Molecular genetics of asymmetric cleavage in the early Caenorhabditis elegans embryo

BACKGROUND: Pharmacological control of blood pressure is usually indicated during aortic cross-clamping (AXC). The aim of this study was to analyze the modulation by isoflurane (ISO), sodium nitroprusside (SNP) and milrinone (MIL) of the systemic circulatory responses to a standardized infra-renal AXC. METHODS: Chloralose-anaesthetized pigs were exposed to AXC at control (no vasoactive drugs) and during the administration of each of the drugs. RESULTS: During control, AXC increased mean arterial pressure (MAP, 17 +/- 4%) and systemic vascular resistance (SVR, 27 +/- 7%), but induced no significant changes in cardiac output (CO), heart rate (HR), pulmonary arterial pressures, pulmonary vascular resistance or central venous pressure. Low-dose ISO (0.7%) and investigated doses of SNP and MIL did not significantly alter this response. High-dose ISO (1.4%, attenuated the AXC-induced increase in SVR, but not in MAP. All drugs decreased non-clamp MAP levels. Therefore, with low-dose ISO and with SNP or MIL, peak MAP during AXC was not significantly different from control non-clamp levels (i.e. prior to pharmacological or surgical interventions). High-dose ISO was associated with a MAP during AXC that was below control non-clamp levels. CONCLUSIONS: The objective that during AXC MAP should not exceed control non-clamp levels was achieveable by ISO, SNP or MIL. The modulating actions of the drugs on MAP during AXC were exerted mainly through reductions in non-clamp levels. This systemic hypotension was associated with decreased CO and SVR during ISO, and with decreased SVR and increased HR during SNP and MIL. Attenuation of the AXC-induced increase in SVR was produced only by 1.4% ISO.     

Seven zinc-finger transcription factors are expressed sequentially during the development of anthers in petunia

BACKGROUND: Little is known about the value of heart rate variability in patients with symptomatic coronary artery disease with a preserved left ventricular function. We hypothesized that in these patients heart rate variability might be a helpful adjunct to conventional parameters to predict clinical events. METHODS: In a prospective 2-year follow-up study ambulatory electrocardiographic recordings were performed in 263 consecutive male patients (mean age 56+/-8 years) with stable angina pectoris and a mean left ventricular ejection fraction of 71%+/-12%. Clinical events consisted mainly of coronary events such as percutaneous transluminal angioplasty or coronary artery bypass graft operation. RESULTS: Low measures of standard deviation of normal R-R intervals, standard deviation of the mean R-R intervals of 5 minutes, and two spectral components of heart rate variability were found in patients who had had an event compared with patients with no event. Adjusted for severity of angina, the presence of a previous myocardial infarction, and the use of beta-blockers in a logistic regression model this relation remained statistically significant for SDNN. Healthy volunteers appeared to have the highest measures of heart rate variability. CONCLUSION: In patients with ischemic heart disease and normal or near normal ventricular function decreased heart rate variability is associated with adverse clinical events.     

Isolation of actin-associated proteins from Caenorhabditis elegans oocytes and their localization in the early embryo

The actin cytoskeleton plays an important, but poorly understood, role in the development of multicellular organisms. To help illuminate this role, we used actin filament affinity chromatography to isolate actin binding proteins from large quantities of Caenorhabditis elegans oocytes. To examine how these proteins might be involved in early development, we prepared antibodies against some of them and determined their distribution in fixed embryos. Three of these proteins co-localize with different subsets of the embryonic actin cytoskeleton. One co-localizes with actin to all cell cortices. The second oscillates between the nucleus and cortex in a cell-cycle-dependent manner. The third is asymmetrically enriched at the anterior cortex of one-cell embryos, showing a temporal and spatial localization suggestive of a function in generating developmental asymmetry. We conclude that biochemistry is a feasible and useful approach in the study of early C. elegans development, and that the embryonic actin cytoskeleton is regulated in a complex fashion in order to carry out multiple, simultaneous functions.     

Homologs of the yeast longevity gene LAG1 in Caenorhabditis elegans and human

LAG1 is a longevity gene, the first such gene to be identified and cloned from the yeast Saccharomyces cerevisiae. A close homolog of this gene, which we call LAC1, has been found in the yeast genome. We have cloned the human homolog of LAG1 with the ultimate goal of examining its possible function in human aging. In the process, we have also cloned a homolog from the nematode worm Caenorhabditis elegans. Both of these homologs, LAG1Hs and LAG1Ce-1, functionally complemented the lethality of a lag1delta lac1delta double deletion, despite low overall sequence similarity to the yeast proteins. The proteins shared a short sequence, the Lag1 motif, and a similar transmembrane domain profile. Another, more distant human homolog, TRAM, which lacks this motif, did not complement. LAG1Hs also restored the life span of the double deletion, demonstrating that it functions in establishing the longevity phenotype in yeast. LAG1Hs mapped to 19p12, and it was expressed in only three tissues: brain, skeletal muscle, and testis. This gene possesses a trinucleotide (CTG) repeat within exon 1. This and its expression profile raise the possibility that it may be involved in neurodegenerative disease. This possibility suggests at least one way in which LAG1Hs might be involved in human aging.     

