Lecture 11 & 12 : Animal development Flashcards
1
Q
What are the three stages of development?
A
- cellular
- tissue
- organ
2
Q
Describe the cellular stage;
A
- cleavage: uniform cell division, leading to a morula (solid ball of cells)
- blastula: morula continues to divide, forming a blastula, (hollow ball of cells)
- the blastula contains a fluid filled cavity called a blastoecel
3
Q
Describe briefly the tissue stage:
A
- gastrulation occurs where 3 germ layers form called endoderm, mesoderm and ectoderm.`
4
Q
Describe the stages of gastrulation
A
Early gastrula :
- blastula cells push inward and form a double layer of cells.
- The inner layer is the endoderm (primitive gut or archenteron) and the outer layer is the ectoderm.
- the hole formed by the inward folding is called the blastopore.
Late stage:
- a middle layer of cells is formed called the mesoderm
5
Q
Describe the organ stage:
A
- nervous system develops from the midline ectoderm by cell thickening to form the neural plate.
- two neural folds develop on either side of the neural plate, forming a curvature structure. The base of the curve is called the neural curve.
- the neural folds come together to form a tubular structure called the neural tube. The anterior end if the tube forms the brain while the rest becomes the spinal cord.
6
Q
What are the 3 interconnected processes of development?
A
- growth : an increase in cell number through cell division
- cellular differentiation: cells become specialized in structure and function
- morphogenesis: cell movement and pattern formation to produce eventual organism shape
7
Q
What is cytoplasmic segregation?
A
- Maternal determinants are mRNA or protein molecules present in the egg cytoplasm that stimulate early development.
- segregation of MDs determine type of cell and organs developing from the 3 germ layers : ectoderm, mesoderm and endoderm.
8
Q
What is induction?
A
- cells can be induced to develop via inducers, released by neighboring cells.
- inducers activate expression of particular genes.
- thus induction requires transcriptional regulation of genes in a precise sequence.
9
Q
Describe an example of Induction
A
- in C. elegans :
- vulva formation induced by anchor cell
- cells closest to anchor cell receive most inducers and develop into inner vulva
- inner vulva cells produce more inducers, acting on neighboring cells to develop in outer vulva.
10
Q
What is Morphogenesis? What enables it? What regulates it?
A
- the construction of the ultimate body shape.
- Pattern formation enables morphogenesis by ensuring proper strategic cell movement and organization.
- Both are regulated by transcription of various gene sets
11
Q
Describe the anterior/posterior axis:
A
- egg polarity genes establish anteroposterior polarity, where anterior will form the head and posterior, the abdomen.
- polarity present in egg before fertilization.
- egg polarity caused by MDs expressed in the form of mRNAs placed in specific positions within the egg.
- When fertilized, MD-mRNAs are translated into proteins that form gradients (morphogens) along anteroposterior axis.
- These morphogens will activate segmentation gene expression.
12
Q
What are the 4 genes related to the segmentation pattern?
A
- Gap genes
- Pair-rule genes
- Segment-polarity genes
- Homeotic genes
13
Q
Describe Gap genes;
A
- zygotic genes
- activates by morphogen gradients
- they divide anteroposterior axis into broad regions
- activate pair rule genes
14
Q
Describe Pair rule genes
A
- Expressed periodically in alternating stripes
- body segments are formed along anteroposterior axis
- their protein products activate or suppress segment-polarity genes
15
Q
Describe Segment polarity genes
A
- ensure each segment has boundaries
- expresses in striped fashion, twice as many stripes as pair-rule genes.
