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Home , Body cavity, Cloaca (embryology), Surface ectoderm

DEVELOPMENT OF THE VERTEBRATE BODY PLAN

Thomas A. Marino, Ph.D. Temple University School of Medicine DEVELOPMENT OF THE VERTEBRATE BODY PLAN Early Development 1. Development of A. B. Surface Ectoderm 2. Development of A. G.I. Tract B. Respiratory Tree C. Pharynx 3. Development of A. Paraxial B. Intermediate Summary of Week 2 Cytotrophoblast Syncyotrophoblast Embryonic Ectoderm Embryonic Mesoderm Embryonic Mesoderm Extraembryonic mesoderm Primive Streak Notochordal Process Epiblast Embryonic Endoderm Amnioblasts

Hypoblast Extraembryonic endoderm Endoderm Trilaminar

So by day 18 of gestation, is nearing completion and the trilaminar Ectoderm mesoderm embryo will begin: 1. 2.Lateral body folding 3.Head and tail folding ! The trilaminar embryo has three layers: Notochord 1.Ectoderm 2.Mesoderm 3.Endoderm Endoderm Trilaminar Embryo

As the third week of gestation is coming to an end, the mesoderm layer paraxial mesodermparaxial mesoderm begins to subdivide into three masses: 1. 1. This will become the . 2.. 1. This will give rise to much of the urogenital system. 2.. 1. This will become 1. Lateral plate splanchnic mesoderm intermediate mesoderm 2. Lateral plate somatic mesoderm lateral mesoderm Ectoderm

Neurulation begins with the notochord cells migrating around the .

Notochord

Neural Plate Ectoderm

As the notochord cells migrate in a cephalic direction, the overlying ectoderm cells will begin Notochord to differentiate into neural ectoderm or the . Neural Plate Ectoderm

Oral Plate

The notochord and the neural Prechordal plate cells will grow cephalically. Plate 1.This growth will stop in the region of the prechordal plate. 2.Cephalic to the prechordal Notochord plate is the oral plate. 1. The oral plate is ectoderm and Neural endoderm without Plate intervening mesoderm. 2. The oral plate demarcates the separation between the prospective oral cavity and the developing gut tube. on – how does neural ectoderm develop? ! •BMP gradients lead to formaon of intermediate and lateral Chordin mesoderm. Noggin ! Follistatin •Chordin, Noggin and Follistan ! form in cranial paraxial ! mesoderm. They bind to and ! inacvate BMP. FGF ! WNT3a •They are present in notochord and paraxial mesoderm and induce ectoderm to become neural plate. ! •WNT3a and FGF do this in the caudal paraxial mesoderm. ! •Without BMP inacvaon the epidermal phenotype is formaon

Neural crest cells form in response to ! Chordin ! Noggin Follistatin Intermediate levels of BMP ! ! ! ! BMP ! This leads to PAX3 expression FGF + WNT3a FOXD3 expression is necessary for neural crest formaon And SLUG expression allows for to neural crest migraon Bone morphogenec protein signalling and vertebrate nervous system development Aimin Liu & Lee A. Niswander Nature Reviews Neuroscience 6, 945-954 (December 2005) The CNS arises from a specialized , the neural plate (1). This process relies on the inhibion of bone morphogenec protein (BMP) signaling. Folding of the neural plate to produce the is triggered by the formaon of a disnct hinge point in the ventral region (the floor plate; 2). At the end of neurulaon, the lateral edges of the neural plate fuse (3) and segregate from the non- neural epithelium to form a neural tube (4). The roof plate and floor plate form at the dorsal and ventral midline of the neural tube, respecvely. The roof plate becomes a new organizing centre that produces BMPs, which provide dorsal paerning informaon. Neural crest cells derive from the dorsal neural tube and migrate out to form the PNS, as well as melanocytes and carlage in the head. Neural crest cells have been shown to form at an intermediate level of BMP signaling. Ectoderm

The next stage of Neural neurulaon in the Groove formaon of the Neural neural tube. The Plate lateral edges of the neural plate will form neural folds and a midline neural groove appears. Fig. 1 (A) Successive images showing the progression of neural tube closure in a stylized vertebrate embryo (rostral = up).

