Regulation of desmocollin transcription in mouse preimplantation embryos

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 743-753 ◽  
Author(s):  
J.E. Collins ◽  
J.E. Lorimer ◽  
D.R. Garrod ◽  
S.C. Pidsley ◽  
R.S. Buxton ◽  
...  
Keyword(s):  
Protein Expression ◽  
Molecular Mechanisms ◽  
Inner Cell Mass ◽  
Splice Variants ◽  
Cell Mass ◽  
Cumulus Cells ◽  
Early Embryo ◽  
Preimplantation Embryos ◽  
Cell Stage ◽  
Cleavage Stages

The molecular mechanisms regulating the biogenesis of the first desmosomes to form during mouse embryogenesis have been studied. A sensitive modification of a reverse transcriptase-cDNA amplification procedure has been used to detect transcripts of the desmosomal adhesive cadherin, desmocollin. Sequencing of cDNA amplification products confirmed that two splice variants, a and b, of the DSC2 gene are transcribed coordinately. Transcripts were identified in unfertilized eggs and cumulus cells and in cleavage stages up to the early 8-cell stage, were never detected in compact 8-cell embryos, but were evident again either from the 16-cell morula or very early blastocyst (approx 32-cells) stages onwards. These two phases of transcript detection indicate DSC2 is encoded by maternal and embryonic genomes. Previously, we have shown that desmocollin protein synthesis is undetectable in eggs and cleavage stages but initiates at the early blastocyst stage when desmocollin localises at, and appears to regulate assembly of, nascent desmosomes that form in the trophectoderm but not in the inner cell mass (Fleming, T. P., Garrod, D. R. and Elsmore, A. J. (1991), Development 112, 527–539). Maternal DSC2 mRNA is therefore not translated and presumably is inherited by blastomeres before complete degradation. Our results suggest, however, that initiation of embryonic DSC2 transcription regulates desmocollin protein expression and thereby desmosome formation. Moreover, data from blastocyst single cell analyses suggest that embryonic DSC2 transcription is specific to the trophectoderm lineage. Inhibition of E-cadherin-mediated cell-cell adhesion did not influence the timing of DSC2 embryonic transcription and protein expression. However, isolation and culture of inner cell masses induced an increase in the amount of DSC2 mRNA and protein detected. Taken together, these results suggest that the presence of a contact-free cell surface activates DSC2 transcription in the mouse early embryo.

scholarly journals Gonadotropin-Releasing Hormone I Analog Acts as an Antiapoptotic Factor in Mouse Blastocysts

Endocrinology ◽  
2005 ◽  
Vol 146 (9) ◽  
pp. 4105-4116 ◽  
Author(s):  
Kazuhiro Kawamura ◽  
Jun Fukuda ◽  
Jin Kumagai ◽  
Yasushi Shimizu ◽  
Hideya Kodama ◽  
...  
Keyword(s):  
Growth Factor ◽  
Molecular Mechanisms ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Blastocyst Stage ◽  
Preimplantation Embryos ◽  
Dependent Manner ◽  
Autocrine Signaling ◽  
Cell Stage ◽  
Induced Apoptosis

Abstract Both GnRH-I and its receptor (GnRHR)-I have been shown to be expressed in the mammalian preimplantation embryo. In this study, we investigated the molecular mechanisms of GnRH-I in the regulation of early embryonic development in mouse. We found that GnRH-I and GnRHR-I mRNAs were detectable throughout early embryonic stages and that expression levels of both increased significantly after the early blastocyst stage. In blastocysts, GnRH-I and GnRHR-I expression was detected in both inner cell mass and trophectoderm cells. The pregnant uterus also expressed both genes, suggesting that preimplantation embryos could be affected by GnRH through both paracrine and autocrine signaling. Treatment with GnRH-I agonist, buserelin, promoted development of two-cell-stage embryos to the expanded and hatched blastocyst stages and inhibited apoptosis in a dose-dependent manner. In contrast, treatment with GnRH-I antagonist, ganirelix acetate, inhibited development of preimplantation embryos beyond the expanded blastocyst stage and induced apoptosis; both effects could be reversed by cotreatment with GnRH-I agonist. GnRH-I antagonist-induced cell death was mediated by disruption of mitochondrial function, release of cytochrome c, and activation of caspase-3. Furthermore, treatment with GnRH-I antagonist decreased expression of two antiapoptotic growth factors, epidermal growth factor and IGF-II, in blastocysts. These results indicate that GnRH-I, acting as an antiapoptotic factor, is an important growth factor in development of mouse blastocysts.

