The oocyte prepares massive quantities of mRNA by performing intensely synthesizing mRNA for a long period of time (even months) and by creating a more stable mRNA environment than in somatic cells. Maternal mRNA Importance Step Overview Enucleation An urchin blastomere underwent centrifugal enucleation, forming one nucleated and one enucleated blastomere. Development Enucleated blastomere gets [...]

All cells in the embryo contain the same genetic information from the zygote. All cells in the embryo are genomically equivalent. Differences that arise between cells are due to differential gene activity, whereby transcription factors bind to enhancers, activating different genes in different cells. This was demonstrated by the blastomere isolation experiment, nuclear transplantation experiment [...]

Antibody An antibody is formed to bind to a particular gene product. Label The antibody is labeled so it is easily visible when bound to its antigen. 2-8 Cells Until the 2-8 cell stage, gene expression is consistent in all cells. Later After the 2-8 cell stage, gene expression begins to vary from cell to [...]

Enucleation Exposing ova to UV radiation enucleates them by destroying genetic material. Transplant Transplant nuclei from a frog blastula into an enucleated ovum. Observe Upon fertilization, the ovum develops normally despite the transplanted nucleus. Transplant Transplant nuclei from a differentiated cell (dermal, epithelial, etc) into enucleated ovum. Observe The ovum can still give rise to [...]

In blastomere separation experiments (aka blastomere isolation experiments) the cells of the early embryo are separated and allowed to develop independent of one another. There is a long history of this type of experiment, with the purpose of ascertaining whether the fate of cells was determined very early during cleavage. Basically, experiments on various species [...]

Intrinsic (aka cytoplasmic) and extrinsic determinants coexist, as shown by two (respective) urchin blastula experiments. Removing the progenitor cell of mesoderm from an urchin blastula results in a mesoderm-lacking larva. However, sagittally halving an entire blastula will result in a normal larva. The phenom of extrinsic determinants is known as regulative development.

Before MBT All embryonic cells undergo cell division at the same time. Zygotic heterochromatin (condensed, hypo-acetylated, H3 methylated). Only maternal mRNAs are translated. MBT Events Activation of zygotic genes. Cell cycle lengthened (G1 & G2 added). Asynchronous cycles of different cells. Development of cellular motility. After MBT Cell division becomes asynchronous Embryo begins transcribing its [...]

At the 8-cell stage, the mammalian embryo undergoes compaction where the spherical and loose blastomeres nestle tight together to establish new cell junctions and form a blastocyst. The blastocyst has an outer trophoblast layer (responsible for implantation into the uterine wall) and an inner cell mass placed eccentrically within the blastocoel. The inner cell mass [...]

Activated after fertilization, cleavage is a period of rapid mitosis that divides cells into a roughly somatic size. Despite appearing uniform, cells are committed to a particular cell fate (insects) or dorsal-ventral position (amphibians). Cleavage depends on maternal mRNAs instead of zygotic genes. Since cleavage depends solely on cytoplasmic factors, enucleated eggs still undergo cleavage [...]

In Xenopus, the Nieuwkoop Center is the dorsal- and vegetal-most region. It gives rise to the Primary Organizer (aka Spemann Organizer or Spemann-Mangold Organizer), which is the region known as the dorsal lip of the blastopore (DLB). Spemann and Mangold’s experiments found that the DLB dorsalizes surrounding tissue, thus forming (along with the SEP) the [...]

Fertilization is the union of a haploid sperm and haploid egg to form a single diploid zygote. This cell will develop into an embryo. Unfertilized Egg The egg is quiescent — it performs no DNA synthesis, cell division nor RNA transcription. There is a reduced rate of translation until fertilization. The egg stores a multitude [...]