105 THE Oct4/Cdx2 EXPRESSION AND CELL FATE OF INDIVIDUAL TWO-CELL BLASTOMERES IN TWO MOUSE STRAINS
M. Katayama and R. M. Roberts
Reproduction, Fertility and Development
20(1) 133 - 133
Published: 12 December 2007
Fertile adults and occasionally twins have been derived from murine blastomeres at the 2-cell stage, indicating that such blastomeres may be equivalently totipotent, but there are conflicting reports that individual blastomeres from 2-cell stage murine conceptuses make different contributions to the embryonic and abembryonic regions of the blastocyst, implying that they differ in developmental potential. Here, we have re-examined this subject using 2 mouse strains, CF1 and NIH Swiss (SW), and 2 experimental approaches, random blastomere destruction at the 2-cell stage by repeated insertion of a needle into its nucleus and lineage tracing with the dye, DiI-CM. The manipulated conceptuses and untreated controls were cultured in KSOM-AA to morula and blastocyst stages (84 or 108 h pc, respectively), fixed, and immunostained for Oct4 and Cdx2. Antigen distribution, number of nuclei (stained by 42,6-diamidino-2-phenylindole), and cell progeny labeled with DiI-CM were examined by confocal laser scanning microscopy. Cell numbers are means ± SD and were analyzed by a Student t-test. Cells positive for Cdx2 were assumed to represent trophectoderm or trophectoderm precursors, ones positive for Oct4 but negative for Cdx2 (Oct+Cdx–) inner cell mass. Ablation of a blastomere failed to prevent developmental progression in either strain, but the total number of cells at both morula (SW 11.4 ± 3.3 v. 19.2 ± 7.1; CF1 10.1 ± 2.5 v. 22.1 ± 6.4) and blastocyst (SW 48.6 ± 7.4 v. 69.4 ± 9.9; CF1 24.8 ± 6.2 v. 53.8 ± 13.5) was significantly reduced. In SW, the average fraction of Oct+Cdx– cells after blastomere ablation was significantly lower (P < 0.05) than in controls in morulae (0.47 ± 0.2 v. 0.65 ± 0.1) but not in blastocysts (0.33 ± 0.1 and 0.34 ± 0.1). In CF1, the fraction of Oct+Cdx– cells was lower (P < 0.05) than controls in both morulae and blastocysts (0.31 ± 0.2 v. 0.58 ± 0.2 and 0.18 ± 0.1 v. 0.27 ± 0.04, respectively). The CF1 morulae fell mainly into 2 groups, one low fraction (≤0.3, 54%) of Oct+Cdx– cells and the other with a more normal fraction (0.3 to 0.8, 43%) relative to controls. A majority of NIH Swiss morulae had an Oct+Cdx– cell fraction >0.4 and in this respect resembled controls. We then examined these strain differences by lineage tracing. The majority of SW blastocysts (65%, n = 34) demonstrated a random localization of DiI-labeled cell progeny (i.e., there was no preferential distribution of labeled cells to either the embryonic or abembryonic poles). By contrast, in CF1 (n = 38), 32% of blastocysts had labeled cells confined to their embryonic end and 42% with DiI-labeled, Cdx2-positive cells clustered at the abembryonic locale. A random localization was observed in 26% of blastocysts. In conclusion, these data confirm that there is plasticity in early mouse development but also suggest that in CF1, but not in SW conceptuses, blastomeres at the 2-cell stage differ in their abilities to contribute to the embryonic pole. Similar strain differences may explain the disagreements among studies on lineage tracing in early cleavage stage conceptuses.
Full text doi:10.1071/RDv20n1Ab105
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