Lectures 3-4 (Quiz 2) Flashcards
What is neurulation and when does it occur?
Neurulation is the folding of the neural ectoderm/plate into the neural tube. It happens after neural induction (as well as post gastrulation)
What is neural tube patterning?
Subdivision of the neural tube into the distinct regions of the central nervous system, and further subdivision of each region.
What are the four main regions of the CNS?
Forebrain, midbrain, hindbrain, and spinal cord?
What are the two body axis, and what does each part stand for?
The anterior-posterior (head-tail) axis, and the dorsal-ventral (back-front).
In addition to neural induction, what role does the dorsal lip play?
Organizing a correctly patterned nervous system in the neighboring ectoderm.
What happens during gastrulation?
Generation of the 3 germ layers. The dorsal lip contains migrating mesodermal (and some endodermal) cells. During gastrulation, blastomeres undergo dramatic movements wherein they change their positions relative to one another to produce three germ layers.
What are blastomeres?
Cell type produced by cell division of zygote post-fertilization.
What are the “new neighbors” that gastrulation brings (aka what are the new, more specific germ layers)?
Head mesoderm, neural ectoderm, chordamesoderm, endoderm, epidermis, and anterior endoderm
How do positional cues. help with neural tube regionalization?
Positional cues established along the embryonic body axes allow cells to choose to become different parts of the CNS.
What are the two steps/signals that lead to neural tube regionalization?
Activators instruct cells to choose neural fate. Transformer specifies different regions in a concentration-dependent manner.
What is a morphogen?
A substance whose concentration gradient drives the patterning/localization of specialized cell types within a tissue.
What are rhombomeres?
Transiently divided segments of the developing neural tube. Each develops its own set of gangllia/neurons and nerves.
How do hox genes help to define Drosophila segments?
Hox genes are a highly conserves gene family - in drosophila expressed in distinct domains along the A-P axis. Segments are made of two parasegments. Differences in hox gene expression specify paraasegment identity.
What is lineage in the context of cell differentiation?
The pattern of cell division that leads from a given precursor cell to a particular set cell types (intrinsic).
What are two ways extrinsic cell-cell signaling help to diversify cell types?
Secreted factors (eg. morphogen gradient) or direct cell-cell communication (eg. membrane bound ligand and receptor)
What are two ways intrinsic cues / lineage help to diversify cell types?
Intrinsically asymmetric cell division, and temporal regulation?
How does neurogenesis in the spinal cord work?
Neural progenitor cells divide repeatedly to produce neurons. Different types of neurons are generated along the D-V axis.
In the spinal cord, how are progenitor cells established, and what is the significance?
Patterning along D-V axis establishes distinct progenitor populations in the spinal cord. Each progenitor population generates a unique type of neuron.
What are the notochord and roof plate?
They are two distinct parts of the spinal cord that help to pattern the ventral and dorsal neural tube, respectively.
How does the notochord help pattern the ventral neural tube?
The notochord secretes the Shh protein, a morphogen whose gradient induces multiple cell types. All 6 ventral neural progenitor populations fail to form without Shh.
What is notch-delta signaling?
Lateral inhibition occurs through notch (receptor) delta (ligand) signaling. It allows only one cell to become a neural precursor from a group of equivalent cells.
What is special/unique about the notch receptor?
Though it is a transmembrane receptor, its intracellular domain is a transcription factor. Binding of delta ligands (and similar ones) to notch eventually releases NCID from the membrane, entering the nucleus to regulate gene expression.
How do numb mutants affect cell fate?
Asymmetric numb localization in dividing precursor cells allows the 2 daughter cells to adopt different fates. Numb loss and gain (symmetric distribution) cause daughter cells to adopt fate of their sibling.
how does notch play a role in cell fates of cells with numb mutants?
Notch mediated cell-cell communication is required for the two daughter cells to adopt different fates after an asymmetric cell division.
What are neuroblasts?
Neural stem cells in embryonic NSC capable of generating a series of different neural cells (called ganglion mother cells).
What allows neuroblasts to generate different neural cells?
Sequential expression of different transcription factors after each division (temporal order of neurogenesis).
What does the chinmo do during neurogenesis?
Temporal control. Chinmo forms a concentration gradient (temporally) which enables larval neuroblasts to generate different neural cells after each division
How many layers of neurons are there in the neocortex?
- Neurons in different layers are different in morphology and function.
What is the a general explanation for temporal regulation of neurogenesis?
During devo, neural stem cells follow a temporal order to make different layers of neurons during neurogenesis (same stem cell makes different neurons at different times), even when they are cultured in vitro.
What are the 4 main parts of development?
Determination, differentiation, morphogenesis, and growth
What are the two ways to make cellls different (intuitive)?
Born different, or identical initially and external signaling leads to differentiation.
