Development of multicellular organisms Flashcards
(89 cards)
1
Q
What is the starting point of life for every multicellular organism?
A
A single cell—a fertilized egg, or zygote
2
Q
What are the three fundamental processes of animal development?
A
- Cell proliferation
- Cell specialization (differentiation)
- Morphogenesis
3
Q
What is cell proliferation?
A
The process that produces many cells from one
4
Q
Define cell specialization or differentiation.
A
The process by which cells take on different characteristics and functions
5
Q
What does morphogenesis refer to?
A
The rearrangement of cells to form structured tissues and organs (cell-cell interaction and cell movement)
6
Q
How does the developmental pathway of a cell branch during development?
A
Based on its internal state and current influences from neighboring cells
7
Q
What changes occur in cells as they become specialized?
A
- Changes in biochemistry
- Changes in shape
- Changes in attachments to other cells and extracellular matrix
8
Q
What do homologous proteins do across different species?
A
Perform the same role and are functionally interchangeable
9
Q
What are the three germ layers formed during gastrulation?
A
- Ectoderm
- Mesoderm
- Endoderm
10
Q
What is the role of ectoderm in development?
A
Gives rise to the epidermis and the nervous system
11
Q
What does mesoderm develop into?
A
- Muscles
- Connective tissues
- Blood
- Kidneys and other components
12
Q
What is the function of the endoderm?
A
Forms the gut tube and its appendages, such as the liver and pancreas
13
Q
What happens to the developmental potential of cells as they differentiate?
A
It becomes progressively restricted
14
Q
What is the term for a cell that can give rise to all cell types?
A
Totipotent or pluripotent
15
Q
What is cell determination?
A
The process through which a cell’s developmental potential is narrowed
16
Q
What is cell memory in developmental biology?
A
The record of past extracellular signals that influences gene expression and behavior
17
Q
What does the term ‘maternal-zygotic transition’ refer to?
A
The point when the embryonic genome is activated after maternal mRNAs and proteins are used up
18
Q
What are the basic animal body plan axes?
A
- Anteroposterior axis
- Dorsoventral axis
- Left-right axis
19
Q
What primarily causes differences between animal species despite conserved developmental mechanisms?
A
Variation in the activity of key development-controlling genes
This variation arises from regulatory DNA associated with coding genes.
20
Q
What role do regulatory elements in noncoding DNA play in development?
A
They determine when, where, and how strongly the gene product is expressed
Changes in regulatory DNA can alter gene regulatory networks without affecting coding DNA.
21
Q
What are the highly conserved signaling pathways involved in spatial patterning during development?
A
TGFβ, Wnt, Hedgehog, Notch, receptor tyrosine kinase (RTK)
These pathways govern most known inductive events in animal development.
22
Q
How does cell memory influence cell response to signals?
A
Previous experiences leave a lasting mark on the state of the cell’s chromatin and transcription regulators
This allows cells with different histories to respond differently to the same signals.
23
Q
What is the principle behind lateral inhibition in cell differentiation?
A
Positive feedback that amplifies initial differences between adjacent cells
This process allows cells to become different from one another, generating fine-grained patterns.
24
Q
What is the effect of asymmetric cell division on cell differentiation?
A
It ensures that daughter cells develop differently by unevenly distributing important molecules
This intrinsic mechanism results in cellular diversity without relying solely on extracellular signals.
25
What is inductive signaling?
A process where cells change their character in response to signals from neighboring cells
## Footnote
This process often involves limited time and space signals affecting a subset of cells.
26
What are morphogens known for in developmental biology?
Exerting graded effects based on their concentration
## Footnote
Different concentrations can lead to distinct developmental pathways for cells.
27
How does combinatorial signaling generate diverse cell responses?
Different combinations of signals received concurrently can lead to varied responses
## Footnote
This allows for complex patterns to arise from a limited number of signaling pathways.
28
What happens when a cell receives a strong signal in the context of lateral inhibition?
It produces less of the signaling molecule, thereby inhibiting its neighbor
## Footnote
This feedback mechanism drives neighboring cells to differentiate into distinct types.
29
What determines the range and steepness of a morphogen gradient?
The speed of diffusion and the half-life of the morphogen
## Footnote
These factors influence how the morphogen affects surrounding cells.
30
What is asymmetric cell division?
A process where daughter cells are born different due to unequal distribution of important molecules during division.
## Footnote
This mechanism is intrinsic to the dividing cell and is common in early development.
31
How does asymmetric inheritance during mitosis affect daughter cells?
