and somatic lateral) Splanchnopleure (endo and splanchnic lateral) Somites reacquire mesenchymal property to becomes secondary mesenchyme Somatopleure

Somitomeres and somite Paraxial

mesoderm

regular segmentation in the segmental plate; developed into whorls of cells to form Somites compacted whorls of cells, bounded by epithelium which separates from the rest Somitomeres

pair of somites forms from the 8th pair of somitomeres. One pair formed every 100 minutes until 50 pairs are formed. Induction from neural tube and notochord to the somites forms First

Sclerotome Dermamyotome (dermatome and myotome)

Antero-posterior

axes Dorso-ventral axes Left and right axes Neural plate lengthen along the anteroposterior axis Cell division of neural plate cells is rostalcaudal

Exposed

gray crescent marks region of initiation of gastrulation in amphibian

In

Sea urchin, animal-vegetal axis appear to establish the antero-posterior axis.Vegetal sequesters maternal components necessary for posterior development Dorso-ventral and lateral established after fertilization

In

tunicates:

Dorso-ventral is determined by cap of cytoplasm in the vegetal pole future dorsal side where gastrulation is initiated

In

C. elegans,

the elongated axis of egg defines future anteroposterior axes position of sperm pronucleus at the nearest oblong becomes the posterior Migration of P-granules to the putative posterior end ABp cells above EMS defines dorsal and ventral