Seismic signal transmission between burrows of the Cape mole-rat,Georychus capensis

Summary Both seismic and auditory signals were tested for their propagation characteristics in a field study of the Cape mole-rat (Georychus capensis), a subterranean rodent in the family Bathyergidae. This solitary animal is entirely fossorial and apparently communicates with its conspecifics by alternately drumming its hind legs on the burrow floor. Signal production in this species is sexually dimorphic, and mate attraction is likely mediated primarily by seismic signalling between individuals in neighboring burrows. Measurements within, and at various distances away from, natural burrows suggest that seismic signals propagate at least an order of magnitude better than auditory signals. Moreover, using a mechanical thumper which could be triggered from a tape recording of the mole-rat's seismic signals, we established that the vertically-polarized surface wave (Rayleigh wave) propagates with less attenuation than either of the two horizontally-polarized waves. Thus, we tentatively hypothesize that Rayleigh waves subserve intraspecific communication in this species.Abbreviations PPM pulses per min - SB simulated burrow - SD standard deviation - SPL sound pressure level     

Effect of dibutyryl cyclic adenosine monophosphate on granulosa cell proliferation, oocyte growth and meiotic maturation in isolated mouse primary ovarian follicles cultured in collagen gels.

Isolated primary follicles from 10-day-old mice were cultured in a collagen gel matrix for 6 days in Minimum Essential Medium + foetal calf serum, followed by culture in unsupplemented medium (control) or in medium containing hypoxanthine (2 mM) or dibutyryl cyclic adenosine monophosphate (dbcAMP, 0.25 mM) for a further 3 or 6 days. Less than 10% of oocytes resumed meiosis during the culture period in all groups. At recovery, the diameter of oocytes at the germinal vesicle stage was recorded and their ability to resume meiosis was determined. Hypoxanthine had little effect on oocyte growth and meiotic competence, but culture in dbcAMP resulted in oocytes that were larger (60.2 +/- 0.6 microns) than those of controls (55.8 +/- 0.5 microns) and more competent to resume meiosis than were controls (42.9% and 10.8%, respectively). The addition of dbcAMP to the culture medium induced a 4-5-fold increase in the number of granulosa cells oocyte compared with controls (3757 +/- 423 and 838 +/- 93, respectively). These results indicate that increased oocyte growth and meiotic competence is primarily mediated via dbcAMP effects on the granulosa cells.     

DNA probes for the Y-chromosome ofSilene latifolia,a dioecious angiosperm

Summary In order to obtain markers for the Y chromosome ofSilene latifolia, we pooled equal weights of leaf tissue from 18 female siblings into one sample and repeated the process with 18 male siblings. Pooling was intended to provide a common genetic background for each sample, leaving the absence or presence of the Y chromosome as the primary difference between the two samples. DNA was extracted from each sample and subjected to polymerase chain reaction (PCR) amplification with arbitrary 10 bp primers. Four of 60 primers used gave an amplification with the male DNA not found among those from the female DNA. Each of these was subsequently shown to provide a reliable marker for the Y chromosome.     

Regulation of proneural gene expression and cell fate during neuroblast segregation in the Drosophila embryo.

The Drosophila embryonic central nervous system develops from sets of progenitor neuroblasts which segregate from the neuroectoderm during early embryogenesis. Cells within this region can follow either the neural or epidermal developmental pathway, a decision guided by two opposing classes of genes. The proneural genes, including the members of the achaete-scute complex (AS-C), promote neurogenesis, while the neurogenic genes prevent neurogenesis and facilitate epidermal development. To understand the role that proneural gene expression and regulation play in the choice between neurogenesis and epidermogenesis, we examined the temporal and spatial expression pattern of the achaete (ac) regulatory protein in normal and neurogenic mutant embryos. The ac protein is first expressed in a repeating pattern of four ectodermal cell clusters per hemisegment. Even though 5-7 cells initially express ac in each cluster, only one, the neuroblast, continues to express ac. The repression of ac in the remaining cells of the cluster requires zygotic neurogenic gene function. In embryos lacking any one of five genes, the restriction of ac expression to single cells does not occur; instead, all cells of each cluster continue to express ac, enlarge, delaminate and become neuroblasts. It appears that one key function of the neurogenic genes is to silence proneural gene expression within the nonsegregating cells of the initial ectodermal clusters, thereby permitting epidermal development.     

