Module 5: Lecture chapter 18 Flashcards Preview

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Flashcards in Module 5: Lecture chapter 18 Deck (68):
1

Overview

Instructions in the genome establish the developmental fate of cells in multicellular organisms.

Developmental pathways consist of sequences of distinct regulatory steps.

The zygote is totipotent, giving rise to all body cells.

Gradients of maternally-derived regulatory proteins establish polarity of the body axis and control transcriptional activation of zygotic genes.

Transcriptional regulation and cell signaling mediate development in animals and plants.

The same set of genes appears to regulate early development in all animals.

2

Gradients of Maternally-derived regulatory proteins establish _____ and control _____.

Gradients of maternally-derived regulatory proteins establish Polarity of the Body Axis and control Transcriptional Activation of Zygotic Genes.

3

_____ and ____ mediate development in animals and plants.

Transcriptional regulation and cell signaling mediate development in animals and plants.

4

The same set of genes appears to regulate early development in _____.

The same set of genes appears to regulate early development in ALL Animals.

5

Development

In multicellular organisms, life begins as a single cell.

With few exceptions, somatic cells contain the same genetic information as the zygote.

In development, cells commit to specific fates and differentially express subsets of genes.

Cells identify and respond to their position in developmental fields.

Daughter cells may differ with respect to regulatory instructions and developmental fate.

6

With few exceptions, _____ contain the same genetic information as the ____.

With few exceptions, somatic cells contain the same genetic information as the zygote.

7

Building the embryo:
Developmental decisions

made at specific times during development

many are binary, e.g., male or female

most are irreversible

many involve groups of cells rather than single cells

Most decisions involve changes in transcription

8

Building the embryo:
In animals, decisions are made to

establish anterior-posterior and dorsal-ventral axes

subdivide the anterior-posterior axis into segments

subdivide dorsal-ventral axis into GERM layers

produce various tissues and organs

*Most decisions involve changes in transcription

9

Most decisions involve changes in ______ .

Most decisions involve changes in transcription

10

Development and the Genome:

-Animal genomes contain tens of thousands of genes, but only a fraction of them control the developmental process

-Development is the attainment of a differentiated state by all cells of an organism

11

Development is ......

the attainment of a differentiated state by all cells of an organism

12

According to the ______, development and differentiation is accomplished by activating and inactivating genes at different times and in different cell types.

According to the Variable Gene Activity hypothesis, development and differentiation is accomplished by activating and inactivating genes at different times and in different cell types.

13

According to the variable gene activity hypothesis, development and differentiation is accomplished by _______ .

According to the variable gene activity hypothesis, development and differentiation is accomplished by activating and inactivating genes at different times and in different cell types.

14

Early stages of embryonic development in Drosophila.

(a) Fertilized egg with zygotic nucleus (2n), shortly after fertilization.

(b) Nuclear divisions occur about every 10 minutes.
9 rounds of division produce a multinucleate cell, the Syncytial Blastoderm.

(c) At the 10th division, the nuclei migrate to the periphery (a.k.a., the cortex) of the egg.
Then 4 additional rounds of nuclear division occur.
A small cluster of cells, the Pole Cells, form at the posterior pole about 2.5 hours after fertilization.
These cells will form the germ cells of the adult.

(d) About 3 hours after fertilization, the nuclei become enclosed in membranes, forming a single layer of cells over the embryo surface, creating the cellular blastoderm.

(e) At about 10 hours after fertilization, the segmentation pattern of the body is clearly established.
Behind the segments that will form the head, t1–t3 are thoracic segments, and a1–a8 are abdominal segments.

(f ) The adult fly showing the structures formed from each segment of the embryo.

15

Early stages of embryonic development in Drosophila.

Reworded...

1. Diploid zygote nucleus is produced by fusion of parental gamete nuclei.

2. 9 rounds of nuclear divisions produce a multinucleated Syncytium.

3. Approximately 4 more divisions occur at the cell Periphery.
Pole cells form at the posterior pole (precursors to germ cells).

4. Nuclei become enclosed in membranes, forming a single layer of cells over embryo surface.

5. Embryo

6. Adult

16

Early stages of embryonic development in Drosophila.