It ensures that the two daughter cells develop differently.
## Footnote
This can occur due to the segregation of different fate determinants into separate blastomeres.
32
What is the role of extrinsic inductive signals in cell differentiation?
They can make daughter cells asymmetric after division, contributing to their different fates.
## Footnote
Extrinsic signals interact with the cells post-division.
33
Define symmetric division.
A division where daughter cells become different due to influences acting on them after their birth.
## Footnote
This contrasts with asymmetric division.
34
What is sequential induction in embryonic development?
A strategy where initial patterns are refined through a series of successive interactions between different cell types.
## Footnote
This generates increasingly complex structures as development proceeds.
35
What is a morphogen?
A signaling molecule that acts over short distances to direct developmental options for cells.
## Footnote
Morphogens typically have an effective range of less than 1 mm.
36
How do initial patterns in embryos become more complex?
Through cell proliferation and sequential inductive interactions that add detail to the initial pattern.
## Footnote
This involves signaling among different cell types to generate new ones.
37
What insights does developmental biology provide regarding adult tissues?
It helps understand cell growth, division, signaling, memory, adhesion, and movement in tissue maintenance and repair.
## Footnote
These mechanisms are similar to those involved in embryonic development.
38
What is the significance of studying early embryos like Drosophila?
They have led to the discovery of conserved signaling pathways crucial for understanding adult tissue maintenance and cancer therapies.
## Footnote
Examples of these pathways include Wnt, Hedgehog, and Notch.
39
What role does regulatory DNA play in development?
It determines the fate of each cell by binding to regulators of transcription and chromatin structure.
## Footnote
This DNA orchestrates the sequential program of development.
40
What is the primary task of a developing multicellular organism?
To create different cell fates in fields of cells and form functional tissues in a spatially ordered manner.
41
What are the primary axes of polarization in embryonic development?
* Anteroposterior (A-P) axis
* Dorsoventral (D-V) axis
* Left-right (L-R) axis
* Animal-vegetal (A-V) axis
42
What does the anteroposterior (A-P) axis specify?
The locations of future head and tail.
43
What does the dorsoventral (D-V) axis specify?
The future back and belly.
44
What defines the animal-vegetal (A-V) axis in many animal eggs?
It defines which parts become internal and which remain external.
45
What initiates the process of symmetry breaking in embryos?
A cue that creates a new axis in the embryo.
46
What are maternal effect genes?
Genes produced by the mother's genome that influence the patterning of the embryo.
47
What are the three fundamental partitions of body regions established by egg-polarity genes?
* Head versus rear
* Dorsal versus ventral
* Endoderm versus mesoderm and ectoderm
48
What are the three groups of genes that control Drosophila segmentation along the A-P axis?
* Gap genes
* Pair-rule genes
* Segment polarity genes
49
What is the function of gap genes in Drosophila development?
Mark out coarse A-P subdivisions of the embryo.
50
What happens when mutations occur in segmentation genes?
They can alter the number of segments or their internal organization.
51
What is a characteristic of the Drosophila egg's shape?
It is shaped like a cucumber.
52
What does the term 'zygotic-effect genes' refer to?
Segmentation genes expressed by the embryo's own genome.
53
What is the role of the maternal effect genes in the early developmental process?
They create landmarks in the oocyte that organize the developmental process.
54
What is the role of Bicoid mRNA in Drosophila development?
Bicoid mRNA encodes a transcriptional activator that determines the head and thoracic regions
## Footnote
Bicoid acts as a morphogen, activating different sets of genes at various positions along the A-P axis.
55
What does Nanos mRNA influence in the Drosophila embryo?
Nanos mRNA governs the formation of the abdomen and is necessary for germ-line development
## Footnote
Localized Nanos mRNA is incorporated into germ cells at the posterior of the embryo.
56
What are the functions of the receptor proteins Toll and Torso?
Toll determines mesoderm formation and Torso determines the formation of terminal structures at the head and tail
## Footnote
Both are activated by localized exposure to extracellular ligands.
57
What are pair-rule genes responsible for in Drosophila development?
Pair-rule genes demarcate repeated groups of cells that will later become segments
## Footnote
They collaborate with gap genes to set up a periodic pattern of segment-polarity gene expression.
58
Which signaling pathways are involved in segment-polarity genes?
Wnt pathway and Hedgehog pathway
## Footnote
Wingless and Hedgehog are key proteins in these pathways, maintaining each other's expression.
59
What are Hox genes and their significance in Drosophila?
