UNSW Embryology

Week 4

© Dr Mark Hill (2008)

Acknowledgements

Introduction

These notes cover the fourth week of embryonic development, which is the beginning of organogenesis, (specific tissues and systems are beginning to differentiate) from the trilaminar embryo. On the embryo surface sensory placodes and limb buds appear. Sensory placodes (otic, lens, nasal) will form specific components of the ear, eye and nose. Limb buds form from ectoderm and mesoderm (somite) components and are the "paddle-like" projections from the trunk which will form all the upper and lower limb components. Within the embryo, this period of organogensis is usually extended to cover until 8 weeks of development. Folding of the embryo continues and the earliest functioning organ is the heart. Other systems such as the circulatory, digestive, urogenital and nervous system begin to all take shape. As systems are beginning to develop, each page in this section is only a brief summary with additional links to specific notes covering these systems/tissues. Note that most tissue development during week 4 are covered in System Development notes.

Embryo Development Week 4 (Carnegie stage 10) (Carnegie stage 13)

Page Links: Introduction | Some Recent Findings | Reading | Objectives | Computer Activities | Development Overview | Molecular Factors | References | Glossary

Related Pages: Placodes | Somite Development | Early Nervous | Early Heart | Abnormalities | Developmental Mechanisms | Epithelial Mesenchymal Transition | Molecular Development | References | Text only page | WWW Links |

Some Recent Findings

Sweetman D, Wagstaff L, Cooper O, Weijer C, Munsterberg A. The migration of paraxial and lateral plate mesoderm cells emerging from the late primitive streak is controlled by different Wnt signals. BMC Dev Biol. 2008 Jun 9;8(1):63.

"...we use long-term video microscopy in chicken embryos to visualize the migration routes and movement behaviour of mesoderm progenitor cells as they emerge from the primitive streak (PS) between HH stages 7 and 10."

Objectives

Understand the ectodermal development of the Sensory Placodes and the structures they form in sensory organs. Understand the mesodermal development of the Somites and the structures that they contribute. Understand the neural tube and neural crest contribution to development of the Early Nervous System. Understand how Abnormalities may develop from errors in folding, somite differentiation, neural crest migration, or closure of neural pores.

Learning Activities

• Work through the Carnegie stages (10-13) covering this period of development.
• Note the extensive changes in the external appearance of the embryo, due mainy to continued folding and growth.
• Begin to look at the specific system development listed below
• Musculoskeletal- somites
• Neural- neural tube
• Cardiovascular- heart development, placenta

Computer Activities

UNSW Embryology: Abnormalities | Sensory Placodes | Somite Development | Early Nervous System | 16 to 19Images - mesoderm and body cavities | 20 to 23Images - the yolk sac and gut formation | 24 to 25Images - mesoderm differentiation | 26 to 30Images - early placentation and fetal membranes | 31 to 34Images- placenta and cord

Embryo Images Online: Early Cell Populations and Establishment of Body Form | Neurulation (Week 4) | Form Changes, Gastrulation Continued and Neural Tube Closure (Weeks 4 and 5) | Neural Crest

Embryology Movies: Fate of the Somite (315Kb) | Vertebrae (366Kb) | Neurulation (468Kb) | Secondary Neurulation (561Kb)

Development Overview

Week 4 (Clinical Week 6)

Day	Stage	Event
22	Stage 10	Neural Crest – differentiation at spinal cord level from day 22 until day 26 Neural – neural folds begin to fuse near the junction between brain and spinal cord, when Neural Crest cells are arising mainly from the neural ectoderm Neural Crest – trigeminal, facial, and postotic ganglia components visible (PMID: 17848161) Brain – rostral neural tube forms 3 primary brain vesicles (week 4) Respire – Week 4 - laryngotracheal groove forms on floor foregut.
23		Heart – begins to beat in Humans by day 22-23, first functioning embryonic organ formed. Week 4 heart tube continues to elongate, curving to form S shape
24	Stage 11	Thyroid – thyroid median endodermal thickening in the floor of pharynx Neural – rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in two areas simultaneously. The two lips, however, behave differently. Optic ventricle appears
25	Stage 12	Pituitary Week 4 – hypophysial pouch, Rathke’s pouch, diverticulum from roof GIT - Liver – septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae (PMID: 9407542) Neural – caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2) Neural – secondary neurulation begins Neural Crest – cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus arteriosus (PMID: 17848161)
26
27
28	Stage 13	Neural – the neural tube is normally completely closed, ventricular system now separated from amniotic fluid. Neural crest at spinal level is segregating, and spinal ganglia are in series with the somites. Spinal cord ventral roots beginning to develop. (PMID: 3354839) GIT - Liver – epithelial cord proliferation enmeshing stromal capillaries (PMID: 9407542) Sense - Smell – Crest comes from the nasal plates (PMID: 15604533) Skin – 4 weeks - simple ectoderm epithelium over mesenchyme Skin – 1-3 months ectoderm- germinative (basal) cell repeated division of generates stratified epithelium; mesoderm- differentiates into connective tissue and blood vessels