Simplified...

1. Single-celled diploid

2. Multinucleate Syncytium

3. Syncytium Blastoderm with Pole Nuclei clustered at posterior end.

4. Cellular Blastoderm

17

master regulatory gene:

necessary and sufficient to determine cell fate

18

morphogen:

master regulator that determines fate at 3 or more concentrations!

19

a morphogen is a master regulator that.....

determines fate at 3 or more concentrations!

20

maternal vs zygotic genes

Maternal genes: gene products are expressed during oogenesis and deposited in the egg; hence expression of maternal gene products is based on genotype of mother!

Zygotic genes: gene products are expressed in the zygote (fertilized egg); hence expression of zygotic gene products is based on genotype of the zygote!

21

Maternal genes:

gene products are expressed during oogenesis and deposited in the egg.

Expression of maternal gene
products is based on genotype of mother!

22

Zygotic genes

gene products are expressed in the zygote (fertilized egg).

Expression of zygotic gene products is based of genotype of the zygote!

23

Drosophila anterior-posterior axis

Determined by gradients of BCD (product of bicoid) and HB-M (product of hunchback)

- mRNA is maternally deposited into the egg
- BCD mRNA is tethered to “–” ends of microtubules via 3’ UTR
- HB-M protein gradient depends on NOS protein
- nos mRNA tethered to “+” end of microtubule via 3’ UTR
- NOS protein gradient blocks translation of hb-m mRNA, resulting in HB-M gradient

Resulting gradients of BCD and HB-M determine axis

24

The Drosophila anterior-posterior axis is determined by......

gradients of BCD (product of bicoid) and HB-M (product of hunchback)

25

HB-M protein gradient depends on _____ .

NOS protein

26

nos mRNA is tethered to the ....

“+” end of the microtubule via 3’ UTR

27

BCD mRNA is tethered to the....

“–” ends of microtubules via 3’ UTR.

28

NOS protein gradient blocks translation of _____, resulting in ____ .

NOS protein gradient blocks translation of hb-m mRNA, resulting in HB-M gradient

29

Bicoid

a morphogen that determines cell fate.

30

The Drosophila dorsal-ventral axis is determined by the ......

gradient of transcription factor DL (encoded by dorsal)

31

Determined by gradient of transcription factor DL (encoded by dorsal)

gradient established by interaction of spz and Toll gene products deposited in oogenesis and released during embryogenesis

SPZ-TOLL complex triggers signal transduction pathway in cells that phosphorylates inactive DL

Phosphorylated DL migrates to nucleus, activating genes for ventral fates

32

In the Drosophila dorsal-ventral axis, the gradient is established by interaction of ___ and ___ gene products deposited in ____ and released during _____.

In the Drosophila dorsal-ventral axis, the gradient is established by interaction of spz and Toll gene products deposited in oogenesis and released during embryogenesis

33

In the Drosophila dorsal-ventral axis, the SPZ-TOLL complex triggers ______ in cells that phosphorylate _____.

In the Drosophila dorsal-ventral axis, the SPZ-TOLL complex triggers Signal Transduction Pathway in cells that phosphorylate Inactive DL.

34

Phosphorylated DL migrates to nucleus, activating genes for ____ fates.

Phosphorylated DL migrates to nucleus, activating genes for ventral fates

35

Positional information

Localization of mRNAs within cell establishes positional information in cases where developmental fields begin as a single cell

Formation of concentration gradients of diffusible molecules establishes positional information in developmental fields

Such diffusible developmental regulatory molecules are known as morphogens

36

Localization of _____ within cell establishes positional information in cases where developmental fields begin as a _____ .

Localization of mRNAs within cell establishes positional information in cases where developmental fields begin as a single cell

37

Formation of _____ establishes positional information in developmental fields.

Such diffusible developmental regulatory molecules are known as _____.

Formation of concentration gradients of diffusible molecules establishes positional information in developmental fields

Such diffusible developmental regulatory molecules are known as morphogens.

