The elusive sizer

Size control has been a topic of interest to cell biologists for over a century, but insights into cell size control mechanisms have until recently been relatively sparse. Determining whether cells have a size measurement mechanism and how it might operate has proven difficult. The nucleocytoplasmic ratio is one of the few conserved features of size control but little is know about how it is measured. Models where growth and division can be uncoupled have been underexploited, but have considerable potential for gaining insights into the contribution of the nucleocytoplasmic ratio to cell size regulation.     

The effects of ponazuril on development of apicomplexans in vitro

We examined the effects of 5 microg/ml ponazuril treatment on developing tachyzoites of Neospora caninum and merozoites of Sarcocystis neurona to better determine the mode of action of this anticoccidial drug. Both parasites develop asexually by endogenesis. Neospora caninum was selected for study because it develops by endodyogeny, which results in two tachyzoites being produced internally, and S. neurona was selected because it develops by endopolygeny which results in many merozoites being produced internally. Ponazuril inhibited development of N. caninum after approximately 48 h post-exposure. Treated tachyzoites of N. caninum developed vacuoles and underwent degeneration. Ponazuril also inhibited development of merozoites of S. neurona. Treated merozoites and maturing schizonts of S. neurona developed vacuoles and underwent degeneration. The ability of S. neurona schizonts to undergo cytokinesis was inhibited. Our results are discussed in relation to previous ultrastructural research on endogenesis of tachyzoites of Toxoplasma gondii undergoing endodyogeny which indicated that ponazuril induced multinucleate stage formation and inhibited cytokinesis. Ponazuril is believed to act on the apicoplast and our study demonstrates that this agent may express its inhibitory effects in different phenotypic manners on different apicomplexan parasites. The enzyme/enzyme systems that are the inhibitory target of ponazuril may be different in these apicomplexans, or the results of inhibition may affect different pathways downstream of its initial site of action in these parasites.     

The elusive yeast interactome

Simple eukaryotic cells such as yeast could contain around 800 protein complexes, as two new comprehensive studies show. But slightly different approaches resulted in surprising differences between the two datasets, showing that more work is required to get a complete picture of the yeast interactome.     

The elusive petroexoccipital articulation

In the present study, 1,869 skulls from the Hamann-Todd Collection were examined (macroscopically and by radiographs) for closure of the petroexoccipital articulation (jugular synchondrosis). The results demonstrated that the petroexoccipital articulation underwent closure between 20 and 50 years of age in most of the human skulls evaluated. Approximately 7–10% of the human skulls underwent complete union of the petroexoccipital articulation before 20 years of age. In 5–9% of the population, the joint remained completely open. After 50 years of age, there was no increase in the frequency of individuals with complete closure. The frequency of “partial closure” was similar (4–8%) for all age groups (20–25, 30–35, 40–45, 50–55, 60–65, and 70+), excluding the 30–35 year old group (17.5%). The time interval necessary for closure to occur appeared to be very short. No significant differences in closure rates due to ethnic origin, gender, or laterality were noted. The utility of the petroexoccipital articulation as an age estimator is discussed. Am J Phys Anthropol 103:365–373, 1997. © 1997 Wiley-Liss, Inc.     

Formin' an invasion machine: actin polymerization in invading apicomplexans

Apicomplexan parasites are motile and invade host cells. The force required for this is generated by an actomyosin motor. In a recent paper, Baum and colleagues suggest that the protein formin regulates the polymerization of actin at the moving junction between parasite and host cell. This finding provides novel insight into the mechanism of host cell invasion.     

The elusive nuclear matrix.

The structure of the interphase nucleus is a major area of current interest in cell biology. It is thought likely that the nucleus is organised around some form of structural matrix and that this matrix will play a role in processes as diverse as chromosome replication and the integration of gene expression. However, the structure of the matrix within the nucleus has remained elusive, largely because attempts to define it have been dogged by technical problems arising from the great complexity of this organelle. This situation is now being changed by the application of in situ analysis and of molecular genetic methodologies which are opening up this hitherto intractable field.     

More covert sex: The elusive females of myrmecolacidae

Among evolutionary biologists, considerable interest currently surrounds organisms that seem to be represented entirely by females. Here we discuss a less familiar problem - that of organisms in which females appear to be lacking. Our main example is the Myrmecolacidae (Strepsiptera), an unusual group of entomophagous parasites with dual hosts. Males parasitize ants and females parasitize orthopterans. Although the free-living adult males are frequently collected, the permanently endoparasitic neotenic females are elusive and are seldom encountered.     

Lipid synthesis in protozoan parasites: A comparison between kinetoplastids and apicomplexans

Lipid metabolism is of crucial importance for pathogens. Lipids serve as cellular building blocks, signalling molecules, energy stores, posttranslational modifiers, and pathogenesis factors. Parasites rely on a complex system of uptake and synthesis mechanisms to satisfy their lipid needs. The parameters of this system change dramatically as the parasite transits through the various stages of its life cycle. Here we discuss the tremendous recent advances that have been made in the understanding of the synthesis and uptake pathways for fatty acids and phospholipids in apicomplexan and kinetoplastid parasites, including Plasmodium, Toxoplasma, Cryptosporidium, Trypanosoma and Leishmania. Lipid synthesis differs in significant ways between parasites from both phyla and the human host. Parasites have acquired novel pathways through endosymbiosis, as in the case of the apicoplast, have dramatically reshaped substrate and product profiles, and have evolved specialized lipids to interact with or manipulate the host. These differences potentially provide opportunities for drug development. We outline the lipid pathways for key species in detail as they progress through the developmental cycle and highlight those that are of particular importance to the biology of the pathogens and/or are the most promising targets for parasite-specific treatment.     