scholarly journals The Aryl Hydrocarbon Receptor Promotes Differentiation During Mouse Preimplantational Embryo Development

2020 ◽  
Author(s):  
Ana Nacarino-Palma ◽  
Jaime M. Merino ◽  
Pedro M. Fernández-Salguero
Keyword(s):  
Embryo Development ◽  
Molecular Mechanisms ◽  
Inner Cell Mass ◽  
Intracellular Localization ◽  
Cell Mass ◽  
Early Embryo ◽  
Mitochondrial Activity ◽  
Differentiation Markers ◽  
Cell Stage ◽  
Pluripotency Factors

ABSTRACTMammalian embryogenesis is a complex process controlled by transcription factors that dynamically regulate the balance between pluripotency and differentiation. Transcription factor AhR is known to regulate Oct4/Pou5f1 and Nanog, both essential genes in pluripotency, stemness and early embryo development. Yet, the molecular mechanisms controlling Oct4/Pou5f1 and Nanog during embryo development remain largely unidentified. Here, we show that AhR is required for proper embryo differentiation by regulating pluripotency factors and by maintaining adequate metabolic activity. AhR lacking embryos (AhR-/-) showed a more pluripotent phenotype characterized by a delayed expression of differentiation markers of the first and second cell divisions. Accordingly, central pluripotency factors OCT4/POU5F1, NANOG, and SOX2 were overexpressed in AhR-/- embryos at initial developmental stages. An altered intracellular localization of these factors was observed in absence of AhR and, importantly, OCT4 had an opposite expression pattern with respect to AhR from the 2-cell stage to blastocyst, suggesting a negative regulatory mechanism of OCT4/POU5F by AhR. Hippo signalling, rather than being repressed, was upregulated in very early AhR-/- embryos, possibly contributing to their undifferentiation at later stages. Consistently, AhR-null blastocysts overexpressed the early marker of inner cell mass (ICM) differentiation Sox17 whereas downregulated extraembryonic differentiation-driving genes Cdx2 and Gata3. Moreover, the persistent pluripotent phenotype of AhR-/- embryos was supported by an enhanced glycolytic metabolism and a reduction in mitochondrial activity. We propose that AhR is a regulator of pluripotency and differentiation in early mouse embryogenesis and that its deficiency may underline the reduced viability and increased resorptions of AhR-null mice.

A novel H+ permeability dominating intracellular pH in the early mouse embryo

Development ◽  
1993 ◽  
Vol 118 (4) ◽  
pp. 1353-1361
Author(s):  
J.M. Baltz ◽  
J.D. Biggers ◽  
C. Lechene
Keyword(s):  
Plasma Membrane ◽  
Intracellular Ph ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Cell Types ◽  
Preimplantation Embryos ◽  
Developmentally Regulated ◽  
Cell Stage ◽  
K Concentration ◽  
Early Mouse

Most cell types are relatively impermeant to H+ and are able to regulate their intracellular pH by means of plasma membrane proteins, which transport H+ or bicarbonate across the membrane in response to perturbations of intracellular pH. Mouse preimplantation embryos at the 2-cell stage, however, do not appear to possess specific pH-regulatory mechanisms for relieving acidosis. They are, instead, highly permeable to H+, so that the intracellular pH in the acid and neutral range is determined by the electrochemical equilibrium of H+ across the plasma membrane. When intracellular pH is perturbed, the rate of the ensuing H+ flux across the plasma membrane is determined by the H+ electrochemical gradient: its dependence on external K+ concentration indicates probable dependence on membrane potential and the rate depends on the H+ concentration gradient across the membrane. The large permeability at the 2-cell stage is absent or greatly diminished in the trophectoderm of blastocysts, but still present in the inner cell mass. Thus, the permeability to H+ appears to be developmentally regulated.

scholarly journals Three-Dimensional Live Imaging of Bovine Preimplantation Embryos: A New Method for IVF Embryo Evaluation

2021 ◽  
Vol 8 ◽  
Author(s):  
Yasumitsu Masuda ◽  
Ryo Hasebe ◽  
Yasushi Kuromi ◽  
Masayoshi Kobayashi ◽  
Kanako Urataki ◽  
...  
Keyword(s):  
Embryo Transfer ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Three Dimensional ◽  
Preimplantation Embryos ◽  
Infrared Light ◽  
Bovine Embryo ◽  
Bovine Embryos ◽  
Cell Stage ◽  
Developmental Potential

