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PubMed1999

Astrocyte proliferation during development of the human retinal vasculature.

Wholemounts of human fetal retinas were labeled with antibodies to Ki67 or proliferating cell nuclear antigen, to map the distribution of proliferating cells in the developing primary vasculature and neural retina. Double labeling was used to determine the relative proportions of endothelial cells (CD34), astrocytes (glial fibrillary acidic protein - GFAP) and microglia (major histocompatability complex class II) associated with the developing vessels. The differentiated region of neural retina (cold spot) was 3.5 mm(2)at 15 weeks gestation (WG), centred on the incipient fovea, and increased in size with age to 80.5 mm(2)by 23-24 WG. Ki67 immunoreactive cells were distributed throughout the developing vasculature at all ages. The mean density of dividing cells in the neural retina increased with gestational age from 146 mm(-2)at 15 WG, to 624 mm(-2)at 23-24 WG. By 20 WG proliferation in the vasculature overlapped the margins of the cold spot, which was almost completely vascularized by 23-24 WG, except for a narrow strip on the horizontal meridian, which included the incipient fovea. Counts of CD34/Ki67 immunoreactive cells indicated that 15-52% of proliferations in the developing vasculature at 18 WG are endothelial cells. In contrast, in the fellow retina 65-85% cells were Ki67/GFAP immunoreactive, indicating proliferation of astrocytes in situ. No dividing microglia were observed. The findings suggest that large numbers of proliferating astrocytes accompany the developing vessels as they migrate across the primate retina.

Antigens, CD34↗
PubMed1983

Capacity of fertilized ova from mature and middle-aged rats to undergo preimplantation development in vitro.

The ability of ova collected from mated middle-aged rats (9-10 months of age) to undergo preimplantation development in vitro was compared to that of younger controls (3-4 months of age). The majority of ova from young rats underwent at least one cleavage division for every 24 h of the 96 h culture period. Seventy-two percent reached the morula/blastocyst stage at the termination of the culture. Aged ova had a reduced capacity to undergo preimplantation development in vitro with the number of fragmented and/or degenerated ova increasing after each day in culture. At the end of the culture period, 81.6% of the ova had degenerated. It is concluded that middle-aged rats ovulate defective ova and that these defective ova account, in part, for the preimplantation losses that characterize middle-aged rats.

Age Factors↗
PubMed1996

Arresting the mitotic oscillator and the control of cell proliferation: insights from a cascade model for cdc2 kinase activation.

We consider a minimal cascade model previously proposed for the mitotic oscillator driving the embryonic cell division cycle. The model is based on a bicyclic phosphorylation-dephosphorylation cascade involving cyclin and cdc2 kinase. By constructing stability diagrams showing domains of periodic behavior as a function of the maximum rates of the kinases and phosphatases involved in the two cycles of the cascade, we investigate the role of these converter enzymes in the oscillatory mechanism. Oscillations occur when the balance of kinase and phosphatase rates in each cycle is in a range bounded by two critical values. The results suggest ways to arrest the mitotic oscillator by altering the maximum rates of the converter enzymes. These results bear on the control of cell proliferation.

CDC2 Protein Kinase↗
PubMed1996

The effect of activin-A on the development of mouse preimplantation embryos in vitro.

PURPOSE: Our purpose was to clarify the involvement of transforming growth factor-beta (TGF-beta) family in the regulation of preimplantation embryo development. METHODS: The effects of activin-A and TGF-beta on the rates of morula and blastocyst formations as well as on the cleavage velocity of a mouse two-cell embryo in vitro were analyzed. The gene expressions of these two growth factors in various developmental stages were also studied using RT-PCR. RESULTS: Activin-A at a concentration of 0.2 ng/ml significantly stimulated not only the rate of morula formation but also the velocity of embryo cleavage, whereas no significant effect was found with TGF-beta. RT-PCR revealed that activin-A subunit mRNA, but not TGF-beta mRNA, was detected in preimplantation mouse embryo at any developmental stage. CONCLUSIONS: Activin-A plays an important role in the regulation of preimplantation mouse embryo development in an autocrine fashion.

