Effective intercellular communication distances are determined by the relative time constants for cyto/chemokine secretion and diffusion

A cell’s ability to effectively communicate with a neighboring cell is essential for tissue function and ultimately for the organism to which it belongs. One important mode of intercellular communication is the release of soluble cyto- and chemokines. Once secreted, these signaling molecules diffuse through the surrounding medium and eventually bind to neighboring cell’s receptors whereby the signal is received. This mode of communication is governed both by physicochemical transport processes and cellular secretion rates, which in turn are determined by genetic and biochemical processes. The characteristics of transport processes have been known for some time, and information on the genetic and biochemical determinants of cellular function is rapidly growing. Simultaneous quantitative analysis of the two is required to systematically evaluate the nature and limitations of intercellular signaling. The present study uses a solitary cell model to estimate effective communication distances over which a single cell can meaningfully propagate a soluble signal. The analysis reveals that: (i) this process is governed by a single, key, dimensionless group that is a ratio of biological parameters and physicochemical determinants; (ii) this ratio has a maximal value; (iii) for realistic values of the parameters contained in this dimensionless group, it is estimated that the domain that a single cell can effectively communicate in is ≈250 μm in size; and (iv) the communication within this domain takes place in 10–30 minutes. These results have fundamental implications for interpretation of organ physiology and for engineering tissue function ex vivo.

Estimation of evolutionary distances under stationary and nonstationary models of nucleotide substitution

Estimation of evolutionary distances has always been a major issue in the study of molecular evolution because evolutionary distances are required for estimating the rate of evolution in a gene, the divergence dates between genes or organisms, and the relationships among genes or organisms. Other closely related issues are the estimation of the pattern of nucleotide substitution, the estimation of the degree of rate variation among sites in a DNA sequence, and statistical testing of the molecular clock hypothesis. Mathematical treatments of these problems are considerably simplified by the assumption of a stationary process in which the nucleotide compositions of the sequences under study have remained approximately constant over time, and there now exist fairly extensive studies of stationary models of nucleotide substitution, although some problems remain to be solved. Nonstationary models are much more complex, but significant progress has been recently made by the development of the paralinear and LogDet distances. This paper reviews recent studies on the above issues and reports results on correcting the estimation bias of evolutionary distances, the estimation of the pattern of nucleotide substitution, and the estimation of rate variation among the sites in a sequence.

Microsatellite variability and genetic distances.

We analyze the within- and between-population dynamics of the distribution of the number of repeats at multiple microsatellite DNA loci subject to stepwise mutation. Analytical expressions for moments up to the fourth order within a locus and the variance of between-locus variance at mutation-drift equilibrium have been obtained. These statistics may be used to test the appropriateness of the one-step mutation model and to detect between-locus variation in the mutation rate. Published data are compatible with the one-step mutation model, although they do not reject the two-step model. Using both multinomial sampling and diffusion approximations for the analysis of the genetic distance introduced by Goldstein et al. [Goldstein, D. B., Linares, A. R., Cavalli-Sforza, L. L. & Feldman, M. W. (1995) Proc. Natl. Acad. Sci. USA 92, 6723-6727], we show that this distance follows a chi 2 distribution with degrees of freedom equal to the number of loci when there is no variation in mutation rates among the loci. In the presence of such variation, the variance of the distance is obtained. We conclude that the number of microsatellite loci required for the construction of phylogenetic trees with reliable branch lengths may be several hundred. Also, mutations that change repeat scores by several units, even though extremely rare, may dramatically influence estimates of population parameters.

Drift distances, times and primary grain sources of the Arctic Ocean, Exp302 (ACEX)

Knowledge of the long-term history of the perennial ice is an important issue that has eluded study because the Cenozoic core material needed has been unavailable until the recent Arctic Coring Expedition (ACEX). Detrital Fe oxide mineral grains analyzed by microprobe from the last 14 Ma (164 m) of the ACEX composite core on the Lomonosov Ridge were matched to circum-Arctic sources with the same mineral and 12-element composition. These precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the ACEX core site in less than a year. Thus the perennial ice cover has existed since 14 Ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0.17 Ma. Both North America and Russia contributed significant Fe grains to the ACEX core during the last 14 Ma.

Tables of oblique photo scale factors and nadir point distances for 70mm photography. For unit altitude, focal lengths: 1.5, 3, 6, and 12 inches, tilts: 0 ̊to 90.̊

"Scale factor system, oblique photo, developmental. Contract NOas 59-6067-c, Aeronautics specification XPH 118 (modified)."

Tables of oblique photo scale factors and nadir point distances. For unit altitude, focal lengths: 6, 12, 24, 36, and 48 inches, tilts: 3 ̊to 90.̊

"Prepared by Cornell University for the U. S. Navy Bureau of Aeronautics under contract NOas 57-585-c."

Etude sur le système solaire; nouvelle loi des distances des planètes et des satellites,

Mode of access: Internet.

The states and territories of the great West : including Ohio, Indiana, Illinois, Missouri, Michigan, Wisconsin, Iowa, Minesota [sic], Kansas and Nebraska ; their geography, history, resources ... comprising their local history, institutions, and laws ; giving a table of distances, and the most direct routes ... also, pointing out the best districts for agricultural, commercial, lumbering, and mining operations /

Mode of access: Internet.

Principales tables de Mr de Mendoza pour la très-prompte réduction des distances... = Mr de Mendoza's principal tables for deducing very readily the longitude from lunar distances..

Edición bilingue inglés-francés.

La Geometrie pratique : Tome second. Contenant la trigoniometrie, ou la mesure des distances par les instrumens geometriques ... /

Mode of access: Internet.

Livre de poste, ou état général des postes aux chevaux du royaume de France.suivi de la carte géométrique des routes desservies en poste, avec désignation des relais et des distances pour l'an 1831.

Mode of access: Internet.

État général et carte géométrique des routes de la République Française, desservies en poste microform : avec designation des relais et des distances, dressé pour ordre du Conseil d'Administration des Relais, suivi d'un etat-général de la poste aux lettres, pour l'an IX.

Mode of access: Internet.

[Traité de l'usage du pantometre : instrument geometrique propre à prendre toutes fortes d'angles, mezurer les distances accessibles & inaccessibles, arpenter & diviser toutes fortes de figure, &c. /

Mode of access: Internet.

Code civil des français : conforme à l'édition originale de l'Imprimerie de la Republique a laquelle on a ajouté les lois transitoires, le tableau de distances de Paris au chef-lieu des Départemens, et une table raisonée des matières.

Mode of access: Internet.

An analysis and summary of Thucydides : with a chronological table of principal events, money, distances, etc. reduced to English terms; a skeleton outline of the geography; abstracts of all the speeches, index, etc. /

Mode of access: Internet.