Strife in the germ line.

The formation of germ cells, their progress through meiosis, and the earliest stages of development are times when the genes in normal organisms are in balanced conflict. One conflict is expressed as meiotic drive, a system which characteristically associated with low fertility. It is argued that the association between carcinoma in situ (CIS) and low fertility can be explained by assuming that some meiotic drive system is operating in the testis. In meiotic drive systems, single haploid sets of chromosomes are frequently prevented from contributing to the next generation. The progression of carcinoma in situ to the near triploidy of germ cell tumors is taken as supportive evidence that meiotic drive systems are operating during tumor formation. Another conflict system is the opposing interests of the genes inherited from each parent. In general, genes inherited from the father promote growth and those from the mother limit the growth of the normal conceptus. In germ cell tumors, it is not known if the chromosomes retain a memory of their parent.

Local reduction of organ size in transgenic mice expressing a soluble insulin-like growth factor II/mannose-6-phosphate receptor.

Genetic evidence suggests that the insulin-like growth factor II (IGF-II)/mannose-6-phosphate receptor (IGF2R) slows growth. A soluble form of IGF2R (sIGF2R) is produced by proteolytic cleavage of the intact cellular receptor and is found at high levels in fetal and neonatal plasma. To test the hypothesis that sIGF2R modulates organ size in vivo, we generated transgenic mice expressing a mouse Igf2r complementary DNA in which the transmembrane domain sequence was deleted. The transgene was driven by the keratin-10 promoter and was expressed at the highest levels in the skin and alimentary canal. Transgenics showed disproportionately reduced size of the alimentary canal, where the wet weight was decreased by 9-20% and the dry weight was decreased by 20-30%, whereas the water content per unit dry weight was not significantly changed. In addition, the circulating levels of IGF-II and the latent form of transforming growth factor-beta1 were increased by 58-77% and 56-140%, respectively, whereas plasma epidermal growth factor levels showed a 24-35% reduction. The serum and tissue activities of four lysosomal enzymes were not affected, with the exception of the colon in the line expressing the transgene at highest levels, where enzyme activities were decreased compared with control values. These results support a significant role for the sIGF2R in local modulation of organ size in vivo.

Increased and persistent circulating insulin-like growth factor II in neonatal transgenic mice suppresses developmental apoptosis in the pancreatic islets.

In rats, a proportion of pancreatic beta-cells are deleted by apoptosis in the second week of postnatal life and replaced by endocrine cell neogenesis from pancreatic ductal epithelium. This coincides with a reduction in pancreatic insulin-like growth factor II (IGF-II) expression, and IGF-II has been shown to act as a beta-cell survival factor in vitro. To examine whether IGF-II regulates beta-cell apoptosis in vivo, an IGF-II transgenic mouse model was used in which mouse IGF-II is overexpressed in skin, gut, and uterus driven by a keratin promoter, so that circulating IGF-II is retained postnatally. Mice were killed between postnatal days 7 and 26, and the pancreas was examined histologically. Apoptotic cells were visualized by the terminal deoxynucleotidyltransferase-mediated deoxy-UTP nick end labeling method, and proliferating cells were examined by immunohistochemistry for proliferating cell nuclear antigen. In nontransgenic mice, serum IGF-II was absent by 26 days, but mean (+/-SEM) values were 45+/-9 ng/ml (n = 5) in transgenic animals. A 2- to 3-fold rise in islet cell apoptosis was seen in normal animals between days 11 and 16, but this was substantially decreased in IGF-II transgenic mice (day 11; control, 12+/-1%; transgenic, 6+/-1%; P < 0.01; n = 5). Consequently, islets from IGF-II transgenic mice had a significantly greater mean area from days 11-16, but the proportions of beta- and alpha-cells and circulating insulin levels were not changed. Islet cell DNA synthesis was increased in transgenic mice on days 13 and 16. The total islet number per section did not alter. The results show that a persistent presence of circulating IGF-II postnatally alters endocrine pancreatic ontogeny in the mouse and largely prevents the wave of developmental apoptosis that precipitates beta-cell turnover in neonatal life.

Decreased skin sensory innervation in transgenic mice overexpressing insulin-like growth factor-II.

Cutaneous sensory innervation was studied in transgenic mice overexpressing insulin-like growth factor II using a keratin promoter. The skin area of these animals is enlarged providing increased target for sensory neurons. L4 dorsal root ganglion cell counts revealed that the total number of sensory neurons was the same in transgenics as control animals. Levels of nerve growth factor per unit weight of skin were also unchanged. The cutaneous nerves of the hindlimb were immunostained with the pan-neuronal marker PGP 9.5 in transgenic and control mice at postnatal day 0 and 21. The innervation in transgenic mice was markedly reduced, particularly in superficial dermis and epidermis and in some areas innervation was completely absent. The effect was greatest in distal skin regions and increased with age. Since insulin-like growth factor II has been reported to be a sensory neurotrophic factor, its effect on neurite outgrowth was tested on embryonic day 14 and 18 mouse lumbar dorsal root ganglion explants in culture. Under these conditions insulin-like growth factor II (5-100 ng/ml) did not have strong growth promoting activity and at embryonic day 18, in the presence of 5-10 ng/ml nerve growth factor, neurite outgrowth was suppressed by insulin-like growth factor II. The results show that increased skin target and availability of nerve growth factor per se do not alter the number of innervating sensory neurons. However, reduced sensory terminal arborization and skin hypoinnervation does occur in the presence of excess insulin-like growth factor-II. It is possible that insulin-like growth factor-II inhibits terminal axon growth directly via receptors on sensory neurons or peripheral glia.

