Embryonic determination

Boklage CE (1976) Embryonic determination of brain programming asymmetry A neglected element in twin-study genetics of human mental development. Acta Genet Med Gemellol 25 244-248. 

Figure 7. Expression pattern of the mouse tyrosinase gene during embryonic development and its recapitulation in transgenic mice as determined by in situ hybridization (Beermann et al., 1992a). Black box, mouse tyrosinase open box, transgene ptrTyrf striped box, ptrTyr5. Interrupted boxes indicate variations between lines. RPE, retinal pigment epithelium e, days of gestation d0.5, newborn.

The Xenopus system has proven instrumental in determining the mechanism controlling exit from mitosis at the metaphase/anaphase transition. Studies in this area have relied heavily on extracts prepared from fully mature oocytes/ unfertilized eggs that are arrested at metaphase of the second meiotic division. Upon Ca2+ addition, anaphase is initiated and the extract enters the first embryonic cell cycle to replicate DNA. The activity responsible for metaphase arrest was discovered by Masui at the same time as MPF (Masui Markert 1971), and given the name cytostatic factor (CSF). CSF has never been purified... 

This suggests that cyclin A2 is not essential for the early embryonic cell cycles. Also D-type cyclins seem to be dispensable for the early mouse embryo cell cycle progression since embryonic stem (ES) cells do not express them at all before differentiation (Savatier et al 1996). We do not know, however, whether the D-type cyclins are also absent in the early embryo. These observations suggest that not only could the first cell cycles of the mouse embryo have specific modifications, but also further embryonic cell cycles are specifically modified as well. Mammalian embryonic cell cycles are probably modified often during development. Such studies could allow us to determine a profile of a minimal cell cycle in mammals which must, however, be much more complex than a simple S M phase embryonic cell cycle of amphibians or insects. 

Asymmetric cell division is a universal mechanism utilized for the generation of cellular diversity during development (for reviews see Horvitz Herskowitz 1992, Guo Kemphues 1996, Shapiro Losick 1997, Jan Jan 1998). Asymmetric cell divisions during Drosophila embryonic development involve both extrinsic cues mediated through Notch and Delta and intrinsic cell fate determinants and play a major role in producing the distinct cell types which are... 

Schweitzer R, Shaharabany M, Seger R, Shilo BZ 1995 Secreted Spitz triggers the DER signaling pathway and is a limiting component in embryonic ventral ectoderm determination. Genes Dev 9 1518-1529... 

It was determined that the minimal peptide sequence required to stimulate pheromone biosynthesis was the C-terminal 5 amino acids, FXPRLamide, and that the carboxy terminus needs to be amidated [148,149]. This sequence was also established as the minimal sequence required for myotropic activity in cockroaches [ 150] and induction of embryonic diapause in B. mori [ 151 ]. Crossreactivity of peptides containing the FXPRLamide motif was also established for myotropic, diapause induction, and pheromone biosynthesis [152-154]. Therefore, the common C-terminal FXPRLamide defines this family of peptides. A partial listing of peptides identified to date is shown in Table 1. 

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