Embryology Test 1 Flashcards
(199 cards)
1
Q
What is the study of embryo?
A
Embryology
2
Q
What includes all developmental processes from conception to death?
A
Ontogeny
3
Q
What is the part from conception to birth or hatching?
A
Embryogeny
4
Q
What is the process by which a cell or part of an embryo become restricted to a given developmental pathway, the point at which a cell becomes committed to specific cell line?
A
Determination
5
Q
What is a complex change involved in progressive specialization of structure and function, often resulting in the formation of luxury moleucles
A
Differentiation
6
Q
Increase in cell numbers
A
Hyperplasia
7
Q
Increase in cell size
A
Hypertrophy
8
Q
What are the six component processes?
A
Determination Differentiation Growth Morphogenesis Induction Integration
9
Q
Generation of form or assumption of new shape
A
Morphogenesis
10
Q
What happens in Anaphase I?
A
Homologous chromosomes move to opposite poles
Each homologue consists of two chromatids
Chromatids are not genetically identical because of crossing-over
Daughter cells will be haploid
11
Q
An effect one embryonic tissue (inductor) has upon another (responder) such that the development course of the responding tissue is qualitatively changed from what it would have been in the absence of the inductor
A
Induction
12
Q
When do the primordial germ cells first appear? Where do they appear?
A
24 days after fertilization
Found in the endodermal layer of yolk sac
13
Q
Migration route of primordial germ cells?
A
Yolk sac –> hindgut epithelium
Through dorsal mesentery
Into developing gonads
14
Q
Teratomas
A
Growths from misdirected migrating primordial germ cells, contains mixtures of highly differentiated tissues
15
Q
Process by which different tissues are brought together and combined to form organs and tissues
A
Integration
16
Q
What are the 5 phases of prophase I
A
Leptotene Zygotene Pachytene Diplotene Diakinesis
17
Q
Growth
A
Permanent increase in mass
18
Q
Hyperplasia
A
Increase in cell numbers
19
Q
What happens in Leptotene?
A
Chromosomes are threadlike
Each chromosome consists of two chromatids
Chromosomes begin to coil
20
Q
What happens in Zygotene?
A
Homologous chromosomes pair (synapsis)
Synaptonemal complex forms
21
Q
Determination
A
Process by which a cell or part of an embryo becomes restricted to a given developmental pathway
22
Q
What happens in Pachytene?
A
Maximum coiling
Tetrads
Crossing-over begins
23
Q
What happens in Diplotene?
A
Crossing-over continues
Chiasmata are well-defined
24
Q
Differentiation
A
Complex changes involved in progressive specialization of structure and function, often resulting in the formation of luxury molecules
25
Hypertrophy
Increase in cell size
26
Integration
Process by which different tissues are brought together and combined to form organs and tissues
27
What happens in Diakinesis
Crossing over is complete
Terminalization
Spindle apparatus is in place
Nuclear membrane is disrupted
28
At what stage is terminalization?
Diakinesis of Prophase I
29
When do chromosomes begin to coil?
Leptotene of Prophase I
30
Induction
An effect one embryonic tissue (inductor) has on another (responder) such that the development course of the responding tissue is qualitatively changed from what it would have been in the absence of the inductor
31
Morphogenesis
Generation of form or assumption of new shape
32
At what stage does the synaptonemal complex form?
Zygotene
33
During what stages does crossing-over happen?
Pachytene & Diplotene
34
At what stage in Prophase I is the nuclear membrane disrupted?
Diakinesis
35
At what stage does maximum coiling occur?
Pachytene of Prophase I
36
What happens in Metaphase I?
Tetrads line up along equatorial plate
| Centromeres do not divide
37
At what stage is the Chiasmata well defined?
Dipletene
38
At what stage do homologous chromosomes move to opposite poles?
Anaphase I
39
At what stage do homologous chromosomes pair (synapsis)?
Zygotene of Prophase I
40
At what stage is crossing-over complete?
Diakinesis of Prophase I
41
What happens in Teleophase I?
Cytokinesis occurs (usually)
Nuclear membrane reform (maybe)
Spindle apparatus disassembles
Chromosomes may uncoil to varying degrees
42
What happens in Prophase II?