The elusive evidence for chromothripsis

The chromothripsis hypothesis suggests an extraordinary one-step catastrophic genomic event allowing a chromosome to ‘shatter into many pieces’ and reassemble into a functioning chromosome. Recent efforts have aimed to detect chromothripsis by looking for a genomic signature, characterized by a large number of breakpoints (50–250), but a limited number of oscillating copy number states (2–3) confined to a few chromosomes. The chromothripsis phenomenon has become widely reported in different cancers, but using inconsistent and sometimes relaxed criteria for determining rearrangements occur simultaneously rather than progressively. We revisit the original simulation approach and show that the signature is not clearly exceptional, and can be explained using only progressive rearrangements. For example, 3.9% of progressively simulated chromosomes with 50–55 breakpoints were dominated by two or three copy number states. In addition, by adjusting the parameters of the simulation, the proposed footprint appears more frequently. Lastly, we provide an algorithm to find a sequence of progressive rearrangements that explains all observed breakpoints from a proposed chromothripsis chromosome. Thus, the proposed signature cannot be considered a sufficient proof for this extraordinary hypothesis. Great caution should be exercised when labeling complex rearrangements as chromothripsis from genome hybridization and sequencing experiments.     

Ecology's dark matter: The elusive and enigmatic niche

Ecologists are often frustrated that their universe, populated by strange and wilful creatures, seems fuzzy and unpredictable. Physicists, in contrast, seem to have it much better. But that's because we usually focus on Newtonian physics. In fact, physicists seem happy to live with all kinds of strange beasts, including dark matter, something they have never seen, but which they nevertheless believe makes up most of the matter in the universe. Here I argue that niches are ecology's dark matter. We are embarrassed by them, because we do not quite know what they are, and yet their presence can be universally felt; otherwise, ecological communities, like galaxies without dark matter, would simply collapse. I describe how we could potentially better describe these dark shapes that haunt our science and why this is important. In particular, I present the outline of a method for demonstrating whether or not plant species have complementary resource-use niches; something that has been difficult to show unequivocally. The presence of such resource-use niches would put to rest once and for all the notion of species equivalence and the neutral world that this assumption entails. I conclude that ecologists should take a leaf out of the physicists’ book and accept that the continued search for the esoteric niche is a legitimate and central (if frustrating) part of ecology.     

The elusive diploic veins: anthropological and anatomical perspective

Diploic veins (Canales diploicae), which were identified in dogs by Dupuytren more than 200 years ago (Hecker [1845] Die anatomische Verhaltnisse und Krankheiten der Venae diploicae und Vasa emissaria. Erfahrungen und Abhandlungen im Gebiete der Chirurgie und Augenheilkunde. Erlangen), have remained inadequately understood and scantily referenced in the anatomical and anthropological literature. The tunnels formed by diploic veins are among the few known skeletal markers of soft tissue alteration. Protected by two bony laminae, diploic vein tunnels often resist postdepositional destruction and may provide a new way to assess living and extinct hominid populations. This basic research was carried out to enable future utilization of the diploic venous channels in anthropologic research. In the present study, diploic venous channels were observed radiographically in 108 human adults aged 19 years and above, 18 infants and children aged 1-18 years (Hamann-Todd Osteological Collection), eight fetuses aged 7-9 months (the Johns Hopkins Collection), and seven nonhuman primates (Hamann-Todd Osteological Collection). In addition, seven documented cases of parents and children were radiographed for genetic evaluation (Osteological Collection of The Hungarian Natural History Museum). Five distinct diploic distribution patterns were identified and described in this study. This was at variance with the impressions reported in dissection-based studies. Independence of diploic vein pattern from demographic (gender and age) and size factors and their tendency to be symmetrical make them amenable and reliable traits for skeletal population study. Diploic vein patterns appeared to be more complicated in humans than in nonhuman primates, raising the possibility of future phylogenetic applications.     

Molecular dissection of host cell invasion by the apicomplexans: the glideosome

Gliding motility is an essential and fascinating apicomplexan-typical adaptation to an intracellular lifestyle. Apicomplexan parasites rely on gliding motility for their migration across biological barriers and for host cell invasion and egress. This unusual substratedependent mode of locomotion involves the concerted action of secretory adhesins, a myosin motor, factors regulating actin dynamics and proteases. During invasion, complexes of soluble and transmembrane micronemes proteins (MICs) and rhoptry neck proteins (RONs) are discharged to the apical pole of the parasite, some protein acts as adhesins and bind to host cell receptors whereas others are involved in the moving junction formation. These complexes redistribute towards the posterior pole of the parasite via a physical connection to the parasite actomyosin system and are eventually released from the parasite surface by the action of parasite proteases.