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vertebrate development > gametogenesis & sex determination > Flashcards

gametogenesis & sex determination Flashcards

1
Q

where are sperm produced

A

seminiferous tubules

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2
Q

where are oocytes produced

A

cortex of the ovary

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3
Q

what are the two ways to form an early germ cell

A

predetermine/ autonomous

and induced formation

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4
Q

what do BMPs do and how do they do it

A

Prevent germ cell differentiation into somatic cells.

Smad signalling to the nucleus, makes fragilis and Blimp1 proteins

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5
Q

what is Blimp1 and what cells does it act on

A

a transcription factor activating Nanos and maintaining Nanog expression.
it acts on Primordial Germ Cells

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6
Q

what does Nanos do?

A

limits differentiation to somatic cells and stops apoptosis

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7
Q

the SRY gene is a member of which family of transcription factors? which protein does it turn on?

A

Sox family. Sox9

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8
Q

what is Sox9, give three things it does

A

an autosomal transcription factor expressed on in a positive feedback loop with its own gene (gonad formation)

it blocks ovary formation by the genital ridge - stops function of the paracrine Wt/beta catenin pathway

activates expression of anti-mullerian hormone

activates expression of FGF9 (in +ve feedback loop with sox9) in the genital ridge

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9
Q

what three genes are involved in the positive feedback loop of male development

A

SRY -> SOX9 -> FGF9

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10
Q

what does Wnt4 do in females

A

a paracrine signal that remains high in the female genital ridge but is lost in males

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11
Q

where are oocytes contained

A

follicles

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12
Q

what are the molecular components that define germ cells

A

Vasa, Nanos, Tudor, Piwi

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13
Q

what do Vasa proteins do?

A

bind mRNA and increase translation efficiency of germ cell specific messages

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14
Q

what do Nanos proteins do

A

bind mRNA and decreases translation efficiency of germ cell specific messages - present in somatic cells (mesoderm/ ectoderm/ endoderm)

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15
Q

what is predetermined (autonomous) formation of germ cells

A

egg is fertilised, embryo divides, at some point in early development a small group of cells is earmarked- here the germ cells are defined by the segregation of Vasa/ Nanos/ Tudor/ Piwi which become concentrated in the cytoplasm of the egg (the germ plasm) (no external signal)

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16
Q

what animals have predetermined formation of germ cells

A

Nematodes, Insects, Fish, Frogs

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17
Q

what type of germ cell formation do mammals have

A

induced formation

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18
Q

what structure of the embryo forms the testis/ovary

A

the genital ridge

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19
Q

what evidence is there against predetermination in humans

A

germ cells appear after gastrulation (day 13-19)

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20
Q

what are P granules

A 
a class of perinuclear RNA granules specific to the germ line - Complexes of RNA and proteins that help to form the gonads.
"germ granules"
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21
Q

what do P granules do

A

they contain inhibitors of gene transcription and prevent the germ cells differentiation into somatic cells - concentrated into P cells

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22
Q

what is the location of PGCs in the human embryo (day24)

A

found in yolk sac (endodermal)

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23
Q

what does every cell in our body start life as

A

pluripotent epiblast cells

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24
Q

what are the pluripotent markers in PGCs

A

Nanog and Sox2

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25
Q

what causes posterior epiblast cells to become PGCs

A

BMPs

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26
Q

why do PGCs migrate to areas outside the embryo proper (humans&mouse to the yolk sac)

A

To separate these cells from paracrine differentiative signals in the rapidly forming embryo

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27
Q

what does E-cadherin do in germ cell development

A

it keeps the PGCs together as a group and stops their migration out of the yolk sac and being lost

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28
Q

what is fragilis

A

a plasma membrane receptor for adhesion with E cadherin (and others)

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29
Q

Induction of mouse germ cell development is done by what group of proteins

A

Bone Morphogenetic Proteins BMPs - BMP4, BMP8b, BMP2

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30
Q

where do BMPs act and on what cells

A

extraembryonic epiblast cells

31
Q

what protein is responsible for specification in mouse germ cell development

A

Blimp1

32
Q

what does Blimp1 do and how

A

Prevent germ cell differentiation into somatic cells.

By transcriptional regulation - activating Nanos and maintaining Nanog

33
Q

if you remove what protein you fail to get PGCs (in an induced formation)

A

BMP(4)

34
Q

what proteins are responsible for PGCs migration to the genital ridge

A

Nanos3, Kit and Dead end1

35
Q

what do Nanos3 and Dead end1 do during migration

A

prevent apoptosis (by binding to mRNAs)

36
Q

what does Kit do during migration of PGCs?

A

prevents apoptosis, stimulates proliferation, and may help line path to gonad (no kit = sterile)

37
Q

what defines the outcome of the PGCs (male/ female)

A

the Y chromosome ‘gene’ expression by the genital ridges and surrounding tissues (ie the somatic cells)

38
Q

What is the SRY gene? - major function?

