The T-cell receptor: just another hypothesis.

Functional activities of T and B lymphocytes and the kinetics of hematopoietic stem cells were studied in mice with inoculated or spontaneous tumors. The development and growth of the tumor inhibited B cells and helper T cells, while the activity of killer T cells and spleen suppressor cells was markedly enhanced. The processes of stem cell migration from the bone marrow were considerably intensified and altered in tumor-bearing mice. Data were obtained suggesting that helper T cells and killer T cells represent nonidentical compartments within the population of thymus-dependent lymphocytes. Immunosuppression during tumor bearing is probably due to an impairment of T lymphocytes cooperating in immune responses, B-lymphocytes and their precursors.     

Ras oncogenes: split personalities

Extensive research on the Ras proteins and their functions in cell physiology over the past 30 years has led to numerous insights that have revealed the involvement of Ras not only in tumorigenesis but also in many developmental disorders. Despite great strides in our understanding of the molecular and cellular mechanisms of action of the Ras proteins, the expanding roster of their downstream effectors and the complexity of the signalling cascades that they regulate indicate that much remains to be learnt.     

Animal personalities: the advantage of diversity

Animals do not always perform to the best of their abilities when faced with difficult choices. New findings on foraging honeybees show that co-existing strategies, where some individuals place more emphasis on accuracy and others on speed, can be advantageous to the colony in a variable environment.     

The Danish Twin Registry: 127 birth cohorts of twins.

The Danish Twin Registry is the oldest national twin register in the world, initiated in 1954 by ascertainment of twins born from 1870 to 1910. During a number of studies birth cohorts have been added to the register, and by the recent addition of birth cohorts from 1931 to 1952 the Registry now comprizes 127 birth cohorts of twins from 1870 to 1996, with a total of more than 65,000 twin pairs included. In all cohorts the ascertainment has been population-based and independent of the traits studied, although different procedures of ascertainment have been employed. In the oldest cohorts only twin pairs with both twins surviving to age 6 have been included while from 1931 all ascertained twins are included. The completeness of the ascertainment after adjustment for infant mortality is high, with approximately 90% ascertained up to 1968, and complete ascertainment of all liveborn twin pairs since 1968. The Danish Twin Registry is used as a source for large studies on genetic influence on aging and age-related health problems, normal variation in clinical parameters associated with the metabolic syndrome and cardiovascular diseases, and clinical studies of specific diseases. The combination of survey data with data obtained by linkage to national health related registers enables follow-up studies both of the general twin population and of twins from clinical studies.     

The multiple personalities of Watson and Crick strands

Background  

In genetics it is customary to refer to double-stranded DNA as containing a "Watson strand" and a "Crick strand." However, there seems to be no consensus in the literature on the exact meaning of these two terms, and the many usages contradict one another as well as the original definition. Here, we review the history of the terminology and suggest retaining a single sense that is currently the most useful and consistent.     

White folks: race and identity in rural America

Abstract

Since the breakdown of the Middle East Peace Summit at Camp David in 2000 and the start of the second Palestinian Intifada there has been a voluminous literature that asserts that hostility to Israel and Zionism is a new form of anti-Semitism. This essay critiques the ‘new anti-Semitism’ view. Reversing the method that Plato uses in the Republic, the analysis moves from microcosm (an imaginary ride on a London bus) to macrocosm (the Middle East). In the process, the author argues that anti-Semitism is best defined not by an attitude to Jews but by the figure of ‘the Jew’. In the light of the analysis, and bearing in mind the variety of possible reasons for hostility to Israel or Zionism, it is difficult to see how the ‘new anti-Semitism’ view can be sustained.     

NGF: not just for neurons.

Nerve growth factor (NFF) is the prototypic member of a family of related neurotrophins (Nts). Although originally defined by its actions in the peripheral and central nervous systems, recent data indicate the presence of extensive interactions between NGF and the endocrine and immune systems steroid hormones are able to modulate the neurosomal expression of NGF, while functional NGF receptors have been detected on cells of the immune system, and increased levels of NGF protein are found during the acute phase of diseases with a significant inflammatory component. These wider functions are likely to be of concern in any attempted therapeutic use of NGF.     

