PubMed Health⌕ Search

Biomedical subjects

K E Latham

Publications and source records attributed to K E Latham.

At least 19 recordsLinked to original sources
PubMed2004

Systems biology of the 2-cell mouse embryo.

The transcriptome of the 2-cell mouse embryo was analyzed to provide insight into the molecular networks at play during nuclear reprogramming and embryonic genome activation. Analysis of ESTs from a 2-cell cDNA library identified nearly 4,000 genes, over half of which have not been previously studied. Transcripts of mobile elements, especially those of LTR retrotransposons, are abundantly represented in 2-cell embryos, suggesting their possible role in introducing genomic variation, and epigenetic restructuring of the embryonic genome. Analysis of Gene Ontology of the 2-cell-stage expressed genes outlines the major biological processes that guide the oocyte-to-embryo transition. These results provide a foundation for understanding molecular control at the onset of mammalian development.

Animals↗
PubMed2004

Maternal and environmental factors in early cloned embryo development.

Cloning by somatic cell nuclear transfer (SCNT) in mammals has revealed the remarkable ability of an oocyte to reprogram somatic cell nuclei and induce them to recapitulate the developmental program. Despite the success, cloning remains very inefficient. This review summarizes recent observations from cloning in mice that reveal some of the likely causes for the present inefficiency. One cause appears to be the slow pace of reprogramming combined with the early onset of genome transcription, which together cause cloned embryos to elaborate many somatic cell characteristics even before the first cleavage division. The altered phenotypes of cloned embryos render standard embryo culture conditions grossly sub-optimum. Another cause appears to be a hitherto unappreciated contribution of spindle-associated factors to early embryo development. As current procedures remove the spindle and associated factors, cloned embryos lack these factors. These observations are providing new insight into basic mammalian embryology. They also reveal possible changes to protocols that could improve the overall success of cloning.

Animals↗
PubMed2003

Reproductive semi-cloning respecting biparental origin. A biologically unsound principle.

The original debate article proposed the use of "semi-cloning" as a viable method for assisted reproduction. This debate counters the proposal as being biologically unsound. Given the fundamental limitations of chromosomal segregation and genomic imprinting, the notion of using the MII oocyte to drive haploidization of a somatic cell genome and thereby obtain a substitute for authentic gametes is ill-conceived and untenable.

Chromosome Segregation↗
PubMed2001

Embryonic genome activation.

Genome activation is one of the first critical events in the life of the new organism. Both the timing of genome activation and the array of genes activated must be controlled correctly. Genome activation occurs in a stepwise manner, with some genes being transcribed well in advance of the major genome activation event, in which most housekeeping genes become activated. Changes in chromatin protein content, particularly histone proteins, and chromatin structure appear to regulate the availability of the genome for transcription and provide for specificity of transcription. Gene enhancers are not initially required for transcription, but become necessary as the chromatin structure is modified. Changes in transcription factor content or activity are also required, and protein synthesis is essential for genome activation during both early and later phases of transcriptional activation. Both the changes in chromatin structure and availability of transcription factors are regulated by cell cycle-dependent mechanisms, thus providing the necessary coordination between these processes and other processes such as DNA replication and cleavage.

Animals↗
PubMed2001

Genomic imprinting disrupted by a maternal effect mutation in the Dnmt1 gene.

Maintenance of genomic methylation patterns in mammalian somatic cells depends on DNA methyltransferase-1 (Dnmt1). Mouse oocytes and preimplantation embryos lack Dnmt1 but express a variant of this protein called Dnmt1o. We eliminated Dnmt1o by deletion of the oocyte-specific promoter and first exon from the Dnmt1 locus. Homozygous animals were normal, but most heterozygous fetuses of homozygous females died during the last third of gestation. Although genomic methylation patterns were established normally in Dnmt1o-deficient oocytes, embryos derived from such oocytes showed a loss of allele-specific expression and methylation at certain imprinted loci. Transient nuclear localization of Dnmt1o in 8-cell embryos suggests that this variant of Dnmt1 provides maintenance methyltransferase activity specifically at imprinted loci during the fourth embryonic S phase.

Animals↗
PubMed2001

Additive efficacy of unoprostone isopropyl 0.12% (rescula) to latanoprost 0.005%.

