Lecture - Mesoderm Development: Difference between revisions
From Embryology
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===Somite Axial Specification=== | ===Somite Axial Specification=== | ||
* rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors | * rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors | ||
===Sclerotome === | ===Sclerotome === |
Revision as of 17:13, 8 August 2011
Objectives
- Understanding of events during the third week of development
- Understanding the process of early somite development
- Understanding the process of body cavity formation
- Brief understanding of the future fate of mesoderm components
- Brief understanding of early heart formation
References
The Developing Human: Clinically oriented embryology
Citation: The developing human : clinically oriented embryology 8th ed. Moore, Keith L; Persaud, T V N; Torchia, Mark G Philadelphia, PA : Saunders/Elsevier, c2008. |
Larsen's human embryology
Citation: Larsen's human embryology 4th ed. Schoenwolf, Gary C; Larsen, William J, (William James). Philadelphia, PA : Elsevier/Churchill Livingstone, c2009. |
UNSW Embryology
Hill, M.A. (2011) UNSW Embryology (11th ed.). Sydney:UNSW. |
Notochord (Axial mesoderm)
Mesoderm
- generated from epiblast cells migrating through the primitive streak
- epiblast cells expressing fibroblast growth factor (FGF2)
- forms a layer between ectoderm and endoderm with notochord down midline
- present before neural tube formation
- divides initially into 3 components
- Paraxial mesoderm - somites - musculoskeletal structures
- Intermediate mesoderm - kidney
- Lateral plate mesoderm - body wall structures
Mesoderm Development
The four images below beginning at week 3 show cross-sections of the trilaminar embryo and the sequence of mesoderm development.
Mesenchyme
- Embryonic connective tissue, describes the cell morphology (Histology is not epithelial organization)
- epithelial to mesenchymal transitions
- mesenchymal to epithelial transitions
Paraxial Mesoderm
Somite Formation
Early somite induction signals in the mouse |
- ball forms through epithelialization and interactions (cell-cell, cell-extracellular matrix, ECM) fibronectin, laminin
- has 2 populations of cells - peripheral columnar and central mesenchymal
- early somite has cavity- somitocoel, cavity is lost during growth
- somite enclosed by ECM connected to nearby tissues
Somite Specification
- Different segmental level somites have to generate different segmental body structures?
- somite has to form different tissues?
- Somite Differentiation
- Compartmentalization accompanied by altered patterns of expression of Pax genes within the somite
Somite initially forms 2 main components
- ventromedial- sclerotome forms vertebral body and intervertebral disc
- dorsolateral - dermomyotome forms dermis and skeletal muscle
Somite Axial Specification
- rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors
Sclerotome
- sclerotome later becomes subdivided
- rostral and caudal halves separated laterally by von Ebner's fissure
- half somites contribute to a single vertebral level body
- other half intervertebral disc
- therefore final vertebral segmentation ‚"shifts"
Dermomyotome
- later divides into dorsal dermatome and ventral myotome
- (MH - This topic of muscle and skeleton development will be covered in 2 later lectures Musculoskeletal Development and Limb Development)
- lateral myotome edge migrates at level of limbs
- upper limb first then lower
- mixes with somatic mesoderm
- dermotome continues to contribute cells to myotome
Myotome
- Myotome component of Somite
- epaxial myotome (dorsomedial quarter) forms the dorsal epimere (erector spinae)
- hypaxial myotome (dorsolateral quarter) forms the ventral hypomere, 3 primary muscle layers which are different at neck, thorax and abdomen
Muscle
- Myoblast determining transcription factor MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed
- basic Helix Loop Helix
- from myotome
Muscle Development Abnormalities
- Duchenne Muscular Dystrophy
- Embryonic muscle development normal and changes occur postnatally
- X-linked dystrophy, large gene encoding cytoskeletal protein - Dystrophin
- progressive wasting of muscle, die late teens
- Becker Muscular Dystrophy, milder form, adult onset
Intermediate Mesoderm
|
Lateral Plate Development
- lying at the surrounding edge of he embryonic disc
- a cavity begins in this week to form within the mesoderm itself
Intraembryonic Coelom
- small spaces (vacuoles) begin appearing within the lateral plate mesoderm
- enlarge forming a single cavity within the lateral plate mesoderm
- divides lateral plate mesoderm into 2 parts at about day 18-19
- this cavity is called the Intraembryonic Coelom
- when the embryonic disc folds the intraembryonic coelom will form all 3 major body cavities:
- Pericardial
- Pleural
- Peritoneal
Coelom is a general term for a "cavity" and can lie within the embryo (intraembryonic) and outside the embryo (extra embryonic). Later anatomical spaces within the embryo and fetus can also be described as coeloms.
Somatic Mesoderm
The intraembryonic coelom divides the lateral plate into 2 portions
- closest to ectoderm
- body wall osteogenic, chrondrogenic and fibrogenic
- except ribs and scapula
Splanchnic Mesoderm
- closest to endoderm
- heart, smooth muscle of gastrointestinal tract (GIT) and blood vessels
- Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline
Somitogenesis
(not to scale) |
||||
gastrulation, notochordal process | ||||
primitive pit, notochordal canal | ||||
Somite Number 1 - 3 neural folds, cardiac primordium, head fold | ||||
Somite Number 4 - 12 neural fold fuses | ||||
Somite Number 13 - 20 rostral neuropore closes | ||||
Somite Number 21 - 29 caudal neuropore closes | ||||
Somite Number 30 leg buds, lens placode, pharyngeal arches | ||||
- Links: Somitogenesis
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, May 19) Embryology Lecture - Mesoderm Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Mesoderm_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G