Lecture - Mesoderm Development
|Embryology - 30 Nov 2020 Expand to Translate|
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- 1 Introduction
- 2 Objectives
- 3 Lecture Resources
- 4 Notochord (Axial mesoderm)
- 5 Mesoderm
- 6 Mesoderm Development
- 7 Mesoderm Overview
- 8 Paraxial Mesoderm
- 9 Somite Formation
- 10 Intermediate Mesoderm
- 11 Lateral Plate Development
- 12 Glossary Links
Having now reached week 3 in development we will now begin to look separately at the 3 transient germ layers (ectoderm, mesoderm and endoderm) formed by the process of gastrulation. Beginning with the mesoderm layer, the middle embryonic connective tissue (mesenchyme) layer. Transient in terms of temporary structures that will become something else later in development.
Mesoderm initially forms a multilayered cellular layer separating ectoderm and endoderm, mesoderm also lies outside the embryo as extra-embryonic mesoderm (covered in placenta lecture). Embryonic mesoderm will form most of the adult connective tissues and muscle.
Towards the end of week 3 this layer begins to "partition" into different transient components based upon their location within the layer and the signals the cells are receiving. This partitioning process can be either in terms of cell differentiation or structural. This lecture will describe these initial regions and the tissues they will eventually form. Note that later lectures (muscle, skeleton, limb, integumentary and heart) will revisit these tissues later in development.
|2015 Group Project Topic - Assisted Reproductive Technology|
Some Potential Topics
- 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
|The following chapter links only work with a UNSW connection.|
|The following chapter links only work with a UNSW connection.
|Link added after Lecture.
Links only work with currently enrolled UNSW students.
Notochord (Axial 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 - urogenital (kidney and genital)
- Lateral plate mesoderm - body wall, body cavities, cardiovascular and GIT structures
The four images below beginning at week 3 show cross-sections of the trilaminar embryo and the sequence of mesoderm development.
| Week 3
Compare this week 3 trilaminar embryo with the week 4 embryo.
(Note - 2 these images are not to scale)
Scanning electron micrograph of a cross-section of a human embryo at week 4 (stage 11).
Note the mesoderm structures now present and their relative position and size within the embryo.
Compare the mesoderm structures to those formed by ectoderm (neural tube and epidermis) and endoderm (epithelia of developing gastrointestinal tract).
Model for Sprouty4 and FGF in mouse mesoderm segmentation
- 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
- rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors
Somite initially forms 2 main components
- ventromedial- sclerotome forms vertebral body and intervertebral disc
- dorsolateral - dermomyotome forms dermis and skeletal muscle
- 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"
- later divides into dorsal dermatome and ventral myotome
- 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 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
- 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
Lateral Plate Development
- lying at the surrounding edge of he embryonic disc
- a cavity begins in this week to form within the mesoderm itself
- 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:
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.
The intraembryonic coelom divides the lateral plate into 2 portions
- closest to ectoderm
- body wall osteogenic, chrondrogenic and fibrogenic
- except ribs and scapula
- 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
(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
- 2015 Course: Week 2 Lecture 1 Lecture 2 Lab 1 | Week 3 Lecture 3 Lecture 4 Lab 2 | Week 4 Lecture 5 Lecture 6 Lab 3 | Week 5 Lecture 7 Lecture 8 Lab 4 | Week 6 Lecture 9 Lecture 10 Lab 5 | Week 7 Lecture 11 Lecture 12 Lab 6 | Week 8 Lecture 13 Lecture 14 Lab 7 | Week 9 Lecture 15 Lecture 16 Lab 8 | Week 10 Lecture 17 Lecture 18 Lab 9 | Week 11 Lecture 19 Lecture 20 Lab 10 | Week 12 Lecture 21 Lecture 22 Lab 11 | Week 13 Lecture 23 Lecture 24 Lab 12 | 2015 Projects: Three Person Embryos | Ovarian Hyper-stimulation Syndrome | Polycystic Ovarian Syndrome | Male Infertility | Oncofertility | Preimplantation Genetic Diagnosis | Students | Student Designed Quiz Questions | Moodle page
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Cite this page: Hill, M.A. (2020, November 30) Embryology Lecture - Mesoderm Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Mesoderm_Development
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G