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PubMed1978

Cell division and cell allocation in early mouse development.

Cell division was observed in intact and dissociated mouse embryos between the 2-cell stage and the blastocyst in embryos developing in culture. Division to the 4-cell stage was usually asynchronous. The first cell to divide to the 4-cell stage produced descendants which tended to divide ahead of those cells produced by its slow partner at all subsequent stages of development up to the blastocyte stage. The descendants of the first cell to divide to the 4-cell stage did not subsequently have short cell cycles. The first cell or last cell to divide from the 4-cell stage was labelled with tritiated thymidine. The embryo was reassembled, and it was found that the first pair of cells to reach the 8-cell stage contributed disproportionately more descendants to the ICM when compared with the last cell to divide to the 8-cell stage.

Animals↗
PubMed1978

Features of cell lineage in preimplantation mouse development.

The cell lineage of the mouse was studied from the 2-cell stage to the blastocyst. Lineage to the 8-cell stage was followed under the microscope. Each cell from the 2-cell stage divided to form two daughter cells which remained attached. Subsequently, these two daughters each produced two descendants; one of these descendants regularly lay deep in the structure of the embryo while the other was peripheral. Lineage to the blastocyst was followed by injecting oil drops into cells at the 8-cell stage, and then following the segregation of these drops into the inner cell mass and trophectoderm. Between the 8-cell stage and the blastocyst, the deep cells contributed more frequently to the inner cell mass than did the peripheral cells.

Animals↗
PubMed1993

Insulin-like growth factor binding protein-4, -5 and -6 mRNAs in the human fetus: localization to sites of growth and differentiation?

The insulin-like growth factor binding proteins (IGFBP) modulate the regulatory actions of insulin-like growth factors (IGF) on fetal growth and development. We have determined the sites of IGFBP-4, -5 and -6 synthesis in 14-18 weeks gestation human fetal tissues using northern blot analysis and in situ hybridization to localize their mRNAs. IGFBP-4, -5 and -6 mRNAs were present in most fetal tissues at this gestational age. IGFBP-4 mRNA (2.3 kb) was widely expressed, most abundantly in kidney, stomach, intestine and lung and least in the liver. IGFBP-5 mRNA (6 kb) was in highest abundance in muscle, skin, stomach and intestine. IGFBP-6 mRNA (1.4 kb) was expressed with greatest abundance in the heart, muscle and skin and least in the liver. In situ hybridization confirmed the widespread occurrence of these mRNAs. The distribution of all three IGFBP mRNAs was similar in each tissue with variations in relative abundance between different regions. In general, IGFBP-4, -5 and -6 mRNAs were prevalent in regions of active cellular division and differentiation, suggesting that the binding proteins they encode specify the sites of IGF activity in the developing fetus. The widespread occurrence of their mRNAs suggests that, like IGFs, they are synthesized in multiple tissues in the fetus and have an autocrine or paracrine mode of action.

Blotting, Northern↗
PubMed1994

Neurogenesis in the vertebrate retina.

Many studies concerned with the control of neurogenesis in the retina, as well as other parts of the nervous system, impose the dichotomy of lineage restrictions versus environmental regulation on the design and interpretation of experiments. Recent work on retinal development has focused primarily on "environmental regulation," and this article will review some observations from these studies that provide clues about signals and mechanisms that control proliferation and cell type determination in the retina. Although still at an early stage, these studies already indicate that regulatory signals are not easily categorized as affecting only proliferation or differentiation, but are instead pleiotropic. Interpretation of these findings will be considered in terms of recent work in other systems, which further demonstrates that signals and regulatory mechanisms cannot be classified so simplistically and which suggests that polarizing regulatory mechanisms in terms of lineage restrictions and environmental regulation underestimates the interplay between these types of mechanisms.

Aging↗
PubMed1994

Protein kinase C--an enzyme and its relatives.

Protein kinase C (PKC) is the major target for tumor-promoting phorbol esters in mammalian cells and a key mediator in signaling via phospholipid hydrolysis. The existence of at least 10 structurally related enzymes comprising the PKC family and their differential expression in mammalian tissues raises the obvious question, what functions do the members of this enzyme family fulfil in normal and malignant cell growth? Although there is a host of experimental approaches and observations relating to this question, the challenge remains to define the roles of individual PKC enzymes in various physiological responses.

Animals↗
PubMed1994

Gonosomal mosaicism in myotonic dystrophy patients: involvement of mitotic events in (CTG)n repeat variation and selection against extreme expansion in sperm.

