2009 Lecture 13

Musculoskeletal Development

Introduction

This lecture is an introduction to the process of musculoskeletal development. In the body, this is mainly about mesoderm differentiation beginning with an embryonic connective tissue structure, the mesenchyme. In the head, this is a mixture of mesoderm and neural crest differentiation, from mesenchyme and ectomesenchyme respectively. The lecture will cover mainly cartilage and bone, as muscle will be covered in the limb lecture and in this week's laboratory.

Lecture Objectives

• Understanding of mesoderm and neural crest development.
• Understanding of connective tissue development.
• Understanding of muscle, cartilage and bone development.
• Understanding of the two forms of bone development.
• Brief understanding of bone molecular development.
• Brief understanding of other bone roles.
• Brief understanding of bone abnormalities.

Textbook References

• The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter 15 the skeletal system
• Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 11 Limb Dev (bone not well covered in this textbook)

• Before we Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
• Essentials of Human Embryology Larson Ch11 p207-228

Summary

The following text is extracted and modified from previous lecture slides and should be used as a "trigger" to remind you of some key concepts.

• Bone DevelopmentSkeleton patterningshape and location of each specific skeletal element2 ossification typesEndochondrial, IntramembranousCell differentiation in skeletonchondrocyte in cartilageosteoblast in boneosteoclast in bonemolecular control of major function of skeletonskeleton growth (fetal, neonatal, puberty)bone remodelling, mineralizationAbnormalities

• Background - Mesoderm Development Somite, somatic Vertebra Development Somite, sclerotome Limb and Axial Development Endochondrial ossification Head Development Intramembranous ossification

