The insertion of mesenchyme cells into the ectoderm during differentiation in Sea urchin embryos

Summary During the course of sea urchin development, from early blastula to pluteus larva, there are two major visible processes toward which all activities seem to be focused. They are the differentiation of the larval skeleton by the primary mesenchyme cells and the differentiation of the primitive gut by the secondary mesenchyme cells. These activities take place within the shell-like layer of epithelial cells, or ectodermal wall. The interactive role of the ectodermal wall with the mesenchyme cells is not yet clearly understood. A number of earlier studies have proposed that the ectoderm may have an inductive influence on the mesenchyme cells and that its inner surface forms a molecular template for guiding the mesenchyme cells. In this report, we suggest an additional role for the ectodermal wall. We show that some primary mesenchyme cells and secondary mesenchyme cells insert between the cells of the ectodermal wall in order to firmly anchor the anlage of the larval skeleton and primitive gut during differentiation. This mechanism may provide a physical basis for maintaining the stable positional relationship of the anlage during development.     

Effect of pathogenic mutations on the structure and dynamics of Alzheimer’s Aβ42-amyloid oligomers

Converging lines of evidence suggest that soluble Aβ-amyloid oligomers play a pivotal role in the pathogenesis of Alzheimer’s disease, and present direct effectors of synaptic and cognitive dysfunction. Three pathological E22-Aβ-amyloid point mutants (E22G, E22K, E22Q) and the deletion mutant E22Δ exhibit an enhanced tendency to form prefibrillar aggregates. The present study assessed the effect of these four mutations using molecular dynamics simulations and subsequent structural and energetic analyses. Our data shows that E22 plays a unique role in wild type Aβ, since it has a destabilising effect on the oligomer structure due to electrostatic repulsion between adjacent E22 side chains. Mutations in which E22 is replaced by an uncharged residue result in higher oligomer stability. This effect is also observed to a lesser extent for the E22K mutation and is consistent with its lower pathogenicity compared to other mutants. Interestingly, deletion of E22 does not destroy the amyloid fold but is compensated by local changes in the backbone geometry that allow the preservation of a structurally important salt bridge. The finding that all mutant oligomers investigated exhibit higher internal stability than the wild type offers an explanation for the experimentally observed enhanced oligomer formation and stability.     

Reproduction and the central project of evolutionary theory

In much of the discourse of evolutionary theory, reproduction is treated as an autonomous function of the individual organism — even in discussions of sexually reproducing organisms. In this paper, I examine some of the functions and consequences of such manifestly peculiar language. In particular, I suggest that it provides crucial support for the central project of evolutionary theory — namely that of locating causal efficacy in intrinsic properties of the individual organism. Furthermore, I argue that the language of individual reproduction is maintained by certain methodological conventions that both obscure many of the problems it generates and serve to actively impede attempts to redress those difficulties that can be identified. Finally, I suggest that inclusion of the complexities introduced by sexual reproduction — in both language and methodology — may radically undermine the individualist focus of evolutionary theory.I am indepted to the Rockefeller Foundation for a Humanities Fellowship that supported this research during the spring of 1986. I am also grateful to Richard Lewontin, Diane Paul, and Lisa Lloyd for many extremely helpful conversations.     

Measurement of Acetylcholine Release in Freely Moving Rats by Means of Automated Intracerebral Dialysis

The present study demonstrates the feasibility of measuring acetylcholine in perfusion samples collected by means of in vivo brain dialysis in the striata of freely moving rats. The output of the dialysis device was directly connected to an automated sample valve of a HPLC-assay system that comprises a cation exchanger, a post-column enzyme reactor, and an electrochemical detector. The presence of an acetylcholinesterase inhibitor (neostigmine) in the perfusion fluid was required for the detection of acetylcholine in the perfusate. Increasing concentrations of neostigmine induced increasing amounts of acetylcholine. Continuous perfusion with a fixed concentration (2 microM) of neostigmine resulted in gradually increasing amounts of collected acetylcholine over time although a considerable variation between successive samples exists. The brain dialysis technique was further validated by studying the effect of various drugs. Systemically administered atropine increased the output of acetylcholine, whereas the addition of tetrodotoxin to the perfusion fluid resulted in a complete disappearance of the neurotransmitter.     

Aspergillus nomius,a new aflatoxin-producing species related to Aspergillus flavus and Aspergillus tamarii

Aspergillus nomius is described and represents a new aflatoxigenic species phenotypically similar to A. flavus. Strains examined were isolated from insects and agricultural commodities. Separation from A. flavus is based on the presence of indeterminate sclerotia and a lower growth temperature. Comparisons of DNA relatedness show A. nomius to have only relatively recently evolved from A. flavus and A. tamarii.     