Conception rates for transferred bovine embryos are lower than those for artificial insemination. Embryo transfer (ET) is widely used in cattle but many of the transferred embryos fail to develop, thus, a more effective method for selecting bovine embryos suitable for ET is required. To evaluate the developmental potential of bovine preimplantation embryos (2-cell stage embryos and blastocysts), we have used the non-invasive method of optical coherence tomography (OCT) to obtain live images. The images were used to evaluate 22 parameters of blastocysts, such as the volume of the inner cell mass and the thicknesses of the trophectoderm (TE). Bovine embryos were obtained by in vitro fertilization (IVF) of the cumulus-oocyte complexes aspirated by ovum pick-up from Japanese Black cattle. The quality of the blastocysts was examined under an inverted microscope and all were confirmed to be Code1 according to the International Embryo Transfer Society standards for embryo evaluation. The OCT images of embryos were taken at the 2-cell and blastocyst stages prior to the transfer. In OCT, the embryos were irradiated with near-infrared light for a few minutes to capture three-dimensional images. Nuclei of the 2-cell stage embryos were clearly observed by OCT, and polynuclear cells at the 2-cell stage were also clearly found. With OCT, we were able to observe embryos at the blastocyst stage and evaluate their parameters. The conception rate following OCT (15/30; 50%) is typical for ETs and no newborn calves showed neonatal overgrowth or died, indicating that the OCT did not adversely affect the ET. A principal components analysis was unable to identify the parameters associated with successful pregnancy, while by using hierarchical clustering analysis, TE volume has been suggested to be one of the parameters for the evaluation of bovine embryo. The present results show that OCT imaging can be used to investigate time-dependent changes of IVF embryos. With further improvements, it should be useful for selecting high-quality embryos for transfer.

213 HOXB9 PROTEIN IS PRESENT THROUGHOUT EARLY EMBRYO DEVELOPMENT IN THE BOVINE

2013 ◽  
Vol 25 (1) ◽  
pp. 255
Author(s):  
C. Sauvegarde ◽  
D. Paul ◽  
R. Rezsohazy ◽  
I. Donnay
Keyword(s):  
Embryo Development ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Mature Oocyte ◽  
Blastocyst Stage ◽  
Early Embryo ◽  
Immature Oocyte ◽  
Cell Stage ◽  
Morula Stage ◽  
Oocyte Stage

Hox genes encode for homeodomain transcription factors well known to be involved in developmental control after gastrulation. However, the expression of some of these genes has been detected during oocyte maturation and early embryo development. An interesting expression profile has been obtained for HOXB9 in the bovine (Paul et al. 2011 Mol. Reprod. Dev. 78, 436): its relative expression increases between the immature oocyte and the zygote, further increases at the 5- to 8-cell stage to peak at the morula stage before decreasing at the blastocyst stage. The main objective of this work is to establish the HOXB9 protein profile from the immature oocyte to the blastocyst in the bovine. Bovine embryos were produced in vitro from immature oocytes obtained from slaughterhouse ovaries. Embryos were collected at the following stages: immature oocyte, mature oocyte, zygote (18 h post-insemination, hpi), 2-cell (26 hpi), 5 to 8 cell (48 hpi), 9 to 16 cell (96 hpi), morula (120 hpi), and blastocyst (180 hpi). The presence and distribution of HOXB9 proteins were detected by whole-mount immunofluorescence followed by confocal microscopy using an anti-human HOXB9 polyclonal antibody directed against a sequence showing 100% homology with the bovine protein. Its specificity to the bovine protein was controlled by Western blot on total protein extract from the bovine uterus and revealed, among a few bands of weak intensities, 2 bands of high intensity corresponding to the expected size. Oocytes or embryos were fixed and incubated overnight with rabbit anti-HOXB9 (Sigma, St. Louis, MO, USA) and mouse anti-E-cadherin (BD Biosciences, Franklin Lakes, NJ, USA) primary antibodies and then for 1 h with goat anti-rabbit Alexafluor 555 conjugated (Cell Signaling Technology, Beverly, MA, USA) and goat anti-mouse FITC-conjugated (Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA) secondary antibodies. Embryos were then mounted in Vectashield containing DAPI. HOXB9 is detected from the immature oocyte to the blastocyst stage. At the immature oocyte stage, it is mainly localised in the germinal vesicle with a weak signal in the cytoplasm. At the mature oocyte stage, HOXB9 labelling is present in the cytoplasm. At the zygote stage, a stronger immunoreactivity is observed in the pronuclei than in the cytoplasm. From the 2-cell stage to the morula stage, the presence of HOXB9 is also more important in the nuclei than in the cytoplasm. HOXB9 is also observed at the blastocyst stage where it is localised in the nuclei of the trophectoderm cells, whereas an inconstant or weaker labelling is observed in the inner cell mass cells. In conclusion, we have shown for the first time the presence of the HOXB9 protein throughout early bovine embryo development. The results obtained suggest the presence of the maternal HOXB9 protein because it is already detected before the maternal to embryonic transition that occurs during the fourth cell cycle in the bovine. Finally, the pattern obtained at the blastocyst stage suggests a differential role of HOXB9 in the inner cell mass and trophectoderm cells. C. Sauvegarde holds a FRIA PhD grant from the Fonds National de la Recherche Scientifique (Belgium).