Chromosomes again condense
Nuclear membranes disappear
Spindle apparatus reforms in each cell
Each chromosome consists of two chromatids
Each daughter cell has one complete set of chromosomes (haploid)
43
What happens in Metaphase II?
Chromosomes line up on equatorial plate?
44
What happens in Anaphase II?
Centromeres divide
Chromosomes move to opposite poles
Each chromosome consists of a single chromatid
45
At what stage are there tetrads?
Pachytene of Prophase I
46
At what stage is the spindle apparatus in place?
Diakinesis of Prophase I
47
Daughter cells in Anaphase I are diploid or haploid?
Haploid
48
At what stage does the nuclear membrane reform?
Teleophase I
| Telophase II
49
At what stage does crossing-over begin?
Pachytene of Prophase I
50
At what stage do tetrads line up along equatorial plate?
Metaphase I
51
At what stage do chromosomes condense again?
Prophase II
52
At what stage does the nuclear membrane disappear?
Prophase I and Prophase II
53
At what stage does cytokinesis occur
Telephase I
| Telophase II
54
At what stage does chromosomes line up on equatorial plate?
Metaphase II
55
At what stage does the spindle apparatus reform in the cell?
Prophase II
56
In prophase II are the daughter cells haploid or diploid?
Haploid
57
What happens in Telephase II?
Chromosomes uncoil
Cytokinesis is complete
Nuclear membrane reform
End result is four genetically unique haploid daughter cells
58
At what stage do each chromosome consist of a single chromatid?
Anaphase II
| Telophase II
59
At what stage do the chromosomes move to opposite poles?
Anaphase II
60
At what stage does the spindle apparatus disassemble?
Telophase I
61
At what stage do centromeres divide
Anaphase II
62
Aneuploidy
Abnormal number of chromosomes
Nondisjunction
Monosomy
Trisomy
63
Euploidy
Change in number of complete sets of chromosomes
Monoploidy
Diploidy
Polyploidy
64
There are how many germ cells at embryonic midterm?
7 million
65
Fetal period characteristics
No follicle
Diploid oogonium not surrounded by follicle cells
1 chromatid/ chromosome
66
Later Fetal period through birth
Diploid primary oocyte
Primordial follicle with a few flattened follicle cells
2 chromatid/ chromosome
67
How many primary oocytes are ovulated?
400
68
Birth to puberty
Diploid primary oocyte
Primary follicle w/ single layer of cuboidal follicle cell
Oocyte & follicle cells are connected via microvilli and gap junctions
Zona pellucida separates primary oocyte from follicular cells
2 chromatids/ chromosome
69
After puberty
Diploid primary oocyte
Secondary follicle w/ multiple layers of follicle cells & beginning of antrum formation
Membrane granulose surrounds outside of follicle cells
2 chromatids/chromosome
Haploid secondary oocyte + haploid polar body
Tertiary follicle w/ multiple layers of follicle cells, corona radiate and large antrum
Mural granulose cells
Cumulus cells
2 chromatids/ chromosome
70
There are how many primary oocytes shortly after birth?
| At what stage of meiosis are they arrested in?
400,000
Diplotene stage of Prophase I
71
Mural granulose cells are found
cells between membrane granulose and antrum
72
Cumulus cells are found
Cells between zona pellucida and antrum
73
How many germ cells are present at birth?
2 million
74
Oocyte and follicle cells are connected by what 2 things?
Microvilli and gap junctions
75
What separates the primary oocyte from the follicular cells?
Zona pellucida
76
How many primary oocytes survive to puberty?
40,000
77
2 factors that lead to meiotic arrest in diplotene?
1) High concentration of cAMP from oocyte and follicular cells
- Inactivates MPF
- Leads to meiotic arrest
2) cGMP from follicular cells that inactivates phosphodiesterase 3A in oocyte
- prevents conversion from cAMP to 5'AMP
- maintains high concentration of cAMP
78
Ovulation
Haploid secondary oocyte with corona radiata and theca cells + haploid polar body
-Granulosa cells develop FSH receptors and LH receptors
-Circulating FSH stimulates granulosa cells to produce estrogen
2 chromatids/chromosome
About 10-12 hrs before ovulation meiosis resumes
1) resumes due to response to LH surge by cumulus cells
2) Cumulus cells shut down gap junctions, cAMP and cGMP can't get to oocyte
3) no cGMP, activates PDE3a, converts cAMP to 5'AMP
4) Decrease cAMP activates MPF and resumes meiosis
79
What develops FSH receptors and LH receptors?
