Chromatin methylation: who's on first?

Two recent studies have exploited Arabidopsis mutants and chromatin immunoprecipitation to reveal the complexity of the interaction between histone H3 methyl K9 and cytosine methylation, two epigenetic marks that characterize silent chromatin.     

Were Gram-positive rods the first bacteria?

At some point in the evolution of life, the domain Bacteria arose from prokaryotic progenitors. The cell that gave rise to the first bacterium has been given the name (among several other names) "last universal ancestor (LUA)". This cell had an extensive, well-developed suite of biochemical strategies that increased its ability to grow. The first bacterium is thought to have acquired a covering, called a sacculus or exoskeleton, that made it stress-resistant. This protected it from rupturing as a result of turgor pressure stress arising from the success of its metabolic abilities. So what were the properties of this cell's wall? Was it Gram-positive or Gram-negative? And was it a coccus or a rod?     

Which came first: insecticides or resistance?

Mutations that confer resistance to insecticides are well documented. However, so far, we have been unable to determine whether these mutations arose before or after the introduction of insecticides. Recently, a landmark study showed that resistance to Malathion can be detected in pinned specimens of Australian sheep blowflies that were collected before the introduction of the insecticide. This finding has numerous implications for our understanding of the prevalence of resistance to new compounds. It also indicates that pre-existing resistance alleles might not carry the fitness cost that is associated with new mutations.     

Stereoscopic vision: what's the first step?

Neurons in primary visual cortex respond to binocular disparity, the raw material of stereoscopic depth perception. Although these neurons are probably essential to depth perception, a recent study has shown that they are unable to compute depth itself.     

Exon-intron-like pattern of the first propagating molecule?

Summary A biogeochemical scenario is proposed, according to which prebiotic self-replication of RNA-like molecules evolved gradually from domain propagation to entire strand replication. The hypothetical replicating entities that formed an evolutionary continuity in time, the prebioectons, were characterized by self-structuring, and started their evolution from strands possessing one or more templatable domains. The inherent self-structuring implies a very early coevolution of the replicating molecules with prebiotic peptides, in line with the cassette model of Cedergren and Grosjean (1987). The proposed approach can be partially tested in the laboratory.     

The first eukaryotic cells — Acid hot-spring algae

The Cyanidiophyceae members (PreRhodophyta) may serve as a transitional algal group bridging the cyanobacteria and the unicellular Rhodophyta. This thermoacidic algal group is composed of three genera containing several species. We suggested placing these algae in progressively evolutionary steps: (Cyanidioschyzon Cyanidium Galdieria). This evolutional ladder is based upon various areas of research like biochemistry, amount of nuclear genome and shape of chloroplast nucleoid, ultrastructure and ecological aspects. The first alga —Cyanidioschyzon — is the cornerstone of this succession; it shows mixed features between cyanobacterium and archaebacteria(Thermoplasma-like cell). It demonstrates simple eukaryotic cellular features and has the smallest amount of nuclear and chloroplast DNA. The intermediate alga in this line,Cyanidium, is also a simple cell, but shows more progressive characterizations than theCyanidioschyzon. The third taxon,Galdieria, is already very close to the unicellular rhodophytes (red algae) and indicates typical advanced eukaryotic characterization. We propose thatCyanidioschyzon (considered to be the simplest eukaryote) may have evolved from an association betweenThermoplasma-like archaebacterium and a thermophilic cyanobacterium. Autogenous (non-symbiotic) compartmental steps may have taken place fromCyanidioschyzon toCyanidium and then toGaldieria, and from this alga (group) towards the other unicellular red algae.Dedicated toDr. Jerome F. Fredrick, an enthusiast of our favorite algaCyanidium, on his retirement from directorship of Dodge Chemical Laboratories in Bronx, NYC.     

Phosphoinositides: older than we first thought?

Despite nearly 50 years of study, it is good to see that phosphoinositides are still capable of springing the odd surprise. Signaling by the second messenger phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) was thought to be absent in yeast, but a recent paper now describes the presence of PtdIns(3,4,5)P(3) in Schizosaccharomyces pombe.     

Pisodonophis boro (ophichthidae: anguilliformes): Specialization for head‐first and tail‐first burrowing?

The rice paddy eel, Pisodonophis boro (P. boro), is of special interest because of its peculiar burrowing habits. P. boro penetrates the substrate tail-first, a technique common for ophichthids, but it is able to burrow head-first as well. P. boro exhibits three feeding modes: inertial feeding, grasping, and spinning. Rotational feeding is a highly specialized feeding mode, adopted by several elongate, aquatic vertebrates and it is likely that some morphological modifications are related to this feeding mode. The detailed morphology of the head and tail of P. boro is examined with the goal to apportion the anatomical specializations among head-first burrowing, tail-first burrowing, and rotational feeding. The reduced eyes, covered with thick corneas may be beneficial for protection during head-first burrowing, but at the same time decreased visual acuity may have an impact on other sensory systems (e.g. cephalic lateral line system). The elongated and pointed shape of the skull is beneficial for substrate penetration. The cranial bones and their joints, which are fortified, are advantageous for resisting high mechanical loads during head-first burrowing. The aponeurotic connection between epaxial and jaw muscles is considered beneficial for transferring these forces from the body to the head during rotational feeding. Hypertrophied jaw muscles facilitate a powerful bite, which is required to hold prey during spinning movements and variability in the fiber angles of subdivisions of jaw muscles may be beneficial for preventing the lower jaw from being dislodged or opened. Furthermore, firm upper (premaxillo-ethmovomerine complex) and lower jaws (with robust coronoid processes) and high neurocranial rigidity are advantageous for a solid grip to hold prey during rotational feeding. The pointed shape of the tail and the consolidated caudal skeleton are beneficial for their tail-first burrowing habits. It is quite likely that the reduction of the caudal musculature is related to the tail-first burrowing behavior because the subtle movements of the caudal fin rays are no longer required.     

Did the first chordates organize without the organizer?

Models of vertebrate development frequently portray the organizer as acting on a largely unpatterned embryo to induce major components of the body plan, such as the neural plate and somites. Recent experiments examining the molecular and genetic basis of major inductive events of vertebrate embryogenesis force a re-examination of this view. These newer observations, along with a proposed revised fate map for the frog Xenopus laevis, suggest a possible reconciliation between the seemingly disparate mechanisms present in the ontogeny of the common chordate body plan of vertebrate and invertebrate chordates. Here, we review data from vertebrates and from an ascidian urochordate and propose that the organizer was not present at the base of the chordate lineage, but could have been a later innovation in the lineage leading to vertebrates, where its role was more permissive than instructive.     

Is Toxoplasma egress the first step in invasion?

The protozoan parasite Toxoplasma gondii maintains an intracellular lifestyle that requires careful timing and coordination when exiting one cell (egress) and entering another (invasion). Here it is argued that T. gondii uses similar molecular mechanisms for egress and invasion, based on common morphology, dependence on motility, and regulation by a calcium-dependent signal transduction pathway. In our view, this strategy is highly advantageous because it allows the parasite to egress rapidly from one cell and immediately invade an adjacent cell, thereby minimizing exposure to the extracellular environment where it could be destroyed by host immune mediators.