The fine structure of cleavage, blastula, and gastrula stages of Fundulus heteroclitus was investigated. Cleavage blastomeres are relatively unspecialized, containing few or poorly developed organelles. Beginning in blastula stages, signs of differentiation were noted, including development of the endoplasmic reticulum and Golgi apparatus and appearance of a primary nucleolus and polyribosomes....

Studies of developmental cell lineage, i.e. of the fate of individual blastomeres that arise in an embryo, were begun in the 1 870s , in the context of the con­ troversy then raging about the "biogenetic," or "recapitulation," law promul­ gated by Ernst Haeckel . The biogenetic law seemed to imply that the early, pre-gastrula stages of metazoan embryogenesis recapitulate the nondifferen­ tiated...

In early vertebrate development, apicobasally polarised blastomeres divide to produce inner non-polarised cells and outer polarised cells that follow different fates. How the polarity of these early blastomeres is established is not known. We have examined the role of Crumbs3, Lgl2 and the apical aPKC in the polarisation of frog blastomeres. Lgl2 localises to the basolateral membrane of blastom...

Horseradish peroxidase injected into individual blastomeres of 32- and 64-cell embryos of Xenopus laevis was identified in cells of the central nervous system (CNS) at larval stages 31 to 39. The CNS received contributions from 24 blastomeres of the 32-cell stage and 38 blastomeres of the 64-cell stage. The region of CNS in which all of the labeled descendants of a single blastomere were disper...

BACKGROUND The zebrafish is emerging as an important genetic system for the study of vertebrate development, and many zygotic mutations affecting embryogenesis have been isolated. The early events in development are under the control of maternal genes but are relatively unexplored. Here, the process of axis specification is investigated. RESULTS The vegetal pole of the zygote transiently cont...

6 Analysis of transcriptome asymmetry within mouse zygotes and embryonic sister blastomeres 85 6.

An animal-vegetal axis exists in the unfertilized eggs of the ascidian Halocynthia roretzi. The first phase of ooplasmic segregation brings the egg cortex to the vegetal pole very soon after fertilization. In the present study, when 5-8% of the egg cytoplasm in the vegetal pole region was removed between the first and second phase of segregation, most embryos exhibited failure of gastrulation, ...

Cell movements in Fundulus blastoderms during gastrulation were studied utilizing time-lapse cinemicrography and electron microscopy. Time-lapse films reveal that cells of the enveloping layer undulate and sometimes separate briefly but remain together in a cohesive layer. During epiboly, the marginal enveloping layer cells move over the periblast as it expands over the yolk sphere. Movement oc...

The developmental capacity of (a) single blastomeres of 4-cell embryos, (Jb) pairs of blastomeres of 8-cell embryos and (c) single blastomeres of 8-cell embryos was studied. The blastomeres were inserted into evacuated foreign zonae pellucidae, embedded in agar, transferred to ligated oviducts of dioestrous ewes, and recovered when their total age was 5-Jto 6̂ days. At lecovery the majority of e...

OBJECTIVE To assess the value of routine screening of nuclear status of day-2 four-cell preembryos for single embryo transfer (SET) in predicting implantation. DESIGN Retrospective analysis. SETTING Private IVF unit. PATIENT(S) A total of 1,985 fresh embryo transfers on day 2 or day 3 were performed from January 2002 to November 2004. In 1,295 (65.2%) of these transfers, SET was performed...