Granulosa cells
80
Circuating FSH stimulates granulosa cells to produce what?
Estrogen
81
Tertiary follicle consists of what four things?
Antrum
Cumulus cells
Zona pellucida
Oocyte
82
Mural granulosa cells
Develop FSH receptors
| Synthesize aromatase in response to FSH
83
What does aromatase do with concern to ovulation?
Aromatase is secreted by mural granulosa cells in response to stimulation by FSH
The aromatase converts testosterone into 17beta-estradiol (estrogens)
Estradiol stimulates the formation of LH receptors on granulosa cells
84
Theca internal cells produce what?
Androgens (testosterone)
85
Role of LH
LH surge shuts down gap junctions between granulosa cells and oocyte
-causes activation of MPF and resumes meiosis
```
LH surge, LH binds to receptors on follicular cells
Activation of adenyl cyclase
Progesterone secretion by follicle cells
Activation of collagenase enzyme
Release of oocyte
```
86
Stages of Spermatogenesis
```
Primordial germ cell (2N)
Spermatogonia (2N)
-Type A (stem cells)
-Type B (leave mitotic cell to enter meiotic cycle under influence of retinoic acid)
Primary spermatocyte (2N)
-First maturation division (meiosis I)
Secondary spermatocyte (N x 2 cells)
-Second maturation division (meiosis II)
Spermatids (N x 2 cells)
```
87
Influence of what causes type B spermatogonia cells to leave the mitotic cell and enter meiotic cycle?
Retinoic acid
88
Testosterone is produced by what?
Theca internal cells
89
Sertoli cells are located where?
Seminiferous tubules within the testis
90
Cells of Leydig
Location?
Function?
Interstitial cells in testis
| Produce testosterone
91
Functions of sertoli cells (6)
1. Physical support & maintenance
2. Maintain and coordinate spermatogenesis
3. Secrete estrogen, inhibin, androgen binding protein & anti-mullerian factor
4. Maintain blood-testis barrier
5. Secrete tubular fluid
6. Phagocytize residual bodies of sperm cells
92
Sperm histones
proamines
93
What sertoli cells also called?
Sustentacular cells
94
Blood Testis Barrier with Sertoli cells
Sertoli cells form an immunological barrier between the forming sperm cells and the rest of the body and spermatogonia
1) surface adhesion complexes bind to sertoli
2) SAC brake down & release spermatids in lumen
3) Laminin frag from SAC plus cytokines and proteninases break down tight junctional proteins
- Developing spermatocytes move closer to lumen
4) Testosterone stimulates formation of new barrier
95
What breaks down the blood testis barrier?
Laminin fragments from surface adhesion complex plus cytokines and proteinases
96
What stimulates formation of a new blood-testis barrier closer to basal lamina?
Testosterone
97
Testosterone effect on Sertoli cells & secondary sex characteristics
Testosterone is carried by blood to sertoli and secondary sex tissues
FSH binds to receptors on Sertoli cells
-Sertoli converts testosterone to estrogen and synthesizes leydig cells stimulatory factor
-Produce androgen binding factor
-Binds to testosterone and carries it to seminferious vesicles
98
Ovulation occurs when?
| Roles of FSH & LH on ovulation?
Ovulation occurs on day 14 of the ovarian cycle
The stimulus for ovulation is a rise in levels of FSH and a sharp peak in LH
(ant. pit)
99
What components of the graafian follicle form the corpus luteum?
The residual theca and granulosa cells proliferate and form a large glandular structure called the corpus luteum
100
Outer part of graafian follicle that remains is made of what and secretes what?
Thecal cells
| Secrete progesterone
101
Fate of corpus luteum without fertilization
Corpus luteum regresses and levels of progesterone and estradiol decrease resulting in beginning of next menstral cycle
102
Inhibin is released by?
| What does it do?
Released by granulose cells
| Inhibits secretion of gonadotropins, esp. FSH, resulting in regression of corpus luteum
103
What is the role of corpus luteum in endometrial cycle?
