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BMS > Genetic and Environmental Influences on Early Human Development > Flashcards

Genetic and Environmental Influences on Early Human Development Flashcards

1
Q

Fewer than 1/2 fertilized human eggs implant and of that, what fraction will give rise to an infant?

A

1/3

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2
Q

Structural abnormalities that can be caused by genetic factors or by environmental factors, or both

A

Congenital malformations (present at birth)

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3
Q

About 6% of individuals are born with congenital malformations. What percentage of perinatal deaths are caused by such abnormalities?

A

20%

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4
Q

The field that has emerged to study abnormal development in embryos

-investigates the causes of congenital abnormalities/birth defects

A

Teratology

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5
Q

7% of congenital abnormalities are known to be caused by

-can be chemical toxins, infections, or maternal deficiency

A

Teratogenic agents

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6
Q

Will often kill embryo in first two prenatal weeks or lead

to spontaneous abortions in the first 6-8 weeks of gestation

A

Teratogenic agents

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7
Q

Teratogens can cause organ-specific abnormalities from days

A

15-60

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8
Q

Genetic factors cause 20-25% of birth defects, where as environmental factors account for

A

5-15%

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9
Q

Most cases of Down syndrome are caused by a deficit in

-produces gamete with 2 copies of chromosome 21

A

Meiosis I

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10
Q

Another cause of Down Syndrome that occurs when the q arms of chromosomes 14 and 21 fuse

-No symptoms

A

Robertsonian translocation

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11
Q

Has the symptoms of distinct facial features, congenital

heart disease, mental and growth retardation

A

Down Syndrome

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12
Q

Almost all alterations in chromosome number will be lethal in

A

Early embryo

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13
Q

Besides trisomy 21, what are two other trisomies where affected individuals survive post natally?

A

Trisomy 13 and trisomy 18

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14
Q

Can be a major result of abnormal genetic composition (esp. trisomy 13)

A

Midline defects

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15
Q

Cleft lip and palate and CNS malformations are characteristic of

A

Trisomy 13

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16
Q

Tend to survive longer with trisomy 18

A

Females

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17
Q

Characterized by intrauterine growth restriction, clenched hands, and low set ears

A

Trisomy 18

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18
Q

Single gene defects can interrupt

A

Specific organ development

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19
Q

Mutations in specific transcription factors can cause developmental disorders in overall body patterning or genesis of

A

Specific organs

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20
Q

A variety of teratogens (such as drugs) can affect development and lead to

A

Deformities

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21
Q

Act during critical times of organ formation

A

Teratogens

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22
Q

Nothing in weeks 1 and 2 of pregnancy is susceptible to

A

Teratogens

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23
Q

What is the most sensitive to teratogens throughout most of the pregnancy?

A

Central Nervous System

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24
Q

The risk of birth defects from many teratogens are highest during the

A

Embyonic Period (3-8 weeks)

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25
Q

Developed as sedative and insomnia treatment. However, if the fetus exposed at 24-36 days,
limb outgrowth is dramatically affected

-Does not effect subsequent digit development

A

Thalidomide

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26
Q

What are three major developmental signaling pathways?

-used at different steps in multiple tissues

A
  1. ) Transforming growth factor beta (TFG-β)
  2. ) Fibroblast growth factor (FGF)
  3. ) Retinoic Acid (RA)
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27
Q

A family of over 30 peptides that bind to serine-threonine kinase receptors

A

TGF-β

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28
Q

Made up of over 20 peptides that bind to tyrosine kinase receptors

A

FGF

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29
Q

Binds to nuclear receptors to regulate gene transcription, and has endogenous enzymatic control of its synthesis and degradation

A

Retinoic Acid (RA; derived from vitamin A)

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30
Q

Signal transduction via receptor kinases occurs when a ligand binds a receptor kinase in the cell exterior, causing a conformational change and phosphorylation cascade on the cell interior. Variations of this theme are used by

A

TGF-β and FGF pathways

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31
Q

Does not bind kinase receptors but instead binds nuclear receptors

-always located in the nucleus

A

Retinoic Acid

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32
Q

TGF-β ligands bind as a

A

Dimer

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33
Q

TGF-β binds to a type II receptor, which causes the receptor to recruit and phosphorylate a

A

Type I receptor

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34
Q

Phosphorylated type I receptor recruits and phosphorylates

A

Smad2 or Smad3

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35
Q

Phosphorylated Smad2 or Smad3 dissociates from the receptor and oligomerizes with

A

Smad4

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36
Q

Unfold when phosphorylated

A

Smads

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37
Q

Migrates to the nucleus, recruits other gene regulatory proteins, and activates transcription of specific target genes

A

Smad2(3)/Smad4 oligomer

38
Q

Can antagonize action of the TGF-β peptide BMP-4 by binding to it and thus preventing BMP-4 dimer formation

A

Chordin, noggin, and lefty

39
Q

What are the three TFG-like peptides we need to know

A
  1. ) TFG-β like (nodal)
  2. ) Mone morphogenetic proteins (BMP-4)
  3. ) Activins
40
Q

Chordin, noggin, and lefty bind the BMP-4 monomer and prevent BMP-4 dimer formation by forming a dimer of their own, which can not bind/activate

A

BMP receptors

41
Q

What are the four FGF receptors?

