Lecture 20. Evo-Devo: How body plans can change through evolution ? Flashcards
What is evo-devo ?
The synthesis of the study of evolution and developmental biology
How is development is regulated ?
Through transcriptional control and regulatory networks
What regions of genes are important ?
The control regions and not just the coding regions
What are developmental regulatory genes referred to as ?
The genetic toolkit for development
What do regulatory genes make up ?
A fraction of all genes
What do regulatory genes encode ?
Either transcription factors or components of signaling pathways
What is the spatial and temporal pattern of regulatory gene expression closely correlated ?
Regions in the animal where the gene functions
What are the three types of changes in developmental regulatory genes that might bring about changes in body plan ?
- Change in number of genes
- Change in the timing and spatial domain of expression
- Change in gene interaction
What was discovered about multicellular animals with organised body plans ?
Contain clusters of Hox genes
How many hox clusters do invertebrates have ?
A single Hox cluster
What happened around 520 million years ago to allow elaboration of the vertebrate body plan ?
Postulation - Cluster duplication
What happens after postulation ?
A second duplication around 425 million years ago yielded four clusters
What does gene duplication facilitate ?
Evolutionary change
What does the presence of more hox genes arranged in additional clusters allow ?
The evolution of more complex and new body parts
What does the change in spatial expression show us ?
Examine the expression of Hox genes in various species can shed further light on how body parts were gained or modified or lost
What are the two main derived features of snakes ?
- limblessness
2. Vertebrae are all of the thoracic type and bear ribs
What is the hox positional code of snakes ?
Complex overlapping expression of 39 hox genes in different anterior posterior locations
How has the hox code gene expression in snakes changed ?
Expansion of Hox gene expression domains along the body axis giving thoracic type code at all points. Also removes the cue to make a forelimb
How are snakes hindlimbs believed to be lost ?
Regression
How do we get out fingers and toes ?
Limbs with fingers/toes acquired a new region of hox gene expression at the distal end of the limb to allow digits to be patterned
How could changes in spatial expression occur ?
By changing the control regions - enhancers driving expression of the hox genes in the embryo
What is extremely important in the evolution of body plans ?
Control regions can also evolve
What do marine spined sticklebacks have ?
Ventral spines to protect from predators
What do lake sticklebacks have ?
Reduced or absent spines
What has causes this recent change in stickleback body plans ?
Lake sticklebacks have specifically lost expression of pitx 1 where ventral spines would form instruction to make a spine. This is missing
What is pax 6 ?
The master regulator of eye development
What type of gene is pax 6 ?
A homeobox gene
What is a mutation in pax6 in drosphilia called ?
Eyeless
What does the mutation in pax 6 in drosphilia lead to ?
Leads to loss of eyes
What is the mutation in pax 6 lead to ?
A phenotype called small eye in the heterozygous state
What does the mutation in pax 6 in humans cause ?
Aniridia, a malformation of the iris
What does forced expression of the pax 6 gene in drosphilia on the leg or antenna lead to ?
The formation of extra ectopic eyes in that site
Where is Ubx expressed in insects ?
Abdominal segements
What does Ubx do in abdominal segments in insects ?
Suppresses limb formation
Where is Ubx expressed in arthropods other than insects ?
Expressed in abdominal segments
What does the Ubx do in arthropods other than insects ?
It does not suppress leg formation
What influences changes in protein sequences of Ubx activity as an activator/ repressor ?
Sequence comparisons
What allows changes in the body plan of organisms ?
Changes in the activity of a positional regulatory gene
What creates morphogenesis ?
Differential growth rates
What is meant by a homologous structure ?
Structures that arise from same structure in common organisms
What can the different relative sizes and shapes of homologous structures be changed by ?
The length of time a particular signaling pathway or organising centre such as AER is active
What are the shapes of skeletal rudiments sensitive to ?
Mechanical stimulation which can be seen in the hippo pathway