What are the three mechanisms for asymmetric cell division?
Establish cell polarity, orient mitotic spindle, localize cell fate determination.
What are early cell divisions in mammals called?
Cleavages
What do we call different cells that are derived from cleavage?
Blastomeres
What is a blastula/blastocyst
What the early embryo becomes when a central fluid filled cavity emerges. Individual blastula cells are called blastomeres.
What are different example of cleavage patterns in animals?
Complete cleavage in frogs, incomplete cleavage in birds and fish, and superficial cleavage in flies.
What helps to establish the body axes and segment identity?
Differential gene expression
What are maternal effects?
When an organism shows the phenotype expected from the mother’s genotype (regardless of its own), due to the mother supplying mRNAs or proteins through the egg.
Which side of the embryo does the egg develop from? And where does the egg develop from/to? (answer in terms of bodily axes)
The egg develops from the posterior side. The nucleus develops from the posterior side, and by the end of development is at the anterior side.
How do maternal effects occur? Are zygotes polarized?
Ovary nurse cells can deposit different regulatory molecules into the eggs along both A-P and D-V axes (zygotes already polarized)
What are two examples of morphogen maternal effect genes?
Bicoid and nanos
Which protein gradient do bicoid and nano help form?
Hunchback proteins
Describe the nanos and bicoid protein gradients from A-P.
Bicoid and nanos gradients help to form hunchback protein gradients. Typically, bicoid protein gradients go from high to low (from A-P), and nano protein gradients go from low to high (from A-P).
How do nanos and bicoid gradients help form hunchback gradients?
Hunchback mRNA distributes evenly, but the hunchback protein does not. Nano translationally represses hunchback, while bicoid transcriptionally activates hunchback. The gradients of both bicoid and nano help to form the hunchback protein gradient .
In drosophila, where is bicoid key in development? Explain
In the anterior region. Bicoid is both necessary and sufficient for anterior (head) development.
What are homeotic genes
Genes that define the role of each segment
What are segment polarity geens
Genes that determine the boundaries and A-P orientation of each segment.
What is the difference between enhancer, promoter, and transcription sequences?
Transcription sequences is where the first DNA nucleotide gets transcribed into RNA. Promoter sequences are near the transcription site (typically) upstream ; this is where transcription factors bind to initiate transcription. Enhancer sequences enhance transcription of an associated gene (when transcription factors bind)
What protein patterns the D-V axis?
The maternal dorsal protein
What is the dorsal protein and what does it do?
It is a transcription factor (needs to be in nucleus), and regulation of whether it can enter the nucleus results in a nuclear gradient.
Explain what high/low threshold genes are, and their signficance for D-V axis patterning.
High threshold genes are only activated when theres a high amount of transcription factors (TF), while low theeshold genes do not need a lot of TF to activate. Mesoderm has more TF, so genes that cause mesodermal induction are high threshold genes. Neural ectoderm have low amounts of TF. As for patterning, low threshold genes turn cells to ectoderm (which makes sense because there is low transcription in the ectoderm). At the embryo’s ventral side, which has high threshold genes, it makes mesoderm instead of ectoderm.
Define the 4 embryonic axes (for amphibians)
Ventral (sperm entry), anterior (animal pole), dorsal, and posterior (vegetal pole), and
Which direction does the cortical cytoplasm rotate?
Toward the site of sperm entry (ventral axis)
After sperm entry, what initiates development
Cortical rotation
How does cortical rotation help to establish the organizer?
Cortical rotation leads to dorsal enrichment of the transcription factor b-catenin, which turns on genes essential for organizer formation
How are mesodermal and ectodermal cells differentially specified?
By the BMP gradient. BMP inhibitors allow dorsal ectoderm to adopt neural state. The BMP gradient allows for differentiation within both mesodermal and ectodermal cells.
Are humans symmetrical from left to right?
Though vertebrates appear to be bilaterally symmetrical, internal organs are located asymmetrically within the body
What determines L-R asymmetry?
Differences in gene expression
How is L-R symmetry broken
By the reversal or nodal flow. Nodal flow is the flow of the nodal cilia from left to right, moving important signaling molecules from L-R, and patterning the L-R axes correctly. Reversing the flow can cause a reversal of internal organs.
When does neurulation happen?
Neurulation / neural induction happens after gastrulation.
What does neurogenic mean in the context of notch-delta signaling?
Notch and delta are neurogenic, meaning they allow a single cell to become neural precursor cells.
Explain how hox genes help determine cell fate/identity?
A mixture of various hox genes decides what body part a cell will differentiate to. If some of those hox genes are missing, you will get a different cell than intended, which is called a homeotic transformation.
What is a temporal gradient?
A change in concentration over time (would graph concentration over time, rather than concentration over A-P axes, for eg.)