• Textbook ReferencesHuman Embryology (3rd ed.) LarsonChapter 11 Limb Dev (bone not well covered in this textbook)The Developing Human (6th ed.) Moore & PersaudChapter 15 the skeletal systemBefore we Are Born (5th ed.) Moore and PersaudCh16,17: p379-397, 399-405Essentials of Human Embryology LarsonCh11 p207-228Human Embryology Fitzgerald and FitzgeraldMolecular biology of the Cell (4th edn)
• Introductionossification of a cartilage formed from mesenchyme2 main forms of ossification IntramembranousskullEndochondrialVertebra, limb long bonesOssification continues postnatallythrough puberty until mid 20sEarly ossification occurs at ends of long bones
• Movie: Ossification SitesEarly Fetal SkeletonEarly Fetal SkeletonVertebra- Sclerotomal cellsMovie: Segmental VertebraEndochondrial OssificationVertebra Cartilage to BoneVertebra Cartilage to BoneMature BoneMature BoneDeveloping JointSkeleton Cell Lineage
• Bone Components
• CellsOsteoblasts, osteocytes, osteroclastsOrganic Matrix95% Type I collagen5% proteoglycans and noncollagenous proteinsOsteopontinOsteocalcin
• Bone Cell TypesChondrocytemesenchymal originOsteoblastmesenchymal origin Osteoclastmonocytic originGenes controlling skeleton patterning and cell differentiation are differentPatterning- Limb BonesBone Mandible Development1st arch prechondrogenic condensation in mouse embryoseveral skeletal elementsarise from a single condensation and persist for varying timeBoneBluecore component gives rise to Meckel‚Äôs cartilage (duration 12h)Brownrostral component forms symphyseal cartilage between two lower jaws (lasts 28h)Greencaudal component that lies across the mandibularhyoid arch boundary (dotted line), (lasts 30h)forms malleusRedmost caudal component (duration of 30h)forms incusPhases of DevelopmentCell Condensationkey stage in skeletal and mesenchymal tissue development Initially dispersed population of cellsgathers together to differentiate into a single cell/tissue typecartilage, bone, muscle, tendon, kidney, lung earliest stage during tissue formationwhen tissue specific genes are up-regulatedCell CondensationExtracellular matrix molecules, cell surface receptors and cell adhesion moleculesinitiate condensation formationset condensation boundariesfibronectin, tenascin, syndecan, and N-CAMHox genes (Hoxd-11-13) and other transcription factors (CFKH-1, MFH-1, osf-2)modulate the proliferation of cells within condensationsCell adhesion indirectly through Hox genes (Hoxa-2, Hoxd-13)directly via cell adhesion molecules (N-CAM and N-cadherin)Cell Condensation Growthregulated by BMPs which activatePax-2, Hoxa-2, Hoxd-11 and other genesceases when Noggin inhibits BMP signallingNext stage of skeletal developmentovert cell differentiationCondensation Formation GenesMesenchyme Condensationcondensation formation (blue) transition from condensation to overt differentiation (green arrow) condensation shown using peanut agglutinin lectinelevated levels of cyclic-AMP and major genes expressed at condensation stage (Pax-1, Pax-9, Sox-9)differentiating cartilage is visualised with Alcian bluemajor genes associated with five stages in condensationInitiate; Set Boundary; Proliferate; Adhere, GrowTwo pathways that stop condensation growth shown in yellow and redCessation of condensation leads to differentiation (green arrow), which involves both upregulation of genes to initiate differentiation and downregulation of genes to terminate condensation.Control of chondrocyte and osteoblast differentiationTranscription FactorsEarly transcription factorsSox9 Late transcription factors Cbfa1 and other factors promote differentiation of type II collagen expressing proliferating chondrocytes into pre-hypertrophic (pre-HC) cells expressing Indian hedgehog (Ihh) and PTH/PTHrP receptorIndian HedgehogIHH acts on Cells in perichondriumfavours production of PTHrPwhich inhibits chondrocyte hypertrophywhereas FGFs/FGFR3 antagonizes Ihh expressionBone collarinduces expression of Cbfa1triggering osteoblast differentiation chondrocytesOver-expression of Cbfa1 induces Ihh expressionHypertrophic Chondrocytes(HCs) secrete VEGFpromoting vascular invasionthen hypertrophic calcified cartilage becomes resorbed by recruited chondroclasts/osteoclasts via MMP9
• OsteoblastsOsteoblasts derived from the bone collarreplace cartilage matrix with a matrix rich in type I collagen leading to bone formationknown molecules affecting differentiation of pre-osteoblasts into osteoblastsHoxa2LeptinCuboidal osteoblastson newly formed bone as well as some osteocytes embedded in the bone matrixOsteoblast Development Cbfa1Yellow - activation domains Green - repression domainsGrey - Runt DNA-binding domain Q/A - glutamine/alanine repeatsPST - proline/serine/threonine-rich regionNLS - nuclear localization signalVWRPY - C-terminal repressor motifRegulation of Cbfa1 expressionRed- Transcription factorsBlue- secreted moleculesBrown- cofactorsGreen- ‚Äúmodifier complexes‚Äù Expression Level RegulationRed Arrows- (activation)blunted lines (repression)Functional Regulation green arrows (activation)blunted lines (repression)Cofactor binding is indicated by a black line.
• Osteoblast DevelopmentCbfa1expressionIn situ hybridization10.5 day mouse embryoArrows - primordia of shoulder bonetrachea (T) - low levels present
• Osteoblast DevelopmentCbfa1 and type II collagen expression14.5 day mouse embryoossifying ribs Cbfa1expressioncartilaginous structuresdo not express Cbfa1type II collagen expression
• Osteoblast Differentiationgenetic control of osteoblast differentiation and functionRed - Transcription factorsBlue - secreted moleculesBlack arrows - stimulatory or inhibitory roles of these moleculesGrey arrows - possible regulatory pathwaysMechanisms of Osteoclast Differentiation
• Leptin Role?bone remodelling thought to be mainly an autocrine-paracrine resorption mechanisms are under control of hormonessuggested this also may regulate bone formationmolecular endocrinology suggests a common central regulation via leptinbone formationbody weightreproduction
• Bone Morphogenic ProteinsFirst BMPs identified by ability to induce ectopic bone formation when implanted under skin of rodentsrecapitulation of all events occurring during skeletogenesisMore than 30 BMPs have been identifiedexpression pattern and analysis of spontaneously mutated or genetically depleted mice show a much broader range of functionactivities localized at sites of epithelial-mesenchymal interactionsincluding but not restricted to the skeleton
• Bone Morphogenetic Proteins BMPslarge family of cytokines related to members of transforming growth factor-beta superfamilyMouse - required for mesoderm formation and for development and patterning of many different organ systemsXenopus - role in gastrulation and neurulation in XenopusExtracellular modifiers of BMP activity may constitute an opposing morphogenetic system
• Endochondrial BoneIntramembranous BoneFgf and receptor expression
• Intramembranous BoneFgf and receptor expression

