Developmental Concepts and Genetic Bases Flashcards
Determination
not visible, but irreversible commitment to differentiation
Differentiation
expression of the developmental commitment; usually involves synthesis of cell-type specific proteins
Morphogenesis
shaping of the multicellular body and its organs; pattern formation
Muscle cell differentiation
- Determination: signals from other cells lead to activation of myoD, committing the cell to becoming a skeletal muscle cell
- Differentiation: synthesis of myoD protein further stimulates myoD and ultimately other muscle cell-specific genes such as myosin
What other function does myoD do besides turning on genes for myosin and other muscle proteins?
Also turns on genes that block cell division (multinucleate muscle cells)
Weismann’s Hypothesis (1892)
Determination is caused by segregation of developmental determinants by cell mitoses (at the cleavage stages)
John Gurdon’s nuclear transplantation experiments in frogs (1968)
- Frog egg cell + UV
- Enucleated egg cell
- Fully differentiated intestinal cell nucleus was transplanted into enucleated cell
- Egg w/ donor nucleus began to develop
- Tadpole
What are the 2 conclusions from Gurdon’s experiment?
- Somatic nuclei are totipotent; therefore, genes are not segregated to different cell types during development
- Prolonged exposure to an egg environment is necessary to allow “de-differentiation” of a somatic nucleus to an egg-like status
Development involves a reversible change in the genetic material: ____________________, not gene segregation
gene regulation
Ian Wilmut and colleagues experiment (1997)
- Starved somatic sheep cells (arrested them in G1 phase of cell cycle)
- Diploid cells were fused w/ enucleated eggs from a different ewe and stimulated to enter S phase
- Embryos were transplanted to the womb of a surrogate mother ewe
- One lamb survived to birth and was genetically identical to Sheep 1 (somatic cells)
What is the name of the famous sheep that was cloned?
Dolly
Carrot root cells and totipotency
A carrot root cell can be induced to form a mass of cells called a callus. The callus can grow an entire new plant, meaning that each plant cell is “totipotent.” This makes transgenic plants easier to make.
What is the “epigenetic landscape”?
the idea that developmental events channel determination to a final differentiated cell fate (totipotency decreases as developmental time goes on)
What are stem cells?
Undifferentiated, dividing cells that are found in embryos and adults
Where are the most adult stem cells found?
bone marrow, skin, and intestine (need frequent cell replacement)
Are adult stem cells totipotent or pluripotent?
Pluripotent: limited ability to differentiate into a restricted number of different cell types
Are embryo stem cells totipotent or pluripotent?
totipotent
How are embryonic stem cells removed?
They are taken from the Inner Cell Mass (ICM) of a blastocyst
Parkinson’s Disease
A common neurodegenerative disease
Cause: progressive degeneration of dopamine-containing neurons in a part of the brain called substantia nigra (SN)
Symptoms: tremor, muscle rigidity and weakness, speech difficulties, dementia, and a blank, mask-like facial expression
How can embryonic stem cells possibly cure Parkinson’s?
Embryonic stem cells can be implanted into the SN region, where they’ll hopefully differentiate into dopamine-producing cells and relieve symptoms of the disease
What is therapeutic cloning?
Process that involved fusing a cell nucleus from the affected person w/ an enucleated egg cell to make a blastocyst. The ICM from this blastocyst can differentiate into the desired tissue for transplantation w/o risk of immune system rejection (from using stem cells from another person)
What are cytoplasmic determinants?
Possible proteins or mRNAs in the egg/zygote that are segregated to different cells in the embryo and that turn on differential gene expression and/or regulate spatial events of development
What is induction?
Communication between different cell types that leads to increasingly specific developmental fates
Induction process
- the release of molecules from one cell that diffuse to adjacent cells and act on signal transduction pathways
- direct cell-to-cell contact of surface molecules on the sending cell to receptor molecules on the receiving cell
Ultimate outcome: turn on/turn off genes in the receiving cell
Why is programmed cell death (apoptosis) a part of development?
Can lead to modeling of the morphology of organs and limbs
Ex: paw development in mouse embryo
What is segmentation?
the formation of patterns during development
Segmentation in Drosophila
-unequal distribution of mRNAs and/or proteins in the egg leads to gradients of morphogens in the zygote
-morphogens: bicoid (anterior larval development) and nanas (posterior larval development)
Developmental steps in Drosophila
- Egg cell w/ nurse cells
- Early embryo that is multinucleate single cell
- Segmented late embryo
- Segmented larva
- Pupariation (imaginal discs)
- Adult w/ clear and complex segmentation pattern
Bicoid and nanas are examples of ___________________________.
maternally determined morphogens
What are the three types of segmentation genes that are induced by maternally determined morphogen gradients?
- Gap genes
- Pair Rule genes
- Segment Polarity genes
Gap genes
define broad areas that regulate pair rule genes
Pair Rule genes
refine the segment locations and regulate segment polarity genes
Segment Polarity genes
determine the final boundaries of each segment
What are homeotic genes?
Genes that define the role of each segment once the locations of segments are established
What happens if there’s mutations in homeotic genes?
The definitions of the role of each segment can be disrupted
Ex: bithorax on a fly (2 sets of abdomens > 2 sets of wings)
Homeobox?
180-nucleotide sequence that encodes a 60-amino acid homeodomain in the protein = Hox genes
What controls differentiation on the anterior-posterior axis of vertebrates and invertebrates?
Hox genes
__________ and ___________ expression of Hox genes follows the same pattern as the linear order on chromosomes
Temporal, spatial
Epigenetic Landscape and its channels
-Morphogens/gradients determine zones
-Regional developmental genes (gap, pair-rule, segment polarity) determine segments
-Hox genes determine identity
-Master developmental genes (myoD) determine subregion
-Specific functional genes (cell-type specific genes) determine function/physiology
Connection of developmental channeling and evolution
homologous limbs, comparative embryology
Neoteny
retention of juvenile characteristics in the adults of species (shrimps)
