BIOL 202 Lecture 6: Prof Moon Lecture 6
Prof Moon Lecture 6:
Developmental genetics II:
Non transcriptional regulation during development
Antibody diversity during B-cell development
Non transcriptional Regulation:
C.elegans and translational control:
Mutagen analysis was done on C. elegans for heterochronic genes- to look for
heterochromic mutations. Heterchronic mutation affect timing of stereotyped divisions.
C.elegans follow a stereotype pattern of growth witch each stage perfectly times. When
heterchronic mutations were observed, some steps of development ended too quick and
some ended very late.
One mutation that was seen was let-7 which affected the V1-4 vulval cell division with steps
L1-4 before becoming an adult. Let-7 mutants repeat the L4 division of the V1-4 in the adult
stages.
When let7 was screened for, it turned out that it wasn’t encoding a protein, it wasn’t
encoding any transcriptional factor (so non transcriptional regulation). Instead let7 encoded
short (22nt) miRNAs derived from double stranded RNA precursors. RISC binds to miRNA
and this complex binds to 3’ UTR region of target mRNAs. This RISC-miRNA complex inhibits
translation of the target mRNA. Result: less target protein made
Let7(wt.)->miRNA produce->RISC +miRNA->attack target mRNA-> lower expression of target
mRNA.
Let7 encodes miRNA that reduce expression of target mRNA. Let7 can produce many
miRNAs that cater to different mRNAs including gene called lin-41. Imagine let7 being
mutated? This would lead to less miRNAs and less targeting, more lin41 protein being
produced. If lin41 is mutated itself, lin41 is not expressed much resulting in lesser protein
made. Either of these mutations disrupt the lineage dividing times V1-4.
Immunogenetics:
Antibodies are produced by our body to fight against diseases.
The immune system is part of the hematopoietic tree (cell syetem:RBCs, WBCs, platelets
etc). There are 2 types of immunities: Adaptive Immunity (antigen-specific defense) : T-cell,
B-cell.
Innate immunity (nonspecific defense but quick response): NK cell, macrophage etc. Any
foreign bacteria or organism will be eaten up by these.
Adaptive immunity (antigen specific immunity)
Antigen: any molecule (usually a protein) that elicits an immune response.
Antibody: (called immunoglobulins) proteins that are present in the blood and other body
fluids that bind to antigens and mark them for destruction by phagocytic cells.
Autoimmune disease: an immune reaction against its own antigens. Body’s immune system
attacks its own tissues and cells.
There are 2 types of adaptive immunity:
- Humoral Immunity (adaptive): this involves production and secretion of antibodies by a
specialized lymphocyte (white cells) called B cells. Secretory.
-Cellular Immunity (adapt): These are also specialized lymphocytes called T cells that
produce T-cell receptors that recognize and bind antigens only found on the body’s own
cells.
B cells and T cells are both lymphocytes and these originate from stem cells in the bone
marrow. They both have different step of development and modes of action but one thing
common in them is that they both recognize a unique non-self-antigen that can elicit
immune response.
How do they make antibodies based on which foreign body/ virus they encounter that they
may have never even seen before?
When B and T cells are developing, each one recognizes a unique antigen with a non self.
Each B or T cell is specific to random non self-antigens. There are many antigens which can
be recognized this way. E.g. 100 cells are produced. This means 100 different antigens can
be recognized by the body. There is a hope that the foreign antigen is recognized for
immune response.