PURPOSE: To evaluate the safety and efficacy of adding unoprostone isopropyl 0.12% vs placebo both given twice daily to latanoprost 0.005% given every evening. METHODS: We treated 41 patients with primary open-angle glaucoma or ocular hypertension with latanoprost 0.005% for 1 month and then randomized each to either placebo or unoprostone isopropyl 0.12% for 8 weeks. Diurnal intraocular pressures were measured at 08:00, 10:00, 12:00, 18:00, and 20:00 hours, both at baseline (time of randomization) and after 8 weeks of treatment. RESULTS: Twenty patients were treated in the placebo group and 21 in the unoprostone isopropyl group. After 8 weeks of treatment in the placebo group, the trough intraocular pressure at 08:00 and the diurnal pressure were 20.4 +/- 3.2 and 19.1 +/- 2.2 mm Hg, respectively. In the unoprostone isopropyl group the pressures were 19.4 +/- 3.3 and 18.0 +/- 1.7 mm Hg (P =.22 and P =.042), respectively. However, eyes with a baseline pressure of 22 mm Hg or greater on latanoprost had an average 3.3 mm Hg greater reduction at trough (P <.01) and a 2.1 mm Hg greater decrease in diurnal pressure (P =.030) after adding unoprostone isopropyl (n = 14 eyes) compared with placebo (n = 16 eyes; P <.001). In addition, the range of the pressures throughout the diurnal curve was reduced from 2.7 mm Hg on latanoprost alone to 1.4 mm Hg after adding unoprostone isopropyl. Adverse events were similar between groups, and no patients were discontinued because of safety reasons. CONCLUSIONS: This study suggests that unoprostone isopropyl can safely improve the diurnal curve characteristics in patients who continue to have an elevated pressure on latanoprost 0.005% alone.

Antihypertensive Agents↗
PubMed2001

The efficacy and safety of latanoprost 0.005% once daily versus brimonidine 0.2% twice daily in open-angle glaucoma or ocular hypertension.

PURPOSE: To evaluate the efficacy and safety of latanoprost 0.005% given topically every evening versus brimonidine 0.2% given topically twice daily in primary open-angle glaucoma or ocular hypertensive patients. METHODS: This was a multicenter, crossover, double-masked comparison. After a 28-day treatment-free period, patients with primary open-angle glaucoma or ocular hypertension were randomized for 6 weeks to brimonidine or latanoprost and then crossed over to the opposite treatment. At baseline and after each treatment period, patients underwent intraocular pressure measurements every 2 hours from 08:00 to 20:00. RESULTS: In 33 patients the mean baseline trough (08:00) was 23.2 +/- 2.1 mm Hg and the diurnal curve pressure was 19.8 +/- 2.7 mm Hg. The trough and diurnal intraocular pressures for brimonidine were 19.6 +/- 3.4 mm Hg and 17.6 +/- 2.2 mm Hg, respectively. Brimonidine statistically reduced the pressure from baseline at each time point except hours 10 and 12 (P =.14 and P =.21, respectively). For latanoprost, the trough and diurnal pressures were 16.2 +/- 2.9 mm Hg and 15.4 +/- 2.5 mm Hg, respectively, and the pressure was statistically reduced at each time point (P <.001) and for the diurnal curve (P <.001). When compared directly, the intraocular pressure level for latanoprost was lower than brimonidine for the diurnal pressure and at each time point (P <.05). One patient was discontinued early from latanoprost treatment because of eyelid swelling; also, latanoprost caused more hyperemia than brimonidine (P =.04). CONCLUSION: This study suggests latanoprost dosed daily in the evening statistically reduces intraocular pressure more during daytime and evening hours than brimonidine dosed twice daily. Brimonidine may not consistently decrease the pressure 10 and 12 hours past dosing from nontreated levels.

Adrenergic alpha-Agonists↗
PubMed2001

Role of protein synthesis in the development of a transcriptionally permissive state in one-cell stage mouse embryos.