BMP2- Clinical StudiesImplantation of recombinant human BMP-2 (rhBMP-2) can augment alveolar ridge in animal models when placed in a periodontal environmentrestore new bone and attachment tissuesClinical studies support ability of rhBMP-2 implants to induce physiologic boneThe bone morphogenetic protein family: multifunctional cellular regulators in the embryo and adult. Wozney JM. Eur J Oral Sci. 1998 Jan;106 Suppl 1:160-6. ReviewPotential applications and delivery strategies for bone morphogenetic proteins. Kirker-Head CA. Adv Drug Deliv Rev. 2000 Sep 15;43(1):65-92. Review

Bone AbnormalitiesAbnormalitiesCongenital Hip DislocationInstability: 1:60 at birth; 1:240 at 1 wk: Dislocation untreated; 1:700congenital instability of hiplater dislocates by muscle pulls or gravityfamilial predisposition female predominanceGrowth of femoral head, acetabulum and innominate bone are delayed until the femoral head fits firmly into the acetabulumAbnormalities- Scoliosisassymetric growth impairment of vertebral bodieslateral deviation of spineLateral flexionForward flexionRotation of vertebral column on long axiscompensated by movement of vertebral column above and below affected region producing a primary and two secondary curvesprogresses rapidly in adolescencebecomes fixed once bone growth is completedHox2a KnockoutSynergistic Interactionsmouse skeleton (a)sternum (b)regions affected by short ear (se) and brachypodism (bp) mutationsSynergistic Interactionsse and bp mutationsaffect different parts of mouse skeletoncoloured red and blue, respectivelyse/se; bp/bp double mutants show the sum of individual phenotypes and also the sternum is affected (green)se and bp gene products, BMP5 and GDF5, respectively, have a synergistic effect in sternal developmentAbnormalities FGF receptors

References

Textbooks

• The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter Chapter 10 The Pharyngeal Apparatus pp201 - 240.
• Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 12 Development of the Head, the Neck, the Eyes, and the Ears pp349 - 418.

Online Textbooks

• Developmental Biology by Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000

• Molecular Biology of the Cell Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002 Search Molecular Biology of the CellBone Is Continually Remodeled by the Cells Within ItImage: Figure 22-52. Deposition of bone matrix by osteoblasts.Image: Figure 22-56. The development of a long bone.

Search

• Bookshelf neural crest

• Pubmed neural crest

UNSW Embryology Links

• Notes: Bone Development | Limb Development | Axial Skeleton Development | Bone Development | Skull | Development Limb | Axial Skeleton| Human Bone | Endochondral Ossification | Skeletal Muscle | Cartilage | Joints

• Lectures: ANAT2341 - Embryology 2008 - Lecture 16
• Movies: Neural Movies

External Links

• UWA Blue Histology Skeletal Tissues - Bone

• University of Kansas Histoweb Bone

• Loyola University Medical Education Network Part 9: Specialized Connective Tissue: Cartilage and Bone | Part 10: Endochondral Ossification

• UNSW Embryology Cartilage and Bone

Terms

annulus fibrosus - the circularly arranged fibers (derived from sclerotome)that together with the nucleus pulposus (derived from notochord) form the intervertebral disc (IVD) of the vertebral column.