J B Wallingford et al. Science 2013;339:1222002

Published by AAAS Fig. 3 Multiple cell behaviors contribute to neural tube morphogenesis. Multiple cell behaviors contribute to neural tube morphogenesis. In this schematic, pink and green cells illustrate convergent extension. By exchanging neighbors specifically in the mediolateral (horizontal) axis, the sheet of cells is elongated in the anteroposterior (vertical) axis. Blue cells illustrate apical constriction. These cells do not move but rather change their shape, leading to a bend in the tissue sheet. [Schematic adapted from (7)]

J B Wallingford et al. Science 2013;339:1222002

Published by AAAS Ectoderm

As the third week comes to Neural Groove an end the Somites neural folds become prominent and they approach one another in the cervical region. Day 20 Ectoderm

The neural tube is Pericardial first formed in the Bulge cervical region. It then connues to Somites form in a cephalic and caudal direcon.

Neural Tube Ectoderm The last two areas to fuse are the Cranial Neuropore cranial neuropore Pericardial Bulge cephalically and the caudal neuropore caudally. Somites

Caudal Neuropore UNSW This link takes you to the University of New South Wales embryology website where you can see an image of an embryo at 22 days of gestaon. Neurulaon is nearly complete. Lateral Body Folding

• As neurulaon occurs the embryo begins lateral body folding. Lateral Body Folding

• Lateral body folding involves: – The ectoderm at either end meeng in the ventral midline. – The endoderm forming the gut tube. Lateral Body Folding • The lateral plate mesoderm will split into somac and splanchnic mesoderm. • In between the two the will form. • This space on both sides will also fuse in the

midline. Body cavity

Somatic mesoderm Splanchnic mesoderm Lateral Body Folding • As the space between the lateral plate somac and splanchnic mesoderm enlarges the lateral body folding connues.

Body cavity 23 Lateral Body Folding

Body cavity

Amniotic Cavity

Gut Tube

• The amnioc cavity will also fold around the embryo. Lateral Body Folding • The two ends of the ectoderm, lateral plate somac mesoderm, lateral plate splanchnic mesoderm and the endoderm connue to migrate ventrally. Lateral Body Folding

• The amnioc cavity and the body cavity also migrate ventrally. Lateral Body Folding

• Now the amniotic cavity surround the embryo which is surrounded by ectoderm. • The fused body cavities are surrounded by lateral plate somatic mesoderm deep to the ectoderm • The lateral plate splanchnic mesoderm surround the gut tube which is a fused tube of endoderm

Somatic mesoderm Splanchnic mesoderm

Body Gut Tube cavity Lateral Body Folding Paraxial mesoderm Intemediate Surface ectoderm mesoderm Neural Tube

Amnioc Cavity

Body Gut Tube Cavity Chorionic Cavity

The embryo is surrounded by the chorionic cavity which surrounds the amniotic cavity. Lateral Body Folding

This is a very nice animaon of lateral body folding that will give you a beer three dimensional sense of the process. However this require the flash plugin. UNSW Embryology

• This is an image from the UNSW embryology website. It shows a 23 – 26 day old embryo (week 6 LMP). The neural tube is fusing with embryo is undergoing lateral body folding. • Another image can be see by clicking here. Surface Ectoderm Neural epidermis, , nails, Crest: cutaneous and mammary glands, gland, cranial and sensory ganglia enamel of teeth, inner ear, and and nerves, medulla of adrenal gland, pigment cells, branchial arch cartilages, head mesenchyme

mesoderm Ectoderm Neural Tube

, retina, pineal body, posterior pituitary

Endoderm

Ectoderm then develops into three main categories: surface ectoderm, neural crest derivatives and neural tube derivatives. Endoderm

• Connuing the discussion of lateral body folding and adding head and tail folding The development of the endoderm can be considered as it develops into: – Pharynx – GI tract – – Caudal urogenital system structures Endoderm

Aer: – Lateral Body Folding – Head and Tail Folding The endoderm consists of: – – – Endoderm

If a sagittal section of the embryo is made and looked at from the side one can see the ectoderm (blue), mesoderm (red) and endoderm (yellow). Endoderm • Dorsal to the ectoderm is the amniotic cavity and ventral to the endoderm is the yolk sac. • The chorionic cavity surrounds these structures. • The connects the embryo to the . • The cephalic end of the embryo is defined by the oral plate.

