ANAT1006- Embryology © Dr Mark Hill, 1999. These are notes from Dr Mark Hill's Introduction to Embryology. A series of 7 Lectures with associated Practical Classes. Below are the Text headings from slides used in the Lecture. The references at the bottom are for interest only, and were used in preparing the lecture. There is also an Acrobat version of the Lecture slides available for viewing or printing, not all slides are present (please read disclaimer). For a comprehensive background in Embryology look at the UNSW Embryo Program available on the Web. This Page: Text headings | References | OMIM | Search Medline | Links | Human Genes | disclaimer | About Acrobat Dr Mark Hill (room G20) Related Pages: UNSW Embryo Program | Exam Announcement | Musculoskeletal dev | musculoskeletal abnormalities | histology | Syndactyly | Congenital Hip Dislocation | musculoskeletal links | Scoliosis | Muscular Dystrophies | antennapedia ANAT1006 Practical Class week 7 stage 13/14 | stage 22 | high power stage 22 Email: m.hill@unsw.edu.au Click here for Acrobat version of slides. Lecture 4 (2.1 Mb) Click here for Acrobat version of this page. Lecture 4htm (50 Kb) Next notes: Lecture 5 Pharynx and Face

Lecture 7- Development of the Musculoskeletal System Muscle and Limbs Embryology Lectures Overview Embryology Lecture 4- Fertilization and Early Development Lecture 5- Early Development 2 Lecture 6- Development of the Nervous System Lecture 7- Musculoskeletal Development -----Break-------------------------------------------- Lecture 10- Pharynx and Face Lecture 12- Angiogenesis and Blood (E & H) Lecture 13- Placenta (E & H) Lecture 4 Overview Musculoskeletal Development axial process mesoderm patitioning and segmentation adult mesoderm products paraxial mesoderm forming somites products of somites limb formation axes Trilaminar Embryo- Axial Process Mesoderm generated from epiblast cells migrating through the primitive streak epiblast cells expressing FGF2(fibroblast growth factor) forms a mesenchymal layer between ectoderm and endoderm with notochord down midline present before neural tube formation divides initially into 3 components paraxial intermediate lateral Intermediate Mesoderm lies between paraxial and lateral mesoderm generates urogenital system Wolffian duct, kidney Lateral Plate Mesoderm intraembryonic coelom divides into 2 parts (day 18-19) Intraembryonic coelom forms 3 body cavities- pericardial, pleural, peritoneal Splanchnic generates heart and smooth muscle of GIT and blood vessels Somatic generates body wall osteogenic, chrondrogenic and fibrogenic except ribs and scapula Mesoderm Paraxial Mesoderm lies adjacent to notochord forms 2 components Head-unsegmented paraxial mesoderm Body- segmented paraxial mesoderm generates trunk muscles, skeleton, dermis of skin, blood vessels, connective tissue Segmented paraxial mesoderm segments called somites first pair of somites (day 20) segmentaion imposes a pattern on nerves, vasculature, vertebra.... somites appear in ordered sequence from cranial to caudal appearance so regular used to stage the embryo Hamburger & Hamilton 1951- chicken thought to be generated by a "clock" probably Notch (Drosophila equivilant clock- Hairy) 1 pair every 90 minutes neural tube begins to close at 4th somite level 44 pairs of somites this number can vary Paraxial Segmentation Stage 13/14 Embryo Somites ball forms through epithelialization and interactions cell-cell cell-extracellular matrix (ECM) fibronectin, laminin has 2 populations of cells peripheral columnar central mesenchymal early somite has cavity- somitocoel cavity is lost will contribute to sclerotome entire ball 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 Axial Specification rostro-caudal axis appears regulated by Pax/Hox expression Family of DNA binding transcription factors Somite Differentiation Compartmentalization is accompanied by altered patterns of expression of Pax genes within the somite. forms 2 main components ventral- sclerotome forms vertebral body and intervertebral disc dorsal- dermomyotome forms dermis and skeletal muscle Sclerotome The sclerotome later becomes subdivided into rostral and caudal halves which are separated laterally by von Ebner's fissure. half somites contribute to a single vertebral level body other half intervertebral disc Muscle MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed. MyoD (myoblast determining bHLH, transcription factor) from myotome dorsomedial quarter- epaxial myotome dorsal epimere (erector spinae) dorsolateral quarter- hypaxial myotome ventral hypomere (3 primary muscle layers) different at neck, thorax and abdomen table of muscles on web page Dermomyotome- Muscle (MyoD) MyoD Pax3 Somite Differentiation migrating neural crest cells enter cranial half will form DRG sclerotome bulges ventromedially towards notochord then surround and engulf notochord not movement of sclerotome, growth of surrounding tissues notochord forming nucleus pulposus of IVD Dermomyotome lateral myotome edge migrates at level of limbs upper limb first then lower mixes with somatic mesoderm dermotome continues to contribute cells to myotome Limb Development forelimbs and hindlimbs are different mid-4th week Human upper limb buds, lower limbs 2 days later upper limbs C5-C8 lower limbs L3-L5 Mesenchyme with ectodermal covering blood vessels forming Apical ectodermal ridge (AER) at tip of bud majority of mitosis just deep to AER progress zone 5th week hand- and footplates ridges form digital rays cell death (apoptosis) removes cells between digits Limbs Stage 20-23 Foot Development Limb Rotation 8th week limbs rotate thumb and toe rostral knee and elbow face outward upper limb rotates dorsally lower limb rotates ventrally Limb Bone endochondrial ossification begins Carnegie stage 18 throughout embryo replacement of cartilage with bone (week 5-12) will be discussed in detail in another lecture Limb Initiation FGF beads can induce additional limb formation 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 activate FGF expression Limb Specification (Fore- Hind-) regulated by T-box genes (transcription factor) Tbx5- forelimb Tbx4 - leg Limb Patterning- Axes Wing as Model chick wing easy to manipulate removal grafting additional ARER, ZPA etc Limb Patterning- Axes Proximodistal Axis AER formed by Wnt7a then AER secretes FGF2, 4, 8 stimulates proliferation and outgrowth Dorsoventral Axis somite provides dorsal signal to mesenchyme which dorsalizes ectoderm ectoderm then signals back (Wnt7a) to mesenchyme to pattern limb Anteroposterior Axis ZPA zone of polarizing activity mesenchymal posterior region of limb addition of extra ZPA duplicated digits signal is Shh Limb Axes Limb Patterning- Axes Signals give positional information which is interpreted by Hox gene expression establishing programs of differentiation. Proximodistal Axis Dorsoventral Axis Anteroposterior Axis Stage 13/14 Forelimb Muscles Limb Development Abnormalities Human Gene Mutations mutation of any of the patterning genes will result in limb abnormalities Will put Table on Web page mutations and terminology Example- Type II syndactyly- HoxD13 musculoskeletal abnormalities | Syndactyly | Congenital Hip Dislocation | Scoliosis Maternal thalidomide Phocomelia short ill-formed upper or lower limbs hyperthermia Muscle Development Abnormalities Muscular Dystrophies Duchenne Muscular Dystrophy X-linked dystrophy large gene encoding cytoskeletal protein- Dystrophin progressive wasting of muscle die late teens Becker Musckular Dystrophy milder form adult onset top of page