axial mesoderm - (=notochord)

cartilage - connective tissue from mesoderm in the embryo forms the initial skeleton which is replaced by bone. In adult, found on surface of bone joints.

centrum - the primordium of the [#vertebral body vertebral body] formed initially by the sclerotome.

clavicle - (L. little key) bone which locks sholder to body.

cloacal membrane- at caudal (anal) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet forms the openings for GIT, urinary, reproductive tracts. (see also [#buccopharyngeal membrane buccopharyngeal membrane])

connective tissue-

costotransverse -

costovertebral -

dermatome -

dermomyotome - dorsolateral half of each somite that forms the dermis and muscle.

ectoderm - the layer (of the 3 germ cell layers) which form the nervous system from the neural tube and neural crest and also generates the epithelia covering the embryo.

endochondrial ossification - the process of replacement of the cartilagenous framework by osteoblasts with bone.

epaxial myotome - the dorsal portion of the myotome that generates dorsal skeletal muscles (epaxial muscles).

erector spinae -

extracellular matrix - material secreted by and surrounding cells. Consists if fibers and ground substance.

fibroblast growth factors - (FGF) a family of at least 10 secreted proteins that bind membrane tyrosine kinase receptors. A patterning switch with many different roles in different tissues. (FGF8 = androgen-induced growth factor (AIGF)

fibroblast growth factor receptor - receptors comprise a family of at least 4 related but individually distinct tyrosine kinase receptors (FGFR1- 4). They have a similar protein structure, with 3 immunoglobulin-like domains in the extracellular region, a single membrane spanning segment, and a cytoplasmic tyrosine kinase domain.

growth factor - usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway. The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg shh)

hox - (=homeobox) family of transcription factors that bind DNA and activate gene expression. Expression of different Hox genes along neural tube defines rostral-caudal axis and segmental levels.

hypaxial myotome - the ventral portion of the myotome that generates ventral skeletal muscles (hypaxial muscles).

intercostal- the region between adjacent ribs, usually comprising intercostal muscles and connective tissue.

intervertebral disc- (IVD) the annulus fibrosus+nucleus pulposus together form the intervertebral disc (IVD) of the vertebral column. This is the flexible region between each bony vertebra that allows the column to be bent.

intervertebral foramina-

lumbar plexus - mixed spinal nerves innervating the lower limb form a complex meshwork (crossing).

mesoderm - the middle layer of the 3 germ cell layers of the embryo. Mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm.

myoblast - the undifferentiated mononucleated muscle cells that will fuse together to form a multinucleated myotube, then mature into a muscle fibre.

MyoD - transcription factor involved in the determination of muscle cells in the somite. A basic helix-loop-helix factor which binds DNA.

myotome - the portion of the dermamyotome that generates skeletal muscle. Has 2 components epaxial (dorsal muscles ) hypaxial (ventral muscles).

neural crest - cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types(=pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG). Neural crest cells migrate into the somites.

osteoblast - The mesenchymal cells that differentiate to form the cellular component of bone and produce bone matrix. Mature osteoblasts are called osteocytes. (More? Musculoskeletal Development - Bone)

osteoclast - Cells that remove bone (bone resorption) by enzymatically eroding the bone matrix. These cells are monocyte-macrophage in origin and fuse to form a multinucleated osteoclast. These cells allow continuous bone remodelling and are also involved in calcium and phosphate metabolism. The erosion cavity that the cells lie iwithin and form is called Howship's lacuna. (More? Musculoskeletal Development - Bone)

osteocyte - The mature bone-forming cell, which form the cellular component of bone and produce bone matrix. Differentiate from osteoblasts, mesenchymal cells that differentiate to form bone. (More? Musculoskeletal Development - Bone)

osteon - The anatomical (histological) unit structure (principal structure) of compact bone. (More? Musculoskeletal Development - Bone)