High plasma insulin-like growth factor-II and low lipid content in transgenic mice: measurements of lipid metabolism.

Transgenic mice were made by introducing extra copies of the mouse insulin-like growth factor-II (IGF-II) gene driven by the bovine keratin 10 promoter (BKVI). The adult plasma IGF-II levels were elevated at least three times in one line. In this line, there was a lower lipid content of both brown and white adipose depots at 2-4 months of age, and 40% less fat in the carcass at 7-9 months. The low lipid phenotype was not detected in the carcass at 2 weeks after birth. The lean characteristic was attributed to circulating IGF-II because the transgene was not expressed in fat. At 2-4 months of age, the transgenes oxidized more oral lipid, and less of this lipid was incorporated into the whole body and the epididymal fat. In contrast, the interscapular brown adipose tissue maintained lipid incorporation and lipoprotein lipase activity despite its reduced size. The altered activity of the brown adipose tissue may account for the gradual onset and persistence of the lean feature of the transgenic mice. There were no substantial changes in lipogenesis which could account for the low fat content. The plasma levels of IGF-I, insulin, glycerol, non-esterified fatty acids, triacylglycerols and glucose were not greatly changed and the pituitary GH content was within the normal range.

Neonatal anuria with maternal angiotensin-converting enzyme inhibition.

The use of angiotensin-converting enzyme inhibitors as antihypertensives has increased rapidly since the introduction of captopril in 1981. Seven cases of neonatal renal failure have been reported in patients with exposure to angiotensin-converting enzyme inhibitors that continued to the time of delivery. Two cases resulted in death of the newborn; the other five patients recovered after peritoneal dialysis. Because the relative frequency of normal outcomes is unknown, these data are insufficient for incidence-rate estimates or risk/benefit analyses. However, given the potential neonatal morbidity and mortality associated with late-pregnancy exposure to angiotensin-converting enzyme inhibitors, alternative therapies in the third trimester should be given consideration. If these drugs must be used in this context, the clinician should be prepared to deal with renal failure and hypotension in the newborn. The Food and Drug Administration invites reports of adverse pregnancy outcomes associated with such exposure.

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.

Clonal analysis of the change in growth phenotype during embryonal carcinoma cell differentiation.

Retinoic acid has been shown to induce the differentiation of mouse embryonal carcinoma cells. Previous workers have reported that bulk cultures of the differentiated derivatives have a slower growth rate and a reduced capacity to form tumours. We have analysed this change in growth rate for a sub-tetraploid EC cell line, PC13 clone 5 MA2, at a clonal level and have shown that the production of cells with a slower growth rate is not a result of cell selection. We have also demonstrated that the action of retinoic acid on growth rate is delayed for approximately 48 h and that the new growth phenotype, once attained, is stable. Finally we have confirmed at a clonal level that the differentiated derivatives of EC cells exposed to retinoic acid have a reduced capacity to form tumours. Clones of EC cells exposed to retinoic acid for longer than 96 h are unable to form tumours in a 30-day period, whilst 87% of their untreated counterparts are able to do so.

Formation and consequences of cell patterns in preimplantation mouse development.

The behaviour of groups of cells was studied in culture during preimplantation mouse development. The following observations were made with intact embryos minus the zona pellucida and with embryos whose cells had been dissociated and recombined. The form of the 4-cell embryo was related to the behaviour of the first cell to divide to this stage. The form of the 8-cell embryo depended on contact between the groups of four cells each derived from a single cell at the 2-cell stage. The form of the 16-cell embryo depended on cell movement during and after division from the 8- to the 16-cell stage. These results suggest that the morphogenetic movements of these early embryonic cells are principally governed by continuous cell interactions after fertilization. The cell surfaces of the embryos were examined with scanning electron microscopy in an attempt to discriminate between the mechanisms which could account for these movements.

Macrophages in haemopoietic and other tissues of the developing mouse detected by the monoclonal antibody F4/80.

