Developmental Genetics and Immunology

totipotent

cell that has the potential to develop into any cell typ e

determination

cell becomes committed to a particular cell fate

cloning experiments

supported hypothesis that all cells contain the same genetic material, but different genes are expressed

• development requires selective expression

developmental stages in fruit flies

embryo → three larval stages → adults

• different genes influence development at each stage

syncytium (early development)

multinucleate cell

syncytial blastoderm

nuclei migrate to the edge of a cell and divide

cellular blastoderm

cell membrane grows around each nucleus

primordial germ cells

nuclei at one end of blastoderm

Step one embryo development

establish axes

• dorsal-ventral and posterior- anterior

step two embryo development

number of segments and orientation of body segments

step three embryo development

determine each identity of each segment

establishing axes

• egg polarity genes

  • transcribed into mRNA during oogenesis

  • morphogen concentration gradient in embryo

egg polarity genes (dorsal-ventral axis)

dorsal - ventral axis

• dorsal gene transcribed and translated in ovary

• protein remains in cytoplasm at dorsal surface

• protein taken up into nuclei at ventral surface

• cactus gene produces protein that binds to and prevents dorsal protein from being taken up by nuclei

• toll gene produces protein that phosphorylates cactus protein causing it to degrade

  • allows dorsal to be taken up by nuclei

• high concentration of dorsal protein activates twist

• low concentration of dorsal protein activates decapentaplegic

egg polarity genes (anterior-posterior axis)

• bicoid transcribed during oogenesis

• bicoid mRNA and protein incorporated into cytoplasm at anterior end

• after fertilization concentration gradient established

• bicoid protein activated hunchback gene that leads to head and thorax

• nanos gene transcribed in ovary and mRNA concentrated at posterior end

  • nanos protein concentration opposite of bicoid

segmentation genes

control the differentiation of the embryo into individual segments

• gap genes → pair rule genes → segment polarity genes

gap genes

divide embryo into broad regions

• mutation: eliminated groups of segments

pair rule genes

development of alternate segments

• mutation: deletion of either even or odd numbered segments

segment- polarity genes

development of individual segments

• mutation: deletion and replacement of mirror image of deleted segment

segment identity

homeotic genes: determine identity of segments

• expressed after fertilization

  • activated by concentrations of proteins from genes associated with segmentation

antennapedia complex

head and anterior thorax segments

bithorax complex

posterior thorax and abdomen segments

apoptosis

controlled cell death

necrosis

injured cells dying in an uncontrolled manner

• cell swells

• bursts to release cell contents

• inflammatory response

eyeless gene

controls eye development in fruit flies

small eye

controls eye development in mice

aniridia

controls eye development in humans

differential expression of sonic hedgehog (shh) and piggy-winkle hedgehog (twhh)

evolution and gene expression

higher expression in cave fish

other eye development genes highly methylated in cave fish

• decrease

antigens

molecules that elicit an immune reaction

antibodies

proteins that bind to antigens and mark them for destruction by phagocytic cells

humoral immunity

production of antibodies by B cells

cellular immunity

depends on T cells

clonal selection

• large pool of lymphocytes

• antigen enters body

  • appropriate lymphocyte recognizes and binds to antigen

  • lymphocyte divides

  • primary response: production of antigen specific B and T cells

• memory cells remain in circulation

• if the same antigen reappears

  • antigen binds to the memory cells

  • gives rise to a secondary immune response