Terms (not yet complete) alar plate- afferent, dorsal horns anlage- (Ger. ) primordium, structure or cells which will form a future structure. apical ectodermal ridge- (=AER) basal plate- efferent, ventral horns. brachial plexus- mixed spinal nerves innervating the upper limb form a complex meshwork (crossing). brain- general term for the central nervous system formed from 3 primary vesicles. buccopharyngeal membrane- (=oral membrane) at cranial (mouth) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet. (see also cloacal membrane) 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) connective tissue- dermomyotome- dorsolateral half of each somite that forms the dermis and muscle. dorsal root ganglia- (=spinal ganglia) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord. dura mater- 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. endoderm- the layer (of the 3 germ cell layers) which form the epithelial lining of the gastrointestinal tract (GIT) and accessory organs of GIT in the embryo. epiblast- the layer (of the bilaminar embryo) that generates endoderm and mesoderm by migration of cells through the primitive streak. The remaing cells form ectoderm. 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. 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. muscle- 3 main types of muscle (smooth, cardiac and skeletal) all derived from mesoderm but different regions. myotome- myoblast- 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. neural tube- neural plate region of ectoderm pinched off to form hollow ectodermal tube above notochord in mesoderm. neuropore- opening at either end of neural tube: cranial=rostral=anterior, caudal=posterior. The cranial neuropore closes (day 25) approx. 2 days (human) before caudal. notochord- rod of cells lying in mesoderm layer ventral to the neural tube, induces neural tube and secretes sonic hedgehog which "ventralizes" the neural tube and may influence somite development. otocyst- (=otic vesicle) sensory placode which sinks into mesoderm to form spherical vesicle (stage 13/14 embryo) that will form components of the inner ear. pharyngeal arches- (=branchial arches, Gk. gill) form structures of the head. Six arches form but only 4 form any structures. Each arch has a pouch, membrane and cleft. pharynx- uppermost end of GIT, beginning at the buccopharyngeal membrane and at the level of the pharyngeal arches. sclerotome- ventromedial half of each somite that forms the vertebral body and intervertebral disc. segmentation- spinal cord- caudal end of neural tube that does not contribute to brain. Note: the process of secondary neuralation contributes the caudal end of the spinal cord. spinal ganglia- (=dorsal root ganglia, drg) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord. spinal nerve- mixed nerve (motor and sensory) arising as lateral pairs at each vertebral segmental level. somatic mesoderm- somite- somitic mesoderm- somitocoel- somitogenesis- 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. 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) top of page

