Analysis of Biological Development (K. Kalthoff)

Updates to Topic 08: Localized Cytoplasmic Determinants

Answers to Questions in Text

Heterotopic Transplantation of Posterior Pole Plasm in Drosophila Eggs (pp. 176-178)

  1. Which control experiments need to be done in order to test whether the ectopic pole cells are formed in response to a component localized in posterior cytoplasm or to the act of injecting any egg cytoplasm? Answer: Control experiments carried out later by Illmensee, Mahowald, and others showed that cytoplasm from egg areas other than the posterior pole, when transplanted to the anterior pole, did not cause the formation of ectopic pole cells.
  2. Which control experiments should be done in order to test whether the ability to form additional gametes is restricted to ectopic pole cells, or whether this ability is acquired by any transplanted embryonic cell? Answer: Transplant anterior blastoderm cells rather than ectopic pole cells to the posterior pole of a host carrying different genetic markers. Test whether the genetic markers of the donor are found in the offspring of the host.


Related Web Sites

Christian Sardet's web site contains contains all on localized cytoplasmic determinants in ascidians and other marine organisms. Many links, great images and movies!

Clarifications and Corrections

p.173, left column, 3rd line from bottom, should read: "... the cyclic appearance, at the vegetal pole, ..."

New Review Articles

Kloc M., Zearfoss N.R., and Etkin L.A. (2002) Mechanisms of subcellular mRNA localization. Cell 108: 533-544

Nishida H. (2002) Patterning the marginal zone of early ascidian embryos: localized maternal mRNAs and inductive interactions. BioEssays 24: 613-624

New Research Articles

Nishida H. and Sawada K. (2001) macho-1 encodes a localized mRNA in ascidian eggs that specifies muscle fate during development. Nature 409: 724-729

The authors identified a localized mRNA, encoded maternally by the macho-1 gene, that acts as a localized cytoplasmic determinant for primary tail muscle in the egg of the ascidian Halocynthia roretzi. The distribution of macho-1 mRNA corresponds closely to that of yellow cytoplasm, which was shown earlier to act as a localized cytoplasmic determinant for the primary muscle cell lineage (see Fig. 8.15 on p.184 of text). Depletion of macho mRNA by injection of antisense deoxyoligonucleotides (see p. 69 and p. 218) interferes specifically with tail muscle formation, as indicated by the lack of muscle-specific marker proteins such as myosin and acetylcholinesterase. Such depleted embryos can be rescued by injecting normal macho mRNA but not by mRNA lacking a region that encodes a functional domain of the macho protein, which is a transcription factor of the zinc-finger type. Oversupply of macho mRNA leads to muscle formation in cell lineages that normally form non-muscle tissues. Thus, macho mRNA is a localized maternal mRNA that is necessary and sufficient for primary tail muscle formation.

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