Activins↗
PubMed1995

Long-lasting persistence of elevated sister-chromatid exchange frequencies induced by perinatal benzo(a)pyrene treatment in rat bone-marrow cells.

In this work the possibility that a mutagenic factor acting in utero or in the perinatal period might lead to elevated mutagenic rates in bone-marrow cells after a considerable period of time was examined. An aromatic hydrocarbon, benzo(a)pyrene was used as the test substance. Benzo(a)pyrene treatments resulted in significantly higher sister-chromatid exchange (SCE)-frequencies in both fetal and neonatal groups in both sexes, even four months after exposure. In a second experiment we examined whether mutagenic exposure suffered in utero could make the individual more susceptible to mutagenic effects in adulthood. Preliminary results indicate that such a possibility could exist.

Animals↗
PubMed2003

PRL-secreting pituitary adenomas in pregnancy.

Dopamine-agonists have significantly increased the number of pregnancies in women with micro- and macro-prolactinomas, as ovulation can be restored in the great majority of these patients. Thus, the main questions regard the possible consequences of high estrogen levels on tumor volume and the possible effects of D2-agonists on fetal development. While the risk of tumor increase is low in patients with prolactin secreting micro-adenoma (MIP), in PRL secreting macro-adenoma (MAP) patients the possibility of tumor growth is enhanced and influenced by previous treatment. Moreover, while it is well known that the exposition for only the first 4 weeks to bromocriptine (BRC) therapy does not affect the outcome of pregnancy, data on the use of BRC during the whole gestation are limited to just over 100 cases. Female pregnant patients with MIP, therefore, must be reassured and medical therapy suspended, with successive clinical follow-up. In the case of pregnant MAP subjects, the best approach from pre-pregnancy debulking, dopamine-agonist therapy interruption and BRC therapy continuation must be agreed on with the patient, and a careful follow-up instituted.

Adenoma↗
PubMed1996

Sequence and transcription of Qa-2-encoding genes in mouse lymphocytes and blastocysts.

The protein product of the mouse preimplantation embryo development (Ped) gene, which controls the rate of preimplantation embryonic cleavage division and subsequent embryo survival, is the Qa-2 antigen. This major histocompatibility complex (MHC) class I b protein is encoded by four genes, Q6, Q7, Q8, and Q9. The present study was undertaken to begin to elucidate which of the four Qa-2-encoding genes are responsible for the Ped gene phenotype in the C57BL/6 mouse (H2(b)). First, restriction maps of the four genes, using 25 restriction enzymes, were created. The RE maps confirmed that Q6 is similar to Q8 and Q7 is similar to Q9, but that the Q6/Q8 gene pair differs from the Q7/Q9 gene pair. The genomic DNA sequences of Q6 and Q8 were determined, as well as the DNA sequences of exons 4 - 8 of Q9, and the 5' regulatory regions of Q6, Q8, and Q9. This DNA sequence information, combined with the published DNA sequence information for the entire Q7 gene and exons 1 - 3 of Q9, allowed us to design primers for reverse transcription-polymerase chain reaction that could distinguish which of the four genes were transcribed in mouse lymphocytes and embryos. It was found that all four genes are transcribed in lymphocytes, but only Q7 and Q9 are transcribed in mouse embryos. Thus, both Q7 and Q9 are candidates for the genes responsible for the Ped gene phenotype.

Amino Acid Sequence↗
PubMed2003

A signal peptide secretion screen in Fucus distichus embryos reveals expression of glucanase, EGF domain-containing, and LRR receptor kinase-like polypeptides during asymmetric cell growth.