Permeabilization ofNeurospora crassa hyphae with toluene-ethanol and filipin

Young hyphae ofNeurospora crassa were made permeable to UDP-glucose and trypan blue by treatment with toluene-ethanol and filipin. Less than 2% of treated cells survived treatment with 8% and 16% toluene-ethanol, while 25% survived treatment with 4% toluene-ethanol. Similarly, 98% of treated cells were killed by treatment with 16 g/ml filipin. Electron microscopy revealed that toluene-ethanol-treated cells lost pieces of plasma membrane and contained a number of vacuole-like structures; filipin-treated cells were less affected. Both filipin- and toluene-ethanol-treated cells were able to incorporate UDP-glucose into insoluble material (likely glycogen and glucan).     

Gall stones in sickle cell disease in the United Kingdom.

The prevalence of gall stones was studied prospectively by abdominal ultrasound examination in 131 patients with sickle cell disease aged 10-65 years. Of 95 patients with homozygous sickle cell disease, 55 (58%) had gall stones or had had a cholecystectomy. Gall stones were present in four out of 24 (17%) patients with haemoglobin S + C disease and two out of 12 (17%) with haemoglobin S beta thalassaemia. The presence of gall stones was not related to sex, geographical origin, or haematological variables and was not associated with abnormal results of liver function tests. Symptoms typical of biliary colic were reported by 32 out of 47 adult patients with gall stones, and cholecystitis or cholestasis was diagnosed in 18. Cholecystectomy was performed in 29 patients with good relief of symptoms in most cases. Postoperative complications were common, occurring in 10 of the 28 patients who could be evaluated, but not generally serious; they were considerably lessened by a preoperative exchange transfusion that reduced the haemoglobin S concentration to below 40%. It is suggested that all patients with sickle cell disease should be screened for gall stones and that elective cholecystectomy should be performed in those with symptoms or complications.     

Ultraviolet photoproducts at the ochre suppressor mutation site in the glnU gene of Escherichia coli: relevance to "mutation frequency decline"

Summary Ochre suppressor mutations induced by UV in the Escherichia coli glnU tRNA gene are CG to TA transitions at the first letter of the anticodon-encoding triplet, CAA. Premutational UV photoproducts at this site have long been known to exhibit an excision repair anomaly (mutation frequency decline or MFD), whereby post-irradiation inhibition of protein synthesis enhances their excision and reduces suppressor mutation yields ten-fold. We sought to clarify the basis of this unique repair response by determining the spectrum of UV photoproducts on both strands of a 36 by region of glnU which includes the anticodon-encoding triplet. We found that four different photolesions are produced within the 3 by sequence corresponding to the tRNA anticodon: (i) on the transcribed strand, TC (6–4) photoproducts and TC cyclobutane dimers are formed in equal numbers at the site of the C to T transition, indicating that this site is a hotspot for the usually less frequent (6–4) photoproduct; (ii) on the nontranscribed strand, TT dimers are found opposite the second and third letters of the anticodon-encoding triplet, adjacent to the mutation site; and (iii) on the nontranscribed strand, an alkali-sensitive lesion other than a (6–4) photoproduct is formed, apparently at the G in the mutation site. We suggest that mutation frequency decline may reflect excision repair activity at closely spaced UV lesions on opposite strands, resulting in double-strand breaks and the death of potential mutants.     

TGF-beta 1-induced inhibition of mouse mammary ductal growth: developmental specificity and characterization

TGF-beta 1, implanted into growing mouse mammary glands, was previously shown to inhibit ductal growth in an apparently normal and fully reversible manner. In this report we extend these findings to show that TGF-beta 1 inhibition is highly specific. In pregnant or hormone-treated mice, doses of TGF-beta 1 that were capable of fully inhibiting ductal elongation had little effect on the proliferation of lobuloalveolar structures. Additionally, the inhibitory action of TGF-beta 1 on ducts is epithelium-specific, resulting in cessation of DNA synthesis in the rapidly proliferating epithelium of mammary end buds, but does not inhibit DNA synthesis in the stroma surrounding the end buds. At the cellular level, transplant studies showed that TGF-beta 1 inhibited the regeneration of mammary ductal cells when implanted into mammary gland-free fat pads by suppressing the formation of new end buds, without inhibiting maintenance DNA synthesis in ductal lumenal epithelium; this observation indicates the potential of TGF-beta 1 to maintain patterning by suppressing adventitious lateral branching. The time-course of TGF-beta 1 inhibition of end buds was rapid, with cessation of DNA synthesis by 12 hr, followed by loss of the stem cell (cap cell) layer. The question of glandular exposure to TGF-beta 1 administered in EVAc implants was also investigated. Incorporation of TGF-beta 1 into EVAc was found not to degrade the hormone, while the release kinetics of the ligand from implants, its retention in the gland, and the demonstrable zone of exposure were consistent with observed inhibitory effects. These results support the hypothesis that TGF-beta 1 is a natural regulator of mammary ductal growth.