UNSW Embryology

Integumentary Development

© Dr Mark Hill (2008)

Acknowledgements

Introduction

The integumentary system covers the surface of the embryo (skin) and its specialized skin structures including hair, nails, sweat glands, mammary glands and teeth. As a system it has contributions from all embryonic layers.

Prospective epidermal cells expressing a cytokeratin gene (green) (Image- Lance Davidson)	Epidermis, dermis, hypodermis, hair follicles and associated glands

Ectoderm forms the surface epidermis and the associated glands. Mesoderm forms the underlying connective tissue of dermis and hypodermis. Neural crest cells also migrate into the forming epidermis and the skin is also populated by specialized sensory endings. There is a detailed developmental overview of all these specific structures.

A recent paper has established a new model for adult epidermal maintenance involving only a single progenitor cell (More? Adult Epidermal Stem Cells).

Page Links: Introduction | Reading | Computer Activities | Objectives | Learning activities | Development Overview | Adult Epidermal Stem Cells | Terms | References

Some Recent Findings

Clayton E, Doupe DP, Klein AM, Winton DJ, Simons BD, Jones PH. A single type of progenitor cell maintains normal epidermis. Nature. 2007 Mar 8;446(7132):185-9. (MRC - Phil Jones Laboratory)

"According to the current model of adult epidermal homeostasis, skin tissue is maintained by two discrete populations of progenitor cells. ...Here we show that clone-size distributions are consistent with a new model of homeostasis involving only one type of progenitor cell. These cells are found to undergo both symmetric and asymmetric division at rates that ensure epidermal homeostasis."

Nature - Milestones in Cutaneous Biology

"Milestones in Cutaneous Biology highlights groundbreaking advances in cutaneous biology over the past 100 years. Since the skin has proven important for researchers in epidermal and dermal structural proteins, cell differentiation, vascular and tumor biology, autoimmunity, photobiology, and the detailed mechanisms and pathophysiology of hundreds of genetic diseases, this subject appeals to a broad audience of biological researchers"

M. Sieber-Blum, M. Grim, Y.F. Hu, V. Szeder Pluripotent neural crest stem cells in the adult hair follicle. Dev Dyn. 2004 Oct;231(2):258-69.

...the adult mouse whisker follicle contains pluripotent neural crest stem cells, termed epidermal neural crest cells (eNCSC)."

Reading

• Human Embryology (2nd ed.) Larson Chapter 14 p443-455
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch20: P513-529
• Before We Are Born (5th ed.) Moore and Persaud Ch21: P481-496
• Essentials of Human Embryology Larson Ch14: P303-315
• Human Embryology, Fitzgerald and Fitzgerald
• Color Atlas of Clinical Embryology Moore Persaud and Shiota Ch15: p231-236
• Selected References- Hair development

Objectives

• Understand the differentiation of the epidermis and dermis.
• Understand the formation of hair and nails.
• Understand the formation of sweat glands, mammary glands.
• Understand the formation of teeth.

Computer Activities

UNSW Embryology:

• Detailed Overview of Skin components
• Teeth Development
• Skin Histology
• Selected references (1999)
  • development of Hair
  • development of Teeth

Embryo Images Unit:

Unit: Limb Development (nails)

Human Embryology Movies:

Video

Learning activities

• Revise the histology structure of the skin and the embryological origin of the layers.
• Describe the neural crest contribution to the skin.
• Compare the origin, types and structure of skin glands formation.
• Review the postnatal puberty endocrine regulation of mammary gland maturation.
• Review the prenatal and postnatal formation of the teeth.

Development Overview

• Ectoderm and Mesoderm Origin

4 weeks

• simple ectoderm epithelium over mesenchyme.

1-3 months

• ectoderm- germinative (basal) cell repeated division of generates stratified epithelium.
• mesoderm- differentiates into connective tissue and blood vessels.

4 months

• basal cell- proliferation generates folds in basement membrane.
• neural crest cells- (melanocytes) migrate into epithelium. These are the pigment cell of the skin.
• embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer.
• Ectoderm contributes to nails, hair follictles and glands.
• Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field.
• Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous and sweat glands.

5 months

• Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands.
• Other cords elongate and coil to form sweat glands.
• Cords in mammary region branch as they elongate to form mammary glands. These glands will complete development in females at puberty. Functional maturity only occurs in late pregnancy.

 

More detailed Overview? of other Integumentary Structures

Adult Epidermal Stem Cells

The following information is from a recent study on mouse skin using a single cell labelling system with longitudinal tracing and confocal imaging.

Organization of the epidermis. Hair follicles contain stem cells located in the bulge (b, green), with the potential to generate lower hair follicle (lf), sebaceous gland (sg, orange) upper follicle (uf) and interfollicular epidermis (IFE, beige). The schematic shows the organization of keratinocytes in the IFE, as proposed by the stem/TA cell hypothesis. The basal layer comprises stem cells (S, blue), transit amplifying cells (TA, dark green), and post-mitotic basal cells (red), which migrate out of the basal layer as they differentiate (arrows).

Projected Z-stack confocal images of IFE wholemounts from AhcreERT R26EYFP/wt mice viewed from the basal surface at the times shown following induction. Yellow, EYFP; blue, DAPI nuclear stain. Scale bar, 20 microns.

Reprinted by permission from Macmillan Publishers Ltd: Nature. 2007 Mar 8;446(7132):185-9, copyright (2007)

Clayton E, Doupe DP, Klein AM, Winton DJ, Simons BD, Jones PH. A single type of progenitor cell maintains normal epidermis. Nature. 2007 Mar 8;446(7132):185-9. (MRC - Phil Jones Laboratory)

"According to the current model of adult epidermal homeostasis, skin tissue is maintained by two discrete populations of progenitor cells. ...Here we show that clone-size distributions are consistent with a new model of homeostasis involving only one type of progenitor cell. These cells are found to undergo both symmetric and asymmetric division at rates that ensure epidermal homeostasis."

References

Reviews

An entire recent issue of International Journal of Developmental Biology on Skin Development Int. J. Dev. Biol. 48:(2004) "Half a century of research into the developmental biology of the integument"

PubMed

Search PubMed Now: term=skin+development | term=hair+development | term=tooth+development | (Requires internet connection)

1999 Reference Lists

Requires no internet connection. Selected Lists of References from PubMed March 1999 search results are available for Department of Anatomy computers without internet access. Computers with internet access can search from either Page 2 or PubMed Internet Access

• Selected references development of Hair
• Selected references development of Teeth
• Selected Research Articles and Reviews

Glossary of Terms

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

Quick Links

Integumentary Development Pages:

Abnormalities | Stage 13/14 | Stage 22 | Histology | Dermatomes | Glands | Mammary Glands | Teeth | Hair | Nails | Keratin | Overview |

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G