scholarly journals Tissue-specific control of expression of the tight junction polypeptide ZO-1 in the mouse early embryo

Development ◽  
1991 ◽  
Vol 113 (1) ◽  
pp. 295-304 ◽  
Author(s):  
T.P. Fleming ◽  
M.J. Hay
Keyword(s):  
Tight Junction ◽  
Contact Area ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Subsequent Development ◽  
Early Embryo ◽  
Cell Contact ◽  
Down Regulation ◽  
Cell Stage ◽  
Daughter Cells

The processes governing differential protein expression in preimplantation lineages were investigated using a monoclonal antibody recognising the tight junction polypeptide, ZO-1. ZO-1 localises to the maturing tight junction membrane domain in the polarised trophectoderm lineage from compaction (8-cell stage) onwards, ultimately forming a zonular belt around each trophectoderm cell of the blastocyst (32- to 64-cell stage). The protein is usually undetectable within the inner cell mass (ICM) although, in a minority of embryos, punctate ZO-1 sites are present on the surface of one or more ICM cells. Since ICM cells derive from the differentiative division of polarised 8- and 16-cell blastomeres, the distribution of ZO-1 following differentiative division in isolated, synchronised cell clusters of varying size, was examined. In contrast to the apical cytocortical pole, ZO-1 was found to be inherited by nonpolar (prospective ICM) as well as polar (prospective trophectoderm) daughter cells. Following division, polar cells adhere to and gradually envelop nonpolar cells. Prior to envelopment, ZO-1 localises to the boundary between the contact area and free membrane of daughter cells, irrespective of their phenotype. After envelopment, polar cells retain these ZO-1 contact sites whilst nonpolar cells lose them, in which case ZO-1 transiently appears as randomly-distributed punctate sites on the membrane before disappearing. Thus, symmetrical cell contact appears to initiate ZO-1 down-regulation in the ICM lineage. The biosynthetic level at which ZO-1 down-regulation occurs was investigated in immunosurgically isolated ICMs undergoing trophectoderm regeneration. By 6 h in culture, isolated ICMs generated a zonular network of ZO-1 at the contact area between outer cells, thereby demonstrating the reversibility of down-regulation. This assembly process was unaffected by alpha-amanitin treatment but was inhibited by cycloheximide. These results indicate that the ICM inherits and stabilises ZO-1 transcripts which can be utilised for rapid synthesis and assembly of the protein, a capacity that may have significance both in maintaining lineage integrity within the blastocyst and in the subsequent development of the ICM.

scholarly journals Nicotinamide Supplementation during the In Vitro Maturation of Oocytes Improves the Developmental Competence of Preimplantation Embryos: Potential Link to SIRT1/AKT Signaling

Cells ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1550 ◽  
Author(s):  
Marwa El Sheikh ◽  
Ahmed Atef Mesalam ◽  
Muhammad Idrees ◽  
Tabinda Sidrat ◽  
Ayman Mesalam ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
In Vitro Maturation ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Akt Signaling ◽  
Developmental Competence ◽  
Preimplantation Embryos ◽  
Vitamin B3 ◽  
Cell Stage

