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CELL1001 > Development Lecture 3 > Flashcards

Development Lecture 3 Flashcards

1
Q

What are the three mechanisms of cell commitment?

A
  1. localised determinants
  2. embryonic induction
  3. Morphogen gradients
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2
Q

What did Anthon van Leeuwenhoek discover?

A

sperm in 1677, he believed he could see the blood vessels and nervous tissue, supporting the idea of Preformation

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3
Q

Who first drew Homunculus and who thought that all future generations where in the Homunculi?

A

Nicolas Hartsoeker drew Homonculus

Nicolas Malebranche suggested the ‘Russian doll effect’

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4
Q

Who observed chick embryos under a microscope and incorrectly drew the Preformation conclusion from it?

A

Marcos Malpighi

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5
Q

Define Preformation

A

Organs and tissues are preformed in the egg/sperm.
Organs and tissues are correctly positioned in embryo
They simple enlarge during development

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6
Q

Define epigenesis

A

Organs and tissue are added gradually, the complexity increases through development

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7
Q

What five developments provided evidence for epigenesis?

A
  1. William Harvey (1578-1657) observed increasing complexity in deer embryos during gestation. He also studied chick and insect embryos and backed up Aristotle
  2. Cell theory - all living things are made from cells and new cells only arise though division of pre-exisiting cells.
    Sperm and eggs are single cells and cannot contain tissues made up of thousands of cells
  3. Hans Driesch - sea urchin embryos are capable of replacing parts that have been deleted. According to preformation, these parts should be permanently deleted.
  4. Gregor Mendel’s pea genetics - why offspring acquire characteristics
  5. Dyes and stains to study embryos
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8
Q

What ‘decisions’ are made that lead to the development of a neuron?

A
  1. which germ layer; ectoderm, endoderm, mesoderm?
    ectoderm (outer) germ layer
  2. Neuroepithelium or dermis?
    neuroepithelium
  3. forebrain, hindbrain, midbrain, spinal cord?
    hindbrain
  4. glia or neuron?
    neuron
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9
Q

Define pluripotent

A

Cell can become any cell, including the germ layers but NOT extraembryonic tissue cell

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10
Q

Define totipotent, give an example

A

Cell can become any cell, including extra embryonic tissue cell

The fertilised egg

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11
Q

Define multipotent

A

Cell can become any call from a specific germ layer

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12
Q

Who came up with the idea of an epigenetic landscape?

A

Conrad Waddington

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13
Q

Define determination

A

The commitment to a specific cell type, mostly irreversible

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14
Q

Define specification

A

commitment to a particular fate that can be changed according to the environment

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15
Q

Define differentiation

A

The process whereby cells acquire their final structure and functional characteristics, often by producing tissue specific proteins

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16
Q

How can specified and determine cells be distinguished experimentally?

A

A determined neuron cell, when located to another environment, will form an ectopic neuronal cell.
A specified neuronal cell when transplanted will not form a neuron because its fate is still determined by the environment

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17
Q

What are the two main mechanisms responsible for specifying cell fate in embryos?

A

Cytoplasmic determinants

Embryonic induction

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18
Q

What is a local determinant?

A

A molecule that can enter nucleus to determine gene expression that will determine cell fate

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19
Q

What did Wilhelm Roux (1850-1924) suggest determines cell fate in embryos?

A
  1. There are molecules that tell a cell what to become

2. The egg was a mosaic of different, unequally distributed determinants for all the different cell types

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20
Q

How did Wilhelm Roux (1850-1824) test his theory of determinants?

A

Roux (1888) killed a single blastomere of a two-cell frog embryo with a hot needle. The surviving blastomere developed into a half-embryo

He concluded that the embryo has a mosaic of different determinants

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21
Q

In reality, what do determinants do in an embryo?

A

There are only few determinants in an embryo and they establish general polarities.
It is rare for determinants to determine cell type fate

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22
Q

Give examples of determinants that do establish polarities

A

In Drosophila, the germ plasm determines germ cells

In Ascidians, the myoplasm determines muscle cells

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23
Q

What evidence supports cytoplasmic inheritance?

A

Transplantation studies
1. Cytoplasm in moved to a new location in the embryo

  1. If the cytoplasm contains local determinants then ectopic cells will form in that place in the embryo
  2. aberration of the determinant, results in the absence of the tissue type which it determines
24
Q

Who used the yellow cytoplasm of Ascidians to first observe local determinants?

A
  1. Edwin Conklin (1863-1952) - observed that ascidians have different coloured cytoplasm within the eggs
    - the coloured cytoplasm always ended up in the same place
    - any cells that acquired the yellow cytoplasm became muscle cells
    - Conklin suggested that the yellow cytoplasm contained muscle determinant
25
Q

What evidence had Laurent Chabry provided that supported Conklin’s observations in Ascidians?

A

Chary selectively killed blastomere from ascidian blastocysts and found that specific blastomeres were responsible for producing a particular set of tissues

26
Q

What did Chary conclude from his experiments on ascidian blastomeres?

A

Each blastomere develops autonomously and does not require interactions with other cells

27
Q

Who discovered macho-1?

A

Hiroki Nishida and Kaichiro Sawada (2001)

28
Q

What is macho-1?

