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Eukaryotic cells express several classes of small RNAs that regulate gene expression and ensure genome maintenance. Endogenous siRNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs) mainly control gene and transposon expression in the germline, while microRNAs (miRNAs) generally function in post-transcriptional gene silencing in both somatic and germline cells. To provide an evolutionary and developmental perspective on small RNA pathways in nematodes, we identified and characterized known and novel small RNA classes through gametogenesis and embryo development in the parasitic nematode Ascaris suum and compared them with known small RNAs of Caenorhabditis elegans. piRNAs, Piwi-clade Argonautes, and other proteins associated with the piRNA pathway have been lost in Ascaris. miRNAs are synthesized immediately after fertilization in utero, before pronuclear fusion, and before the first cleavage of the zygote. This is the earliest expression of small RNAs ever described at a developmental stage long thought to be transcriptionally quiescent. A comparison of the two classes of Ascaris endo-siRNAs, 22G-RNAs and 26G-RNAs, to those in C. elegans, suggests great diversification and plasticity in the use of small RNA pathways during spermatogenesis in different nematodes. Our data reveal conserved characteristics of nematode small RNAs as well as features unique to Ascaris that illustrate significant flexibility in the use of small RNAs pathways, some of which are likely an adaptation to Ascaris' life cycle and parasitism.

Dravet syndrome (DS) is an intractable pediatric epilepsy syndrome, starting in early childhood. This disorder typically manifests with febrile status epilepticus, and progresses to a multifocal epilepsy with febrile and non-febrile seizures with encephalopathy. Most cases are due to a mutation in the SCN1A gene. This article reviews treatments for DS, with an emphasis on pharmacotherapy. While many medications are used in treating the seizures associated with DS, these patients typically have medically refractory epilepsy, and polytherapy is often required. First-line agents include valproate and clobazam, although there are supportive data for topiramate, levetiracetam, stiripentol and the ketogenic diet. Other agents such as fenfluramine are promising therapies for Dravet syndrome. Sodium channel-blocking anticonvulsants such as carbamazepine and lamotrigine are generally contraindicated in this syndrome. Nonpharmacologic therapies (such as neurostimulation or surgery) are understudied in DS. Because DS is a global encephalopathy, pharmacologic treatment of non-epileptic manifestations of the disease is often necessary. Attention-deficit hyperactivity disorder is often encountered in patients with DS, and psychostimulants can be helpful for this indication. Other psychoactive drugs are less studied in this context. Extrapyramidal and gait disorders are often encountered in DS as well. While DS is a severe epileptic encephalopathy with a high (up to 15 %) mortality rate in childhood, careful pharmacologic management can improve these patients' clinical picture and quality of life.

Metazoan spliced leader (SL) trans-splicing generates mRNAs with an m2,2,7G-cap and a common downstream SL RNA sequence. The mechanism for eIF4E binding an m2,2,7G-cap is unknown. Here, we describe the first structure of an eIF4E with an m2,2,7G-cap and compare it to the cognate m7G-eIF4E complex. These structures and Nuclear Magnetic Resonance (NMR) data indicate that the nematode Ascaris suum eIF4E binds the two different caps in a similar manner except for the loss of a single hydrogen bond on binding the m2,2,7G-cap. Nematode and mammalian eIF4E both have a low affinity for m2,2,7G-cap compared with the m7G-cap. Nematode eIF4E binding to the m7G-cap, m2,2,7G-cap and the m2,2,7G-SL 22-nt RNA leads to distinct eIF4E conformational changes. Additional interactions occur between Ascaris eIF4E and the SL on binding the m2,2,7G-SL. We propose interactions between Ascaris eIF4E and the SL impact eIF4G and contribute to translation initiation, whereas these interactions do not occur when only the m2,2,7G-cap is present. These data have implications for the contribution of 5′-UTRs in mRNA translation and the function of different eIF4E isoforms.

Cap-dependent translation initiation in eukaryotes is a complex process involving many factors and serves as the primary mechanism for eukaryotic translation (37, 44). The first step in the initiation process, recruitment of the m 7 G (7-methylguanosine)-capped mRNA to the ribosome, is widely considered the rate-limiting step. It begins with recognition of and binding to the m 7 G cap at the 5Ј end of the mRNA by the eukaryotic translation initiation factor 4F (eIF4F) complex, which contains three proteins: eIF4E (a cap-binding protein), eIF4G (a scaffold protein with RNA binding sites), and eIF4A (an RNA helicase). eIF4G's interaction with eIF3, itself a multisubunit complex that interacts with the 40S ribosome, facilitates the actual recruitment of capped RNA to the ribosome. With the help of several other initiation factors, the small ribosomal subunit scans the mRNA from 5Ј to 3Ј until a translation initiation codon (AUG) in appropriate context is identified and an 80S ribosomal complex is formed, after which the first peptide bond is formed, thus ending the initiation process (37, 44). The AUG context can play an important role in the efficiency of translation initiation (23, 44). The length, structure, and presence of AUGs or open reading frames in the mRNA 5Ј untranslated region (UTR) can negatively affect cap-dependent translation and ribosomal scanning. In general, long and highly structured 5Ј UTRs, as well as upstream AUGs leading to short open reading frames, can impede ribosome scanning and lead to reduced translation (23, 44). In addition, 5Ј UTRs less than 10 nucleotides (nt) in length are thought to be too short to enable preinitiation complex assembly and scanning (24). Thus, several attributes of the mRNA 5Ј UTR are known to negatively affect translation initiation, whereas only the AUG context and the absence of negative elements are known to have a positive effect on translation initiation (44).Two of the important mRNA features associated with capdependent translation, the cap and the 5Ј UTR, are significantly altered by an RNA processing event known as spliced leader (SL) trans splicing (3,8,17,26,36,47). This takes place in members of a diverse group of eukaryotic organisms, including some protozoa, sponges, cnidarians, chaetognaths, flatworms, nematodes, rotifers, crustaceans, and tunicates (17,28,39,55,56). In SL trans splicing, a separately transcribed small exon (16 to 51 nucleotides [nt]) with its own cap gets added to the 5Ј end of pre-mRNAs. This produces mature mRNAs with a unique cap and a conserved sequence in the 5Ј UTR. In metazoa, the m 7 G cap is replaced with a trimethylguanosine (TMG) cap (m 2,2,7 GpppN) (27,30,46,49). In nematodes, ϳ70% of all mRNAs are trans spliced and therefore have a TMG cap and an SL (2). In general, eukaryotic eIF4E proteins do not effectively recognize the TMG cap (35). This raises the issues of how the translation machinery in trans-splicing

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