Hox genes permanently specify the A-P characters of the segments
## Footnote
Homeotic mutations can transform body parts into structures appropriate to other positions.
60
What is the function of Hox proteins in segment identity?
Hox proteins act as transcription regulators that give segments their positional value
## Footnote
They can activate or repress hundreds of target genes.
61
What is the relationship between egg-polarity genes and segment-polarity genes?
Egg-polarity genes create a transient pattern that is remembered by segment-polarity genes
## Footnote
This memory helps maintain segmental organization throughout the organism's life.
62
What happens to the initial pattern of gap and pair-rule genes as embryonic development progresses?
The initial pattern disintegrates but induces the expression of segment-polarity and Hox genes
## Footnote
This results in a stabilization of the expression patterns.
63
What happens if all the Hox genes in an embryo are deleted?
The body segments in the larva will all be alike.
## Footnote
Hox genes are critical for segment identity in embryonic development.
64
How does each Hox protein give a segment its permanent identity?
Hox proteins are transcription regulators that bind to gene regulatory DNA, targeting a different set of genes for activation or repression.
## Footnote
Hox proteins control genes involved in various cellular functions.
65
What is the relationship between the order of Hox genes and their expression along the A-P axis?
The sequence of Hox genes ordered along the chromosome corresponds almost exactly to the order of their expression along the A-P axis.
## Footnote
This suggests a process of gene activation linked to chromatin structures.
66
What happens to the pattern of Hox gene expression as development proceeds?
The pattern undergoes complex adjustments but maintains a permanent record of A-P position.
## Footnote
This memory influences segment identity in both larvae and adult structures.
67
How do Trithorax and Polycomb group proteins interact with Hox genes?
Trithorax proteins help maintain Hox gene transcription, while Polycomb proteins repress genes that are not activated.
## Footnote
This balance is crucial for maintaining correct gene expression during cell division.
68
What is the consequence of a mutation that activates the Toll pathway everywhere in Drosophila?
Dorsal protein becomes concentrated in the nuclei everywhere, leading to a ventralized embryo.
69
What is the significance of the embryonic state of activation or repression in Hox genes?
It provides a heritable record of positional information that is maintained as cells divide.
## Footnote
This is essential for proper segment identity and tissue differentiation.
70
Describe the general strategy of pattern formation in animal embryos.
It involves a cascade of transcription regulators and signaling pathways that sequentially subdivide the embryo.
## Footnote
This principle is conserved across various animal species.
71
What is pattern refinement in embryonic development?
Pattern refinement is used during the development of all animal embryos, including vertebrates.
72
What does conservation in pattern formation refer to?
Conservation is not restricted to the general strategy of pattern formation but extends to many of the molecules involved.
73
How do the earliest phases of vertebrate development compare among species?
The earliest phases are surprisingly variable, even between closely related species.
74
What is the relationship between Hox genes and vertebrate development?
Hox genes control the anterior-posterior (A-P) axis and are highly conserved across species.
75
How many Hox complexes are found in mice and humans?
There are four Hox complexes: HoxA, HoxB, HoxC, and HoxD.
76
What is the significance of Hox gene expression patterns?
They are expressed in a head-to-tail series along the axis of the embryo, similar to Drosophila.
77
What is the role of MyoD in development?
MyoD acts as a trigger for the development of specific cell types or organs.
78
What happens when the Eyeless gene is artificially expressed in Drosophila leg precursors?
A well-organized eye-like organ develops on the leg.
79
What does the Notch signaling pathway inhibit in sensory organ precursor cells?
Differentiation into sensory organ precursors.
80
What leads to a single sensory organ precursor cell emerging from a cluster?
A positive feedback loop generated by stronger Delta signaling.
81
What determines the fate of daughter cells during asymmetric cell division?
Intrinsically asymmetric segregation of molecules.
82
How does Numb affect the fates of daughter cells?
It inhibits Notch signaling in one daughter cell.
83
What can variations in regulatory DNA lead to?
Extremely different tissues and body structures.
84
What is the main conclusion regarding regulatory DNA in animal evolution?
Differences in regulatory DNA primarily account for the diversity in body plans.
85
What do Hox genes determine in Drosophila segments?
Segment identity.
86
What signaling gradient is established along the dorsoventral axis in Drosophila?
A gradient of Dorsal protein.
87
What is Eyeless necessary for in Drosophila?
Generating eye structures.
88
What process results in different cell types through the activation of the Notch signaling pathway?
Lateral inhibition.
89
What is the main driver of anatomical changes in species according to recent evolutionary evidence?
Changes in regulatory DNA sequences.
