Tandem organization of StarkB element (22.8 kb) in the maize B chromosome

A very large repetitive element (StarkB, 22.8 kb) is present in the maize B chromosome, presumably not organized as tandem arrays. Results of the current study are contrary to this notion. Out of eighteen StarkB-carrying sequences, nine were the expected internal fragment of StarkB, and nine others were fragments spanning two StarkB elements. One of the two StarkB components, GrandeB, was flanked in all clones with identical target sequences, as opposed to other Grandes that are associated with different target sequences. Also observed was a prominent Southern signal associated with a fragment representing the junction of two adjacent StarkB units. A clone possessing a structure inverse to that of the second component of StarkB is proposed to be the initial element into which a GrandeB inserted to derive StarkB. Most, if not all, isolated StarkB arrays were not the original form, being disrupted by the invasion of various mobile elements intertwined with various stages of amplification. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nucleotide sequence data reported are available in the GenBank database under the accession numbers EF468500 to EF468511, EU528676, and FJ386410 to FJ386429.     

Angiotensin IV in the central nervous system

The mammalian brain harbors a renin-angiotensin system (RAS), which is independent from the peripheral RAS. Angiotensin II is a well-studied member of the RAS and exerts most of the known angiotensin-mediated effects on fluid and electrolyte homeostasis, autonomic activity, neuroendocrine regulation, and behavior. This review summarizes a mass of compelling new evidence for the biological role of an active (3-8) fragment of angiotensin II, named angiotensin IV. Angiotensin IV binds to a widely distributed binding site in the brain, but which is different from the known angiotensin II receptors AT1 and AT2. Angiotensin IV has been implicated in a number of physiological actions, including the regulation of blood flow, the modulation of exploratory behavior, and processes attributed to learning and memory. Furthermore, angiotensin IV may also be involved in neuronal development. Collectively, the available evidence suggests that angiotensin IV is a potent neuropeptide, involved in a broad range of brain functions.     

How did the platypus get its sex chromosome chain? A comparison of meiotic multiples and sex chromosomes in plants and animals

The duck-billed platypus is an extraordinary mammal. Its chromosome complement is no less extraordinary, for it includes a system in which ten sex chromosomes form an extensive meiotic chain in males. Such meiotic multiples are unprecedented in vertebrates but occur sporadically in plant and invertebrate species. In this paper, we review the evolution and formation of meiotic multiples in plants and invertebrates to try to gain insights into the origin of the platypus meiotic multiple. We describe the meiotic hurdles that translocated mammalian chromosomes face, which make longer chains disadvantageous in mammals, and we discuss how sex chromosomes and dosage compensation might have affected the evolution of sex-linked meiotic multiples. We conclude that the evolutionary conservation of the chain in monotremes, the structural properties of the translocated chromosomes and the highly accurate segregation at meiosis make the platypus system remarkably different from meiotic multiples in other species. We discuss alternative evolutionary models, which fall broadly into two categories: either the chain is the result of a sequence of translocation events from an ancestral pair of sex chromosomes (Model I) or the entire chain came into being at once by hybridization of two populations with different chromosomal rearrangements sharing monobrachial homology (Model II).     

The Comstockiella system of chromosome behavior in the armored scale insects (Coccoïdea: Diaspididae)

