Making germ cells

Question 1

What are the two fates of primordial germ cells?

Answer 1

Oogonia -> oocytes
Spermatogonia -> spermatocytes

Question 2

Germ cells that are fundamentally different from somatic cells live a(n)
a) Infinite life
b) Finite life

Answer 2

a) Infinite life

Question 3

Germ cells that are not fundamentally different from somatic cells live a(n)
a) Infinite life
b) Finite life

Answer 3

b) Finite life

Question 4

In nematodes, certain regions of chromatin are degraded in ____________ cells and all chromatin is retained in _____________ cells

Answer 4

Somatic; germ

Question 5

In Drosophila, pole cells segregated at _____________ end of embryo contain ____________ cell determinants

Answer 5

Posterior; germ

Question 6

In C. elegans, aggregates of mitochondria, RNA and protein in egg become segregated to _____________ cells

Answer 6

Germ

Question 7

What does embryo biopsy search for?

Answer 7

The presence of mutations in the embryo by genetic analysis of one of the germ cells

Question 8

What are the key events of differentiation of the PGCs?

Answer 8

PGC determination, sex determination, PGC migration and gametogenesis

Question 9

Which cells of the embryo of a mouse form the embryo?

Answer 9

Posterior and anterior epiblast

Question 10

How many anatomical positions of newly specified PGCs can be found in mouse and in humans?

Answer 10

Mouse: one
Humans: two

Question 11

PGCs arise from the _____________ epiblast

Answer 11

Posterior

Question 12

What experiment was done to determine that PGCs came from the posterior epiblast?

Answer 12

Cells from the distal tip of epiblast were transplanted to the posterior epiblast
Normally, they would give rise to neuroectoderm cells
Yet, they differentiated into PGCs

Question 13

What cell signaling pathways are important in PGC specification?

Answer 13

Wnt and TGFb pathways

Question 14

What is the mechanism of Wnt signaling?

Answer 14

Wnt binds to its receptor
This activates b-Cat which translocate to the nucleus and activates the transcription of genes
In the absence of Wnt, b-Cat is bound up and degraded in the cytoplasm

Question 15

What is the mechanism of TGFb signaling?

Answer 15

TGFb and BMP bind to their receptors
SMAD proteins are activated and translocated to the nucleus to activate gene transcription

Question 16

BMP is secreted by which cell type?

Answer 16

Extraembryonic ectoderm cells

Question 17

What are some roles of the genes responsible for specification of PGCs?

Answer 17

DNA-binding domain regulator and TM protein/viral entry

Question 18

DNA methylation modifies which nucleotide within the chromatin?

Answer 18

Cytosine

Question 19

Which enzyme mediates DNA methylation?

Answer 19

DNMT1

Question 20

DNA methylation can be transmitted ____________ DNA replication and therefore is _____________ during cell proliferation

Answer 20

After; heritable

Question 21

DNA methylation of _________ ____________ is linked to the repression of gene expression

Answer 21

Gene promoters

Question 22

When does the DNA of PGCs become demethylated?

Answer 22

When they are specified

Question 23

What is totipotency?

Answer 23

Ability to acquire a pattern of any cell type

Question 24

DNA demethylation may help give germ cells ________________

Answer 24

Totipotency

Question 25

SRY was discovered in the _____________ chromosomes of __________

Answer 25

Y; males

Question 26

XX mice carrying SRY develop as _____________

Answer 26

Males

Question 27

How was the male-determining gene located in humans?

Answer 27

Translocate the region of Y chromosome to the X chromosome and observe through DNA sequencing where the region of Y-chr was found in X-chr of phenotypic males having XX genotype

Question 28

Which domain in SRY gene binds to DNA?

Answer 28

HMG domain

Question 29

What is the role of SRY in somatic cells of the genital ridge when it is expressed?

Answer 29

Production of testosterone from differentiation of Sertoli cells and Leydig cells

Question 30

What is the role of SRY in somatic cells of the genital ridge when it is not expressed?

Answer 30

Secondary female sexual differentiation from the differentiation of pre-granulosa cells and pre-theca cells

Question 31

SRY turns on the expression of _____________ gene in the genital ridge

Answer 31

Sox9

Question 32

Does Sox9 expression require SRY in other tissues?

Answer 32

No

Question 33

Sox9 gene expression leads to ____________ sex determination

Answer 33

Male

Question 34

Which other gene is required for male sex determination?

Answer 34

Fgf9

Question 35

Which genes are required for female sex determination?

Answer 35

Wnt4 and Rspo1

Question 36

Wnt4 and Rspo1 mutations lead to _____________

Answer 36

Partial female-to-male sex reversal

Question 37

What proteins are required for female sex determination?

Answer 37

b-Cat/Lef1 and FoxL2

Question 38

Germ cells in ____________ maintain mitotic arrest until puberty, while germ cells in ___________ enter meiosis

Answer 38

Males; females

Question 39

Which gene is correlated with the entry into meiosis?

Answer 39

Stra8 turned on by retinoic acid

Question 40

How does RA activate the expression of Stra8?

Answer 40

Retinol binds to Stra6 and is metabolized to retinoic acid by retinol dehydrogenase and retinal dehydrogenase CRABP carries RA to the nucleus where it activates the expression of Stra8

Question 41

Why don't XY germ cells respond to environmental RA?

Answer 41

Cyp26b1 degrades RA in embryonic male gonads

Question 42

True or false: Mice lacking Cyp26b1 will enter meiosis

Answer 42

True

Question 43

Which cells in male gonads block RA from acting?

Answer 43

Sertoli cells

Question 44

Gonochorism occurs when individuals reproduce as one ___________ throughout their lifetime

Answer 44

Sex

Question 45

Protogyny occurs when individuals first reproduce as _____________, change sex once with increasing size/age and then reproduce as ____________

Answer 45

Females; males

Question 46

Protoandry occurs when individuals first reproduce as _____________, change sex once with increasing sex/size and then reproduce as _______________

Answer 46

Males; females

Question 47

Bidirectional sex determination is when individuals can change sex more than once, in either ______________, throughout their lifespan

Answer 47

Direction

Question 48

Simultaneous sex determination is when individuals produce gametes of both _____________ at the same ____________

Answer 48

Sexes; time

Question 49

Mullerian duct gives rise to _____________ gonads and Wolffian duct gives rise to ____________ gonads

Answer 49

Female; male

Question 50

What triggers Mullerian duct regression?

Answer 50

AMH (Anti-Mullerian hormone)

Question 51

What is the phenotype of individuals with 5-a-reductase lacking the ability to convert testosterone to di-hydrotestosterone?

Answer 51

Females at birth, male external genitalia form at puberty, some individuals produce functional sperm