Pax - name derived from Drosophila gene 'paired' (prd) the 'paired box' is a amino end 124 amino-acid conserved domain (signature aa 35-51: P-C-x(11)-C-V-S). Transcription factor of the helix-turn-helix structural family, DNA binding, and activating gene expression. In human, nine member proteins from Pax-1 to Pax-9. Regulate differentiation of many different tissues. Some members of the family (PAX3, PAX4, PAX6, PAX7) also contain a functional homeobox domain.

pedicle -

primary centre of ossification - the first area where bone growth occurs between the periosteum and cartilage.

sacrum -

sclerotome - ventromedial half of each somite that forms the vertebral body and intervertebral disc.

segmentation - to break a solid structure into a number of usually equal size pieces.

somatic mesoderm - derived from lateral mesoderm closest to the ectoderm and separated from other component of lateral mesoderm (splanchnic, near endoderm) by the intraembryonic coelom.

somite - segmental block (ball) of mesoderm formed from paraxial mesoderm adjacent to notochord (axial mesoderm). Differentiates to form initially sclerotome and dermamyotome (then dermotome and myotome).

somitic mesoderm-

somitocoel - a transient cavity that appears within each of the the early forming somites then is lost.

somitogenesis - the process of segmentation of the paraxial mesoderm to form "mesoderm balls" beginning cranially (humans day20) and extending caudally at 1 somite/90 minutes until approx. 44 pairs have been formed.

sonic hedgehog - (=shh) secreted growth factor that binds patched (ptc) receptor on cell membrane. SHH function is different for different tissues in the embryo. In the nervous system, it is secreted by the notochord, ventralizes the neural tube, inducing the floor plate and motor neurons. In the Limb it is secreted by the zone of polarizing activity (ZPA) organizing limb axis formation.

tarsal -

Tbx - T-box genes (transcription factor) involved in mouse forelimb (Tbx4) and hindlimb (Tbx5) specification.

transcription factor- a factor (protein or protein with steroid) that binds to DNA to alter gene expression, usually to activate. (eg steroid hormone+receptor, Retinoic acid+Receptor, Hox, Pax, Lim, Nkx-2.2).

transverse abdominal m.-

trochanter-

vertebral body- formed by centrum, vertebral arch, facets for ribs. It is the mature vertebral structure formed by the 5 secondary ossification centers after puberty.

vertebral column - name given to the complete structure formed from the alternating segments of vertebra and intervertebral discs which support the spinal cord.

vertebral foramen - the dorsal cavity within each vertebra, generated by the vertebral arch that surrounds the spinal cord.

vertebral canal -

Wnt7a - The designation 'Wnt' was derived from 'wingless' and 'int'. The Wnt gene was first defined as a protooncogene, int1. Humans have at least 4 Wnt genes: Wnt7a gene is at 3p25 encoding a 349aa secreted glycoprotein. A patterning switch with different roles in different tissues. The mechanism of Wnt distribution (free diffusion, restricted diffusion and active transport) and all its possible cell receptors are still being determined. At least one WNT receptor is Frizzled (FZD). The Frizzled gene family encodes a seven-transmembrane receptor.

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

Course Content 2009

Embryology Introduction | Cell Division/Fertilization | Cell Division/Fertilization | Week 1&2 Development | Week 3 Development | Lab 2 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Lab 3 | Early Vascular Development | Placenta | Lab 4 | Endoderm, Early Gastrointestinal | Respiratory Development | Lab 5 | Head Development | Neural Crest Development | Lab 6 | Musculoskeletal Development | Limb Development | Lab 7 | Kidney | Genital | Lab 8 | Sensory - Ear | Integumentary | Lab 9 | Sensory - Eye | Endocrine | Lab 10 | Late Vascular Development | Fetal | Lab 11 | Birth, Postnatal | Revision | Lab 12 | Lecture Audio | Course Timetable

---

Cite this page: Hill, M.A. (2024, May 6) Embryology 2009 Lecture 13. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_13

What Links Here?

© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G