![]() ![]() if constrict is along the plan of the 2nd cleavage each morula blastopore nucleus is capable of developing int an embryo (nuclear equvalency) nuclear equivalency only occurs id the initial constriction i along the plane of the normal 1st cleavage (bisecting gray crescent) Result: 2 newt embryos formed Nuclear equivalence - components of the gray crescent direct normal development Perchyordal plate - head mesoderm why do the 1st IMZ cells that move inside the embryo become head mesoderm rather than notochord_ the involute more anteriorly Axis determination amphibians 1)dorsal vegetal cells induceĢ) DMZ to initiate gastrulation Experiment: test of nuclear equivalency (does every nucleus in the early embryo have the same potency?) 1) constrict a newt zygote with a hair, leaving the nucleus on one sideĢ) Allow cleavage to 16-cell stage (only cells on the side that contains nucleus will divide)ģ) Allow one of the nuclei to migrate to other side of the constricted zygoteĤ)Complete the separation of the 2 halves. shape is bottle cells Gastrulation initiatio mechanisms 1) Cells of the inner Marginal zone (IMZ at the site of blastopore formation) elongate inward)Ģ) Bottle cells invaginate to form the blastoporeģ) Involuting mesoderm cells move toward animal pole forming archenteron What happens with bottle cells while forming the archenteron - bottle shape is not needed for the extension of the archenteron, so they -respread (loose their bottle shape) What becomes the dorsal mesoderm IMZ cells (dorsal blastopore lip) determined DMZ tissue directs the conditionally specified presumptive endoderm to form a blastopore like structure take DMZ cel and place them on region of presumptive endoderm (ventral marginal zone) the graft sinks to form a blastopore lip like groove. one tadpole develops from the ventral blastopore What happens ifīlastopore is UV radiated and the dorsal vegetal blastopore embryo becomes mass of ventral tissue What does UV radiation due to the blastula Destry maternal DNA Dorsal vegetal cells induve marginal zone cells to initiate gastrulation Dorsal Marginal Zone cells are induced by vegetal cells, to become determined to initiate gastrulation Experiment: Transplantation of a dorsal blastopore lip graft. conjoined twin tadpoles develop What happens if the recipient of transplant vegetal blastopore is UV radiated and the dorsal vegetal blastopore from the donor is put in recipients ventral side. Results: transplanted blastomeres induced formation of 2nd blastopore Take a dorsal vegetal blastomere from the donor and place it in the ventral region of the recipient cell movement result in a rotation of embryonic axes the marginal zone blastula cells labeled Dorsal (D) - involute to become dorsal mesoderm Transplant and vegetal blastomeres experiment - both donor and recipient are normal (64 cell embryo) The remaining outer layer of cells become ectoderm The gray crescent future gastrulation initiation site gastrulation initation the dorsal side of the embryo - opposite of ventral side the archenteron extend and the tissue partitions into mesoderm and endoderm hybridization of this antisense RNA with the EP-cadherin mRNA prevents translation of the message Amphibian gastrulation, what forms the gray crescent dorsal lip of blastopore Amphibian gastrulation, what forms the ventral lip the dorsal lip expands laterally, eventually forming the ventral lip what happened during amphibian gastrulation - sheets of cells move Result: an abnormal blastula - adhesion between blastomeres reduced Antisense RNA technology - Inject egg with RNA oligonucleotide complementary to EP-cadherin mRNA (maternal) important for proper formation of blastula Catherine depletion - 4 chromosome, all copies of gene on each must be blocked (difficult) interacts wit cadherins from neighboring cells linked to actin cytoskeleton inside the cell maintains tissue integrity by linking cells to keep them properly positioned ![]() EP -cadherin Cell surface glycoprotein in amphibians ![]()
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