Post on 16-Oct-2014
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