On the nature of thumbs

Asymmetric regulation of Hox gene expression pre-dates the appearance of tetrapod digits, and was co-opted in the development of 'thumbness'. This asymmetric expression correlates with independent morphological evolutionary variation of digit 1.     

The nature of thymidine kinase in the human-mouse hybrid cell

In order to characterize the thymidine kinase in human-mouse somatic cell hybrids derived from mouse parental cells lacking thymidine kinase, we have examined the electrophoretic migration on starch gel and the heat sensitivity of this enzyme in human, mouse, and hybrid cells. The enzyme of hybrid cells migrates similarly to that of human fetal liver and human diploid fibroblasts and faster than that of either L or A₉ mouse cells. It is less sensitive to heat than that of the mouse cells. Therefore, the human group E chromosome provides human thymidine kinase for the hybrid cell. The electrophoresis of thymidine kinase makes possible the search for variants.Aided by U.S.P.H.S. Grant No. HD 00486.     

On the halophytic nature of mangroves

Scientists have discussed the halophytic nature of intertidal plants for decades, and have generally suggested that inherent differentiation of an obligate halophyte from a facultative halophyte relates strongly to whether the plant can survive in fresh water, and not much else. In this mini-review, we provide additional insight to support the pervasive notion that mangroves as a group are truly facultative halophytes, and thus add discourse to the alternate view that mangroves have an obligate salinity requirement. Indeed, growth and physiological optima are realized at moderate salinity concentrations in mangroves, but we maintain the notion that current evidence suggests that survival is not dependent upon a physiological requirement for salt.     

On the nature of population extremes

Summary Much ecology considers only the typical size of a population, yet extreme values may be of particular importance. Unusually low numbers may doom a population to extinction and unusually high numbers may pose an economic threat. Extreme values may also determine the evolutionary traits that predominate. Obviously, even for a fixed variance in annual numbers, the observed maximum and minimum population size will increase the more years that we count the population. Interestingly, over the time scales of available data (<100 years), most animal populations have an observed variance in annual numbers that increases the more consecutive years we use in its calculation. Consequently, populations will meet extreme values more quickly than if the variance were constant. We quantify the increases in variance for diatoms, insects, and vertebrates, first correcting the data for overall differences in variance. Short- and long-lived species are not consistently different. Species that cycle in density have relatively small increases relative to those that do not cycle. Species in marine ecosystems have larger increases than those in terrestrial and freshwater systems. All these results suggest that the system in which a species is embedded — rather the species' own characteristics — plays the crucial role in determining the nature of population extremes.     

On the fundamental nature of perception

The process of recognition or isolation of one or several entities from among many possible entities is termed intellego perception. It is shown that not only are many of our everyday percepts of this type, but perception of microscopic events using the methods of quantum mechanics are also intellego in nature. Information theory seems to be a natural language in which to express perceptual activity of this type. It is argued that the biological organism quantifies its sensations using an information theoretical measure. This, in turn, sets the stage for a mathematical theory of sensory perception.     

On the nature of the tumor-initiating cell

Certain aspects of tumors that may influence areas of basic biology and medicine are reviewed. The hypothesis that malignant stem cells evolve from normal stem cells, is considered. Information is being accumulated on the possibility that certain cell populations that can be propagated as cell lines in vitro can produce cells with features of differentiated cells in addition to others that maintain the line and, in some cases may also initiate tumor formation in vivo. Up to the present time, there is evidence to show that cancer stem cells persist in many cell lines. Tyrosine kinase inhibition produces combinations of autophagy and apoptosis in the human erythroleukemia cell line TF-1 hinting at a heterotypic aggregation of cells containing cancer stem cells. Finally, the mechanisms of cancer development, invasion and metastasis are operatively defined. The purpose of this paper is to review some of the salient features of cancer stem cells in support of the proposal that research in neoplasia be increased. Rather than presenting details of various studies, we have attempted to indicate general areas in which work has been done or is in progress. It is hoped that this survey of the subject will demonstrate a variety of opportunities for additional research in human neoplasia.