Summary The Comstockiella chromosome system occurs in the armored scale insects and the closely allied palm scales. During development of the males, the paternal chromosome set becomes heterochromatic and remains so until spermatogenesis. With the exception of one chromosome, the heterochromatic complement loses its differential aspect during early spermatogenesis and its members pair with their euchromatic homologues There is but one division during which the two components of each bivalent separate to opposite poles. Both division products form sperm.One pair of chromosomes, the D pair, always shows differential behavior. The D pair usually does not form a bivalent. The heterochromatic homologue, D^H, divides equationally and is eliminated by anaphase lagging or telophase ejection; its daughter halves remain as pycnotic residues during the early phases of spermiogenesis. The euchromatic homologue, D^E, also divides equationally to contribute to both of the telophase nuclei. Compensation for the division of the D^E univalent may occur during either the early or late phases of spermatogenesis.In some species the D pair is a fixed entity, analogous to the sex chromosomes in this regard. In other species, more than one pair may be elected to the D role, but only one at a time, and always the same one within each cyst.Taxonomic evidence indicates the Comstockiella system was derived from the lecanoid system, previously known from the work of the Schraders and others. In the lecanoid system, the paternally derived heterochromatic set divides equationally, along with the euchromatic set, during the first spermatogenic division. During the second spermatogenic division, the two sets are segregated from each other. The two euchromatic derivatives form sperm while the heterochromatic derivatives persist for a while as pycnotic residues. Both the lecanoid and Comstockiella systems occur in some species often in the same testis, but only one of the two systems within any one cyst.The discussion is devoted to an analysis of the mode of inheritance expected in the Comstockiella system and its evolutionary derivation. The Comstockiella system may have been derived in a step-by-step fashion from the lecanoid. The two systems differ by four processes which occur at spermatogenesis in the Comstockiella but not the lecanoid system; these are (1) deheterochromatization, (2) chromosome pairing, (3) compensation for the extra division of the D^E chromosome, and (4) lagging or ejection to eliminate the D^H chromosome.In addition, the residual genetic effects of the heterochromatic set may have undergone considerable change before the lecanoid system could evolve into a Comstockiella. Once the evolutionary step were otherwise possible, mechanistic features would aid and abet the emergence of the new system even though it lacked immediate selective advantage.The variable-D aspect of some examples of the Comstockiella system cannot be readily understood in terms of known examples of chromosome behavior; an admittedly highly speculative hypothesis is offered in an attempt to explain the situation.The diaspidid system, in which the paternal chromosomes are eliminated at late cleavage, is believed on taxonomic grounds to have stemmed from the Comstockiella, and forms the final stage of the four-step evolutionary sequence. Necessary changes for the derivation of the diaspidid system from the Comstockiella are discussed.This work was begun during the tenure of a Guggenheim Memorial Fellowship, 1956–57, and has subsequently been supported in part by grants from the National Science Foundation (G-4497 and G-9772).     

The discovery of the human chromosome number in Lund, 1955–1956

The correct determination of the human diploid chromosome number as 46, by J-H Tjio and A Levan, at the University of Lund, Sweden, occurred 50 years ago, in December 1955; the finding was published in April 1956, ending a period of more than 30 years when the number had been thought to be 48. The background to the discovery and the surrounding factors are reassessed, as are the reasons why previous investigators persistently misidentified the precise number. The necessity for multiple technological advances, the power of previously accepted conclusions in influencing the interpretation of later results, and the importance of other work already undertaken in Lund, are all relevant factors for the occurrence of this discovery, the foundation for modern human cytogenetics, at this particular time and place.     

The life – history of the peach silver mite,Aculus fockeui (Acari: Eriophyidae) in Egypt

The peach silver mite Aculus fockeui (Nalepa and Trouessart) successfully developed from egg to adult stage when reared on a nectarine or peach leaflet attached with soft lateral divided branch dipped in test tube at different constant temperatures and 70% r.h. The effect of temperature on the development, reproduction and population growth was investigated. Below 20°C all activity ceased and by 33°C the adult began to slow down and cease all activity. At least of 34% of the generation time was spent in the egg stage at 29°C. Adult longevity decreased with increasing temperature. Fecundity was highest at 29°C with 43.16 eggs per female. Life table parameters showed that the population of A. fockeui on nectarine leaves multiplied 30.04 times in a generation time of 18.49 days at 29°C, while the population on peach leaves increased 13.87 times in a generation time of 19.18 days under the same conditions.     

Abundance and individual size of American eel (Anguilla rostrata) in the St. Lawrence River over the past four decades

Changes in abundance indicators and the mean size of American eel (Anguilla rostrata LeSueur) in the lower St. Lawrence River (SLR) over the past 40 years were assessed to determine the chronology of the species decline and the possible effect of hydroclimatic factors on that trend. Daily catches at commercial weirs and at an experimental fishery were used to model the long-term trend in silver eel availability. Eel landings started declining in the mid-1980s; whereas the modelled catch-per-unit-effort (CPUE) index shows a monotonic declining trend since the late 1960s. Landings and CPUEs were not strongly correlated, and landings cannot be a valid proxy for silver eel abundance in the SLR. Variations in summer river discharge contributed to interannual fluctuations in CPUE by affecting eel availability to the fishing gears. No relationship was found between CPUE and the North Atlantic Oscillation index of climatic variability. Correlations between hydroclimatic variables lagged by 1–20 years and CPUE indices revealed no measurable effect of riverine hydroclimatic variability on eel recruitment. The average size of silver eels increased by 30% between 1997 and 2007, as a result of poor recruitment during the mid-1980s. Since the onset of the silver eel decline preceded the major decline in recruitment in the mid-1980s, we suggest that the decline in spawning stock size was not due to poor recruitment but rather to large-scale mortality factors associated with high exploitation in upstream Lake Ontario and to construction of hydropower dams in the late 1950s.     