In pregnancy, the corpus luteum continues to produce progesterone which maintains that early embryo until the placenta begins to produce sufficient hormones to maintain pregnancy
104
Proliferative phase
1. Endometrial growth increases the endometrial thickness from 1-2 mm to 8-10 mm by day 14
2. Blood vessels & glands grow
3. Cells that initiate growth come from bases of the glands that formed previous endometrium that were deep enough to survive the loss
4. Proliferation phase is due to increase in levels of estradiol secreted by the grandulose cells of the developing ovarian follicle
5. Near the end of this phase is sharp rise in estradiol levels
105
Vasoconstriction by what?
Prostaglandins
106
Secretory phase
1. During the phase levels of estrogen decrease & the endometrial growth stops
2. Mucous glands develop more fully and begin secretion
3. The spiral arterioles in this area expand & heavily vascularize the area
4. The secretory phase is controlled by rising levels of progesterone, secreted by both the granulose & theca cells of the ovarian follicle
107
Graffian follicle prior to ovulation
Mature Graafian follicle
- expansion of follicle (FSH & LH)
- Thickening of outer layers of follicle
- Rupture of follicle wall (24 hr after surge)
108
Fertilization age
Date age of embryo at time of fertilization
109
Menstrual age
Date age is from start of last menstrual period, 2 weeks greater
110
Rapid egg transport is through where and what hormone is required?
Isthmus
| Progesterone
111
What contributes to semen and with what?
Seminal vesicles: fructose and prostaglandins
-Fructose provides energy
Prostate: citric acid, Zn, Mg, Phosphate
112
pH of upper vagina
4.3
| Adjusts to 7.2 for sperm
113
What is the optimal pH for sperm motility and is where?
6.0-6.5 in the cervix
114
Fertilization in the oviduct occurs where?
Ampulla
115
What is the purpose of capacitation? What occurs
Required for sperm to undergo acrosomal reaction
-Occurs inside uterine in isthmus
-Requires binding of sperm to tubule epithelium
-Involves:
1. Removal of cholesterol from sperm surface
(acts to inhibit premature capacitation)
2. Removal glycoproteins (epididymus)
116
Where does capacitation occur in the female tract?
Inside the uterine tube in Isthmus
117
Major enzyme of acromsome?
Hyaluronidase
118
Penetration of Corona Radiata (4)
1. Fusion of the outer acrosomal membrane with the sperm plasma membrane creates portals through which the contents of the acrosome can be released
2. Fragmentation of fused acrosomal membrane and plasmalemma of the sperm results in the release of acrosomal enzymes
3. Hyaluronidase is one the major enzymes in the acrosome
4. Swimming movements of spermatozoa help in the penetration through the corona radiata
119
Function of ZP3
Zp3 is one of four glycoproteins that make up the ZP
Attachment of sperm to the ZP is mediated by ZP3 protein
ZP3 protein stimulates acrosomal reaction in mammals
1. Acts through a G protein in the sperm plasma membrane
(Leads to influx of calcium through sperm plasma membrane, exchange of sodium and hydrogen increase pH, then penetration)
120
What is the most important enzyme involved in the penetration of the zone pellucida
Acrosin (serine proteinase)
aka zona lysin
Remains attached to the portion of the acrosomal membrane that fuses to the remaining sperm plasmalemma and overlies nucleus
Digest small hole through ZP
121
Fast block
Consists of a rapid depolarization of egg plasmalemma
-70 to +10 mV within 2-3 sec (to min)
Fast block temporarily prevents polyspermy and allows time for the egg to establish slow block
122
Slow block
Most characterized by release of polysaccharides from the cortical granules located just under the plasmalemma of the egg
- Polysaccharides enter perivitelline space (between plasmalemma and the zona pellucida) and become hydrated
- Hydration produces a swelling that increases the width of the perivitelline space
123
Role of phospholipase C zeta in metabolic activation of the egg following fertilization?
