Making germ cells Flashcards
What are the two fates of primordial germ cells?
Oogonia -> oocytes
Spermatogonia -> spermatocytes
Germ cells that are fundamentally different from somatic cells live a(n)
a) Infinite life
b) Finite life
a) Infinite life
Germ cells that are not fundamentally different from somatic cells live a(n)
a) Infinite life
b) Finite life
b) Finite life
In nematodes, certain regions of chromatin are degraded in ____________ cells and all chromatin is retained in _____________ cells
Somatic; germ
In Drosophila, pole cells segregated at _____________ end of embryo contain ____________ cell determinants
Posterior; germ
In C. elegans, aggregates of mitochondria, RNA and protein in egg become segregated to _____________ cells
Germ
What does embryo biopsy search for?
The presence of mutations in the embryo by genetic analysis of one of the germ cells
What are the key events of differentiation of the PGCs?
PGC determination, sex determination, PGC migration and gametogenesis
Which cells of the embryo of a mouse form the embryo?
Posterior and anterior epiblast
How many anatomical positions of newly specified PGCs can be found in mouse and in humans?
Mouse: one
Humans: two
PGCs arise from the _____________ epiblast
Posterior
What experiment was done to determine that PGCs came from the posterior epiblast?
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
What cell signaling pathways are important in PGC specification?
Wnt and TGFb pathways
What is the mechanism of Wnt signaling?
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
What is the mechanism of TGFb signaling?
TGFb and BMP bind to their receptors
SMAD proteins are activated and translocated to the nucleus to activate gene transcription
BMP is secreted by which cell type?
Extraembryonic ectoderm cells
What are some roles of the genes responsible for specification of PGCs?
DNA-binding domain regulator and TM protein/viral entry
DNA methylation modifies which nucleotide within the chromatin?
Cytosine
Which enzyme mediates DNA methylation?
DNMT1
DNA methylation can be transmitted ____________ DNA replication and therefore is _____________ during cell proliferation
After; heritable
DNA methylation of _________ ____________ is linked to the repression of gene expression
Gene promoters
When does the DNA of PGCs become demethylated?
When they are specified
What is totipotency?
Ability to acquire a pattern of any cell type
DNA demethylation may help give germ cells ________________
Totipotency
SRY was discovered in the _____________ chromosomes of __________
Y; males
XX mice carrying SRY develop as _____________
Males
How was the male-determining gene located in humans?
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
Which domain in SRY gene binds to DNA?
HMG domain
What is the role of SRY in somatic cells of the genital ridge when it is expressed?
Production of testosterone from differentiation of Sertoli cells and Leydig cells
What is the role of SRY in somatic cells of the genital ridge when it is not expressed?
Secondary female sexual differentiation from the differentiation of pre-granulosa cells and pre-theca cells
SRY turns on the expression of _____________ gene in the genital ridge
Sox9
Does Sox9 expression require SRY in other tissues?
No
Sox9 gene expression leads to ____________ sex determination
Male
Which other gene is required for male sex determination?
Fgf9
Which genes are required for female sex determination?
Wnt4 and Rspo1
Wnt4 and Rspo1 mutations lead to _____________
Partial female-to-male sex reversal
What proteins are required for female sex determination?
b-Cat/Lef1 and FoxL2
Germ cells in ____________ maintain mitotic arrest until puberty, while germ cells in ___________ enter meiosis
Males; females
Which gene is correlated with the entry into meiosis?
Stra8 turned on by retinoic acid
How does RA activate the expression of Stra8?
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
Why don’t XY germ cells respond to environmental RA?
Cyp26b1 degrades RA in embryonic male gonads
True or false: Mice lacking Cyp26b1 will enter meiosis
True
Which cells in male gonads block RA from acting?
Sertoli cells
Gonochorism occurs when individuals reproduce as one ___________ throughout their lifetime
Sex
Protogyny occurs when individuals first reproduce as _____________, change sex once with increasing size/age and then reproduce as ____________
Females; males
Protoandry occurs when individuals first reproduce as _____________, change sex once with increasing sex/size and then reproduce as _______________
Males; females
Bidirectional sex determination is when individuals can change sex more than once, in either ______________, throughout their lifespan
Direction
Simultaneous sex determination is when individuals produce gametes of both _____________ at the same ____________
Sexes; time
Mullerian duct gives rise to _____________ gonads and Wolffian duct gives rise to ____________ gonads
Female; male
What triggers Mullerian duct regression?
AMH (Anti-Mullerian hormone)
What is the phenotype of individuals with 5-a-reductase lacking the ability to convert testosterone to di-hydrotestosterone?
Females at birth, male external genitalia form at puberty, some individuals produce functional sperm
