The steps of L/R axis establishment that are similar across species - Answers1. Some initial symmetry breaking event in the early embryo
2. Magnification of that asymmetry by the L/R organizer. The LRO is a transient, midline-located structure
3. The LRO establishes patterns of asymmetric gene e...
BIO 467 EXAM 2 - LEFT/RIGHT AXIS
Questions & Answers 100%
The steps of L/R axis establishment that are similar across species - Answers1. Some
initial symmetry breaking event in the early embryo
2. Magnification of that asymmetry by the L/R organizer. The LRO is a transient,
midline-located structure
3. The LRO establishes patterns of asymmetric gene expression in the lateral plate
mesoderm (an influx in Ca2+-->nodal production-->Pitx2 expression on left side)
4. The L/R asymmetry is elaborated at a morphological level
LROs in the various model systems - AnswersChick: Henson's node
Mice: the node (a transient structure at the posterior end of the notochord)
Frogs: midline region of the posterior gratrocoel roof plate
Fish: Kupfer's vesicle (fluid-filled structure at the end of the tailbud)
situs solitus - Answersnormal L/R arrangement of organs
solitus inversus - AnswersReversal of the L/R asymmetry. Often an individual can
live/die normally because what matters more is that they is an asymmetry, not
necessarily on what side
right or left isomerism - Answersboth sides are specified as right or as left -- there is no
asymmetry
situs ambiguous - Answersthe L/R axis is random - lethal
molecular vs morphological asymmetry - AnswersMolecular L/R asymmetry is already in
place shortly after gastrulation. The embryo is initially symmetrical is reference to L/R
morphology (ie even though there is asymmetry of gene expression just after
gastrulation, the phenotype is not seen until around the time of organogenesis)
tissues that exhibit L/R asymmetry - AnswersThe tissues that exhibit L/R in adults are
derivatives or endoderm or lateral plate mesoderm. These two tissues are very closely
opposed in early development
lateral plate mesoderm - AnswersDerived from the splanchnic layer and is located
furthest from the midline. There is differential gene expression in the lateral plate which
signals to the endoderm beneath it.
splanchnic layer - AnswersThe layer closest to the endoderm that gives rise to the
lateral plate mesoderm.
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