Nicotinamide (NAM), the amide form of vitamin B3, plays pivotal roles in regulating various cellular processes including energy production and maintenance of genomic stability. The current study aimed at deciphering the effect of NAM, when administered during in vitro maturation (IVM), on the developmental competence of bovine preimplantation embryos. Our results showed that low NAM concentrations reduced the oxidative stress and improved mitochondrial profile, total cleavage and 8–16 cell stage embryo development whereas the opposite profile was observed upon exposure to high NAM concentrations (10 mM onward). Remarkably, the hatching rates of day-7 and day-8 blastocysts were significantly improved under 0.1 mM NAM treatment. Using RT-qPCR and immunofluorescence, the autophagy-related (Beclin-1 (BECN1), LC3B, and ATG5) and the apoptotic (Caspases; CASP3 and 9) markers were upregulated in oocytes exposed to high NAM concentration (40 mM), whereas only CASP3 was affected, downregulated, following 0.1 mM treatment. Additionally, the number of cells per blastocyst and the levels of SIRT1, PI3K, AKT, and mTOR were higher, while the inner cell mass-specific transcription factors GATA6, SOX2, and OCT4 were more abundant, in day-8 embryos of NAM-treated group. Taken together, to our knowledge, this is the first study reporting that administration of low NAM concentrations during IVM can ameliorate the developmental competence of embryos through the potential regulation of oxidative stress, apoptosis, and SIRT1/AKT signaling.

scholarly journals Analysis of accessible chromatin landscape in the inner cell mass and trophectoderm of human blastocysts

2020 ◽  
Vol 26 (9) ◽  
pp. 702-711
Author(s):  
Min Yang ◽  
Xin Tao ◽  
Shiny Titus ◽  
Tianhua Zhao ◽  
Richard T Scott ◽  
...  
Keyword(s):  
Epigenetic Regulation ◽  
Inner Cell Mass ◽  
Cell Mass ◽  
Cell Lineage ◽  
Distal Region ◽  
Chromatin Accessibility ◽  
Early Embryo ◽  
Preimplantation Embryos ◽  
Accessible Chromatin ◽  
Human Preimplantation Embryos

Abstract Early embryonic development is characterized by drastic changes in chromatin structure that affects the accessibility of the chromatin. In human, the chromosome reorganization and its involvement in the first linage segregation are poorly characterized due to the difficulties in obtaining human embryonic material and limitation on low input technologies. In this study, we aimed to explore the chromatin remodeling pattern in human preimplantation embryos and gain insight into the epigenetic regulation of inner cell mass (ICM) and trophectoderm (TE) differentiation. We optimized ATAC-seq (an assay for transposase-accessible chromatin using sequencing) to analyze the chromatin accessibility landscape for low DNA input. Sixteen preimplantation human blastocysts frozen on Day 6 were used. Our data showed that ATAC peak distributions of the promoter regions (<1 kb) and distal regions versus other regions were significantly different between ICM versus TE samples (P < 0.01). We detected that a higher percentage of accessible binding loci were located within 1 kb of the transcription start site in ICM compared to TE (P < 0.01). However, a higher percentage of accessible regions was detected in the distal region of TE compared to ICM (P < 0.01). In addition, eight differential peaks with a false discovery rate <0.05 between ICM and TE were detected. This is the first study to compare the landscape of the accessible chromatin between ICM and TE of human preimplantation embryos, which unveiled chromatin-level epigenetic regulation of cell lineage specification in early embryo development.

170 EXPRESSION PATTERN OF THE Sox2 GENE IN BOVINE OOCYTES AND IN VITRO-DERIVED EMBRYOS

2008 ◽  
Vol 20 (1) ◽  
pp. 165 ◽  
Author(s):  
T. A. L. Brevini ◽  
S. Antonini ◽  
F. Cillo ◽  
G. Pennarossa ◽  
S. Colleoni ◽  
...  
Keyword(s):  
Expression Pattern ◽  
Inner Cell Mass ◽  
False Negative ◽  
Cell Mass ◽  
Preimplantation Embryos ◽  
Cell Stage ◽  
Developmental Potential ◽  
Sox2 Expression ◽  
Bovine Oocytes