Myotonic dystrophy (DM) is caused by abnormal expansion of a polymorphic (CTG)n repeat, located in the DM protein kinase gene. We determined the (CTG)n repeat lengths in a broad range of tissue DNAs from patients with mild, classical, or congenital manifestation of DM. Differences in the repeat length were seen in somatic tissues from single DM individuals and twins. Repeats appeared to expand to a similar extent in tissues originating from the same embryonal origin. In most male patients carrying intermediate- or small-sized expansions in blood, the repeat lengths covered a markedly wider range in sperm. In contrast, male patients with large allele expansions in blood (> 700 CTGs) had similar or smaller repeats in sperm, when detectable. Sperm alleles with > 1,000 CTGs were not seen. We conclude that DM patients can be considered gonosomal mosaics, i.e., combined somatic and germ-line tissue mosaics. Most remarkably, we observed multiple cases where the length distributions of intermediate- or small-sized alleles in fathers' sperm were significantly different from that in their offspring's blood. Our combined findings indicate that intergenerational length changes in the unstable CTG repeat are most likely to occur during early embryonic mitotic divisions in both somatic and germ-line tissue formation. Both the initial CTG length, the overall number of cell divisions involved in tissue formation, and perhaps a specific selection process in spermatogenesis may influence the dynamics of this process. A model explaining mitotic instability and sex-dependent segregation phenomena in DM manifestation is discussed.

Aged↗
PubMed1993

Development to blastocysts of one- to two-cell equine embryos after coculture with uterine tubal epithelial cells.

Development of 1- to 2-cell in vivo fertilized equine embryos cultured with or without uterine tubal epithelial cells (UTEC) was studied. One- to 2-cell embryos (n = 26) were collected surgically from the uterine tubes of pony mares 1 day after ovulation. Four- to 8-cell embryos (n = 9) were collected 2 days after ovulation. Presumptive zygotes and 2-cell embryos were cultured with (n = 17) or without (n = 9) UTEC, and all 4- to 8-cell embryos were cocultured with UTEC as positive controls. Uterine tubal epithelial cells were used as cell suspensions within 2 weeks after initiation of cultures. Embryos were cultured to blastocysts or until the embryo had morphologic degeneration. Six presumptive zygotes failed to cleave in vitro. Development to blastocysts of 1-cell (4 of 11) and 2-cell (2 of 6) embryos cocultured with UTEC was similar. Coculture of 1- to 2-cell embryos with UTEC significantly (P = 0.05) improved development to blastocysts, compared with culture in medium alone (35 vs 0%, respectively); however, development to blastocysts of 1- to 2-cell embryos cocultured with UTEC was less (P < 0.025) than that of 4- to 8-cell embryos cocultured with UTEC (35 vs 89%, respectively).

Analysis of Variance↗
PubMed1996

The subependymal zone: "brain marrow".

From all of the studies of developmentally regulated molecules as well as the impressive proliferation of cells within the SEZ, we would like to propose that the SEZ of the adult brain, from the lateral ventricles of the cerebrum to the central canal of the spinal cord, represents a potential "brain marrow" from which stem and progenitor cells can be further studied and exploited for cell replacement and circuitry repair paradigms for neurological disease. Without question the SEZ is not as regenerative or pleuripotential as bone marrow or other hematopoietic systems, but there are definitely some elements in common. Bone marrow contains a pleuripotent stem cell that under certain conditions (e.g. the presence of certain growth factors and cytokines) gives rise to erythroblasts and myeloblasts whose progeny include erythrocytes, monocytes, thrombocytes and macrophages. Different growth factors can likewise affect the proliferation as well as differentiation of adult CNS stem and progenitor cells, again contributing to diverse cellular phenotypes. The roles for matrix molecules in these events are yet to be discovered, however, there is evidence to suggest that matrix molecules, including tenascin, do interact with hematopoietic stem cells (Yoder and Williams, 1995) to possibly affect their proliferation and differentiation. Future studies might reveal a similar role for the dense ECM expression within the SEZ proliferative/migratory pathway.

Animals↗
PubMed1994

Signaling molecules that mediate the actions of FGF.

Signaling by fibroblast growth factor (FGF) is critical for cellular growth and differentiation. We have studied the role of FGF and its receptor in development and also the signaling pathways utilized by these molecules. Transgenic mice expressing a dominant negative FGF receptor specifically in lung tissue fail to develop lungs. These findings suggest that FGF signaling is important for airway branching and alveolar formation. In Xenopus embryos, FGF is involved in the development of posterior structures. Induction of mesoderm by FGF is mediated by the serine-threonine kinase RAF. The expression of a dominant negative RAF selectively blocks the mesoderm-inducing action of FGF. Expression of activated RAF accentuated the development of posterior structures Other intracellular molecules that are involved with FGF signaling include RAS, a low-molecular weight GTP-binding protein. We have identified a novel gene (RIP, for RAS-interacting protein) that contains a RAS-binding domain. This domain is found in at least one other protein, ralGDS. Both RIP and ralGDS bind to activated RAS suggesting that these proteins are likely candidates for mediators of RAS function. These findings help elucidate the role of FGF signaling in development.

Animals↗
PubMed1997

[Apoptosis: cellular and clinical aspects].