Zygotes of the brown alga Fucus distichus (L.) Powell develop polarity prior to the first embryonic cell division and retain a pattern of asymmetric growth during early embryogenesis. In order to identify F. distichus polypeptides secreted during asymmetric cell growth, we used a functional assay in Saccharomyces cerevisiae to screen a cDNA library generated from asymmetrically growing Fucus embryos for sequences encoding polypeptides that function as signal peptides for secretion. We isolated and sequenced 222 plasmids containing Fucus cDNAs encoding signal peptide activity. The cDNA inserts from these plasmids were translated in silico into 244 potential polypeptide sequences, 169 of which are predicted to contain signal peptides. BlastP analysis of the Fucus sequences revealed similarity between many Fucus proteins and cell surface proteins that function in development in other eukaryotes, including epidermal growth factor (EGF)-like repeat-containing proteins, plant leucine-rich repeat (LRR)-receptor kinases, and algal beta-1, 3-exoglucanase. However, most of the isolated Fucus polypeptides lack similarity to known proteins. The isolation of cDNAs encoding secreted Fucus proteins provides an important step toward characterizing cell surface proteins important for asymmetric organization and growth in fucoid embryos.

Amino Acid Sequence↗
PubMed2001

Evolutionarily conserved nuclear migration genes required for early embryonic development in Caenorhabditis elegans.

The nudF and nudC genes of the fungus Aspergillus nidulans encode proteins that are members of two evolutionarily conserved families. In A. nidulans these proteins mediate nuclear migration along the hyphae. The human ortholog of nudF is Lis1, a gene essential for neuronal migration in the developing cerebral cortex. The mammalian ortholog of nudC encodes a protein that interacts with Lis1. We have identified orthologs of nudC and Lis1 from the nematode Caenorhabditis elegans. Heterologous expression of the C. elegans nudC ortholog, nud-1, complements the A. nidulans nudC3 mutant, demonstrating evolutionary conservation of function. A C. elegans nud-1::GFP fusion produces sustained fluorescence in sensory neurons and embryos, and transient fluorescence in the gonad, gut, vulva, ventral cord, and hypodermal seam cells. Fusion of GFP to C. elegans lis-1 revealed expression in all major neuronal processes of the animal as well as the multinucleate spermathecal valves and adult seam cells. Phenotypic analysis of either nud-1 and lis-1 by RNA interference yielded similar phenotypes, including embryonic lethality, sterility, altered vulval morphology, and uncoordinated movement. Digital time-lapse video microscopy was used to determine that RNAi-treated embryos exhibited nuclear positioning defects in early embryonic cell division similar to those reported for dynein/dynactin depletion. These results demonstrate that the LIS-1/NUDC-like proteins of C. elegans represent a link between nuclear positioning, cell division, and neuronal function.

Animals↗
PubMed2000

Growth in the pre-fusion murine allantois.

Prior to fusion with the chorion, the extraembryonic mesoderm of the murine (Mus musculus) allantois differentiates with distal-to-proximal polarity into at least two cell lineages: a chorio-adhesive cell lineage called mesothelium, and the endothelium of the umbilical vasculature. How the allantois grows is less clear, but cell proliferation and addition of mesoderm from the underlying primitive streak appear to play important roles. The aim of this study was to analyze growth in the murine allantois. Techniques of histology and microsurgery were used to examine pre-fusion allantoises at nine developmental timepoints that differed by approximately 2 h. Cell counts revealed that allantoic size increased over time. Two hours of exposure to colcemid enhanced mitotic figures, which were used to calculate the relative number of proliferating cells (mitotic index, MI) in pre-fusion allantoises at each developmental timepoint. Cell proliferation was highest in nascent allantoises and showed signs of slowing by two somite pairs. By five to six-somite pairs, when most allantoises are attaching to the chorion, the overall MI decreased significantly. No regional differences in the mitotic index were observed at any developmental stage. Total cell numbers and the mitotic index were then used to discover the extent of streak contribution to pre-fusion allantoises. Cell proliferation and streak activity were highest in nascent allantoises, after which growth occurred predominantly by cell proliferation. Formation of allantoic regenerates by microsurgical removal and culture in intact conceptuses provided independent confirmation that, as the allantois matured, the primitive streak ceased to be a major contributor to its growth. Thus, the allantois grows by both mitosis and addition of mesoderm from the streak. That the periods of highest cell proliferation and streak activity coincided raises intriguing questions concerning their interplay in the control of growth in the murine allantois.

Allantois↗
PubMed2001

Proliferation and differentiation of pituitary somatotrophs and mammotrophs during late fetal and postnatal periods.