Connecting stalk Oral plate

Amniotic Cavity

Yolk Sac

Chorionic Cavity Endoderm • The cephalic end of the embryo grows the fastest and as it does the moves into a cephalic position and move the oral plate ventrally and caudally. • This leaves two cul-de-sacs at either end of the gut tube called the foregut and hindgut.

foregut hindgut

brain

Oral plate Endoderm The gut tube begins at the oral plate, starts as the foregut, continues as the midgut which is still continuous with the yolk sac and then becomes the hindgut ending as the cloacal plate. foregut hindgut

midgut

Cloacal Plate

Oral Plate

Allantois

Yolk Sac ENDODERM A diverticulum from the connecting stalk called the allantois connects to the Amnioc cavity hindgut and this fusion region is now called the cloaca. Uterine Cavity

Chorionic Yolk Cavity Sac Cloaca Hindgut Tail Allantois

Connecting Stalk Midgut

Back Vitelline Stalk Vitelline

Head Foregut

Cephalicend (green) Caudalend (blue) Cloaca

1. 2. 1.

Hindgut(purple) Midgut Foregut(yellow)

3.

2.

1. The gut tubegutTheisdivided intothree regions: The endoderm gives rise to four Endoderm major components: mesoderm 1.Pharynx Ectoderm 2.Respiratory epithelium 3.GI tract and associated glands. 4.Caudal urogenital system

G.I.: epithelium of G.I. tract , Endoderm ! Caudal UG system: Pharynx: Respiratory: urethra epithelial parts of: epithelial parts of: pharynx trachea thyroid bronchi tympanic cavity tonsils, parathyroids Gastrulaon

Ectoderm

Amnioc Cavity Paraxial mesoderm ! Intermediate mesoderm ! Lateral plate mesoderm

The mesoderm initially Yolk Sac is subdivided into three masses: Endoderm 1. paraxial mesoderm Notochord 2. intermediate mesoderm 3. lateral plate mesoderm Mesoderm

• The first part of the mesoderm to examine is the lateral plate ! ! mesoderm and Lateral plate specifically the mesoderm: Splanchnic Somac ! mesoderm ! Splanchnic

42 Mesoderm Looking down on the embryo, the lateral Oral plate plate splanchnic mesoderm begins to Blood see a proliferation of Islands cells that form blood islands. ! These blood island are forming in the lateral mesoderm and continue cephalically located cephalic to the oral plate. Blood Islands ! ! ! Endocardial Heart Tube

The blood islands consist of angiogenic cell clusters that will become cells that will form the: 1. endothelium of blood vessels. 2. heart tube. 3. blood cells. Mesoderm Three sites of

early blood Chorion island Connecting stalk

formaon: Cardiogenic area – cardiogenic area – yolk sac – chorion and connecng yolk sac stalk Mesoderm Endocardial heart tube

Take a cross section in the plane of the dotted line, and looking at the section from the caudal region, shows the location of the endocardial heart tubes in the splanchnic mesoderm. Mesoderm

The following images Endocardial demonstrate that during heart tube lateral body folding the endocardial heart tubes will come together to form the heart tube. Dorsal Aortae

Endocardial heart tube The endocardial heart tubes will come toward the midline. ! They will be continuous with newly forming dorsal aortae. By day 21the ends of the heart tube have fused and form the heart tube. It is located ventral to the gut tube. The first region to fuse is the prospective ventricular region. ! At this point the heart starts to beat. Mesoderm The fused heart tube consists of Foregut Dorsal Aorta the endocardium (red) the, myocardium from primary and secondary heart fields (green stipple) and Heart intervening cardiac Body mesenchyme Cavity (jelly) in green.