The time of onset of gene transcription in the mouse embryo is temporally regulated. A prominent feature of this regulation is a change during the one-cell stage from a transcriptionally nonpermissive state to a transcriptionally permissive state. During the early one-cell stage, the cytoplasm is either inadequate or suppressive for nuclear gene transcription, but by the late one-cell stage, the cytoplasm acquires the ability to support gene transcription either in endogenous nuclei or exogenous nuclei introduced microsurgically. We have investigated the role of protein synthesis in this cytoplasmic transition. Nuclei from two-cell stage embryos treated with alpha-amanitin were used to evaluate the transcriptional permissiveness of late one-cell stage cytoplasm, as indicated by the production of transcripts from four genes that are specifically transcribed at elevated rates during the two-cell stage. Two of these genes were transcribed following nuclear transfer to late one-cell stage cytoplasm, and two were not transcribed. Treatment of the recipient cytoplasm with cycloheximide to inhibit protein synthesis from the early to the late one-cell stage inhibited the transcription of the two genes that were transcribed in the untreated, late one-cell stage recipients. These results indicate that acquisition of the transcriptionally permissive state during the one-cell stage is facilitated by protein synthesis, and that the transcriptional permissiveness in the late one-cell stage cytoplasm is limited to certain genes.

Amanitins↗
PubMed2001

Genetic and epigenetic factors affecting blastomere fragmentation in two-cell stage mouse embryos.

We report here that mouse embryos can exhibit a significant incidence of blastomere fragmentation at the two-cell stage. The incidence of this is influenced by both the maternal and paternal genotype. Embryos from C57BL/6 mothers exhibit a very low incidence of fragmentation at the two-cell stage in crosses involving males of C57BL/6, DBA/2, AKR/J, or SJL strains but exhibit a significantly increased incidence of fragmentation in crosses involving C3H/HeJ males. Increased fragmentation is seen in embryos from C3H/HeJ females crossed with C57BL/6 males but not with C3H/HeJ males. Embryos obtained from reciprocal (C57BL/6 x C3H/HeJ) F1 hybrid females also exhibit an increased incidence of fragmentation at the two-cell stage when the hybrid females are mated to either C57BL/6 or C3H/HeJ males. Interestingly, the results differ significantly between reciprocal F1 hybrid females, indicating a parental origin effect, possibly a result of either genomic imprinting or differences in mitochondrial origin. We conclude that the incidence of blastomere fragmentation at the two-cell stage in the mouse is under the control of more than one genetic locus. We also conclude that blastomere fragmentation is affected by both parental genotypes. These results are relevant to understanding the genetic control blastomere fragmentation, which may contribute to evolutionary processes, affect the success of procedures such as cloning, and affect the outcome of assisted reproduction techniques.

Amanitins↗
PubMed2000

Translation of maternal messenger ribonucleic acids encoding transcription factors during genome activation in early mouse embryos.

Embryonic genome activation (EGA) in mice is sensitive to treatment with cycloheximide, indicating that protein synthesis plays an important role in mediating EGA. We hypothesized that regulated maternal mRNA recruitment may control the time of EGA by controlling the time of appearance of certain transcription factors (TFs). We also hypothesized that synthesis of other TFs may contribute to EGA independently of controlling the timing of EGA. To test these hypotheses, we used sucrose density gradient fractionation coupled to a quantitative reverse transcription-polymerase chain reaction method to compare polysomal mRNA abundances of specific TF mRNAs between metaphase II oocytes, 1-cell-stage embryos, and 2-cell-stage embryos. We observed a 2-cell-stage-specific increase in polysomal abundance of mouse TEA DNA binding domain 2 (mTEAD-2) mRNA, coincident with the first appearance of mTEAD activity in the early embryo. The mRNAs encoding Sp1, TATA binding protein, and cyclic AMP response element binding protein did not undergo translational recruitment, but exhibited differences in polysomal abundance. We also observed a continuous, high proportion in the polysomal fraction for the mRNA encoding ribosomal protein L23 mRNA, which contrasted with the patterns observed for other maternal transcripts. These observations are consistent with the hypothesis that regulated recruitment of maternal TF mRNAs may control the time of activation of some genes during EGA, and that continuous synthesis of other TFs, like Sp1, may facilitate EGA.

Animals↗
PubMed2000

Effects of X chromosome number and parental origin on X-linked gene expression in preimplantation mouse embryos.

