Musculoskeletal System - Appendicular Skeleton Development
- 1 Introduction
- 2 Some Recent Findings
- 3 Textbooks
- 4 Objectives
- 5 Development Overview
- 6 Limb Axis Formation
- 7 Week 5
- 8 Week 6
- 9 Week 7
- 10 Week 8
- 11 Limb Rotation
- 12 Fetal Growth
- 13 Limb Bone
- 14 Shoulder and Pelvis
- 15 Wing as Limb Model
- 16 Mouse Limb Model
- 17 Bat Limb Model
- 18 Molecular
- 19 References
- 20 Additional Images
- 21 External Links
- 22 Glossary Links
The mesoderm forms nearly all the connective tissues of the musculoskeletal system. Each tissue (cartilage, bone, and muscle) goes through many different mechanisms of differentiation.
The musculoskeletal system consists of skeletal muscle, bone, and cartilage and is mainly mesoderm in origin with some neural crest contribution.
The intraembryonic mesoderm can be broken into paraxial, intermediate and lateral mesoderm relative to its midline position. During the 3rd week the paraxial mesoderm forms into "balls" of mesoderm paired either side of the neural groove, called somites.
Somites appear bilaterally as pairs at the same time and form earliest at the cranial (rostral,brain) end of the neural groove and add sequentially at the caudal end. This addition occurs so regularly that embryos are staged according to the number of somites that are present. Different regions of the somite differentiate into dermomyotome (dermal and muscle component) and sclerotome (forms vertebral column).
Bone is formed through a lengthy process involving ossification of a cartilage formed from mesenchyme. Two main forms of ossification occur in different bones, intramembranous (eg skull) and endochondrial (eg limb long bones) ossification. Ossification continues postnatally, through puberty until mid 20s. Early ossification occurs at the ends of long bones.
Musculoskeletal and limb abnormalities are one of the largest groups of congenital abnormalities.
|Factor Links: AMH | hCG | BMP | sonic hedgehog | bHLH | HOX | FGF | FOX | Hippo | LIM | Nanog | NGF | Nodal | Notch | PAX | retinoic acid | SIX | Slit2/Robo1 | SOX | TBX | TGF-beta | VEGF | WNT | Category:Molecular|
Some Recent Findings
|More recent papers|
This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
Search term: Appendicular Skeleton Development
<pubmed limit=5>Appendicular Skeleton Development</pubmed>
Search term: Limb Skeleton Development
<pubmed limit=5>Limb Skeleton Development</pubmed>
|Keith L. Moore, T.V.N. Persaud, Mark G. Torchia. (2011). The Developing Human: clinically oriented embryology (9th ed.). Philadelphia: Saunders.
|Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone Chapter 18 - Development of the Limbs (chapter links only work with a UNSW connection).
- Identify the components of a somite and the adult derivatives of each component.
- Give examples of sites of (a) endochondral and (b) intramembranous ossification and to compare these two processes.
- Identify the general times (a) of formation of primary and (b) of formation of secondary ossification centres, and (c) of fusion of such centres with each other.
- Briefly summarise the development of the limbs.
- Describe the developmental abnormalities responsible for the following malformations: selected growth plate disorders; congenital dislocation of the hip; scoliosis; arthrogryposis; and limb reduction deformities.
Below is a very brief overview using simple figures of 3 aspects of early musculoskeletal development. More detailed overviews are shown on other notes pages Mesoderm and Somite, Vertebral Column, Limb in combination with serial sections and Carnegie images.
|Cells migrate through the primitive streak to form mesodermal layer. Extraembryonic mesoderm lies adjacent to the trilaminar embryo totally enclosing the amnion, yolk sac and forming the connecting stalk.|
|Paraxial mesoderm accumulates under the neural plate with thinner mesoderm laterally. This forms 2 thickened streaks running the length of the embryonic disc along the rostrocaudal axis. In humans, during the 3rd week, this mesoderm begins to segment. The neural plate folds to form a neural groove and folds.|
|Segmentation of the paraxial mesoderm into somites continues caudally at 1 somite/90minutes and a cavity (intraembryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.
Note intraembryonic coelomic cavity communicates with extraembryonic coelom through portals (holes) initially on lateral margin of embryonic disc.
|Somites continue to form. The neural groove fuses dorsally to form a tube at the level of the 4th somite and "zips up cranially and caudally and the neural crest migrates into the mesoderm.|
|Mesoderm beside the notochord (axial mesoderm, blue) thickens, forming the paraxial mesoderm as a pair of strips along the rostro-caudal axis.|
|Paraxial mesoderm towards the rostral end, begins to segment forming the first somite. Somites are then sequentially added caudally. The somitocoel, is a cavity forming in early somites, which is lost as the somite matures.|
|Cells in the somite differentiate medially to form the sclerotome (forms vertebral column) and dorsolaterally to form the dermomyotome.|
|The dermomyotome then forms the dermotome (forms dermis) and myotome (forms muscle).
