Early Preimplantation Development Research Articles

A Tetranucleotide Repeat Mouse Minisatellite Displaying Substantial Somatic Instability during Early Preimplantation Development

The highly variable mouse minisatellite Hm-2 is located on chromosome 9 and consists of GGCA tetranucleotide repeats with alleles containing up to 5000 repeat units. This locus is unstable with a germline mutation rate to new length alleles of at least 3.6% per gamete. Hm-2 also shows substantial somatic instability, producing mutational mosaicism detectable in 20% of adult mice. Analysis of allele dosage in mice carrying somatic mutations, plus studies of mosaicism in mouse embryos and extraembryonic tissues, suggests that somatic mutant alleles preferentially arise during preimplantation development and particularly during the first two cell divisions after fertilization.

Purine utilisation, de novo synthesis and degradation in mouse preimplantation embryos.

The importance of de novo purine synthesis as opposed to the reutilisation of metabolites by salvage pathways, and the nature of the excretory product(s) of purine degradation, have been examined in cultured preimplantation mouse embryos. In the presence of azaserine and mycophenolic acid, which inhibit de novo purine synthesis, embryo cleavage was blocked prior to compaction, the precise stages at which this occurred depended on whether the cultures were established on day 1 or day 2 after fertilisation, and indicated that salvage pathways were insufficient to fulfil the demand for nucleotides during early preimplantation development. The end-product of purine degradation appeared to be xanthine, which was excreted in very small amounts on days 1, 2 and 3, with a pronounced rise from the early to late blastocyst. Uric acid formation or excretion could not be detected. Exogenous hypoxanthine and adenine, which partially inhibited development, were taken up by the embryos and converted to xanthine, most probably by salvage pathways, since the enzyme xanthine oxidase, which converts hypoxanthine directly to xanthine and then to uric acid, could not be detected. Exogenous guanine had little effect on development and was also converted to xanthine, but in this case, the conversion was probably in a single step, via the enzyme guanase.

Structural relationship and posttranslational modification of stage-specific proteins synthesized during early preimplantation development in the mouse.

The synthesis of stage-related proteins characteristic of meiotic maturation and early preimplantation development occurs in the absence of significant transcription. Previous work indicated that some of the stage-related proteins typical of the early postfertilization period are synthesized in unfertilized oocytes at the same time that they are detected in fertilized eggs. This observation has led to the suggestion that protein synthesis in newly fertilized eggs is regulated by an intrinsic developmental program initiated during the resumption of meiosis (meiotic maturation) and supported in part by previously untranslated mRNA. It also has been proposed that the rapid and complex changes in protein synthesis that characterize this period may involve differential gene expression or selective protein degradation, or both. To date, cell-free translation of oocyte RNA has not demonstrated the existence of a sizeable population of preformed mRNA that could support the observed changes in protein synthesis. I have tested the notion that the apparent changes in protein synthesis during early development in the mouse may be derived from families of proteins related both in amino acid sequence and posttranslational modification. The findings show that many changes in protein synthetic patterns related to early development after fertilization are independent of fertilization and involve the posttranslational modification of proteins with identical or very similar primary structures. The results are discussed with respect to current interpretations of quantitative and qualitative changes in protein synthesis during early mammalian development as they relate to differential gene expression and presumed activation of preformed mRNA.

Nuclear transplantation in mus musculus: Developmental potential of nuclei from preimplantation embryos

Genomic exchange of a mammalian cell has been attempted by entirely replacing the nuclear genome of the mouse egg with a nucleus from an embryonic cell via nuclear transplantation. Its biological applicability to experimental embryology has first been probed on the mouse blastocyst. After mechanical isolation of the trophectoderm (TE) and inner cell mass (ICM) from LT/Sv or CBA/H-T6 blastocysts and subsequent dissociation into single cells, their nuclei were transplanted singly into fertilized C57BL/6 eggs from which the female and male pronucleus were removed after nuclear injection. Of the 179 eggs injected with TE nuclei, 68 (38%) survived microsurgery and 34 cleaved, but most of them became arrested during early preimplantation development. Biochemical analysis of 25 TE nuclear-transplant embryos showed that nuclei from TE cells were not capable of initiating nor supporting development beyond preimplantation without participation of the egg genome. Of the 363 eggs injected with ICM nuclei, 142 (39%) survived micromanipulation and were cultured in vitro. From the 96 cleaving eggs, 48 embryos reached the late preimplantation stage. Biochemical or karyotypic analyses of 54 ICM nuclear-transplant embryos at various preimplantation stages for either strain-specific variants of glucosephosphate isomerase (GPI) or chromosomal markers (T6 translocation) revealed that, in most instances, the transplanted nuclei successfully promoted development of the recipient eggs. A total of 16 nuclear-transplant embryos originating from ICM nuclei were transferred into the uteri of pseudopregnant ICR/Swiss females in order to allow development to term. Three liveborn mice, two females and one male, were derived exclusively from the transplanted ICM nuclei as judged by their coat color, karyotype and GPI enzyme pattern. Furthermore, in subsequent matings, two of the nuclear-transplant mice, one female and one male, gave rise to several normal progeny all of which exhibited the nuclear-donor phenotype. Our results demonstrate that nuclei from ICM cells of the mouse blastocyst are not yet restricted in their differentiation capacities but rather remain developmentally equivalent to the totipotent zygote nucleus.

Localization of Intracisternal a Particle Antigens in Neoplastic Cells and Preimplantation Mouse Embryos

The stage specific appearance of a retravirus, termed the Intracisternal A particle (IAP) is a normal feature of early preimplantation development. To date, all feral and laboratory strains of Mus musculus and even Asian species such as Mus cervicolor and Mus pahari express the particles during the 2-8 cell stages. IAP form by budding into the endoplasmic reticulum and appear singly or as groups of donut-shaped particles within the cisternae (fig. 1). IAP are also produced in large numbers in several neoplastic cells such as certain plasmacytomas and rhabdomyosarcomas. The role of IAP, either in normal development or in neoplastic behavior, is unknown.

The effect of spatial arrangement on cell determination during mouse development

ABSTRACTThe effect of cell position on cell determination was studied in mouse embryos. Embryos and parts of embryos were combined during early preimplantation development. The differentiation of cells in these composites was followed either by prelabelling some cells with tritiated thymidine or by combining cells which synthesized different electrophoretic variants of glucose phosphate isomerase.It was found that each blastomere of a 4-cell embryo could form both the trophoblast and the inner cell mass of the blastocyst. However, when blastomeres of a 4-cell embryo were placed on the outside of other 4-cell embryos then (a) they tended to form the outside layer of the blastocyst, (b) they tended to develop into the trophoblast and the yolk sac on the 10th day of pregnancy, (c) they tended not to form the coat colour of the foetus. Four-to eight-cell embryos which were completely surrounded by other blastomeres had lost the capacity to form vesicles at the blastocyst stage.We could find no evidence for the segregation of morphogenetic factors at the 4- and 8-cell stages of mouse development and concluded that at these stages cell position could determine the development of blastomeres.