test 2 head and neck Flashcards
Mesenchyme forming head and neck is derived from 3 major sources ___
neural crest
paraxial mesoderm
lateral plate mesoderm
neural plate mesoderm gives rise to ___ of the head
paraxial mesoderm gives rise to ___ of the head
lateral plate mesoderm give rise to ___ of the head
Patterning of the head and neck mesenchyme is closely coordinated with patterning of ___
neural epithelium
•Vertebrate embryos pass through a ___ after organogenesis-recreating evolutionarily conserved structures that are highly resistant to evolutionary change
phylotypic stage
___ segmentation is characteristic of the phylotypic stage
•Hindbrain
Variation in vertebrate morphology arises after this conserved stage. What stage?
phylotypic stage
___ segmentation is a conserved strategy used by
vertebrates for organizing the diverse craniofacial features
Hindbrain
Rhombomeres: segments composed of ___ epithelial cells from Neurulation;
ECTODERMAL
___ are precursors to hindbrain and peripheral neurons
rhombomeres
rhombomeres not only produce neuronal tissue, they also coordinate ___ formation through interactions with mesodermal, ectodermal, and endodermal cells.
craniofacial
rhombomeres directly contribute cells to ___ through the Epithelial to Mesenchymal Transition and migration of Neural Crest cells.
craniofacial bones and cartilages
the neural tube closes and forms three major segments
forebrain (prosencephalon)
midbrain (medsencephalon)
hindbrain (rhombencephalon)
rhombomeres are formed by segmentation of ___ and the neural crest undergoes ___ through EMT.
hind brain
delamitation
Hox in mammals vs Hox in fly
control expression from cranial to caudal
mammals have duplication of Hox genes
4 orthologous sets of paralogs
4 ___ sets of paralogs
orthologous
An orthologous gene is a gene in different species that evolved from a common ancestor by speciation.
Paralogs are homologous genes/proteins that are related or produced by duplication within a genome followed by subsequent divergence.
hox genes in mammals
An ___ is a gene in different species that evolved from a common ancestor by speciation.
orthologous gene
___ are homologous genes/proteins that are related or produced by duplication within a genome followed by subsequent divergence.
Paralogs
The Hox code defines ___segmentation
rhombomere
the 2nd rhombomere is controlled by ___
Hox A2
pharyngeal arches are derived from ___
mesoderm and neural crest (ectoderm that went through EMT to become mesenchyme)
pharyngeal cleft is derived form ___
ectoderm
pharyngeal pouch is derived from
endoderm
The dramatic migration of neural crest cells from rhombomeres into mesoderm results in the formation of the ___
pharyngeal arches
___ are exclusive derivatives of Pharyngeal arches that develop into gills of fish, and Pharyngeal arches are the proper ___ term.
Branchial arches
mammalian
Cells in the rhombomeres progressively lose the ability to respond to environmental signals. ie, their epigenetic identity becomes progressively ___ over time
fixed
No evidence of pre-programming of fate- there is ___ in the Hox code, but the ___ is lost with time.
- plasticity*
- plasticity*
Cells transplanted from one rhombomere to another adopt new identities, unless they are transplanted in ___, where they maintain their original identity by ___ and ___
larger groups
Cell-Cell communication, mutual reinforcement of identity.
Note in the hindbrain, ___ is observed in single dispersed cells and ___ in cell groups or clusters.
plasticity
autonomy
The ___ plays an important role in Hox code expression in neural crest cells of the rhombomeres.
mesoderm
•Rhombomere ablation does not affect patterning of the mesoderm (pharyngeal arch), endoderm (pharyngeal pouch) or outlying ectoderm (pharyngeal cleft)-initial patterning is NOT DEPENDENT on the ___
neural crest.
mesodermal arch and endodermal pouch patterning evolved ___ rhombomere patterning
before
The cranial mesoderm provides maintenance signals that ___ the program of Hox expression, but cannot ___ Hox gene expression in neural crest cells.
elaborate
initiate
mesoderm helps Hox but cannot make Hox
Hoxa2 expression is a critical determinant of ___ arch structures. It is necessary and sufficient for ___ arch identity
2nd
explain how Hox works basically
signaling molecules bind with transcription factors (Hox code)
which trigger phenotypic gene down stream which specify cells identity
___ is the source of an inductive BMP signal to the neural crest.
•Pharyngeal endoderm
___ has also been shown to promote the formation of branchial arch components in amphibians by directing neural crest cells towards a chondrogenic fate.
pharyngeal endoderm
Pharyngeal endoderm plays a major role in establishing and patterning the ___.
branchial arches
•Ectodermal clefts play an inductive role in ___ of the neural crest
odontogenesis (formation and eruption of teeth)
odontogenesis
formation and eruption of teeth
pharyngeal arch get most of their neural crest cells from which rhombomeres?
even number rhombomeres
old number rhombomeres (migrate rostrally and caudally)
what is the biggest pharyngeal arch and what supplies it
Nerve V, rhombomere 1,2,3
pharyngeal arch 1 is formed by ___ and makes ___
NC cells from R1 and 2 (and a bit of 3)
(the mandibular arch), forming jawbones, incus, malleus, as well as cranial nerves.
Some of these cells also pulled by epidermis to form fronto-nasal process, making the forehead, mid-nose, and primary palate.
There are six pairs of pharyngeal arches.
In mammals, the ___ is a short-lived rudiment, so the pairs are numbered ___
fifth
I, II, III, IV, VI. There should be no V.
pharyngeal arch 2 is formed by ___ and makes __
rhombomere 4 and some of 3 and 5
partial hyoid bone, stapes and facial nerve
pharyngeal arch 3 and 4 is formed by ___ and makes __
rhombomere 6-8 and some of 5
partial hyoid bone, thymus, parathyroid, thyroid, various cartilages and contribute to cardiac outflow tracts.
pharyngeal pouches are __ derivatives and lead to __
endodermal
internal membranes:
pharyngeal clefts are __ derivatives and lead to __
ectodermal
cervical sinus and external auditory meatus
pharyngeal arch 1 forms which prominences?
dorsal maxillary
ventral mandibular
5 facial prominences (primordia)
Frontonasal: Forehead, bridge of nose
Medial nasal: Philtrum of upper lip, crest/tip of nose
Lateral Nasal: Ala of nose
Maxillary: Upper lip
Mandibular: Lower lip
what is the area where the upper lip and nose fuse
philtrum
Upper lip is formed by which prominences fusing
Maxillary prominences fuse with
medial nasal prominences
the lower lip and jaw are formed by what prominence fusing
mandibular prominences fuse at midline
stomodeum
primitive mouth
formation of the palate
first the medial nasal prominences will fuse to form the intermaxillary segment (primary palate)
then the maxillary process will fuse to form the secondary palate
___ are extensions of Maxillary prominences
Palantine shelves
when things go wrong with palatine shelf
cleft palate, tongue stuck to palate, palate stuck to mandible, cyclopia and holoprosencephaly
cyclopia
caused by cyclopamine which inhibits Shh
Cyclopamine is teratogenic by inhibiting sonic hedgehog signaling (Shh) via smoothened (Smo) inhibition
exposure to this toxin during different days of gestation can lead to minor to severe issues, day 22-30= cleft palate
nested expression of ___ genes– specifies upper and lower jaw identity in ___ and teleosts–is a primitive feature of the mandibular, hyoid and gill arches of ___.
Dlx
mammals
jawed vertebrates (sharks)