Neural crest cells migrate beside and through somite.
|The myotome differentiates to form 2 components dorsally the epimere and ventrally the hypomere, which in turn form epaxial and hypaxial muscles respectively. The bulk of the trunk and limb muscle coming from the Hypaxial mesoderm. Different structures will be contributed depending upon the somite level.
Limb skeletal muscle arises from the hypomere region of the myotomes adjacent to the developing upper (C5-C8) and lower (L3-L5) limb buds.
Limb Axis Formation
Four Concepts - much of the work has been carried out using the chicken and more recently the mouse model of development.
- Limb Initiation
- Proximodistal Axis
- Dorsoventral Axis
- Anteroposterior Axis
Mouse limb Patterning Images
- Mouse Limb Images: Tbx3 and Tbx2 forelimb E10 | Alx3 and Gli3 forelimb E10 | Fgf and Hox forelimb E10.5 | Bmp4 forelimb E11.5 | Bmp4 hindlimb E11.5 | Shh forelimb E11.5 | Fgf8 hindlimb E11.5 | Sox9 forelimb E12.5 | Msx2 forelimb E12.5 | Shh hindlimb E12.5
- Fibroblast growth factor (FGF) coated beads can induce additional limb
- FGF10 , FGF8 (lateral plate intermediate mesoderm) prior to bud formation
- FGF8 (limb ectoderm) FGFR2
- FGF can respecify Hox gene expression (Hox9- limb position)
- Hox could then activate FGF expression
Note that during the embryonic period there is a rostrocaudal (anterior posterior) timing difference between the upper and lower limb development
- this means that developmental changes in the upper limb can precede similar changes in the lower limb (2-5 day difference in timing)
Forelimb and hindlimb (mouse) identity appears to be regulated by T-box (Tbx) genes, which are a family of transcription factors.
- hindlimb Tbx4 is expressed.
- forelimb Tbx5 is expressed.
- Tbx2 and Tbx3 are expressed in both limbs.
Related Research - PMID: 12490567 | Development 2003 Figures | Scanning electron micrographs of E9 Limb bud wild-type and Tbx5del/del A model for early stages of limb bud growth | PMID: 12736217 | Development 2003 Figures
Tbx3 and Tbx2 expression in E9.75 to 10.5 wild-type mouse embryonic forelimb.
- Anteroposterior - (Rostrocaudal, Craniocaudal, Cephalocaudal) from the head end to opposite end of body or tail.
- Dorsoventral - from the spinal column (back) to belly (front).
- Proximodistal - from the tip of an appendage (distal) to where it joins the body (proximal).
- Apical Ectodermal Ridge (AER) formed by Wnt7a
- then AER secretes FGF2, 4, 8
- stimulates proliferation and outgrowth
The developing limb can be described along the proximodistal axis as having three main regions:
- Stylopod - the proximal region the limb, the skeletal component of the upper limb (forelimb) is the humerus, and for the lower limb (hindlimb) is the femur.
- Zeugopod - the mid-section of the limb , the skeletal components of the upper limb (forelimb) are the radius and ulna, and for the lower limb (hindlimb) are the tibia and fibula.
- Autopod - the distal region the limb, the musculoskeletal component of the upper limb (forelimb) is the hands, and for the lower limb (hindlimb) is the foot.
- Somites - provides dorsal signal to mesenchyme which dorsalizes ectoderm
- Ectoderm - then in turn signals back (Wnt7a) to mesenchyme to pattern limb
- name was derived from 'wingless' and 'int’
- Wnt gene first defined as a protooncogene, int1
- Humans have at least 4 Wnt genes
- Wnt7a gene is at 3p25 encoding a 349aa secreted glycoprotein
- patterning switch with different roles in different tissues
- mechanism of Wnt and receptor distribution still being determined (free diffusion, restricted diffusion and active transport)
One WNT receptor is Frizzled (FZD)
- Frizzled gene family encodes a 7 transmembrane receptor
Fibroblast growth factors (FGF)
- Family of at least 17 secreted proteins
- bind membrane tyrosine kinase receptors
- Patterning switch with many different roles in different tissues
- FGF8 = androgen-induced growth factor, AIGF
- comprise a family of at least 4 related but individually distinct tyrosine kinase receptors (FGFR1- 4) similar protein structure
- 3 immunoglobulin-like domains in extracellular region
- single membrane spanning segment
- cytoplasmic tyrosine kinase domain
- Zone of polarizing activity (ZPA)
- a mesenchymal posterior region of limb
- secretes sonic hedgehog (SHH)
- note digit 1 (thumb/big toe) is the only digit that forms independent of SHH activity.
- apical ectodermal ridge (AER), which has a role in patterning the structures that form within the limb
- majority of cell division (mitosis) occurs just deep to AER in a region known as the progress zone
- A second region at the base of the limbbud beside the body, the zone of polarizing activity (ZPA) has a similar patterning role to the AER, but in determining another axis of the limb
|Carnegie stage 13||Carnegie stage 14||Carnegie stage 15|
Digital rays become visible on the upper limb.
|Carnegie stage 18||Carnegie stage 19|
Digital rays become visible on the lower limb.