References

Links: Textbooks | Online Textbooks | Search Textbooks | Reviews | Articles | Search PubMed | Glossary

Specific references can also be found on each notes page and Selected References 1999

Textbooks

• Human Embryology (2nd ed.) Larson Ch
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud
• Before we Are Born (5th ed.) Moore and Persaud Ch
• Essentials of Human Embryology Larson Ch
• Human Embryology Fitzgerald and Fitzgerald Ch2 p8-14
• UNSW Embryology Selected Week 3 References

Online Textbooks

Developmental Biology (6th ed) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Figure 11.24. Implantation of the mammalian blastocyst into the uterus | Early Mammalian Development

Search NLM Online Textbooks "blastocyst implantation" : Developmental Biology | Endocrinology | Molecular Biology of the Cell | The Cell- A molecular Approach

Reviews

von Dassow M, Davidson LA. Variation and robustness of the mechanics of gastrulation: the role of tissue mechanical properties during morphogenesis. Birth Defects Res C Embryo Today. 2007 Dec;81(4):253-69.

Rohde LA, Heisenberg CP. Zebrafish gastrulation: cell movements, signals, and mechanisms. Int Rev Cytol. 2007;261:159-92.

Nance J, Lee JY, Goldstein B. Gastrulation in C. elegans. WormBook. 2005 Sep 26:1-13.

Kodaman PH, Taylor HS Hormonal regulation of implantation. Obstet Gynecol Clin North Am. 2004 Dec;31(4):745-66, ix.

Articles

Pézeron G, Mourrain P, Courty S, Ghislain J, Becker TS, Rosa FM, David NB. Live analysis of endodermal layer formation identifies random walk as a novel gastrulation movement. Curr Biol. 2008 Feb 26;18(4):276-81.

Nakaya Y, Sukowati EW, Wu Y, Sheng G. RhoA and microtubule dynamics control cell-basement membrane interaction in EMT during gastrulation. Nat Cell Biol. 2008 Jun 15.

Yao S, Xie L, Qian M, Yang H, Zhou L, Zhou Q, Yan F, Gou L, Wei Y, Zhao X, Mo X. Pnas4 is a novel regulator for convergence and extension during vertebrate gastrulation. FEBS Lett. 2008 Jun 25;582(15):2325-32.

Sweetman D, Wagstaff L, Cooper O, Weijer C, Munsterberg A. The migration of paraxial and lateral plate mesoderm cells emerging from the late primitive streak is controlled by different Wnt signals. BMC Dev Biol. 2008 Jun 9;8(1):63.

Güney M, Erdemoglu E, Oral B, Karahan N, Mungan T. Leukemia inhibitory factor (LIF) is immunohistochemically localized in tubal ectopic pregnancy. Acta Histochem. 2008 Feb 6;

Alisch RS, Jin P, Epstein M, Caspary T, Warren ST. Argonaute2 is essential for mammalian gastrulation and proper mesoderm formation. PLoS Genet. 2007 Dec 28;3(12):e227.

Hu W, Feng Z, Teresky AK, Levine AJ. p53 regulates maternal reproduction through LIF. Nature. 2007 Nov 29;450(7170):721-4.

Ralston A, Rossant J. How signaling promotes stem cell survival: trophoblast stem cells and shp2. Dev Cell. 2006 Mar;10(3):275-6.

Yang W, Klaman LD, Chen B, Araki T, Harada H, Thomas SM, George EL, Neel BG. An Shp2/SFK/Ras/Erk Signaling Pathway Controls Trophoblast Stem Cell Survival. Dev Cell. 2006 Mar;10(3):317-27.

Search Feb 2008 "blastocyst implantation" 7,336 reference articles of which 1,029 were reviews.

Search PubMed: term = week 3 embryonic human development | gastrulation | somite formation |

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

Week 4 Pages:

Introduction | Abnormalities | Placodes | Somite Development | Early Nervous System | References | Text only | WWW Links | Week 1 | Week 2 | Week 3 | Week 4 |

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