MESODERM intro etc

Gastrulation

_______ specifies mesoderm between endoderm and ectoderm.

neural tube

Synchronous with _______ formation

paraxial
intermediate
lateral plate mesoderm

Lateral to the neural tube, thick bands of mesoderm cells differentiate into ______, ________, and _________

paraxial mesoderm
intermediate mesoderm
lateral plate mesoderm
chordamesoderm
head mesoderm

5 mesodermal subtypes

paraxial mesoderm

Early ____________ which lacks somites and takes form of bilateral streaks of continuous mesenchymal cells

Somites

Epithelial “Block-like” clusters of cells

somites

bilaterally positioned adjacent to the neural tubes

presomitic mesoderm

somites are Formed from the cells of the__________

dermomyotome
sclerotome

derivatives of somites

myotome
dermatome

portions of the dermamyotome

myotome

forms the skeletal muscles

dermatome

forms the back dermis

sclerotome

forms the vertebral and rib cartilage

syndetome
arthrotome

progenitor zones of sclerotome

syndetome

arise from the most dorsal sclerotome cells generates tendons

arthrotome

most internal cells of the sclerotome that becomes the vertebral joints

Bone Morphogenic Protein

SPECIFICATION OF PARAXIAL MESODERM

Mesodermal subtypes are specified along the mediolateral axis by increasing amounts of ____________________

lateral plate mesoderm

High BMP levels (lateral): Promote ______________ (e.g., circulatory system, body cavities).

paraxial mesoderm
intermediate mesoderm

Low BMP levels (medial): Allow _________ (somite-forming tissue) and ___________ gonads).

Noggin

Transplanting ______ (BMP inhibitor) into lateral plate mesoderm converts it into paraxial mesoderm, demonstrating BMP’s role in lateral fate determination.

Noggin

SHAPES THE BMP GRADIENT

notochord
somitic mesoderm

Noggin is secreted by the ____________ and later by _______

BMP4

Noggin Inhibits ______, creating a BMP concentration gradient critical for mediolateral patterning.

Fox transcription factors

___________ DEFINE REGIONAL IDENTITY

Fox1

Expressed in lateral plate mesoderm under high BMP signaling.

Foxc1
Foxc2

Expressed in paraxial mesoderm (somites) under low BMP signaling.

intermediate mesoderm

loss of Foxc1 and Foxc2, paraxial mesoderm is respecified into ___________ highlighting their role in somite commitment

Tbx6

used for specification of presomitic mesoderm
- represses Sox2 gene

Mesogenin 1

Acts upstream of Tbx6 as a "master regulator" of PSM fate.

neural tissue

loss of Tbx6 in mouse converts the presumptive somitic mesoderm into

Tbx6
Mesogenin

_____ and ______ suppress ectodermal fates (e.g., neural Sox2 expression).

Somitogenesis

process of segmentation of the paraxial mesoderm to form somites, beginning cranially and extending caudally

periodicity
fissure formation
epithelialization
specification
differentiation

components of somitogenesis

otic vesicle

somitogenesis begins at the _____ and proceeds caudally

somitomeres

Cells organize into __________, which undergo a mesenchymal-to-epithelial transition (MET) to form SEM of Somite and Neural Tube Structures epithelial somites.

neuromesodermal progenitors

Axis elongation depends on __________ in the tailbud, which contribute to both neural and mesodermal lineages

Caudal Progenitor Zone

___________ contains neuromesodermal progenitors (NMPs), bipotential stem cells expressing Sox2 (neural) and Tbx6 (mesodermal).

neural tube
paraxial mesoderm

NMPs contribute to both ______ and ________

Cell division cycle 25 A

In zebrafish, NMPs migrate from the dorsal medial zone into the tailbud, where they mix, divide (via _________ or Cdc25a), and enter the PSM.

cell proliferation
cell migration
intertissue adhesion

Elongation is driven by: (AXIS ELONGATION – CAUDAL PROGENITOR ZONE & TISSUE FORCES)

Fibronectin matrix links PSM to notochord
Notochord vacuole inflation

Intertissue adhesion process:

Cdc25a

Progenitor cells transiently express _______ in the maturation zone to trigger a round of division

Mesoderm posterior a
Ephrin receptor A4
Ephrin ligand B2
Integrin α5

SOMITE FORMATION VIA MET AND BOUNDARY SIGNALING

1. Somite formation begins with ___________ (Mesp a) expression in the rostral half of forming somites.
2. Mesp activates __________ (EphA4)
3. EphA4 induces ________ (ephrin-B2) in adjacent cells. This creates cell repulsion and boundary formation.
5. _______/fibronectin matrix stabilizes the boundary

Cdc42 downregulation
Integrin alpha 5 activation

MET is regulated by:

epithelial shell

SOMITE FORMATION VIA MET AND BOUNDARY SIGNALING creates an ________ around central mesenchymal cells, resulting in boundaries.

clock-wavefront model

The current predominant model to explain synchronized somite formation

Notch-Delta signaling

The “clock” refers to oscillating __________ (e.g., Hairy1, lunatic fringe) that controls the timing of somite formation across the PSM.

FGF8
retinoic acid

The “wavefront” consists of opposing gradients

FGF8

High in the caudal (tailbud) → low in the rostral (anterior PSM). keeps cells immature (“wavefront” consists of opposing gradients)

retinoic acid

Opposes FGF8 (high rostral → low caudal). promotes readiness for boundary formation

somitomere-IV

The determination front is the axial level in the PSM where cells become competent to form somite boundaries. It is positioned at ___________, where Fibroblast Growth factor 8 (FGF8) levels drop and retinoic acid levels rise, signaling readiness for segmentation

Fibroblast Growth factor 8

The determination front is the axial level in the PSM where cells become competent to form somite boundaries. It is positioned at somitomere –IV, where ___________ levels drop and retinoic acid levels rise, signaling readiness for segmentation.

Chick Delta-like 1

o Somitomere flipping experiments showed that cells become determined to form boundaries at position S–IV (four somites behind the current one),

▪ __________ (c-delta1) expression stabilizes.