Chapter 5 Flashcards by Alyza Gia Kudera

What genes are expressed by cells in the AVE during the bilaminar disc stage?

Genes expressed by AVE cells include OTX2, LIM1, and HESX1

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Which secreted factors are expressed by AVE cells to establish head formation?

AVE cells secrete Cerberus and Lefty, members of the TGF-B family.

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What is the role of Cerberus and Lefty during early embryonic development?

Cerberus and Lefty inhibit nodal activity, establishing the cranial end of the embryo.

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How do Cerberus and Lefty influence nodal expression?

Cerberus and Lefty inhibit nodal expression at the caudal end, allowing nodal activity to continue and establishing the primitive streak.

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What is the function of the primitive streak?

The primitive streak is established and maintained by nodal expression. It is responsible for forming the central axis of the embryo.

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What happens once the primitive streak is formed?

NODAL upregulates genes responsible for dorsal and ventral mesoderm formation, as well as the formation of head and tail structures.

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How does nodal expression influence mesoderm formation?

NODAL upregulates genes involved in dorsal and ventral mesoderm formation

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Which member of the TGF-B family is involved in the establishment of the cranial end of the embryo?

Nodal, a member of the TGF-B family, is inhibited by Cerberus and Lefty to establish the cranial end.

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What are the consequences of Cerberus and Lefty absence at the caudal end?

The absence of Cerberus and Lefty allows nodal expression to continue, leading to the establishment and maintenance of the primitive streak

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What role does NODAL play in embryonic development?

NODAL activates genes responsible for dorsal and ventral mesoderm formation, as well as head and tail structure formation after the primitive streak is established

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Derived from inner mass of embryo
Can be obtained from embryo after IVF (reproductive
cloning

Embryonic stem cells

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can form any cell or tissue;
■ has potential to cure disease

Pluripotent

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introduction of nuclei to enucleated oocyte

Therapeutic cloning or Somatic Nuclear Transfer:

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restricted in ability to form different cell or
tissue type

Adult stem cells: Multipotent

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Lost within 2-3 weeks of fertilization
○ 50% of pregnancies end in spontaneous abortion
○ PCR can detect genetic defects

Abnormal zygotes`

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Due to the constant erosion of the sinusoids by
the Trophoblast.
Maternal blood begins to flow through the
trophoblastic system

Uteroplacental
Circulation

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Maternal capillaries which are congested and
dilated, maternal blood enters the lacunar system

Sinusoids (Maternal
sinusoids)

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Fine, loose connective tissue that appears
between the Cytotrophoblast and Exocoelomic
cavity.

Extraembryonic
Mesoderm

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The large space or cavity formed by the
extraembryonic mesoderm

Extraembryonic Cavity
aka Chorionic Cavity

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Additional cells that are produced by the
Hypoblast.

Secondary Yolk Sac or
Definitive yolk sac

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The pinch portion of the Secondary yolk sac,
which are found in Extraembryonic coelom or
Chorionic cavity.

Exocoelomic Cysts

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Expansion that forms a large cavity from the
extraembryonic coelom

Chorionic cavity

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Formed from the connecting stalk (the place
where extraembryonic mesoderm transverses
the chorionic cavity)

Umbilical Cord

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where the formation begins
○ A narrow groove with slightly bulging regions on the either
side.
■ cells of the epiblast migrate toward this area
○ Clearly evident at 15-16th day embryo

Primitive Streak

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cephalic end of primitive streak ○ Slightly elevated area surrounding the primitive pit

Primitive Node

an inward movement of the epiblast towards the primitive streak then detaches and slips beneath it

INVAGINATION

It controls the cell migration and specifications ○ Synthesized by the primitive streak

FIBROBLAST GROWTH FACTOR 8 (FGF8)

controls and down regulating by FGF8 ● A protein that binds the epiblast cells together

E-CADHERIN

source of all 3 germ layers

Epiblast

solid cord of cells formed by endoderm cells; underlies neural tube and basis for axial skeleton

DEFINITIVE NOTOCHORD

indentation of epiblast; temporarily connects amniotic fluid and yolk sac cavities

Neurenteric canal

formed at caudal end of embryonic disc ○ Consist of endoderm and ectoderm cells; no intervening mesoderm ○ Similar characteristic with oropharyngeal membrane

Cloacal membrane

Diverticulum that appear on 16th day

alloenteric diverticulum or allantois

Occurs BEFORE and AFTER period of gastrulation

ESTABLISHMENT OF THE BODY OF AXES

Express genes essential for head formation ○ Establishes cranial end of embryo prior to gastrulation

Anterior visceral endoderm (AVE)

Initiates and maintains primitive streak ○ Upregulates genes responsible for formation of dorsal and ventral mesoderm; tail and head structures

Nodal (member of TGF-beta)

Centralizes mesoderm to contribute to kidneys

Bone morphogenetic protein 4 (BMP4)

"The Organizer"

Node

Dorsalized into notochord, somite, and somitomeres

Cranial mesoderm

Maintains node ○ Induces regional specificity in forebrain and midbrain ○ Without this = embryo fail to gastrulate properly; lack forebrain and midbrain

HNF-3B (beta)

Laterality

Induces nodal expression

FGF 8

Homeobox-containing transcription factor ○ Responsible for left sidedness ○ Repeated expression on left side of heart, stomach, gut ○ Organs assume normal asymmetrical body positions

PITX2

Acts barrier to prevent left-sided signals from crossing over

Lefty

Repressor for left sided gene expression on the right ○ Inhibitory

Sonic hedgehog (SHH)

Establishes laterality ○ Concentrated on left side ○ Broken down by monoamine oxidase (MAO) on right side ○ Leads to situs inversus and dextrocardia when altered

Serotonin (5HT)

a transcription factor ○ Restricted to right lateral plate of the mesoderm ○ Regulates genes for establishing right side

SNAIL

becomes paraxial mesoderm

LATERAL EDGES OF THE NODE

intermediate mesoderm

Midstreak region

extraembryonic mesoderm

CAUDAL MOST PART OF STREAK

lateral plate mesoderm

Caudal Part

shows regressive changes until it disappears towards the end of the 4th week.

Primitive streak

Deficiency of the midline in craniofacial structures ○ May be caused by high doses of alcohol (kills cells in the anterior midline of the germ disc) ○ small forebrain, 2 lateral ventricles are often merge into one, eyes are close together (hypotelorism) and closed

Holoprosencephaly

insufficient mesoderm is formed in the caudal-most region of the embryo

Caudal Dysgenesis (sirenomelia)

is caused by mutations in zinc finger transcription factor ZIC3

X-linked Heterotaxy

stage of trophoblast wherein it consists of cytotrophoblastic core covered by a syncytial layer at the beginning of 3rd week ○ Mesodermal cells penetrate the core of primary villi and grow towards the decidua

Primary Villi

formed when the mesodermal cells penetrate the core of primary villains grow towards decidua

Secondary Villi

formed at the end of 3rd week when mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessels. ○ Capillaries in this villi make contact with capillaries developing in the mesoderm of the chorionic plate in the connecting stalk.

Tertiary Villi (Definitive Placental Villi)

villi extension from chorionic plate to decidua basalis

Stem/ Anchoring Villi

branch from the sides of stem villi. This is the site for exchange of nutrients and other factors.

Free (Terminal) Villi

attaches the embryo to its trophoblastic shell and later on develops into umbilical cord.

Connecting Stalk