Amnioc Cavity ! • UNSW Embryology - This is a scanning electron microscope image of the fused heart tube. ! • UNSW Embryology 1 - This is a series of images showing the fusion of the heart tube. Mesoderm

Ectoderm

Paraxial mesoderm Amnioc Cavity ! Intermediate mesoderm ! Lateral plate mesoderm

The medial mass of mesoderm is called the paraxial mesoderm and Yolk Sac later the .

Notochord Endoderm Dermatome Myotome

Paraxial mesoderm ->Somite Sclerotome The somite will become subdivided into three components: 1. Dermatome - the connective tissue of the skin. 2. Myotome - skeletal muscle cells. 3. Sclerotome - give rise to cartilage and bone of ribs and vertebrae WNT Dermomyotome

PAX3

Scleretome SHH (PAX1)

Initially the dermatome and myotome are fused with the dermatome in between the two masses of myotome. Signals from the notochord and neural tube influence the developmental fate of the the somite. The medial mass of myotome cells will become the muscles of the back. The lateral mass of myotome cells will become the muscle of the body wall and extremities.

Body wall and Extremity Muscles Back (epaxial) muscles DermisMYF5

MYOD Mesoderm

• Intermediate mesoderm will Intermediate develop into mesoderm Amnioc Cavity components of the urinary and reproducve systems. Yolk Sac

56 Development of the Kidneys • By day 23 intermediate mesoderm (orange and navy) is identified lateral to the paraxial mesoderm (red). • Intermediate mesoderm is organized into: • • mesonephrose • metanephros Mesoderm • The intermediate tubules mesoderm gives rise to: – Kidney tubules (blue)

– Ducts of the urinary and Primordial germ cells reproducve systems Ducts Body epithelium – Gonads – The gonads form from epithelium covering the intermediate mesoderm (green) and migrang

primordial germ cells. 58 1. Skeletal muscles, Urogenital system Mesoderm 2. Skeleton (except ) including : 3. Dermis of skin Paraxial Mesoderm 1. Kidneys 4. Connective tissue 2. Gonads, 3. Ducts, 4. Accessory glands Lateral Mesoderm

Intermediate Mesoderm 1. Connective tissue of viscera. 2. Serous membranes of: A. pleura, B. C. 3. Blood and lymph cells 4. Cardiovascular system 5. Lymphatic system • Early Embryology: Where are we now and where are we going. ! • View the CNN Report

60 Timing of pregnancy

Embryology/ Gestational Age Clinical Age Beginning of last Ovarian follicle Day 0 menstrual period matures

Day 0 Proliferative phase Ovulation Day 14 of menstrual cycle Day 1 Secretory phase of Fertilization Day 15 menstrual cycle. Day 6 - 7 Implantation Blastocyst Day 20 - 21

Day 14 Primary villi in the Bilaminar disk Day 28 placenta Day 15 First menstrual Gastrulation Begins Day 29 period missed Pregnancy loss

• Approximately 30% of the fertilized eggs are carried successfully. • Of the 70% that are unsuccessful almost 1/3 are lost prior to implantation. • About 40% of postimplantation pregnancies abort spontaneously, • Clinically only 10 - 15% are observed. Pregnancy loss • Studies on aborted material demonstrates 50 - 60% have chromosomal anomalies. • Very early losses closer to 70% • Higher spontaneous loss in older women. • Other reasons for loss: – Genital tract abnormalities. – Infections – Endocrine and metabolic anomalies – Hematologic and immune disorders Chances of Conception*

In one month In six months In one year

Early 20's 25% 75% 94%

Late20's/early30's 15% 38-47% 70-85%

Late30's 10% 22-24% 65-70%

* from iVillageHealth.com. Average Time to Conception*

No. of months

Early 20's 4-5

Late 20's 5-7

Early 30's 7-10

Late 30's 10-12

* from iVillageHealth.com. http://www.msnbc.msn.com/id/19031210