Diploid androgenetic mouse embryos, possessing two sets of paternally inherited chromosomes, and control fertilized embryos were used to examine the relative effects of X chromosome number and parental chromosome origin on androgenone viability and X-linked gene expression. A significant difference in efficiency of blastocyst formation was observed between XX and XY androgenones in some experiments, but this difference was not uniformly observed. Significant effects of both X chromosome number and parental origin on X-linked gene expression were observed. Male and female control embryos expressed the XIST: RNA initially. This expression was followed by a preferential reduction in XIST: RNA abundance in male embryos, indicating that dosage compensation for the X chromosome may normally require the downregulation of XIST: RNA expression in male embryos, in conjunction with the production of stable XIST: transcripts in female embryos. By the late blastocyst stage, XX control embryos expressed significantly more XIST: RNA than did XY embryos. Unlike their normal counterparts, XX androgenones did not express significantly more XIST: RNA than did XY androgenones at the late blastocyst stage. Androgenones exhibited severe repression of the Pgk1 gene, but during development to the late blastocyst stage Pgk1 mRNA expression increased in XX androgenones and decreased in XY androgenones. Thus, the initial repression of the Pgk1 gene in XX androgenones was lost as the XIST: RNA declined in abundance, and this loss was correlated with a failure of XX androgenones to express significantly more XIST: RNA than did XY androgenones. These results indicate that androgenones may lack a factor that is expressed from the maternal genome and required for dosage compensation in preimplantation embryos. The results also indicate that early dosage compensation in preimplantation embryos may normally be reversible, thus providing flexibility to meet different developmental requirements of the embryonic and extraembryonic lineages.

Animals↗
PubMed1999

Genetic variation in trophectoderm function in parthenogenetic mouse embryos.

The developing oocyte constitutes the source of a unique and essential molecular legacy that supports embryo metabolism for a substantial period after fertilization and that also directs important epigenetic events that prepare the embryonic genome for transcription and faithful execution of the developmental program. Parthenogenetically activated embryos provide a useful tool with which to examine how maternally derived factors contribute to early development. They also provide a means for evaluating genetic effects on the maternal genomic imprinting process. We report here that the genetic background of the oocyte affects trophectoderm function at the blastocyst stage. Parthenogenetic embryos obtained from activated (B6D2)F1 oocytes hatch efficiently in culture, whereas parthenogenones from C57BL/6 oocytes hatch less efficiently. Fertilized embryos of both strains hatch efficiently. The (B6D2)F1 parthenogenones also undergo blastocoel re-expansion after treatment with cytoskeletal inhibitors more rapidly than do C57BL/6 parthenogenones and exhibit a moderately greater abundance of the Na+, K(+)-ATPase alpha 1 subunit mRNA. Surprisingly, parthenogenones of both strains undergo blastocoel re-expansion more rapidly than do their normal fertilized counterparts. Parthenogenones of both types are able to attach efficiently in culture after removal of the zona pellucida. These observations indicate that significant genetic effects of maternal genotype on trophectoderm function are revealed in the absence of a paternal genetic contribution and that trophectoderm function also differs between parthenogenetic embryos and fertilized embryos. The differences observed between parthenogenetic and fertilized embryos indicate a likely role for one or more imprinted genes in the development of hatching and blastocoel expansion ability. The effect of maternal genotype on parthenogenetic embryo phenotype is consistent with possible differences in maternal genome imprinting or differences in ooplasm composition that have long-term effects on development. The specific differences in hatching and blastocoel re-expansion between parthenogenones of the two strains may be the result of differences in the activity or expression of a hatching enzyme or other molecules that affect fluid accumulation within the blastocyst, such as components of junctional complexes or proteins that regulate Na+, K(+)-ATPase activity.

Animals↗
PubMed1999

Epigenetic modification and imprinting of the mammalian genome during development.

Genomic imprinting in mammals results in the differential expression of maternal and paternal alleles of certain genes. Recent observations have revealed that the regulation of imprinted genes is only partially determined by epigenetic modifications imposed on the two parental genomes during gametogenesis. Additional modifications mediated by factors in the ooplasm, early embryo, or developing embryonic tissues appear to be involved in establishing monoallelic expression for a majority of imprinted genes. As a result, genomic imprinting effects may be manifested in a stage-specific or cell type-specific manner. The developmental aspects of imprinting are reviewed here, and the available molecular data that address the mechanism of allele silencing for three specific imprinted gene domains are considered within the context of explaining how the imprinted gene silencing may be controlled developmentally.