Metabolic activation of egg is initiated by release of calcium within egg cytoplasm in response to introduction of phospholipase C zeta by sperm
124
Pronucleus
Is the nuclear material of the head of the spermatozoan (male pronucleus) or of the oocyte (female pronucleus) after the oocyte has been penetrated by spermatozoan
- Each pronucleus carries a haploid set of chromosomes
- The male pronuclei consists of decondensed nuclear material
- A pronuclear membrane, derived from endoplasmic reticulum of the egg, typically forms around the female chromosomal material
125
What introduces phospholipase C zeta to the cytoplasm?
Sperm
126
Zygote
Is the term used to denote the single-cells stage of which the male and female pronuclei have fused together and share a common membrane, establishing the diploid chromosome number
127
Inside-Out Hypothesis
Fate of balstomere is determined by its position within the embryo, not from intrinsic properties
128
Cell polarity Model
```
Fate of blastomere depends on plane of cell division during cleavage
Parallel
-outer: trophoblast (polar)
-inner: inner cell mass (apolar)
Perpendicular
-Both daughter cells trophoblast
```
129
Trophoblast cells are what layer
| Forms what?
Outer layer cells
| Forms extra embryonic structures including placenta
130
Inner Cell Mass are what layer
| Forms what?
Inner mass of cells
| Forms embryo proper plus some extra embryonic structures
131
What makes the blastocyst polarized?
The eccentric placement of blastocoel and inner cell mass
1. Embryonic pole marks the pole of the blastocyst where the inner cell mass is located
2. Abembryonic pole marks the opposite side
132
Invertebrates and non-mammalina genetic control of cleavage
Early control of cleavage is through gene products transcribed from the material genome and embryonic gene products often do not appear until after blastulation
133
Mammalian embryo genetic control of cleavage
Maternal gene products are produced but generally degraded by the 2 cell stage
By the four cell stage, most transcription is via the embryonic genome
134
Cdx-2
1. Essential for trophoblast cell differentiation
| 2. Antagonistic toward Oct-4
135
Oct-4
1. Expressed in developing oocytes and zygote
2. Required to permit cleavage to proceed to 2-cell stage
3. Expressed in all morula cells
4. May play a role in the maintenance of the undifferentiated state
136
Nanog
1. Produced by inner cells in the late morula stage
2. Maintains integrity of inner cell mass along with Oct4
3. Without nanog, inner cell differentiate into endoderm
4. Without Oct4, inner cell differentiate into trophoblast
137
Sox2
1. First expressed in 8 cell stage
| 2. Along with Oct-4 it helps to control regulation of genes involved in differentiation
138
Genomic imprinting
Is differential gene expression depending on whether a chromosome is inherited from the male or female parent
- It refers to observations that expression of certain genes derived from the egg differs from the expression of the same genes derived from the sperm
- Due to DNA methylastion differences in sperm and eggs
139
Methylation of DNA
1. In mammals methylation is erased in the germ cells of each generation and then re-established in the course of gamete formation
2. Sperm and eggs undergo different levels of methylation resulting in the differential expression of male and female alleles in the offspring
140
Prader Willi
mental retardation
Obese
Mutation from father
Chrom 15
141
Angelmann syndome
Uncontrolled muscle movement
Large mouth
Seizures
Mother mutation
142
Barr bodies
| What do they tell us about a person's genome?
Barr bodies are inactivated X chromosome
| Show genome is female
143
Regulation
1. Refers to ability of embryo to compensate for removal of structures or for addition of structures
2. At the cellular level, this means that the fates of cells in a regulative system are not irretrievably fixed, and the cells can still respond to environmental cues
144
Identical twins
Product of single fertilized egg
| More commonly arise by subdivision of the inner cell mass in a blastocyst or splitting of the epithelial epiblast
145
Dizygotic twins
Product of fertilization of 2 ovulated eggs, mechanism for formation involves endocrine control of ovulation
146
Common attachment site for parasitic twins
Oral region
Mediatinum
Pelvis
147
Bateson's rule?