A

FGFR-1 through FGFR-4

42
Q

Critical for early axis formation and for development of several organs, particularly bone and cartilage

A

FGFs

43
Q

Helps present FGF to tyrosine kinase receptors and presumably helps stabilize the active dimeric receptor even though FGF is a monomer

A

Cell surface/transmembrane Heparin Sulfate

44
Q

The inner cell mass (ICM) is the source of all

A

Embryonic tissues and stem cells

45
Q

Changes in molecular identity of cells occur prior to organization of specific cell types in

A

Early embryonic Development

46
Q

Early fetal lineages are already specified in a mixture of cells as noted by different transcription factor expression before they are sorted to

A

Different regions

47
Q

This tissue will arise from the portion of the epiblast (blue) that is at the posterior end of the embryo via movement through the primitive streak

A

Mesoderm

48
Q

Will form connective tissue and will control nervous system formation

A

Mesoderm

49
Q

When does the primative streak form?

A

14 days in

50
Q

The embryonic endoderm and mesoderm are derived from cells that enter the

A

Primative streak

51
Q

First to enter embryo during gastrulation

A

Endodermal cells

52
Q

Arise from the epiblast and enter the interior of the embryo, spread extensively, and give rise to dorsal and ventral derivatives

A

Mesoderm

53
Q

What are some dorsal mesoderm derivatives?

A

Bone, cartilage, and muscle

54
Q

What are some ventral mesoderm derivatives?

A

Kidney and blood

55
Q

The area of active invagination into the inner embry

A

Node

56
Q

A major determinant of mesoderm formation in the mammal

-mutation in mice caused a complete lack of mesoderm

A

The TGF-β peptide “nodal”

57
Q

“Nodal” is expressed in posterior region of embryo called the

-where mesoderm will form

A

Node

58
Q

Using the gene sequence of nodal as a probe, nodal expression was found in the

A

Primative streak

59
Q

Acts to generally inhibit initial mesoderm and nervous system development

A

BMP-4

60
Q

BMP-4 can be inhibited by the antagonists

A

Chordin, noggin, and lefty

61
Q

Initially induced by nodal at an earlier stage, which then both limits nodal expression as well as contributes to anterior head structure formation

A

Anterior visceral endoderm (AVE)

62
Q

“Nodal” expression begins even earlier and first induces another important region of the early embryo, which is called the

A

Anterior visceral endoderm (AVE)

63
Q

The Anterior visceral endoderm (AVE) is required for differentiation of

A

Anterior Structures

64
Q

Induced AVE in turn produces inhibitors that suppress nodal expression in most of embryo except for a small region at posterior end called the

A

Node

65
Q

There, at the “node” region, nodal expression increases to the “threshold” level needed for mesoderm to form and for

A

Primative streak formation

66
Q

Noggin and Chordin are produced at the

A

Node

67
Q

A transcription factor that will allow anterior structures to be induced in mesoderm moving anterior

-Also produced at the node

A

Goosecoid

68
Q

In addition to nodal, several other genes also affect mesoderm formation. One example of this is the T-box transcription factor

A

Brachyury

69
Q

Knockout of brachyury in mice leads to deficient

A

Posterior mesoderm (“tail-less” phenotype)

70
Q

Directs anterior mesoderm formation, which in turn directs head patterning

A

Goosecoid

71
Q

Too much gooscoid can lead to

A

Conjoined twins

72
Q

Sirenomelia defects reflect decreased posterior mesoderm and possibly result from too little

A

Chordin, Noggin, brachury, or FGF (or too much retinoic acid)

73
Q

Expressed in the forming mesoderm and leads to the formation of right and left sides

A

FGF peptide FGF8

74
Q

FGF in mesoderm promotes continued chordin and noggin expression, which in turn continue to inhibit

A

BMP-4

75
Q

The inhibition of BMP-4, especially in the dorsal region, promotes more mesoderm production as well as neural tissue development from

A

Ectoderm

76
Q

A major regulator of FGF is

A

Retinoic Acid (RA)

77
Q

Endogenous RA is produced and normally active in only small areas of the embryo where it activates

A

Nuclear RA receptors RAR and RXR

78
Q

Results in much reduced posterior structures and some transformation of posterior structures to anterior structures

A

Excess retinoic acid

79
Q

A potent teratogen at very low doses

A

Retinoic acid

80
Q

Despite this teratogenicity, 13-cis-retinoic acid is prescribed for

A

Acne (accutane)

81
Q

Also teratogenic at very high concentrations (10,000 units/day) because it will alter in vivo retinoic acid levels

A

Vitamin A

82
Q

Has reciprocal inhibitory actions with an FGF isoform

A

Retinoic acid

83
Q

RAldh2 (synthetic RA enzyme) is present in somite-derived mesoderm and thus RA is made by somites adjacent to neural tube and released. This RA binds to RA receptors in “stem” zone containing

A

FGF expressing cells

84
Q

Maintenance of posterior FGF is needed for the development of

A

Posterior structures

85
Q

Gradually turns off FGF8 from rostral to caudal

A

RA

86
Q

Since the body axis forms from rostral to caudal, RA gradually shuts off FGF8 in a tightly controlled manner that allows

A

Posterior structures to form

87
Q

Needed to allow posterior structures to keep

forming normally, and if it is turned off prematurely, there will be deficits in these structures

A

FGF8

88
Q

Excess RA will turn off

-results in posterior structure deficiencies

A

FGF8

89
Q

Direct the development of posterior structures

A

5’ Hox genes

90
Q

Causes FGF to turn off prematurely. Thus activation of more 5’ genes in the Hox cluster will not proceed, and as a consequence, posterior mesoderm will be reduced

A

Excess RA

BMS (62 decks)

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