Rapid analysis of glycolipid anchors in amphiphilic dimers of acetylcholinesterases

1. We describe two simple procedures for the rapid identification of certain structural features of glycolipid anchors in acetylcholinesterases (AChEs). 2. Treatment with alkaline hydroxylamine (that cleaves ester-linked acyl chains but not ether-linked alkyl chains) converts molecules possessing a diacylglycerol, but not those with an alkylacylglycerol, into hydrophilic derivatives. AChEs in human and bovine erythrocytes possess an alkylacylglycerol (Roberts et al., J. Biol. Chem. 263:18766-18775, 1988; Biochem. Biophys. Res. Commun. 150:271-277, 1988) and are not converted to hydrophilic dimers by alkaline hydroxylamine. Amphiphilic dimers of AChE from Drosophila, from mouse erythrocytes, and from the human erythroleukaemia cell line K562 also resist the treatment with hydroxylamine and likely possess a terminal alkylacylglycerol. This indicates that the cellular pool of free glycolipids used as precursors of protein anchors is distinct from the pool of membrane phosphatidylinositols (which contain diacylglycerols). 3. Pretreatment with alkaline hydroxylamine is required to render the amphiphilic AChE from human erythrocytes susceptible to digestion by Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PI-PLC) (Toutant et al., Eur. J. Biochem. 180:503-508, 1989). We show here that this is also the case for the AChE from mouse erythrocytes, which therefore likely possesses an additional acyl chain in the anchor that prevents the action of PI-PLC. 4. In two sublines of K562 cells (48 and 243), we observed that AChE either was directly susceptible to PI-PLC (243) or required a prior deacylation by alkaline hydroxylamine (48). This suggests that glycolipid anchors in AChE of K562-48 cells, but not those in AChE of K562-243 cells, contain the additional acylation demonstrated in AChE from human erythrocytes. These observations illustrate the cell specificity (and the lack of species-specificity) of the structure of glycolipid anchors.     

An intronic duplication in the alanine: glyoxylate aminotransferase gene facilitates identification of mutations in compound heterozygote patients with primary hyperoxaluria type 1

Summary We report here the identification of a duplication within the first intron of the gene encoding human alanine:glyoxylate aminotransferase (AGT); this duplication is closely linked to two point mutations associated with peroxisome-to-mitochondrion mistargeting of AGT in primary hyperoxaluria type 1 (PH1) patients. Polymerase chain reaction amplification of regions of the AGT gene including the insertion site from individuals heterozygous for this duplication, produces allele-specific fragments of different sizes. We have taken advantage of this to identify a nonsense mutation within a non-expressed allele of a compound heterozygote PH1 patient with mitochondrial AGT.     

The ATP-sensitive potassium channel in pancreatic B-cells is inhibited in physiological bicarbonate buffer

The effects of bicarbonate buffer (HCO3-/CO2) on the activity of the two K+ channels proposed by some to control the pancreatic B-cell membrane response to glucose were studied. Single K+-channel records from membrane patches of cultured B-cells dissociated from adult rat islets exposed to a glucose- and bicarbonate-free medium (Na-Hepes in place of bicarbonate) exhibit the activity of both the ATP-sensitive as well as the [Ca2+]i-activated K+ channels. However, in the presence of bicarbonate-buffered Krebs solution, the activity of the ATP-sensitive K+ channel is inhibited leaving the activity of the K+ channel activated by intracellular [Ca2+]i unaffected. In the absence of bicarbonate (Hepes/NaOH in place of bicarbonate), lowering the external pH from 7.4 to 7.0 also has differential effects on the two K+ channels. While the K+ channel sensitive to ATP is inhibited, the K+ channel activated by a rise in [Ca2+]i is not affected. To determine whether the response of the B-cell in culture to bicarbonate is also present when the B-cell is functioning within the islet syncytium, the effects of bicarbonate removal on membrane potential of B-cells from intact mouse islets were compared. These studies showed that glucose-evoked electrical activity is also blocked in bicarbonate-free Krebs solution. Furthermore, in the absence of bicarbonate and presence of glucose (11 mM), electrical activity was recovered by lowering the pHo from 7.4 to 7.0. The ATP-sensitive K+-channel activity is greatly reduced by physiologically buffered solutions in pancreatic B-cells in culture. The most likely explanation for the bicarbonate effects is that they are mediated by cytosolic pH changes. Removal of bicarbonate (keeping the external pH at 7.4 with Hepes/NaOH as buffer) would increase the pHi. Since the activity of the [Ca2+]i-dependent K+ channels is not affected by the removal of the bicarbonate buffer, our patch-clamp data in cultured B-cells indicate an involvement of [Ca2+]i-activated K+ channels in the control of the membrane potential. For the B-cell in the islet, we propose that the burst pattern of electrical activity (Ca2+ entry) is controlled, at least in part, by the [Ca2+]i-activated K+ channel.