A critical evaluation of the ubiquitin–proteasome system in Parkinson's disease

The evidence for impairment in the ubiquitin proteasome system (UPS) in Parkinson's disease (PD) is mounting and becoming increasingly more convincing. However, it is presently unclear whether UPS dysfunction is a cause or result of PD pathology, a crucial distinction which impedes both the understanding of disease pathogenesis and the development of effectual therapeutic approaches. Recent findings discussed within this review offer new insight and provide direction for future research to conclusively resolve this debate.     

A gene (Bmn) controllingβ-mannosidase activity in the mouse is located in the distal part of chromosome 3

A gene (Bmn) with a major effect on -mannosidase activity in kidney and liver of the house mouse was revealed by assay with the synthetic substratep-nitrophenyl--d-mannoside. Activity is low in DBA/2J and CSB mice and high in C57BL/6J mice. By the use of the BXD series of recombinant inbred strains and by crosses between C57BL and CSB, it was possible to map the gene to the distal part of chromosome 3 by demonstration of linkage to a gene for cadmium resistance,cdm, as well as to theAdh-3 locus.This work was supported by Swedish Natural Science Research Council Project B-BU 2992-108.     

Evidence for cospeciation events in the host–symbiont system involving crinoids (Echinodermata) and their obligate associates,the myzostomids (Myzostomida,Annelida)

Although molecular-based phylogenetic studies of hosts and their associates are increasingly common in the literature, no study to date has examined the hypothesis of coevolutionary process between hosts and commensals in the marine environment. The present work investigates the phylogenetic relationships among 16 species of obligate symbiont marine worms (Myzostomida) and their echinoderm hosts (Crinoidea) in order to estimate the phylogenetic congruence existing between the two lineages. The combination of a high species diversity in myzostomids, their host specificity, their wide variety of lifestyles and body shapes, and millions years of association, raises many questions about the underlying mechanisms triggering their diversification. The phylogenetic relationships, inferred using a three-genes dataset (18S rDNA, 16S rDNA, and COI) and two-genes dataset (18S rDNA, and COI) for the myzostomids and crinoids, respectively, were congruent with the literature. The overall congruence between the two phylogenies was statistically significant according to topology-based, distance-based, and data-based approaches: a significant pattern of cophylogeny was found, though not perfect probably resulting from occasional host switches, duplications or extinction events. A minimum of 8 cospeciation events was estimated, which is significantly higher than it would have been expected due to chance alone.     

Protein kinase C isoforms in the enteric nervous system

C kinases (PKCs) are a family of enzymes essential for the transduction of signals in a diverse range of cell types, including neurons. The different isoforms vary in their activation requirements. Therefore, cell-specific expression of different isoforms has implications for PKC-mediated control of organ function. This study has investigated the types and distributions of PKC isoforms in the small intestine of the guinea-pig, with particular emphasis on their localisation in myenteric neurons, using immunohistochemistry and western blotting techniques. Three PKC isoforms, , and , were detected in the calbindin-immunoreactive subset of intrinsic primary afferent neurons, but not in other myenteric neurons. Both and immunoreactivities were also located in interstitial cells of Cajal. In contrast to these isoforms, immunoreactivity for PKCs and was present in all myenteric neurons of the ileum. PKC immunoreactivity was detected primarily in the glial network, as shown through double labelling with antibodies to the glial filament protein, S100b. Myenteric neurons were also weakly immunoreactive for this isoform. PKC immunoreactivity was very highly expressed in smooth muscle, but was largely absent from neurons. Immunoreactivity for RACK1, a binding protein for PKC, was detected in both calbindin-immunoreactive neurons and in smooth muscle cells. This study indicates a selective distribution of PKC isoforms to specific cell types. Isoform-specific activity of these enzymes could provide a means through which targeted modulation of intestinal function is achieved.     

The hypothalamic–pituitary–gonadal axis: A switch-controlled,condition-sensitive system in the regulation of life history strategies

This article is part of a Special Issue “Puberty and Adolescence”.     

