Exam 2

Question 1

List the three areas of mesoderm in the early embryo.

Answer 1

1) Paraxial (segmental plate) Mesoderm
2) Intermediate Mesoderm
3) Lateral Plate Mesoderm

Question 2

Describe the mesoderm subdivisions including their location

Answer 2

1) Paraxial (segmental plate) mesoderm - Thick column of mesoderm closest to and parallel with the notochord
2) Intermediate mesoderm - narrow column of mesoderm and lateral to the paraxial mesoderm
3) Lateral plate mesoderm - Thin plate of mesoderm lateral to intermediate mesoderm

Question 3

Characterize the fate of the three areas of mesoderm in the early embryo

Answer 3

1) Paraxial mesoderm - Becomes segmented into somites
2) Intermediate mesoderm - Gives rise to urogenital system
3) Lateral plate mesoderm - Splits to form lining of body cavities and mesoderm of most internal organs as well as limbs

Question 4

Distinguish between somitomeres and somites

Answer 4

1) Somitomeres - Initial pairs of segments of mesenchyme that begin to develop along and on either side of the neural plate in the paraxial mesoderm
2) Somites - Dense blocks of mesoderm that form along the notochord caudal of somitomeres

Question 5

In relation to the somitomeres, at what position does the first pair of somites form?

Answer 5

The first pair of somites forms caudal to the 7th pair of somitomeres at the expense of the 8th pair of somitomeres

Question 6

What is the relationship of ephrin B, Wnt-6, snail, and paraxis to somite formation?

Answer 6

1) Ephrin B is a ligand expressed from the posterior border of the anterior somite which prevents mixing of two adjacent somites since Eph A receptor is expressed at the anterior border of a somite. The resulting factor is the development of a fissure between two adjacent somites.
2) Wnt-6 is a signaling molecule that is secreted by the ectoderm dorsal to somites. It up-regulates the production of paraxis.
3) Paraxis production and down-regulation of snail results in the transformation of mesenchymal cells into an epithelial cell type

Question 7

Relate Shh, noggin, Pax1 and Pax9 to the formation of the sclerotome

Answer 7

1) Shh and Noggin originating from notochord act on the ventromedial wall of the neural tube
2) Causes the expression of Pax1 and Pax9 in the ventral half of the somite which will now be called the sclerotome

Question 8

Sclerotome gives rise to what?

Answer 8

Veterbral column

Question 9

Determination front of Clock and Wavefront model

Answer 9

The point at which there is a balance of FGF-8 and Retinoic Acids in concentration that prepares them for interring the process of segmentation (somite formation)

Question 10

Describe the formation of the dermomyotome and the factors and pathways involved

Answer 10

G

Question 11

What is a dermomyotome

Answer 11

Somites will split to form dermatomes and myotomes, but before they splitting the dorsal-lateral part of a somite is collectively referred as the dermomyotome

Question 12

How is the dermomyotome formed?

Answer 12

Wnt genes in dorsal neural tube cause the transformation of dorsal half of somite into dermomyotome

Question 13

What causes the separation fo dermomyotome into dorsal dermotome and ventral myotome?

Answer 13

Dermomyotome expresses Pax3, Pax7, and paraxis genes that cause the separation of dermomyotome into dorsal dermotome and ventral myotome

Question 14

How is the Intermediate Mesoderm formed

Answer 14

1) BMP from lateral ectoderm and Activin from paraxial mesoderm creates the future intermediate mesoderm which expresses Pax-2

Question 15

Which two genes is the cranial and caudal extent of the intermediate mesoderm dependent on?