38

Complex pattern: Drosophila

Successive interpretation of established, changing, and new gradients

Largely due to changes in transcription

Genes targeted by gradients of maternal A-P and D-V transcription factors are cardinal genes
- respond to these factors at enhancers and silencers
- similar genes in other animals

39

Genes targeted by gradients of maternal A-P and D-V transcription factors are ____ .

Genes targeted by gradients of maternal A-P and D-V transcription factors are Cardinal Genes

40

cardinal genes

Genes targeted by gradients of maternal A-P and D-V transcription factors are cardinal genes

They respond to these factors at enhancers and silencers.
There are similar genes in other animals.

41

Drosophila development

Developmental fate determined through transcription-factor interactions

A-P cardinal genes = gap genes

Bifurcation of development: targets of gap gene encoded transcription factors

42

Bifurcation of development

targets of gap gene encoded transcription factors

- one branch to establish correct number of segments
- one branch to assign proper identity to each segment

43

A-P cardinal genes

= gap genes

Kruppel and knirps (mutants have gap in normal segmentation)

promoters have differential sensitivity to BCD and/or HB-M

establishes different developmental fields along embryo, roughly defining segments

44

Segment number

gap gene products activate several different pair-rule genes

expression produces repeating pattern of 7 stripes, each offset

pair-rule products act combinatorially to regulate transcription of segment-polarity genes

expressed in offset pattern of 14 stripes

45

gap gene products activate ______

pair-rule genes

- several different pair-rule genes
- expression produces repeating pattern of 7 stripes, each offset

46

pair-rule products act combinatorially to regulate .....

Transcription of Segment-Polarity genes

- expressed in offset pattern of 14 stripes

47

Segment identity

gap gene products target cluster of homeotic gene complexes

- encode homeodomain transcription factors
- mutations alter developmental fate of segment

e.g., Bithorax (posterior thorax & abdomen) and Antennapedia (head and anterior thorax)

48

_____ products target cluster of homeotic gene complexes

gap gene products target cluster of homeotic gene complexes

- encode homeodomain transcription factors
- mutations alter developmental fate of segment

49

Pattern formation

Transcriptional response to gradients (asymmetrical distribution) of transcription factors

Memory of cell fate

Cell-cell interactions

50

Memory of cell fate

- intracellular and intercellular positive-feedback loops
e.g., homeodomain protein binds to enhancer elements of its own gene, ensuring continued transcription

- Pattern formation

51

Cell-cell interactions

- inductive interaction commits groups of cells to same developmental fate

- lateral inhibition results in neighboring cells assuming secondary fate

52

results in neighboring cells assuming secondary fate.

lateral inhibition

53

5 Generalizations

Asymmetry of maternal gene products establishes positional information used for early development

Successive rounds of expression of genes encoding transcription factors establish axes and body part identity

Positive feedback loops maintain differentiated state

Components of one developmental pathway are also found in many others

Differences in types and concentrations of transcription factors result in different outputs

54

______ of maternal gene products establishes positional information used for early development.

Asymmetry of maternal gene products establishes positional information used for early development.

55

______ maintain differentiated state

Positive feedback loops maintain differentiated state

56

Developmental parallels

Early animal development follows fundamentally similar pattern

Remarkable similarity among homeotic genes
- 1 HOM-C cluster in insects
-4 HOX clusters in mammals
paralogous to insect cluster
expressed in segmental fashion in early development

Knockout and genome studies suggest animal development uses same regulatory pathways

57

Remarkable similarity among homeotic genes:
______ cluster(s) in insects

1 HOM-C cluster in insects

58

Remarkable similarity among homeotic genes:
____ cluster(s) in mammals

4 HOX clusters in mammals

59

Evolutionary conservation of regulatory gene function:

Eyeless/small eye

60

Flower is organized into 4 concentric rings:

whorl 1: leaflike sepals

whorl 2: petals

whorl 3: stamen (contain pollen)

whorl 4: carpels (fused to stigma bearing ovules)

61

whorl 1

leaflike sepals

62

whorl 2

petals

63

whorl 3

stamen (contain pollen)

64

whorl 4

carpels
(fused to stigma bearing ovules)

65

Sepals

Class A

66

Carpels

Class C

67

Petals

Class A & Class B

68

Stamens

Class B & Class C