When duplicated structures are joined during critical development stages, one structure is the mirror image of the other
148
Functions of Zona pellucida
1. It promotes maturation of the oocyte and follicle
2. Serves as a barrier that normally allows only sperm of same species to access the egg
3. It initiates the acrosomal reaction
4. After fertilization, the modified zona pellucida prevents any additional spermatozoa from reaching the zygote
5. During the early stages of cleavage, it acts as a porous filter through which certain substances secreted by the uterine tube can reach the embryo
6. Because it lacks histocompatibility (leukocyte) antigens, the zona pellucida serves an as immunological barrier between the mother and antigenitically different embryo
7. It prevents blastomeres of the early cleavage embryo from dissociating
8. It facilitate the differentiation of trophoblastic cells
9. It normally prevents premature implantation of the cleaving embryo into the wall of the uterine tube
149
Ectopic pregnancy
| Common occur?
Implantation other than uterine wall
Most common is a tubal pregnancy
-Ampulla
-Next isthmus
150
Homeobox
The highly conserved sequence of 180 nucleotides in the gene that encode the homeodomain
151
Homeodomain
Highly conserved domain of 60 amino acids
| A homeodomain is a type of helix loop helix region
152
X inactivation is brought about by the action of what?
Xist
153
What prevents the mother's immune system from recognize the embryo as a foreign body?
Interleukin-2
154
Homeobox-containing genes
Are activated in a 3 to 5 direction (opposite of transcription)
155
Helix-loop-Helix genes
Codes for basic helix loop helix transcription factors
Basic regions of proteins bind to DNA
Involved in homodimerization and heterodimerization
Important in myogenesis
156
Zinc finger transcription factors
These proteins have zinc ions bound to polypeptides chain that cause the chain to form finger-like projections that can be inserted into the DNA helix
Gene families: Sox and WT1
157
Sox Genes
Sox transcription factors have a high-mobility group domain that binds to minor groove on DNA helix rather than major groove
Sox gene family includes SRY gene
158
WT1
Is important for the development of the embryonic kidney and the adult kidney
It takes name from child kidney tumor
159
Egg polarity Genes
Egg polarity genes are important in the establishment of the dorsal-ventral and anterior posterior axis in the fruit fly
160
Genes that establish the dorsal ventral axis
Dorsal, Cactus, Toll
161
Genes that establish the anterior posterior axis
Bicoid, Nanos, Hunchback
162
Morphogen
A protein that varies in concentration and causes different developmental responses as a result of the concentration differences
163
Dorsal protein
Expressed in ovary
164
Cactus protein
Expressed in the ovary and binds to the dorsal protein and traps it in the cytoplasm
165
Toll
Expressed in ovary and leads to the degradation of the cactus protein, allowing the dorsal protein to move into the nuclei of the ventral cells
166
Bicoid protein
Expressed in the ovary, regulates expression of genes responsible for anterior structures and stimulates hunch back (forms a gradient with high concentration at anterior end)
167
Nanos
Expressed in the ovary and regulated the expression of genes responsible for posterior structures. Inhibits translation of hunchback mRNA
168
Hunchback
Forms a gradient with high concentration at anterior end
169
Segmental genes
1. These are 25 segmentation genes that are transcribed after fertilization; so they do not exhibit a genetic maternal effect
2. Expression of the segmentation genes is regulated by the Bicoid and Nanos protein gradients
3. Three classes of segmentation gene include:
a. Gap genes
b. pair rule genes
c. segment-polarity genes
170
Gap genes
Delete adjacent segemnts
171
Pair rule genes
Delete same part of pattern in every other segment
172
Segment-polarity genes
Affect polarity of segment
173
Homeotic genes
1. Determine the identity of individual segments
2. Products of homeotic genes activate other genes that encode these segment-specific characteristics
3. Expressed after fertilization
4. Activated by concentration of products of gap, pair-rule, and segment polarity gens
5. Contain homeobox
6. Two major groups of homeotic genes
- Antennapedia complex (Hox genes)
- Bithorax complex (Hox genes)
174
Antennapedia complex
Affects development of head and thorax
175
Bithorax complex
Affects development of posterior thorax and abdominal segments
176
Signaling Factor families
Transforming Growth Factor Beta superfamily
Fibroblast Growth Factor Family
Hedgehog family
Wnt family
177
Transforming Growth Factor Beta Superfamily
```
TGF-beta
Activin
Inhibin
Mullerian inhibiting substance
Decapentaplegic
Vg1
BMP
Nodal
Glial cell line neurotrophic factor
Lefty
```
178
Hedgehog Family
Desert
Indian
Sonic hedgehog
179
Process of lateral inhibition
1) Type of signaling between a dominant cell and neighboring cells
2) Dominant cell refers to a cell in a population that begins to differentiate along a particular path
3) Dominant cell expresses Delta signaling molecules on its cell membrane
4) Delta then binds to Notch receptors on neighboring cells and via the Delta-Notch pathway represses genes in the neighboring cells
180
In the absence of Wnt, what is bound to an intracellular destruction complex within the target cell (wnt pathway)
beta-catenins
181
Role of nanog in the establishment of the epiblast and hypoblast
Cells entering inner cell mass earliest express nanog and are destined to become epiblast cells
182
Role of Gata6 in the establishment of the epiblast and hypoblast
Cells entering inner cell mass later express gata6 and are destined to become hypoblast cells
183
Roles of Wnt and TGF-beta on formation of primitive streak?