Sox2 is a member of the Sox (SRY-related HMGbox) family. It acts to maintain developmental potential and marks the pluripotent lineage of the early mouse embryo; in particular, as in the case of Oct-4 and Nanog, Sox2 is expressed specifically in the inner cell mass (ICM) and in the epiblast of this species. Moreover, it plays an important role in the transcription network that maintains stem cell pluripotency, interacting with other factors such as Oct-4 and Nanog. Little information is available on this gene in bovine; therefore aims of the present study were: a) to identify and characterize the Sox2 expression profile in bovine oocytes and preimplantation embryos; and b) to investigate its expression pattern in ICM and trophectoderm (TE). Bovine oocytes and embryos were obtained by in vitro maturation and fertilization; blastocysts at Day 7 post-insemination underwent microsurgery to separate TE from ICM. mRNA was isolated from 3 pools, each consisting of 5 MII oocytes, 2-, 4-, 8-, and 16-cell embryos, morulae, blastocysts, ICMs, and TEs. Semi-quantitative analysis of Sox2 expression was performed in the exponential phase of PCR amplification using rabbit globin as exogenous control. Data were analyzed with one-way ANOVA, followed by multiple pairwise comparisons with Tukey test (SigmaStat 2.03, SPSS, Inc., Chicago, IL, USA). Values are presented as mean � SEM and differences of P ≤ 0.05 are considered significant. In order to rule out false negative results, PCR amplifications of isolated ICMs and TEs were extended to the plateau phase. Fragment identity was confirmed by sequencing. Comparison of bovine Sox2 cDNA sequence (EMBL AM774325) with databases revealed a 98%, 93%, and 87% homology with sheep, human, and mouse, respectively. Sox2 mRNA was detectable in oocytes as well as in embryos at the different developmental stages analyzed. Semi-quantitative expression studies revealed that Sox2 was present as both maternal and embryonic transcript; in particular, a statistically significant increase from the 8-cell stage, concomitant with embryo genome activation, was observed. Differently from the mouse, Sox2 was expressed in both bovine ICM and TE, resembling the profile previously shown for Oct-4 (van Eijk et al. 1999 Biol. Reprod. 60, 1093–1103), and suggesting that Sox2 expression might be regulated by Oct-4 also in bovine, as described in mouse and human. These findings also suggest that its expression may become restricted to the ICM only at the expanded hatched stage, as previously described for Oct-4 in pig embryos (Vejlsted et al. 2006 Mol. Reprod. Dev. 73, 709–718). This work was supported by PRIN 2006, FIRST 2005, TECLA-MIUR, and EUROSTELLS-ESF.

Two CDC25 homologues are differentially expressed during mouse development

Development ◽  
1995 ◽  
Vol 121 (7) ◽  
pp. 2047-2056 ◽  
Author(s):  
D. Wickramasinghe ◽  
S. Becker ◽  
M.K. Ernst ◽  
J.L. Resnick ◽  
J.M. Centanni ◽  
...  
Keyword(s):  
Inner Cell Mass ◽  
Cell Mass ◽  
Developmental Expression ◽  
Preimplantation Embryos ◽  
Mouse Development ◽  
Cell Stage ◽  
Phosphatase Domain ◽  
Cell Cycles ◽  
Stage Of Development ◽  
Drosophila Homolog

The cdc25 gene product is a tyrosine phosphatase that acts as an initiator of M-phase in eukaryotic cell cycles by activating p34cdc2. Here we describe the cloning and characterization of the developmental expression pattern of two mouse cdc25 homologs. Sequence comparison of the mouse genes with human CDC25 genes reveal that they are most likely the mouse homologs of human CDC25A and CDC25B respectively. Mouse cdc25a, which has not been described previously, shares 84% sequence identity with human CDC25A and has a highly conserved phosphatase domain characteristic of all cdc25 genes. A glutathione-S-transferase-cdc25a fusion protein can hydrolyze para-nitro-phenylphosphate confirming that cdc25a is a phosphatase. In adult mice, cdc25a transcripts are expressed at high levels in the testis and at lower levels in the ovary, particularly in germ cells; a pattern similar to that of twn, a Drosophila homolog of cdc25. Lower levels of transcript are also observed in kidney, liver, heart and muscle, a transcription pattern that partially overlaps, but is distinct from that of cdc25b. Similarly, in the postimplantation embryo cdc25a transcripts are expressed in a pattern that differs from that of cdc25b. cdc25a expression is observed in most developing embryonic organs while cdc25b expression is more restricted. An extended analysis of cdc25a and cdc25b expression in preimplantation embryos has also been carried out. These studies reveal that cdc25b transcripts are expressed in the one-cell embryo, decline at the two-cell stage and are re-expressed at the four-cell stage, following the switch from maternal to zygotic transcription which mirrors the expression of string, another Drosophila homolog of cdc25. In comparison, cdc25a is not expressed in the preimplantation embryo until the late blastocyst stage of development, correlating with the establishment of a more typical G1 phase in the embryonic cell cycles. Both cdc25a and cdc25b transcripts are expressed at high levels in the inner cell mass and the trophectoderm, which proliferate rapidly prior to implantation. These data suggest the cdc25 genes may have distinct roles in regulating the pattern of cell division during mouse embryogensis and gametogenesis.

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