Alleles↗
PubMed1999

Mechanisms and control of embryonic genome activation in mammalian embryos.

Activation of transcription within the embryonic genome (EGA) after fertilization is a complex process requiring a carefully coordinated series of nuclear and cytoplasmic events, which collectively ensure that the two parental genomes can be faithfully reprogrammed and restructured before transcription occurs. Available data indicate that inappropriate transcription of some genes during the period of nuclear reprogramming can have long-term detrimental effects on the embryo. Therefore, precise control over the time of EGA is essential for normal embryogenesis. In most mammals, genome activation occurs in a stepwise manner. In the mouse, for example, some transcription occurs during the second half of the one-cell stage, and then a much greater phase of genome activation occurs in two waves during the two-cell stage, with the second wave producing the largest onset of de novo gene expression. Changes in nuclear structure, chromatin structure, and cytoplasmic macromolecular content appear to regulate these periods of transcriptional activation. A model is presented in which a combination of cell cycle-dependent events and both translational and posttranslational regulatory mechanisms within the cytoplasm play key roles in mediating and regulating EGA.

Animals↗
PubMed1999

Comparison of protein synthesis patterns in mouse cumulus cells and mural granulosa cells: effects of follicle-stimulating hormone and insulin on granulosa cell differentiation in vitro.

Successful development of mammalian oocytes requires correct interactions between developing oocytes and associated granulosa cells. Development of oocyte-granulosa cell complexes from preantral follicles in vitro does not produce oocytes competent to develop to blastocysts at the same frequency as for oocytes that develop in vivo. Addition of either FSH or insulin to cultures of oocyte-granulosa cell complexes does not improve the frequency of blastocyst development, and the combination of both insulin and FSH is deleterious. Here, high-resolution 2-dimensional PAGE (2D-PAGE) and computerized gel image analysis were used to compare patterns of protein synthesis in cumulus cells and mural granulosa cells of small antral follicles, and then to assess effects of FSH and insulin on the differentiation of oocyte-associated granulosa cells (OAGCs) in vitro. Culture of OAGCs without FSH or insulin resulted in failure to synthesize many proteins at rates characteristic of cumulus cells. Either hormone used alone caused many cumulus cell proteins that were decreased in control cultures to be synthesized at nearly normal cumulus cell rates, and also caused the synthesis of other proteins to be increased or decreased. The two hormones added together produced the greatest change in protein synthetic pattern, including overexpression or underexpression of many proteins not affected by either hormone alone. Addition of these hormones to culture media thus appeared insufficient to elicit a normal cumulus cell phenotype in OAGCs and could lead to complex changes in protein synthesis that may be deleterious to oocyte development. The high-resolution 2D-PAGE approach described here should be a valuable tool in studies on oocyte and granulosa cell development in vitro, since phenotype can be evaluated globally through the display of over 1000 newly synthesized proteins rather than relying upon the expression of just a few genes.

Animals↗
PubMed1998

Defects in regulation of apoptosis in caspase-2-deficient mice.

During embryonic development, a large number of cells die naturally to shape the new organism. Members of the caspase family of proteases are essential intracellular death effectors. Herein, we generated caspase-2-deficient mice to evaluate the requirement for this enzyme in various paradigms of apoptosis. Excess numbers of germ cells were endowed in ovaries of mutant mice and the oocytes were found to be resistant to cell death following exposure to chemotherapeutic drugs. Apoptosis mediated by granzyme B and perforin was defective in caspase-2-deficient B lymphoblasts. In contrast, cell death of motor neurons during development was accelerated in caspase-2-deficient mice. In addition, caspase-2-deficient sympathetic neurons underwent apoptosis more effectively than wild-type neurons when deprived of NGF. Thus, caspase-2 acts both as a positive and negative cell death effector, depending upon cell lineage and stage of development.

Amyotrophic Lateral Sclerosis↗