Begin the process of induction of primitive streak
184
What are the three classical molecular markers expressed by nodal cells
Chordin
Goosecoid
Hepatic nuclear factor-3 beta (Foxa-2)
185
Chordin
1. Signaling molecules associated with the node
2. Involved in neural induction and expression of nodal of the left side of the embryo, key element in setting of left-right asymmetry
186
Goosecoid
Homeodomain transcription factor
Activates chord in, noggin, and other genes
If ectopically expressed, stimulates formation of secondary body axis
187
Hepatic nuclear factor-3 beta (Foxa-2)
Transcription factor
Establishment of midline structures cranial to node
In absence, notochord and the floor plate fail to form
188
Bottle cells
| What role do they play
1. Epithelial cells head towards primitive groove and change shape to bottle shape, thrust themselves through primitive groove
2. Breaks down cell adhesion molecules becomes free and irregular shaped
3. Transforming cells are freed from the basal lamina and lose E-cadherins
4. Epitehlial mesenchymal cell transformation is correlated with expression of transcription factors snail
5. changes in the shape of a cell as it migrates along the epiblast through the primitive streak (bottle cell) and away from the groove as a mesenchymal cell that will become part of the mesodermal germ layer.
(same cell can later assume epithelial configuration as part of somite)
189
Role of E-caherin and N-cadherin in epithelial mesenchymal transition
1) Prior to induction ectoderm expresses both E-cadherin and N-CAM
2a) After neural tube induction, overlying ectoderm only expresses E-cadherin
2b) After neural tube induction, neural tube ectoderm expresses N-CAM and N-cadherin
190
What transcription factor is correlated with epithelial mesenchymal cell transformation
Snail
191
Source and role of Cerebrus-like signaling molecule in development of anterior posterior axis
1. From the anterior visceral endoderm
| 2. inhibits development of posterior structures
192
DSource and role of Dkk-1 signaling molecule in development of anterior posterior axis
1. From Anterior visceral endoderm
2. Blocks Wnt
3. Inhibits development of posterior structures
193
Effects of Foxa-2 on early primitive streak stage
Multiple targets
Establishment of primitive node
Initiates notochord functions
Establishes midline structures cranial to node
194
In the late primitive streak stage, what signaling molecule is necessary for normal head function?
Cerebrus- related 1
| Origin: prechordal plate
195
In the late primitive streak stage, what signaling molecule is released from the primitive streak activate Hox gene?
Retinoid acid, Wnt, and FGF
| Targets Cdx to activate Hox
196
Experiments for neural induction
1. The dorsal lip of the blastopore was grafted beneath the belly ectoderm of another host
2. Result: secondary nervous system and body axis formed in the area of the graft
3. Hensen's node from one avian embryo to another induces the formation of secondary neural tube
4. The dorsal lip is the organizer because of its ability to stimulate the formation of a secondary body axis
5. In higher vertebrate, the primitive node and the notochordal process at as the neural inductor and the overlying ectoderm is the responding tissue
197
What is the first sign of asymmetry in early developemnt
Involves the beating of cilia around the primitive node
198
Role of Nodal
Symmetry breaking molecules in the left side of the embryo
Swept to left side of primitive node by ciliary current
Stimulates mulitple gene expression pathways via: Pitx-2
199
Lefty1
Left side of the primitive streak
Expresed on left side of the embryo
Blocks diffusion of molecules to the right side
