Intracellular pH-regulatory mechanisms are acquired by growing mouse oocytes with meiotic competence, and these mechanisms become fully active when the oocytes develop to the germinal vesicle (GV) stage as shown in CF1 and Balb/c strains mice. On the other hand, there is some evidence showing that intracellular pH-regulatory mechanisms are inhibited at the stages of Metaphase I (MI) and II (MII...

In many species where oocytes lack centrosomes, sperm contribute both genetic material and centriole(s) to the zygote. Correct centriole organization during male meiosis is critical to guarantee a normal bipolar mitotic spindle in the zygote. During Caenorhabditis elegans male meiosis, centrioles normally undergo two rounds of duplication, resulting in haploid sperm each containing a single tig...

The volvocine algae represent an excellent model lineage in which to study evolution of female and male genders based on comparative analyses of related species. Among these species, Volvox carteri has been extensively studied as a model of an oogamous and complex organism. However, it may have unique derived features that are not present in other species of Volvox. Therefore, information regar...

It has been known for more than 100 years that when spherical zygotes of the brown alga Fucus are subjected to a gradient of light, the plane of the first cell division is always perpendicular to the light axis. As illustrated in Figure 1, the resulting cell plate divides the zygote into two unequal cells; the smaller rhizoid cell emerges from the shaded portion of the gradient, whereas the lar...

Although around 1-4% of human zygotes have been found to be tripronuclear, there is little information about the subsequent development and chromosomal composition of embryos that derive from these zygotes. Herein, we report a pregnancy and subsequent delivery of a healthy newborn after the transfer of a blastocyst that developed from a tripronuclear zygote that had a euploid microarray result.

Chimeras are individuals with tissues derived from more than one zygote. Interspecific chimeras have tissues derived from different species. The biological consequences of human-animal chimeras have become an issue of ethical debate. Ironically, human-animal chimeras with human blood, neurons, germ cells, and other tissues have been generated for decades. This has facilitated human biological s...

Both Drosophila neuroblasts and Caenorhabditis elegans zygotes use a conserved protein complex to establish cell polarity and regulate spindle orientation. Mammalian epithelia also use this complex to regulate apical/basal polarity. Recent results have allowed us to compare the mechanisms regulating asymmetric cell division in Drosophila neuroblasts and the C. elegans zygote.

A review of published reports showed that the sex ratio (proportion of boys) was low among infants conceived after ovulation had been induced. The difference between the observed sex ratio and an expected one of 0 . 514 was highly significant. These findings suggest that maternal gonadotrophin concentrations at the time of conception directly affect the sex of the zygote.

TALE homeodomain proteins regulate development in many eukaryotes. Now, Lee et al. (2008) report that two TALE homeodomain proteins control zygote development of the unicellular green alga Chlamydomonas. This implicates TALE gene loss and diversification in the evolution of new diploid body plans that appeared when land plants evolved from algal ancestors over 450 million years ago.

DNA demethylation, a process involving DNA repair, is critical for reprogramming of the paternal genome during the oocyte-to-zygote transition. A new study by Ladstätter and Tachibana-Konwalski shows that a Chk1-mediated zygotic checkpoint monitors the cohesin-dependent repair of DNA lesions arising from DNA demethylation, which prevents zygotes carrying unrepaired lesions from entering mitosis.