Molecular Embryology and Trunk Development Flashcards
surface ectoderm induced by
High BMP4 and low Shh
neural crest induced by
Intermediate BMP4 and Shh
neural tube induced by
low BMP4 and high Shh
SNAIL/SLUG
specifies neural crest cell fate/promotes cells migration
specification of the mesoderm
BMP4 concentration gradient
lateral plate mesoderm (lpm) IB
high BMP4
intermediate mesoderm(im) IB
intermediate BMP4
paraxial mesoderm (pm) IB
low BMP4, differentiates into somites
Hox proteins
transcription factors responsible for craniocaudal body segmentation, e.g. Hoxa1, Hoxd13
homeobox genes
4 chromosomes, 13 gene clusters that code for Hox proteins. Provide spatial/temporal colinearity of gene expression & development
Somite development order
Cranial to caudal. RA (cranial) promotes Hox gene expression. FGF8 (caudal) inhibits Hox.
someite differentiation front
located where RA signal overpowers FGF8 signal
RA
induces paraxial mesoderm to form somites via Hox. intercellular signaling molecule that guides development of the posterior portion of the embryo.
Shh (effect on mesoderm)
from notocord induces sclerotome
Wnt (effect on mesoderm)
from neural tube/surface ectoderm induces myotome
NT-3 (effect on mesoderm)
from neural tube induces dermatome
myotome
part of a somite that forms the muscles of the animal. cells express MyoD or Myf5.
dermatome
differentiate into dermis. the dorsal portion of the paraxial mesoderm somite which gives rise to dermis.
scleratome (signal + TF)
SHH -> Pax1
myotome (signal + TF)
WNT -> MRF (Myf5 + MoyD)
dermatome (signal + TF)
NT-3 -> Pax3
NODAL
a secretory protein that induces lateral plate mesoderm to form left-side structures by promoting expression of Pitx2.
Pitx2
responsible for the establishment of the left-right axis, the asymmetrical development of the heart, lungs, and spleen, twisting of the gut and stomach, as well as the development of the eyes. locally expressed in the left lateral mesoderm, tubular heart, and early gut which leads to the asymmetrical development of organs and looping of the gut.
dorsalization
BMP4 from ectoderm promoting expression of Pax 3 & Pax 7
ventralization
Shh from the notocord antagonizes BMP4 (represses Pax 3 & Pax 7)
SLUG
promotes migration of neural crest cells
BMP4
signaling molecule secreted by the lateral plate mesoderm required for the early differentiation of the embryo and establishing of a dorsal-ventral axis. It is secreted from the dorsal portion of the notochord, and acts in concert with sonic hedgehog (released from the ventral portion of the notochord) to establish a dorsal-ventral axis for the differentiation of later structures as well as inducing posterior neural tube (sensory)
left-right asymettry
FGF8 cause cilia that preferentially sweep toward the left sidethat activates NODAL which induces LPM to promote Pitx2 induced left side development.
primitive node
releases NODAL. Where invagination occurs.
FGF8
expression at primitive streak controls cell migration
somitomeres
form skeletal muscle in head, don’t dorm bony structures that come from somites. form on sides of cranial neural tube. do not segregate into sclerotome, dermatome, and myotome.
sclerotome
differentiate into axial skeleton. cells express PAX1.
SHH and Noggin expression
induces sclerotome development
hypaxial division
myotome posterolateral origin. MyoD expression. body wall and limb muscles. anterior primary rami.
epaxial division
myotome posteromedial origin. Myf5 expression. intrinsic back muscles. posterior primary rami
ossification
begins in utero by 7 weeks. primary centers form by 7 weeks and are active until age 6. secondary ossification is complete around 25 years of age. at birth vertebrae consist of three bony parts united by cartilage.
intervertebral discs
form from notochord and mesenchyme of somites. notochord forms nucleus pulposus. mesenchyme forms anulus fibrosus
resegmentation
occurs as each vertebra forms from the fusion of the caudal half of the sclerotome of one somite and the cranial half of the sclerotome of the subjacent somite. somites surround neural tube and notochord.
intersegmental arteries
visceral mesoderm, initally between somites and finish at mid-vertebrae.
spinal nerves
outgrowth of neural tube, initially at mid-somite, finish between vertebrae.
myotomes
come from paraxial mesoderm, initially within somite and finish to span vertebrae, allowing for movement of the vertebral column)
ribs
bony part derived from sclerotome portion of paraxial mesoderm. cartilaginous part derived from sclerotome cells that migrated.
sternum
derived from parietal layer of lateral plate mesoderm.
cleft sternum
right and left halves do not fuse appropriately.
accessory, forked, or fused ribs
loss of function mutation of various Hox genes, can lead to accessory cervical or lumbar ribs.
hemivertebra
malformations of the spine resulting in wedge-shaped vertebrae that can cause an angle in the spine (such as kyphosis, scoliosis, and lordosis).
spondylolysis
fracture of pars interarticularis due to congenital developmental defects or trauma
spondylolisthesis
dislocation between adjacent vertebrae subsequent to spondylolysis.
failure of neuropores to close results in:
ancephaly, spina bifida, rachischisis. Can be indicated pre-birth with a-feroprotin increase inmaternal serum tests.
rachischisis
severe caudal failure, in which neural tissue is exposed and often becomes necrotic)
folic acid supplement reason
intake prior to and during pregnancy can decrease incidence of neural tube defects by as much as 70%
mesoderm differentiation
lateral plate, intermediate, paraxial. Driven by BMP4 concentration gradient.
SHH
induces ectoderm to form neuroectoderm which undergoes neurulation to form neural tube and neural crest, then induces anterior neural tube (motor).
epaxial derivatives
non-migratory myoblasts, i.e. back muscles.