top of page

References Recent Limb Development Reviews Johnson RL, et al.           [See Related Articles] Molecular models for vertebrate limb development. Cell. 1997 Sep 19;90(6):979-90. Review. No abstract available. PMID: 9323126; UI: 97462899. Graham A, et al.           [See Related Articles] Limb development: Farewell to arms. Curr Biol. 1999 May 20;9(10):R368-70. Review. PMID: 10339420; UI: 99272754. Cell Tissue Res. on Limb Development. April 1999 MH- yummy, a whole issue of all the latest in limb development, with wonderful pictures. In the UNSW Biomed library. Buscher D, et al.           [See Related Articles] Muscle development during vertebrate limb outgrowth. Cell Tissue Res. 1999 Apr;296(1):131-9. Review. Fernandez-Teran M, et al.           [See Related Articles] The recombinant limb as a model for the study of limb patterning, and its application to muscle development. Cell Tissue Res. 1999 Apr;296(1):121-9. Review. PMID: 10199972; UI: 99216345. Theil T, et al.           [See Related Articles] Gli genes and limb development. Cell Tissue Res. 1999 Apr;296(1):75-83. Review. PMID: 10199967; UI: 99216340. Xu X, et al.           [See Related Articles] Fibroblast growth factor receptors (FGFRs) and their roles in limb development. Cell Tissue Res. 1999 Apr;296(1):33-43. Review. PMID: 10199963; UI: 99216336. Cohn MJ, et al.           [See Related Articles] Molecular control of vertebrate limb development, evolution and congenital malformations. Cell Tissue Res. 1999 Apr;296(1):3-17. Review. PMID: 10199960; UI: 99216333. Brand-Saberi B, et al.           [See Related Articles] Genetic and epigenetic control of muscle development in vertebrates. Cell Tissue Res. 1999 Apr;296(1):199-212. Review. PMID: 10199980; UI: 99216353. Dietrich S.           [See Related Articles] Regulation of hypaxial muscle development. Cell Tissue Res. 1999 Apr;296(1):175-82. Review. PMID: 10199977; UI: 99216350. Kalcheim C, et al.           [See Related Articles] Myotome formation: a multistage process. Cell Tissue Res. 1999 Apr;296(1):161-73. Review. PMID: 10199976; UI: 99216349. Blagden CS, et al.           [See Related Articles] Extrinsic influences on limb muscle organisation. Cell Tissue Res. 1999 Apr;296(1):141-50. Review. PMID: 10199974; UI: 99216347. Ng JK, et al.           [See Related Articles] Molecular and cellular basis of pattern formation during vertebrate limb development. Curr Top Dev Biol. 1999;41:37-66. Review. PMID: 9784972; UI: 99001151. Bamshad M, et al.           [See Related Articles] Reconstructing the history of human limb development: lessons from birth defects. Pediatr Res. 1999 Mar;45(3):291-9. Review. PMID: 10088644; UI: 99186505. Kosher RA.           [See Related Articles] Syndecan-3 in limb skeletal development. Microsc Res Tech. 1998 Oct 15;43(2):123-30. Review. PMID: 9822999; UI: 99040333. Wolpert L.           [See Related Articles] Pattern formation in epithelial development: the vertebrate limb and feather bud spacing. Philos Trans R Soc Lond B Biol Sci. 1998 Jun 29;353(1370):871-5. Review. PMID: 9684284; UI: 98348909. Innis JW, et al.           [See Related Articles] Limb development: molecular dysmorphology is at hand!Clin Genet. 1998 May;53(5):337-48. Review. PMID: 9660051; UI: 98321488. Zou H, et al.           [See Related Articles] BMP signaling and vertebrate limb development. Cold Spring Harb Symp Quant Biol. 1997;62:269-72. Review. No abstract available. PMID: 9598360; UI: 98260722. Zguricas J, et al.           [See Related Articles] Genetics of limb development and congenital hand malformations. Plast Reconstr Surg. 1998 Apr;101(4):1126-35. Review. PMID: 9514351; UI: 98173286. Irvine KD, et al.           [See Related Articles] Dorsal-ventral signaling in limb development. Curr Opin Cell Biol. 1997 Dec;9(6):867-76. Review. PMID: 9425353; UI: 98086468. Niswander L.           [See Related Articles] Limb mutants: what can they tell us about normal limb development? Curr Opin Genet Dev. 1997 Aug;7(4):530-6. Review. PMID: 9309186; UI: 97454724. Robertson KE, et al.           [See Related Articles] Recent molecular advances in understanding vertebrate limb development. Br J Plast Surg. 1997 Feb;50(2):109-15. Review. PMID: 9135427; UI: 97281119. Burke R, et al.           [See Related Articles] Hedgehog signaling in Drosophila eye and limb development - conserved machinery, divergent roles? Curr Opin Neurobiol. 1997 Feb;7(1):55-61. Review. PMID: 9039793; UI: 97192274. Niswander L.           [See Related Articles] Growth factor interactions in limb development. Ann N Y Acad Sci. 1996 Jun 8;785:23-6. Review. No abstract available. PMID: 8702137; UI: 96280879. Thaller C, et al.           [See Related Articles] Retinoid signaling in vertebrate limb development. Ann N Y Acad Sci. 1996 Jun 8;785:1-11. Review. No abstract available. PMID: 8702114; UI: 96280877. Newman SA.           [See Related Articles] Sticky fingers: Hox genes and cell adhesion in vertebrate limb development. Bioessays. 1996 Mar;18(3):171-4. Review. PMID: 8867729; UI: 97021369. Recent Sonic Hedgehog Articles/Reviews Levin M. [See Related Articles] Left-right asymmetry in vertebrate embryogenesis. Bioessays. 1997 Apr;19(4):287-96. Review. Marigo V, et al. [See Related Articles] Biochemical evidence that patched is the Hedgehog receptor. Nature. 1996 Nov 14;384(6605):176-9. Marigo V, et al. [See Related Articles] Regulation of patched by sonic hedgehog in the developing neural tube. Proc Natl Acad Sci U S A. 1996 Sep 3;93(18):9346-51. Roessler E, et al. [See Related Articles] Mutations in the human Sonic Hedgehog gene cause holoprosencephaly. Nat Genet. 1996 Nov;14(3):357-60. Recent Clinical Articles  Pruitt SD, et al.           [See Related Articles] Functional status in limb deficiency: development of an outcome measure for preschool children. Arch Phys Med Rehabil. 1998 Apr;79(4):405-11. PMID: 9552106; UI: 98211833. Cohn MJ, et al.           [See Related Articles] Molecular control of vertebrate limb development, evolution and congenital malformations. Cell Tissue Res. 1999 Apr;296(1):3-17. Review. PMID: 10199960; UI: 99216333. UNSW Embryo References Somite Reviews Somitogenesis Abstracts Mesoderm Review List top of page

