Sea urchin fertilization is marked by a massive conversion of molecular oxygen to hydrogen peroxide by a sea urchin dual oxidase, Udx1. This enzyme is essential for completing the physical block to polyspermy. Yet, its expression is maintained during development, as indicated by the presence of both Udx1 mRNA and Udx1 protein enriched at the surface of all non-mesenchymal blastomeres. When hydr...

We have characterized the expression pattern of a class I fork head/HNF-3 gene (HrHNF3-1) of the ascidian Halocynthia roretzi. Zygotic HrHNF3-1 expression was detectable as early as the 16-cell stage, and the transcript was evident in blastomeres of the endoderm, notochord and mesenchyme lineages of the early embryos. After the late gastrula stage, HrHNF3-1 was also expressed in the presumptive...

Previous studies have demonstrated that aneuploidy in human embryos is surprisingly frequent with 50-80% of cleavage-stage human embryos carrying an abnormal chromosome number. Here we combine non-invasive time-lapse imaging with karyotypic reconstruction of all blastomeres in four-cell human embryos to address the hypothesis that blastomere behaviour may reflect ploidy during the first two cle...

Primordial germ cell (PGC) development in the zebrafish is poorly understood. The expression of vasa RNA, the only molecular marker so far found to be expressed in fish PGCs, suggests its function in the establishment of the germline. The protein product of vasa is present throughout the life cycle in the germline of Drosophila, Caenorhabditis and Xenopus. The expression pattern of the Vasa pro...

A dark spot was found to appear in each blastomere of the vegetal surface of blastulae of Rana rugosa, Hyla arborea. The spot divided into two before division of the blastomere, so that one new spot was allotted to each daughter cell. These dark spots were formed at early blastula stage, and persisted until the end of yolk plug stage. Cytological observations showed that each dark spot correspo...

Leech embryos develop via stereotyped cell divisions, many of which are unequal. The first division generates identifiable cells, blastomeres AB and CD, which normally follow distinct developmental pathways. When these two cells are dissociated and cultured in isolation, their fates remain distinct and are reminiscent of normal development, but their typical cleavage patterns are disrupted; cel...

The mechanism by which a surface pole of microvilli is generated in mouse 8-cell blastomeres has been investigated. 4-cell and 8-cell embryos (or cell couplets) were incubated for precise times during their respective cell cycles in medium containing cytochalasin D (CCD) to disrupt the microfilament system. The blastomeres were analysed immediately for the distribution and state of organization...

The CCCH finger protein PIE-1 is a regulator of germ cell fate that segregates with the germ lineage in early embryos. At each asymmetric division, PIE-1 is inherited preferentially by the germline daughter and is excluded from the somatic daughter. We show that this asymmetry is regulated at the protein level by two complementary mechanisms. The first acts before cell division to enrich PIE-1 ...

We have measured the expression of 41 maternal mRNAs in individual blastomeres collected from the 8 to 32-cell Xenopus laevis embryos to determine when and how asymmetry in the body plan is introduced. We demonstrate that the asymmetry along the animal-vegetal axis in the oocyte is transferred to the daughter cells during early cell divisions. All studied mRNAs are distributed evenly among the ...

The mechanism by which a surface pole of microvilli is generated in mouse 8-cell blastomeres has been investigated. 4-cell and 8-cell embryos (or cell couplets) were incubated for precise times during their respective cell cycles in medium containing cytochalasin D (CCD) to disrupt the microfilament system. The blastomeres were analysed immediately for the distribution and state of organization...