L-chromosome inheritance and the problem of chromosome “imprinting” in Sciara (Sciaridae,Diptera)

The loss of the L-chromosomes from the germ line of a newly-collected strain of Sciara impatiens was used as a genetic marker to test whether the supernumeraries in this genus obey the rule of origin which governs the behavior of the regular homologues at first meiotic anaphase in the male. Reciprocal crosses between a normal strain which possessed L's and the no-L line yielded F₁ males whose germ cells contained L-chromosomes of paternal or of maternal origin. Cytological study of the gonads of these males showed that in all instances, irrespective of their origin, the L-chromosomes were conserved. To demonstrate that the L's thus conserved are not lost subsequently during spermiogenesis, the F₁ males derived from normal fathers were bred to females from the no-L line; the gonads of the test-cross progeny showed that these individuals had inherited L-chromosomes. The failure of the paternal L's to obey the rule of origin during spermatogenesis indicates that the supernumeraries in this genus are not subject to the reversible imprinting which the regular complement undergoes. And the genetic effects of exclusively paternal or maternal L-chromosomes on germ cell development and maturation are indistinguishable. Concomitant with the loss of L's from the germ line, the newly-collected strain of S. impatiens underwent an abrupt alteration from unisexual families to variable sex ratios. These ratios are discussed in relation to the problem of sex determination in S. ocellaris, a species which sustained L-chromosome loss during the course of evolution. Discussed also are some new unpublished data which reveal, unexpectedly, a genetic affinity between ocellaris and impatiens. The no-L line of impatiens, which has been kept in laboratory culture for approximately four years, provides a unique opportunity to examine the conditions under which the supernumeraries are retained or lost and also to determine more precisely the nature of their genetic effects.It is a pleasure to acknowledge support by the National Science FoundationIt is a pleasure to acknowledge support by the National Science Foundation     

A sauropodomorph tooth increases the diversity of dental morphotypes in the Cañadón Asfalto Formation (Early – Middle Jurassic) of Patagonia

This communication aims to describe an isolated sauropodomorph tooth (MPEF-PV 10860) from the Cañadón Asfalto Formation and test its phylogenetic relationships with other sauropodomophs. The novelty of this specimen implies a combination of features present in non-sauropod sauropodomorphs (coarse denticles at 45° with respect to the margin, absent marginal grooves and lingual concavity) and others previously referred to as synapomorphic of Sauropoda and subgroups of this lineage (D-shaped cross section, enamel-wrinkling). A comparison with formerly defined sauropod tooth morphotypes from Cañadón Asfalto highlights major differences in enamel-wrinkling, having a simpler and more homogeneous pattern. The crown proportions, compared with other sauropodomorph teeth, retrieve MPEF-PV 10860 within the morphospace of sauropods in two different age-ratio scatterplots, and the phylogenetic analysis depicts this specimen in multiple positions within Sauropodiforms but outside Eusauropoda, indicating the presence of both eusauropods and non-eusauropods in the Cañadón Asfalto Formation, and of a putative new species.     

Male-Driven Evolution Among Eoaves? A Test of the Replicative Division Hypothesis in a Heterogametic Female (ZW) System

Because avian females are heterogametic, the reverse of mammals, avian sex chromosomes undergo significantly different patterns and numbers of DNA replications than do those in mammals. This makes the W (female-specific) and the Z chromosomes an excellent model system for the study of the replicative division hypothesis, which purports that DNA substitution rate is determined by the number of germline replications. The sex-specific chromosome in birds (the W) is predicted to change at the slowest rate of all avian chromosomes because it undergoes the fewest rounds of replication per unit of evolutionary time. Using published data on gametogenesis from a variety of sources, we estimated the ratio of male-to-female germline replications (c) in galliforms and anseriforms to be approximately 4.4. The value of c should predict the value of the ratio of male-to-female mutation rates (α_m) if the replicative division hypothesis is true. Homologous DNA sequences including an intron and parts of two exons of the CHD gene were obtained from the W and the Z chromosomes in ostrich, sage grouse, canvasback duck, tundra swan, and snow goose. The exons show significantly different nucleotide composition from the introns, and the W-linked exons show evidence of relaxed constraint. The Z-linked intron is diverging ≈ 3.1 times faster than the W-linked intron. From this, α_m was calculated to be approximately 4.1, with a confidence interval of 3.1 to 5.1. The data support the idea that the number of replicative divisions is a major determinant of substitution rate in the Eoavian genome. Received: 19 January 1999 / Accepted: 8 June 1999     

Variation in the Ichnofauna of the Collio Formation (Lower Permian) in the South-Alpine Region (Northern Italy)

In the Collio Formation (Lower Permian) of the South-Apine region (North Italy) paleobiodiversity consists of tetrapod footprints, invertebrate traces and rarer plants, and is characterized by an absolute poverty of taxa that becomes more acute from the lower to the upper part of the Collio Formation. Regionally, the drop in diversity can be explained by joint tectonic and climatic change; humid evergreen environments became mainly dry. Examination of ichnofossil distribution supports this hypothesis.