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

Embryo stage 14 SEM

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

Online References

UNSW Embryology Limb Development
Embryo Images Limb Unit
International J. Dev. Biology Vol 46 Special Issue- Limb Development 2002

Glossary Links

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Course Content 2009

Cite this page: Hill, M.A. (2024, May 2) Embryology 2009 Lecture 14. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_14

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