The conjoined twins of L?wen.

This paper discusses an unusual etching of unlike-sex conjoined twins of the syncephalus type dated 1547. The authenticity of the case is discussed in terms of the biological plausibility of such twins and in the light of mediaeval understanding of the twinning process. Unlike-sex syncephalic twins may occur as a result of dispermic fertilisation, or be an erroneous depiction of an asymmetrical anomaly of the external genitalia of a like-sex pair, mimicking the genitals of the other sex. On the other hand, the L?wen etching conforms with mediaeval beliefs that conjoined twins are divine punishment and therefore were used for ecclesiastical and perhaps commercial purposes. The historical context of the drawing, in which the relation between religion, media, and medicine satisfied the eagerness of the public for curios of Nature, is no longer valid. Thus the L?wen etching opens a window to the past from which modern medicine can be appreciated.     

The proteasome: not just degrading anymore

The proteasome is a large multiprotein complex that has a critical role in the degradation of ubiquitylated proteins. A fascinating paper in this issue of Cell (Lee et al., 2005) now reveals that the proteasome recruits the SAGA histone acetyltransferase complex to a target promoter during gene activation. This finding adds to the growing body of evidence indicating that the proteasome has nonproteolytic functions.     

Conjoined twins: theoretical embryologic basis.

A theoretical basis for the embryology of conjoined twins was formulated from clinical experience with ten cases and extensive review of pertinent embryologic and clinical literature, including over 500 cases. Regarding the age old question of fusion or fission, it is concluded that there is no known embryologic process by which conjoined twins can be formed by fission but firm evidence to support fusion in all cases. Whether the fusion occurs between embryos on one embryonic disc or on two is of no consequence since they are all monovular. Intact ectoderm will not fuse to intact ectoderm, and all seven types of conjoined twins are explained by seven possible sites of union in the early embryo. One new term is proposed: parapagus, from the Greek para, meaning "side," combined with pagus, meaning "fixed"; this is the group formerly called dicephalus or diprosopos. These anterolaterally united parapagus twins must result from two nearly parallel notochords in close proximity; craniopagi and pygopagi from fusion at the cranial and caudal neuropores, respectively; cephalopagi and ischiopagi from union at the pharyngeal and cloacal membranes, respectively; thoracopagi from merging of the cardiac anlage; and omphalopagi from fusion of the umbilicus or of the edges of two embryonic discs in any area not including the above sites. Parasitic twins result from embryonic death of one twin, leaving various portions of the body vascularized by the surviving autosite. The rarity of cases (2) not easily explained by the above theories, and the nearly 6% of twins with two umbilical cords arising from the placenta would seem to support these conclusions. Should one wish to learn the methods of a conjurer, he might vainly watch the latter's customary repertoire, and, so long as everything went smoothly, might never obtain a clue to the mysterious performance, baffled by the precision of the manipulations and the complexity of the apparatus; if, however, a single error were made in any part or if a single deviation from the customary method should force the manipulator along an unaccustomed path, it would give the investigator an opportunity to obtain a part or the whole of the secret.(ABSTRACT TRUNCATED AT 400 WORDS)     

The probability of dizygosity of phenotypically concordant twins.

A basic element in the determination of the zygosity of a twin pair is the proportion of genotypically concordant pairs among the dizygotic pairs. Two methods to derive this proportion are in common use: the first method requires a laborious enumeration of parental genotypic mating types, and the second method relies on a set of formulas, one for each of the possible combinations of genotypes of two full sibs. In this paper the relation between both methods is uncovered. The set of formulas of the second method is reduced to a single general formula, of which the connection with the ITO method (Li and Sacks 1954) is indicated. By applying both methods in turn to an example concerning the MNS blood group system (Fisher 1951), Fisher's way of performing the calculations according to the first method is unraveled, and the preferability of the second method is made clear. Next, formulas are derived for the probability of genotypic or phenotypic concordance of dizygotic twins when direct information on the genotype or phenotype of one of the parents is available. The case of an X-linked locus is also considered. To facilitate applications, tables are given.