2009 Lecture 14
Limb Development
Introduction
This lecture is an introduction to the events in limb development. Initially somites develop and then begin to differentiate forming sclerotome, dermomyotome and then dermatome and myotome. The lateral portion of the hypaxial myotome edge migrates at level of limbs (upper limb first then lower) and mixes with somatic mesoderm. Meanwhile the dermotome continues to contribute cells to myotome.
The appendicular skeleton consists of: Shoulder girdle, Upper limb (arm, hand), Pelvic girdle, Lower limb (leg, foot).
UNSW Embryology Limb Development | Limb Abnormalities 2008 Lecture 2008 Lecture | 1 slide/page | 4 slide/page | 6 slide/page
Lecture Objectives
- Understanding of limb positioning
- Understanding of differences in developmental timing of upper and lower limbs
- Understanding of regions and factors determining limb axes
- Understanding of limb rotation
- Understanding of limb muscle, blood vessel, bone and nerve formation
- Brief understanding of limb molecular factors
- Brief understanding of limb 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 Development
- Before we Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
- Essentials of Human Embryology Larson Ch11 p207-228
Limb Buds
- Limbs are initially undifferentiated mesenchyme (mesoderm) with an epithelial (ectoderm) covering.
- Blood vessels then begin forming, the largest (marginal vein) is adjacent to tip of the limbbud.
Upper and Lower Limb
Limb development occurs at different times for forelimbs and hindlimbs. In the mid-4th week, human upper limb buds first form and lower limbs about 2 days later. The limbs form at vertebra segmental levels C5-C8 (upper limbs) L3-L5 (lower limbs).
Limb Axis Formation
Four Concepts
- Limb Initiation
- Proximodistal Axis
- Dorsoventral Axis
- Anteroposterior Axis
Limb Initiation
- 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
T-box genes shown in mice to specify future limb identity
- forelimb =Tbx4
- hindlimb=Tbx5
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
Apical Ectodermal Ridge
Wing as Limb Model - chicken wing easy to manipulate, Removal and addition, Grafting additional AER, ZPA
Online References
- UNSW Embryology Limb Development
- Embryo Images Limb Unit
- International J. Dev. Biology Vol 46 Special Issue- Limb Development 2002
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, June 18) Embryology 2009 Lecture 14. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_14
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G