Proliferation of somatotrophs and mammotrophs in the rat pituitary during late fetal and postnatal periods up to 4 weeks after birth was quantitatively studied with the double immunostaining of bromodeoxyuridine and the hormones produced by them. Somatotrophs were first detected in 18.5-day fetuses and rapidly increased in number throughout the periods studied. The cells labeled with both anti-BrdU and anti-GH were few in number until shortly before birth and then increased conspicuously during the first 10 days after birth. Mammotrophs were detected at gestational day 19.5 but they were few until the second week after birth, when their number began to increase rapidly. The percentage of the number of the cells double-labeled with both anti-BrdU and anti-GH to all somatotrophs was 8.3% at the most. This was about the same as that of corticotrophs during the late fetal period and that of thyrotrophs in the early postnatal period. In contrast, the percentage of double-labeled cells to all mammotrophs was 3.8% as a maximum, which is lower than the values for somatotrophs, corticotrophs, or thyrotrophs, indicating a smaller contribution of mitosis to mammotroph proliferation. It is possible that this smaller contribution is compensated for by transdifferentiation of cells committed to become the somatotroph lineage. However, coexistence of GH and PRL was not observed in the present material.

Animals↗
PubMed1986

Pattern formation during vulval development in C. elegans.

Previous studies have shown that the development of the vulva of the C. elegans hermaphrodite involves six multipotential hypodermal cells as well as the gonadal anchor cell, which induces vulval formation. Our further examination of the interactions among these seven cells has led to the following model. Each hypodermal precursor cell becomes determined to adopt one of its three potential fates; each of these fates is to generate a particular cell lineage. In the absence of cellular interactions each precursor cell will generate the nonvulval cell lineage; an inductive signal from the anchor cell is required for a precursor cell to generate either of the two types of vulval cell lineages. The inductive signal is spatially graded, and the potency of the signal specifies which lineage is expressed by each of the tripotential precursor cells.

Animals↗
PubMed1988

Proliferation of Schwann cells in a developing feline lumbar ventral spinal root.

Schwann cell proliferation in the L6 ventral spinal root of cat fetuses and young kittens was studied by light microscopical autoradiography and electron microscopy. The proliferative activity reached a maximum 35 days after mating. This is about one week before the immature alpha-axons begin to myelinate and about one month before birth (63 days after mating) when the myelination of the immature gamma-axons starts. The proliferative activity was already quite low 45 days after mating and ceased completely after birth. Calculations based on the observed number of Schwann cell nuclei per 100 axons showed that the number of Schwann cells already present 45 days after mating was equal to or even a little higher than the observed adult number. Necrotic nucleated Schwann or endoneurial cells were not observed. I conclude that Schwann cell proliferation in the L6 ventral spinal root is already nearly finished when the first immature alpha-axons begin their myelination and that myelination of the immature gamma-axons begins without a preceding increase in Schwann cell proliferative activity.

Aging↗
PubMed1995

Immunosuppressive activity of angiogenin in comparison with bovine seminal ribonuclease and pancreatic ribonuclease.

Angiogenin, a member of the pancreatic-like ribonuclease family with a special biological action (RISBAses), is a basic protein that induces blood vessel formation. Another member of these special ribonucleases, bovine seminal ribonuclease (BS RNase), displays biological properties, including aspermatogenic, embryotoxic, antitumor and immunosuppressive activities. The effects of two angiogenin preparations tested on the biological activities mentioned above are reported and compared with those of BS RNase and RNase A. In contrast to RNase A, which was ineffective in all biological activities tested, angiogenin suppressed significantly the proliferation of human lymphocytes stimulated by phytohemagglutinin or concanavalin A or by allogenic human lymphocytes (mixed lymphocyte culture). However, angiogenin did not affect the growth of human tumor cell lines, development of cow and mouse embryos and spermatogenicity in mice. On the basis of these results, angiogenin is the first monomeric ribonuclease described so far that displays immunosuppressive activity similar to that of the dimeric BS RNase. The immunosuppressive activity of angiogenin might synergize with the effect on neovascularization of tumor tissues and thus contribute to the development of tumor.

Animals↗