A

Maternal macho-1 is localised to the yellow cytoplasm of the egg at the 16- and 32- cell stages

It is localised to cells that give rise to muscles

Macho-1 is a transcription factor that regulated muscle-specific genes (m-actin, m-myosin, myf, tbx6, snail)

29
Q

What happens (and why) when macho-1 is injected into ascidian embryonic cells that aren’t yellow?

A

they become muscle cells because muscle-specifc genes are turned on by macho-1

30
Q

What is mosaic development and give an example?

A

Ascidians
The egg is a mosaic of different local determinants that specific cell types

If you take blastomeres of the blastocyst and separate them from each other, each blastomere should develop into different part of the embryo

31
Q

What scientists separated sea urchin blastomeres at the two cell stage, the four cell stage and the eight cell stage?

A

Hans Driesch

32
Q

What happens when sea urchin blastomeres are separated and what is this called?

A

each blastomere forms a perfectly normal larva, just smaller than normal

REGULATIVE DEVELOPMENT

33
Q

What type of development do sea urchins follow?

A

Regulative

34
Q

True or false:

  1. Mammalian embryos are regulative
  2. If you separate ascidian blastomeres, each blastomere forms a normal, but smaller, larva
A
  1. true

2. false

35
Q

How are identical twins formed

A
  1. Blastomeres are separated

2. the inner cell mass divides

36
Q

What is a tetragametic chimera?

A

An individual that is made of two genetically distinct cell types

37
Q

Define competence

A

the ability of a cell to respond to a signal

38
Q

What is embryonic induction?

A

The process where cells communicate with each other to change their cell fates

39
Q

What is necessary for embryonic induction?

A
  1. signalling cell

2. responding cell

40
Q

Who separated newt blastomeres as they were undergoing the first cleavage division and found that two small but otherwise normal tadpoles grow?

A

Hans Spermann (1869-1941)

41
Q

True or false:

Human blastomeres can be separated up to the 8 cell stage and form normal embryos

A

false - only up to the 4 cell stage

42
Q

How can chimeras help geneticists?

A

Help to understand whether genes act autonomously (mutant cells continue to form the mutant phenotype)

or non autonomously (mutant phenotype is rescued by normal cell)

43
Q

How did Hans _ demonstrate embryonic induction?

A

Spermann

He transplanted small regions of the amphibian embryo into new locations
e.g. the notochord of a new gastrula into the ventral side of a similarly stages host, which formed a second dorsal axis (i.e. a conjoined twin)

44
Q

How did Spermann’s student _ demonstrate that the conjoined twin from the notochord transplantation was made of host cells or transplanted cells?

A

Hilde Mangold

  1. Transplanted prospective notochord cells from lightly pigmented gastrula into the ventral region of darkly-pigmented hosts
  2. She found that transplanted cells always formed the notochord of the conjoined twin but the nervous system of the conjoined twin was formed from host cells that would usually form the epidermis

THE GRAFTED CELLS HAD CHANGED THE FATE OF HOST CELLS

45
Q

What is neural induction?

A

Grafted notochord instructs ectoderm to form nervous system

46
Q

Why did Mangold & Spermann term the amphibian notochord ‘the organiser’?

A

The notochord changed the fate of host cells

47
Q

How does neural induction work in amphibians?

A
  1. The prospective notochord involuted inside the embryo during gastrulation and moves beneath the dorsal ectoderm
  2. The prospective notochord induced the overlying ectoderm to form the neural plate
  3. The prospective notochord also acts on adjacent mesoderm cells, instructing them to form muscle
48
Q

How do conjoined twins arise?

A

A transplant places a second notochord on the ventral side of the embryo

49
Q

Who transplanted the primitive node to a new location in the epiblast?
What did he observe

A

Conrad Waddington

Induction by the notochord

The node is the source of notochord cells in the avian gastrulae

The transplanted node continues to form the notochord
IT ALSO recruited host cells to form a second embryo, including much of the nervous system

50
Q

What is the structure of the distinct neuronal subtypes along the dorsal ventral access of the vertebrate spinal cord?

A 
V3 interneurons
MN
V2 interneurons
V1 interneurons
V0 interneurons
Floor plate
Notochord
51
Q

How can you distinguish between the different neuronal subtypes in the ventral half of the vertebrate spinal chord?

A

Each population expresses a different set of transcription factors

52
Q

How was neuronal specification in the vertebrate spinal cord demonstrated?

A

A section of the notochord was removed from the chick embryo

The notochord was grafted adjacent to the lateral wall of the neural tube

Where the notochord was removed - neural tube failed to specify into floor plate, ventral interneurons or motoneurons

The floor plate was formed by the neural tube, adjacent to the grafted notochord

The floor plate induced ectopic ventral interneurons and motor neutrons when grafted into the ventral wall of the neural tube

53
Q

What happens when a floor plate is grafted into the ventral side of the neural tube?

A

The floor plate induceds ectopic ventral interneurons and motor neutrons when grafted into the ventral wall of the neural tube

54
Q

What happens when the notochord is grafted adjacent to the ventral side of the neural tube?

A

The notochord induced the floor plate and the floor plate indicted ventral interneurons and motor neurons

55
Q

what signal is responsible for the inductive activities of the floor plate an notochord?

A

Sonic hedgehog (Shh)

56
Q

How did _ use sea urchin embryos to support epigenesis?

A

Hans Driesch - sea urchin embryos are capable of replacing parts that have been deleted. According to preformation, these parts should be permanently deleted.

CELL1001 (3 decks)

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