Answer 15

1) Hox-4 through Hox-11

Question 16

Differentiate between the intraembryonic coelom and the extraembryonic coelom

Answer 16

Initially they are continuous, but are seperated during the lateral folding of the yolk sac area. Here the small channels connecting the intraembryonic and extraembryonic coeloms are closed when the ventral body wall is completely sealed

Question 17

Distinguish between somatic and splanchnic mesoderm

Answer 17

Lateral plate mesoderm divides into two layers

1) Dorsal Layer associated with he ectoderm = Somatic Mesoderm
2) Ventral Layer associated with the endoderm and expresses Foxf-1= Splanchnic mesoderm

Question 18

Describe the formation of the lateral plate mesoderm

Answer 18

Lateral Plate Mesoderm is associated with BMP-4 expression which causes its molecular and cellular properties, but the development of the lateral plate depends on balance between media living influences emanating from the neural tube, notochord, and lateralizing influences produced by lateral ectoderm

Question 19

Somatopleure

Answer 19

Combination of somatic mesoderm and ectoderm

Question 20

Splanchnopleure

Answer 20

Combined endoderm and splanchnic mesoderm

Question 21

Describe the cardiac crescent and cardiogenic mesoderm

Answer 21

1) Cardiac Crescent is a U shaped arrangement in the cardiogenic mesoderm consisting of heart-forming cells that form the outflow tract, ventricles, and atria
2) Cardiogenic Mesoderm is the mesodermal layer that develops into the hear

Question 22

List the genders important in early heart formation

Answer 22

1) Nkx-2
2) MEF2
3) GATA4

Question 23

List the factors that induce the formation of the cardiac crescent

Answer 23

BMPs and FGFs that act on the Anterior Visceral Endoderm

Question 24

Describe the early formation of the heart including the pericardial cavity

Answer 24

1) Early heart-forming cells arise in epiblast and migrate through primitive streak
2) Cells migrating trough anterior primitive streak form outflow tract
3) Cells migrating through middle of primitive streak form ventricles
4) Cells entering streak most posteriorly form atria
5) Bilaterally paired tubes form cardiac tubes from the cardiogenic mesoderm and fuse beneath the forget with the outer layer being the myocardium, inner layer forming endocardium, and the specialized extracellular matrix between the two layers forms the cardiac jelly
6) Pericardial Cavity is developed from the space between the cardiogenic plate and oropharyngeal membrane

Question 25

Secondary (anterior) heart field

Answer 25

1) Located in the splanchnic mesoderm on the posteromedial side of the cardiac crescent
2) The secondary heart field refers to the splanchnic mesoderm caudal to the outflow tract. It constitutes a source of cells that gives rise to both the most distal outflow tract myocardium and the ventricles and atria

Question 26

cytodifferentation vs histogenesis

Answer 26

Cytodifferentiation: Cells going under increasing speacialization in a given tissue

Histogenesis: Various cell types develop in concert to form specific tissues

Question 27

Describe the formation of a multiple layered epidermis, including the derivatives from the intermediate layer

Answer 27

1) Outer layer of skin at end of first month = Periderm
2) Dermal mesenchyme activates of p63
3) p63 triggers three layered epidermis formation
4) mIR-203 inactivated p63
5) Basal layer (germination layer) losses association with intergrins which allows basal layer to terminally differentiate undergo mitosis which develops intermediate layer
6) Stratum spinosum will be characterized by appearance of keratohyalin granules
7) Stratum granulosum below the superficial peridermal layer will be connected to each other via fillagrin (a histidine rich protein)
8) Apoptosis occurs with peridermal cells at about 6mo and these cells will be sloughed off

Question 28

Characteristics of Volar pad influence on Epidermal Ridge

Answer 28

1) High, round volar pads = whorl epidermal ridge formation
2) Low volar pad = arch ridge formation
3) Intermediate height volar pad = loop formation
4) Early formation = whorl formation
5) Late formation = arch formation

Question 29

What is the molecular basis for albinism?

Answer 29

1) Melanocytes are unable to express pigmentation because they lack Tyrosinase
2) Tyrosinase converts Tyrosine into melanin

Question 30

True or False: Albinos have normal # of melanocytes

Answer 30

True

Question 31

List major groups of immigrant cells, tell where they are derived from, and list basic functions

Answer 31

1) Melanoblast - Neural Crest
- Migration from neural crest -> embryonic dermis -> Epidermis
- Function to produce pigment by mid pregnancy

2) Langerhan’s Cells - Bone Marrow
- Arise from precursors in bone marrow and invade the epidermis
- Function as APC