A

sex determining region of the Y chromosome. (a transcription factor
- The mammalian Testis Determining Factor TDF

39
Q

which is the shared evolutionary male gene

A

Sox9

40
Q

what is Fgf9? give three functions

A
  • Paracrine signalling molecule formed by the somatic cells of the genital ridge

causes proliferation and differentiation of some genital ridge cells to form Sertoli cells and formation of chords of cells - gives the tubular structure of the testis later

Represses (with Sox9) the Wnt/B-catenin path so blocks ovary formation

Coordinates differentiation pathway of PGCs

41
Q

where is testosterone produced

A

The interstitial cells between the seminiferous tubules in the testes

42
Q

What does the Wolffian duct develop into?

A

Vas deferens, epididymis, seminal vesicle

43
Q

loss of the androgen receptor results in what

A

female appearance but with retained testes

44
Q

what three proteins lead to female development

A

Wnt, beta-catenin, follistatin

45
Q

in some reptiles expression of Sox9 is related to what

A

temperature

– Alligator eggs incubated at 33degreesC 100% male, 30degreesC 100% female

46
Q

in birds and some reptiles high levels of what drives expression of Sox9 -

A

high levels of DMRT1 present on the Z chromosome drive expression of Sox9 - a gene dosage system (male ZZ, female ZW)

47
Q

what does the Mullerian duct develop into

A

the ovarian ducts, uterus cervix and top of vagina

48
Q

the fate of the PGCs depend upon the gender of the ______ not that of the ______

A

The fate of the PGCs depends upon the gender of the ridge not that of the PGCs

49
Q

when do quiescent PGCs restart meiosis (in males)

A

puberty

50
Q

what is induced formation of early germ cells

A

the germ cell formation occurs after implantation into the uterus and Vasa/ Nanos/ Tudor and Piwi are not present in the egg but their expression is induced by signalling molecules (paracrine molecules) from neighbouring cells

51
Q

describe the germ cell creation in C.elegans

A

Vasa/ Nanos/ Tudor and Piwi are concentration in P granules, these are retained in the P cells (P1-P4) in the germ plasm - p granules are markers for the germ plasm to segregate to the p1 then p2 then p3 then p4 cell during each division

52
Q

how was induction (formation of germ cells) proved

A
  • The PGCs form in the posterior (back) part of the epiblast – if you replace these cells in a embryo with anterior epiblast cells (front) from a embryo expressing GFP - these new cells will go on to form GFP expressing PGCs
  • If you remove BMP(4) the inducer – by gene knockout- you fail to get PGCs
53
Q

what are the main factors for sexual differentiation in males and females

A

Nanos2 in males

Stra8 in females

54
Q

how many cells are Blimp1 positive in mouse at embryonic day 6.5

A

6

55
Q

in you inject a DNA solution containing the SRY gene into a XX female mouse what happens

A

you get a male mouse

56
Q

where is SRY expressed

A

in somatic cells of the genital ridge

57
Q

what does Sox9 do at the genital ridge

A

blocks ovary formation by stopping function of the paracrine Wnt/beta-catenin pathway

58
Q

in mammals what drives Sox9 expression

A

SRY gene

59
Q

sertoli cells induce differentiation of what in males

A

differentiation of mesenchymal cells in the genital ridge to form interstitial cells- which produce testosterone

60
Q

what are two things does testosterone do in the embryo

A
  • Allows growth of the Wolffian (mesonephric) duct to form the epididymis and the vas deferens
  • Drives the secondary sex determinants
61
Q

what remains high in the female genital ridge but is lost in males

A

Wnt4

62
Q

what does follistatin do in the genital ridge

A

induces the genital ridge to form an epithelium (granulosa cells) and surrounding the PGCs forming follicles

63
Q

over expression of beta catenin in males causes what

A

an ovary to form

64
Q

what has high levels in the male genital ridge but is reduced in the female

A

FGF9

65
Q

what causes the female PGCs to enter meiosis

A

Retinoic acid diffuses into the PGCs and causes expression of Stra8 (the ‘master switch’ for meiosis)

66
Q

where is retinoic acid made

A

in the mesonephros

67
Q

what is the the principal excretory organ during early human embryonic life (4—8 weeks).

A

Mesonephros

68
Q

where does the gonad develop

A

on the medial surface of the mesonephros

69
Q

what does the mesonephros form in males and females

A

forms parts of the epididymis and vas deferens in males, but regresses, in females

70
Q

What stops PCGs in male fetal testis entering meiosis?

A

Stra8 levels do not rise in male PCGs because fiboblast growth factor 9 (FGF9) is produced by male gonadal ridge cells and

a) Induces Cyp26b1 which degrades RA before it reaches the PCGs
b) Represses Stra8 expression – so inhibits meiosis entry

71
Q

what is Cytochrome P26b1 (Cyp26b1)

A

an enzyme involved in the degradation of retinoic acid - absent in females, only present in male gonads. driven by Sox9/FGF9

72
Q

both sexes make retinoic acid but it is _______________ in male gonads

A
  • Both sexes make RA but is only metabolised in male gonads
73
Q

Loss of Cyp26B1 enzyme in males results in what

A

male PGCs entering meiosis in utero this results in an infertile male (has testis but no sperm)

vertebrate development (10 decks)

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