Removal of damaged cells is essential for the maintenance of life in multicellular organisms. The process of self destruction, apoptosis, eliminates surplus or damaged cells as part of the pathophysiological defence system. Apoptosis is essential in structural and functional organogenesis during embryological development. The physiological regulation of tissue kinetics is a product of both cell proliferation and cell death. Internal and external regulatory stimuli regulate the balance between apoptosis and mitosis by genetic interaction. Apoptosis is characterized by condensation of chromatine as a result of DNA degradation, formation of blebs in the plasma and nuclear membranes, condensation of cytoplasma, formation of vesicular apoptotic bodies, and phagocytosis by neighbouring cells without inflammatory response. A number of observations indicate that programmed cell death plays an important role in the regulation of cytofunctional homeostasis and defense against accumulation of damaged cells, eg with DNA alterations. Dysregulation of the apoptotic gene program, eg by mutations, may not only lead to loss or degeneration of tissue, but also to hyperproliferative and tumorigenic disorders. New evidence indicates that apoptosis regulation is important both in aging processes and diseases such as: neuropathies, immunopathies, viral infections, cancer, etc. Pharmacological intervention designed to modulate apoptosis seems to raise new possibilities in the treatment of disease.

Apoptosis↗
PubMed1997

Proliferative stimulation of lymphocytes by calmodulin binding proteins isolated from amniotic fluid.

In view of the role of calmodulin and calmodulin binding proteins in modulating the second messenger functions of Ca2+, we studied the presence of such proteins in amniotic fluid, which may be considered as a dynamic medium for promoting foetal growth. Affinity chromatography of amniotic fluid proteins revealed the presence of calmodulin binding proteins in samples obtained either at 28 or 36 wk of pregnancy. The relative content of these proteins increased in amniotic fluid from 1.5 mg/g total protein at 28 wk to 3.6 mg/g at full term of pregnancy. Culturing murine splenocytes in presence of the isolated calmodulin binding proteins (10 micrograms protein/10(6) cells) resulted in nearly 4-fold enhancement of 3H-thymidine incorporation into them as compared to controls. In comparison, similar incorporation of the radiolabel into lymphocytes obtained from cord blood was enhanced only by 2 fold in presence of calmodulin binding proteins, though at a much lower protein concentration (50 ng/10(6) cells). SDS-PAGE on 12.5 per cent gels of eluates obtained from calmodulin-agarose columns, followed by overlay of corresponding western blots with biotinylated calmodulin revealed the presence of a 68 kDa calmodulin binding protein in samples collected either at 28 wk or at full-term of pregnancy. In addition, the amniotic fluid also contained 83 kDa calmodulin binding protein at 28 wk. This first-time demonstration of mitogenic, calmodulin binding proteins in amniotic fluid suggests that such mitogens may participate in promoting foetal growth.

Amniotic Fluid↗
PubMed1997

[Fetal human myocardium. Proliferation of the myocytes and development of the cardiac interstitium in the last two gestational trimesters].

PURPOSE: To determine prenatal myocardial quantitative changes by using stereology. METHODS: Twenty-six human fetuses were studied (16 in the 2nd trimester and 10 in the 3rd trimester). The hearts were dissected, weighted, fixed in the Bouin's solution for 12 h, embedded in paraplast, sectioned and stained by HE and trichrome of Gomori. Ten random microscopic fields were analyzed by heart. The following parameters were studied: Vv[myocyte] and Vv[interstitium] (%) (the volume densities of the cardiac myocyte and interstitium), and Nv[myocyte] (1/mm3) (the numerical density of the cardiac myocytes) by the dissector method. The total number of myocytes (N[myocyte]) and the mean volume of the myocytes (V[myocyte]) were also determined. The differences were tested by the Mann-Whitney non-parametric test. RESULTS: The cardiac weight increased of 1.95 to 9.1 g, the Vv[myocyte] decreased from 85.18 to 77.78% and the Vv[interstitium] increased from 14.83 to 22.22%. The Nv[myocyte] decreased from 68.86 x 10(4) to 57.40 x 10(4)/mm3. The V[myocyte] increased from 1214.38 to 1412.31 microns3 and the N[myocyte] increased from 1.36 x 10(9) to 5.06 x 10(9) myocytes. These differences were statistically significant (p < 0.05). CONCLUSION: These results suggest the development of the myocardium at the end of the fetal human period as being mainly hypertrophic to the myocyte and the cardiac interstitium.

Adult↗
PubMed1997

[Lymphangion development in human fetuses].

In human fetuses lymphangion development is a combined process of morpho- and histogenesis guided by lymph flow. Its peculiarities determine unevenness of growth and differentiation of lymphatic vessels in longitudinal and circular orientation, successive formation of valves, muscular cuffs and tensors and muscular coat between external and subendothelial layers.

Cell Differentiation↗