Assessing normal embryogenesis in Caenorhabditis elegans using a 4D microscope: variability of development and regional specification

Caenorhabditis elegans is renowned for its invariant embryogenesis. This pattern of development is in apparent contrast to other organisms from Drosophila to higher vertebrates. With the aid of a 4D microscope system (multifocal, time-lapse video recording system) which permits the extensive documentation and analysis of cell divisions, cell positions, and migrations in single embryos we have analyzed normal embryogenesis of C. elegans. The instrumentation reveals a naturally occurring variability in cell division timing, cell positioning, and cell-cell contacts which could not have been detected by the direct observation used earlier (Sulston et al., 1983, Dev. Biol. 100, 64-119). Embryos are very flexible and produce an essentially invariant premorphogenetic stage from variable earlier stages. An analysis of the distribution of the descendants of the early founder blastomeres at the premorphogenetic stage shows that these establish discrete regions in the embryo, a process involving a considerable amount of cell movement, which again varies in different embryos. Only cell fate assignment remains invariant. However, as shown earlier, this is not due to an autonomous invariant specification of cell fates but due to the fact that cell-cell interactions occur very early when the topology of blastomeres in the embryo is still sufficiently precise to ensure reproducible patterns of inductions. A new concept that founder blastomeres produce embryonic regions in the embryo can explain the striking complexity of the lineage per se and also the complicated asymmetric lineage patterns by which the bilateral symmetry of the embryo is established. Many cells, including bilateral homologs, were apparently chosen for a specific fate solely by their position in the embryo, irrespectively of the lineage descent by which the cells are created. We postulate that the production of regions by cell-cell interactions is the pivotal principle guiding the embryogenesis of C. elegans and that the embryogenesis of the worm follows the same basic principles as embryogenesis in other organisms.     

Aging in the nematode Caenorhabditis elegans: major biological and environmental factors influencing life span

The free-living nematode Caenorhabditis elegans is an excellent experimental system for the study of aging. The present study identifies some of the major biological and environmental factors influencing life span as a prelude to more detailed genetic and biochemical analyses. Life span can be altered during any part of the life cycle by a change in either temperature or food concentration. Parental age and parental life span both have relatively small effects on progeny life span. The nematode accumulates fluorescent pigment resembling lipofuscin, and becomes less sensitive to ultra-violet radiation as it ages.     

Isolation of a gene expressed during early embryogenesis from the region of 22q11 commonly deleted in DiGeorge syndrome

DiGeorge syndrome (DGS) is one of several syndromes associated with deletions within the proximal long-arm of chromosome 22. The region of chromosome 22q11 responsible for the haploinsufficiency syndromes (the DiGeorge Critical Region or DGCR) has been mapped using RFLPs, quantitative Southern blotting and FISH. Similar deletions are seen in the velo-cardio-facial syndrome (VCFS) and familial congenital heart defects. It is not known whether the phenotypic spectrum is the result of the hemizygosity of one gene or whether it is a consequence of contiguous genes being deleted. However, the majority of patients have a large (> = 2Mb deletion). In this paper we report the isolation of a gene, lab name T10, encoding a serine/threonine rich protein of unknown function which maps to the commonly deleted region of chromosome 22q11. Studies in the mouse indicate that it maps to MMU16 and is expressed during early embryogenesis. Although not mapping within the shortest region of overlap for DGS/VCFS, and therefore not the major gene involved in DGS, the expression pattern suggests that this gene may be involved in modifying the haploinsufficient phenotype of hemizygous patients.     

A highly conserved centrosomal kinase, AIR-1, is required for accurate cell cycle progression and segregation of developmental factors in Caenorhabditis elegans embryos

S. cerevisiae Ipl1, Drosophila Aurora, and the mammalian centrosomal protein IAK-1 define a new subfamily of serine/threonine kinases that regulate chromosome segregation and mitotic spindle dynamics. Mutations in ipl1 and aurora result in the generation of severely aneuploid cells and, in the case of aurora, monopolar spindles arising from a failure in centrosome separation. Here we show that a related, essential protein from C. elegans, AIR-1 (Aurora/Ipl1 related), is localized to mitotic centrosomes. Disruption of AIR-1 protein expression in C. elegans embryos results in severe aneuploidy and embryonic lethality. Unlike aurora mutants, this aneuploidy does not arise from a failure in centrosome separation. Bipolar spindles are formed in the absence of AIR-1, but they appear to be disorganized and are nucleated by abnormal-looking centrosomes. In addition to its requirement during mitosis, AIR-1 may regulate microtubule-based developmental processes as well. Our data suggests AIR-1 plays a role in P-granule segregation and the association of the germline factor PIE-1 with centrosomes.     

The maternal par genes and the segregation of cell fate specification activities in early Caenorhabditis elegans embryos

After fertilization in C. elegans, activities encoded by the maternally expressed par genes appear to establish cellular and embryonic polarity. Loss-of-function mutations in the par genes disrupt anterior-posterior (a-p) asymmetries in early embryos and result in highly abnormal patterns of cell fate. Little is known about how the early asymmetry defects are related to the cell fate patterning defects in par mutant embryos, or about how the par gene products affect the localization and activities of developmental regulators known to specify the cell fate patterns made by individual blastomeres. Examples of such regulators of blastomere identity include the maternal proteins MEX-3 and GLP-1, expressed at high levels anteriorly, and SKN-1 and PAL-1, expressed at high levels posteriorly in early embryos. To better define par gene functions, we examined the expression patterns of MEX-3, PAL-1 and SKN-1, and we analyzed mex-3, pal-1, skn-1 and glp-1 activities in par mutant embryos. We have found that mutational inactivation of each par gene results in a unique phenotype, but in no case do we observe a complete loss of a-p asymmetry. We conclude that no one par gene is required for all a-p asymmetry and we suggest that, in some cases, the par genes act independently of each other to control cell fate patterning and polarity. Finally, we discuss the implications of our findings for understanding how the initial establishment of polarity in the zygote by the par gene products leads to the proper localization of more specifically acting regulators of blastomere identity.