OMIM Human Genetic Diseases Syndactyly List Syndactyly I Syndactyly II Syndactyly III Syndactyly IV Syndactyly V Myotonic Dystrophy Congenital Hip Dislocation Congenital Hip Dislocation List Scoliosis List Arthrogryposis

Medline Searches Clicking below will perform a new search of Medline with the listed text. sonic+hedgehog[TITL] congenital+dislocation+hip[TITL] arthrogryposis[TITL] syndactyly[TITL] scoliosis[TITL] duchenne+muscular+dystrophy[TITL] autosomal+recessive+muscular+dystrophy[TITL]

WWWLinks UNSW Embryo UNSW Embryo Program | musculoskeletal dev | musculoskeletal abnormalities | histology | Syndactyly | Congenital Hip Dislocation | musculoskeletal links | Scoliosis | Muscular Dystrophies | antennapedia | NCBI- Muscle Overview | NCBI- Myotonic Dystrophy | NCBI- Marfan Syndrome Australian Statistics 1981-1992 ANAT1006 Practical Class week 7 stage 13/14 | stage 22 | high power stage 22 Human Genes notch | delta | sonic hedgehog | homeobox | lim | dystrophin | fgf NCBI Genes and Disease Muscle Overview Myotonic Dystrophy Nobel Prize for Medicine 1995 Illustrated presentation Consequences of discovery

Disclaimer The Acrobat document does not contain all slides from lecture, copyright does not allow the republishing of some commercial and/or research images. The document is for educational purposes and personal use only and should not be reproduced for other purposes. This document and attached pages © Dr M. Hill, 1999. top of page

About Acrobat Some information is available as PDF documents (electronic paper) that appears on the screen as it would appear on paper. These documents can also be printed out. A WWW plug-in is needed to view the document within a WWW Browser and/or a free PDF reader to open the downloaded document. Both plug-in and reader are available free from this site. Also availalable from Locally. top of page

m.hill@unsw.edu.au Date Last Modified: 9/9/99 This site maintained by Dr M. Hill