Embryonic stem cell research is regulated by different forms of the subsidiarity principle, i.e. research on embryos should only be conducted if no suitable alternatives exist. Four types are discussed: animal versus human material, adult versus embryonic stem cells, affected or at risk embryos versus healthy embryos, and supernumerary versus research embryos. Three major arguments regarding th...

Knowledge on determination and differentiation in the mammalian embryo has not kept pace with discoveries in other phyla. Current concepts overlook well-established pathways leading to polarity in oocytes and embryos of other phyla, modern principles of totipotency in plants and animals, and axis formation in lower vertebrates. Various models derived from invertebrates and frogs could be releva...

The modern animal biotechnologies, such as animal cloning, transgenesis, sex determina‐ tion, stem cells, designing new livestock, must be performed on animal gametes includ‐ ing sperm and oocytes, and embryos based on embryology theory. Currently, some key biotechnologies in embryology have become the most powerful tool for animal scientists and breeders to improve genetic construction of anim...

In the sea urchin embryo, the animal-vegetal axis is defined before fertilization and different embryonic territories are established along this axis by mechanisms which are largely unknown. Significantly, the boundaries of these territories can be shifted by treatment with various reagents including zinc and lithium. We have isolated and characterized a sea urchin homolog of GSK3β/shaggy, a li...

The mesoderm of amphibian embryos such as Xenopus laevis arises through an inductive interaction in which cells of the vegetal hemisphere of the embryo act on overlying equatorial and animal pole cells. Three classes of 'mesoderm-inducing factor' (MIF) that might be responsible for this interaction in vivo have been discovered. These are members of the transforming growth factor type beta (TGF-...

In the sea urchin embryo, the animal-vegetal axis is defined before fertilization and different embryonic territories are established along this axis by mechanisms which are largely unknown. Significantly, the boundaries of these territories can be shifted by treatment with various reagents including zinc and lithium. We have isolated and characterized a sea urchin homolog of GSK3beta/shaggy, a...

background: the selection of pre-embryos for transferred is based on morphological appearance. but some poor quality cleaved embryos also can be cultured to the blastocyst stage and implanted. objective: to assess the clinical pregnancy outcomes of blastocyst transfer which developed from poor quality embryos. materials and methods: a total of 109 cleaved embryos with poor quality were cultured...

Loss of mesodermal competence (LMC) during Xenopus development is a well known but little understood phenomenon that prospective ectodermal cells (animal caps) lose their competence for inductive signals, such as activin A, to induce mesodermal genes and tissues after the start of gastrulation. Notch signaling can delay the onset of LMC for activin A in animal caps [Coffman, C.R., Skoglund, P.,...

In sea urchin embryos, the animal-vegetal axis is specified during oogenesis. After fertilization, this axis is patterned to produce five distinct territories by the 60-cell stage. Territorial specification is thought to occur by a signal transduction cascade that is initiated by the large micromeres located at the vegetal pole. The molecular mechanisms that mediate the specification events alo...