Macrophages are widely distributed in lymphohaemopoietic and other tissues of the normal and diseased adult, where they play an important role in host defence and repair. Although the development of haemopoiesis has been well studied in several species, the ontogeny of the mononuclear phagocyte system remains poorly understood. We have used a highly specific mAb, F4/80, to examine the distribution of mature macrophages in the developing mouse, with special reference to their presence in the haemopoietic microenvironment. Monocytes and macrophages were first seen in embryos on day 10 in the yolk sac and liver as well as in mesenchyme. In liver, spleen and bone marrow, there was expansion of this population associated with the initiation of haemopoiesis on days 11, 15 and 17, respectively. Macrophages in these sites formed part of the haemopoietic stroma and their extensively spread plasma membrane processes could be seen making intimate contacts with clusters of differentiating haemopoietic cells. F4/80+ cells were widely dispersed in undifferentiated mesenchymal tissue in organs such as lung, kidney and gut. Numbers of F4/80-labelled cells increased concomitantly with organ growth and local mitoses were evident, as well as actively phagocytic macrophages. Our studies establish that macrophages are among the earliest haemopoietic cells to be produced during development and that they are relatively abundant in fetal tissues in the absence of overt inflammatory stimuli. Their distribution is correlated with the sequential migration of haemopoiesis and they constitute a prominent component of the stroma in fetal liver, spleen red pulp and bone marrow. Apart from a role in haemopoietic cellular interactions, their highly developed endocytic and biosynthetic activities suggest that macrophages contribute major undefined functions during growth, turnover and modelling of fetal tissues.

Tactical control of ovine Campylobacter abortion outbreaks with a bacterin.

Abortions due to Campylobacter fetus fetus (C. fetus fetus) were diagnosed in three Canterbury ewe flocks 6 weeks prior to lambing. In two of the flocks, two inoculations of a C. fetus fetus bacterin, 10 days apart, reduced the incidence of abortions in the treated ewes to about one third and one half respectively of the level in the control ewes in the same flock. The treatment had no effect in a third flock where an outbreak had been in progress for 2 weeks before investigations started. The results confirm earlier Scottish work where pregnant sheep were inoculated with a C. fetus fetus vaccine following artificial challenge with C. fetus fetus. This inoculation significantly reduced the number of C. fetus fetus abortions. The results also indicate that treatment must start very early in an outbreak.

Wilms' tumour-suppressor protein isoforms have opposite effects on Igf2 expression in primary embryonic cells, independently of p53 genotype.

The p53 protein has been proposed as a modulator of the Wilms' tumour-suppressor protein (WT1) transcriptional regulation activity. To investigate this putative p53 role, the promoter P3 of the mouse insulin-like growth factor II gene (Igf2) was used as a target for WT1 regulation in primary cell cultures derived from p53 wild-type (p53+/+) and knock-out (p53-/-) mouse embryos. In these cells, the WT1 transcriptional activity was observed to be independent of p53 genotype. Furthermore, the two WT1 zinc finger (ZF) isoforms were for the first time found to have opposite effects on gene expression from a single promoter in the same cell type, WT1[-KTS] activating Igf2 P3, whereas WT1[+KTS] repressed its activity. In addition, we have mapped the WT1 binding sites and investigated the effect on WT1 binding activity of individual ZF deletions and Denys-Drash syndrome point mutations to this target.

Epidermal growth factor receptors increase during the differentiation of embryonal carcinoma cells.

Mouse teratocarcinoma stem cells (embryonal carcinoma, or EC cells) bind very small amounts of mouse epidermal growth factor (EGF) and the latter hormone seems to have no stimulatory effect on the growth of two cloned lines of EC cells. However, when EC cells are induced to differentiate into large flat endodern-like cells (END cells), EGF receptors increase in number reaching a plateau in 6 to 8 days. At 8 to 10 days after induction, END cells multiply very slowly, but when EGF is added (3 x 10(-10) M) to the medium, cell division is stimulated and a further change in morphology occurs. This letter describes the binding characteristics and numbers of the EGF receptors on EC and END cells and shows that exogenous retinoic acid increases the numbers of EGF receptors on END cells. We were unable to find endogenous competing factors produced by EC cells. Such factors could account for the lack of detectable binding of EGF on these cells. As EC cells differentiate to END cells, so the ability of the cells to form tumours is reduced. Since this change is accompanied by an increase in the number of EGF receptors there may be a relationship between these two events.

Appearance of interferon inducibility and sensitivity during differentiation of murine teratocarcinoma cells in vitro.

Pluripotential embryonal carcinoma (EC) cells do not produce interferon after treatment with a wide variety of inducers, nor are they sensitive to its action. Several differentiated lines derived from the EC cells, however, both produce and are sensitive to mouse interferon. Differentiation of EC cells in vitro is accompanied by development of interferon inducibility and sensitivity.

Growth and the distal tip of mouse chromosome 7.

This review concerns the general problem of understanding growth control in the whole organism, starting with a saltatory change in size generated by a chromosome translocation or a mutation in a single gene. In particular, changes in insulin-like growth factor-II levels, by genetic and embryological manipulation, have major effects on wet weight size, but the intermediary events that link these levels to this measure of growth are uncertain. Thus it is currently impossible to eliminate any of the intermediary candidate processes that have been observed in model systems, including changed rates of apoptosis, cell multiplication, protein synthesis, capillary permeability and fluid transport.

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.

The zootype and the phylotypic stage.

What is it that defines an animal? The definition provided here, made on the basis of developmental biology, suggests methods for resolving phylogenetic problems.