Human Embryo (stage 19) showing direction of limb rotation.
|<Flowplayer height="320" width="285" autoplay="true">fetal growth.flv</Flowplayer>||Embryonic period - the external appearance of both the upper and lower limb has been formed.
Play the associated animation to observe the relative change in limb dimensions.
|Carnegie stages for limb elements appearance|
|Humerus||16||16 — 17||21 — 22|
|Radius||16||17||21 — 23|
|Ulna||16||17 — 18||17 — 23|
|Hand||17||17 — 21||In fetus1and after birth|
|Femur||17||17—18||22 — 23|
|Tibia||17||17 — 23||22 — 23|
|Fibula||17||17 — 18||In fetus|
|Foot||17 — 18||18 — 23 or later||in fetus and after birth|
|1 Intramembranous ossification at the tips of the distal phalanges of the hand may be in horizon xxiii.|
|Reference - O'Rahilly R. Gray DI. and Gardner E. Chondrification in the hands and feet of staged human embryos. (1957) Carnegie Instn. Wash. Publ. 611, Contrib. Embryol., 36:|
Bone formation within the limb occurs by endochondral ossification of a pre-existing cartilage template. Ossification then replaces the existing cartilage except in the regions of articulation, where cartilage remains on the surface of the bone within the joint. Therefore bone development in the limb is initially about cartilage development or chondrogenesis.
In addition, there are two quite separate aspects to this development.
- Pattern - where the specific regions will commence to form cartilage, which will be different for each cartilage element.
- Chondrogenesis - the differentiation of mesoderm to form cartilage, which will be essentially the same program for all cartilage templates.
A recent study has identified that the overlying limb surface ectoderm potentially inhibits limb early chondrogenesis through Wnt6 signaling.
Shoulder and Pelvis
The skeletal shoulder consists of: the clavicle (collarbone), the scapula (shoulder blade), and the humerus. Development of his region occurs through both forms of ossification processes.
The skeletal pelvis consists of: the sacrum and coccyx (axial skeleton), and pelvic girdle formed by a pair of hip bones (appendicular skeleton). Before puberty, he pelvic girdle also consists of three unfused bones: the ilium, ischium, and pubis. In chicken, the entire pelvic girdle originates from the somatopleure mesoderm (somite levels 26 to 35) and the ilium, but not of the pubis and ischium, depends on somitic and ectodermal signals.
Wing as Limb Model
- chicken wing easy to manipulate
- removal, addition and rotation of limb regions
- grafting additional AER, ZPA
- implanting growth factor secreting structures
Mouse Limb Model
|Mouse limb skeleton cartoon
Fore-limb and hind-limb buds for stages E9.5 to E13.5. Hindlimbs are morphologically delayed by about half a day.
|Change in cell types and tissue formation as a function of mouse developmental stage.|
- Links: Mouse Development
Bat Limb Model
Images of the bat embryo Miniopterus schreibersii fuliginosus at embryonic Stages 13-17.
(aer - apical ectodermal ridge; chp - chiropatagium; eb - elbow; kn - knee)
Fibroblast Growth Factors
- Fgf8 - morphogen gradient forms by a source-sink mechanism with freely diffusing molecules.
T-box Transcription Factors
The HAND2 gene encodes a basic helix-loop-helix (bHLH).
- <pubmed>20644713</pubmed>| PMC2903596 | PLoS
- <pubmed>20644711</pubmed>| PMC2903592 | PLoS
- <pubmed>20386744</pubmed> Cite error: Invalid
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- <pubmed>17194222</pubmed>| PMC1713256 | PLoS Genet.
- <pubmed>20092640</pubmed>| PMC: 2824742 | BMC Dev Biol.
<pubmed>20347761</pubmed> <pubmed>20386744</pubmed> <pubmed>19207183</pubmed>
Search April 2010
- Limb Development - All (776) Review (108) Free Full Text (196)
- apical ectodermal ridge - All (95) Review (2) Free Full Text (31)
- zone polarizing activity - All (15) Review (2) Free Full Text (7)
- Limb Images: 274-278 Spinal Column and Lower Limb | 279-284 Lower Limb | 285-288 Knee | 289 Os Coxae | 290 Femur | 291 Tibia | 292 Fibula | 293 Foot | 294 | 295 | 296 | 297 | 298-299 | 300 Forearm and Hand | 301 Upper Limb Joints | 302 Clavicle | Upper Limb Ossification 1 | Upper Limb Ossification 2 | Bone Development Timeline
- Skeleton and Connective Tissues: Connective Tissue Histogenesis | Skeletal Morphogenesis | Chorda Dorsalis | Vertebral Column and Thorax | Limb Skeleton | Skull Hyoid Bone Larynx
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- Embryo Images - apical ectodermal ridge | AER and vascular channel
- The Jackson Laboratory - Mouse Strains - Limb Patterning Defects
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Cite this page: Hill, M.A. (2019, October 16) Embryology Musculoskeletal System - Appendicular Skeleton Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Musculoskeletal_System_-_Appendicular_Skeleton_Development
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G