3) Merkel Cell - Neural Crest
- Arise from neural crest
- Function = Flow adapting mechanoreceptors

Question 32

Describe the source of dermal cells in various parts of the skin

Answer 32

1) Dorsal surface of body: Mesenchyme from dermatome
2) Ventral and Lateral surface of body: Mesenchyme from lateral plate mesoderm
3) Cranial and Anterior Neck: Mesenchyme mostly from cranial neural crest
4) Trunk dermis: From somatic dermatomes (aggregated mesenchymal cells develop tight junctions)
5) Limb Dermis: From lateral plate mesoderm
6) Face and Anterior Neck: Neural Crest

Question 33

What are Dermal Cells?

Answer 33

Mesenchymal cells that are loosely aggregated, interconnected by tight junctions, and secrete thin watery matric rich in glycogen and hyaluronic acid

Question 34

What signaling causes the transformation of mesenchymal cells into Dermal cells? Where does it come from?

Answer 34

Ectodermal Wnt signaling

Question 35

Describe the innervation, vascularization, and cell differentiation timing in Trunk Dermis

Answer 35

1) Sensory innervation occurs after week 8
2) Vascularization occurs
3) By 3rd month fibroblasts develop

Question 36

@ the 3rd month, Mesenchymal cells turn into Fibroblasts and secrete what?

Answer 36

1) Type I collagen
2) Type III collagen
3) Elastic Fibers

Question 37

Describe the pathways leading to the formation of dermis on various surfaces of the body

Answer 37

1) Ectoderm signals the development o the embryonic subectodermal mesenchyme into the dermis

Question 38

Inductive Induction

Answer 38

One germ layer instructs another on how to differentiate

Question 39

Commonalities of Epidermal Derivative: Hair, Nails, Mammary Glands

Answer 39

1) Development involves ectodermal-mesodermal interactions and inductions
2) Begin as epidermal down growths (ingrowths) into mesenchyme

Question 40

Epidermal Derivatives: Ectoderm contributions

Answer 40

1) Hair follicle, Hair shaft, Sebaceous Glands, Nails, Eponycium, Hyponychium, Secretory and duct components of mammary glands

Question 41

Epidermal Derivatives: Mesenchyme Contributions

Answer 41

1) Hair papilla, outer hair follicle and arrector muscles

Question 42

Cycle of growth and shedding steps

Answer 42

1) Anagen = Hair Growth
2) Catagen= Slight follicular regression
3) Telogen = Hair stops growing; Resting phase
4) Exogen = hair shedding occurs after Telogen

Question 43

Ectodermal Placode development

Answer 43

1) Ectoderm
- Wnt-1: acts on mesoderm; stimulates Wnt-11 of mesoderm
- Noggin and Edar: Block BMP and allows epidermal placode formation

2) Mesoderm- acts on ectoderm
- Wnt-11 and FGF -> Stimulate Noggin
- Edna -> Stimulates Edar

Question 44

Dermal Papilla Induction: Epidermal Induction

Answer 44

1) Epidermal Placode stimulates aggregation of mesenchymal cells which forms the dermal papilla
2) Dermal Papilla stimulates epidermal down growth
3) Edar stimulates Shh signaling which induces cyclin D1 causing increased cell proliferation and further downgrowth of epidermal placode
4) Final differentiation of hair primordia involves Hox genes

Question 45

Nail development

Answer 45

1) Primary nail field overlies a mesenchymal nail bed and extends proximally as the proximal matrix
2) Nail grows close to end of finger tip
- much of nail is covered by a thin eponychium which will eventually degenerate

Question 46

What is the first morphological evidence of mammary glands

Answer 46

Milk Lines

Question 47

What are Milk lines

Answer 47

2 bonds of ectodermal thickening running along ventrolateral body walls of the embryo at 6 weeks

Question 48

Expression of what molecule marks milk lines

Answer 48

Wnt expression within ectodermal cells

Question 49

Testicular Feminization

Answer 49

1) Genetically biological males are insensitive to male hormones (androgens)
- Normal ectoderm + TFM mesoderm with testosterone allows for mammary duct all growth patterns similar to developing femal