Liquid-liquid phase separation is responsible for formation of P granules, nucleoli, and other membraneless subcellular organelles composed of RNA and proteins. Efforts to understand the physical basis of liquid organelle formation have thus far focused on intrinsically disordered proteins (IDPs) as major components that dictate occurrence and properties. Here, we show that complex coacervates composed of low complexity RNA (polyuridylic acid, polyU) and short polyamines (spermine and spermidine) share many features of IDP-based coacervates. PolyU/polyamine coacervates compartmentalize biomolecules (peptides, oligonucleotides) in a sequence- and length-dependent manner. These solutes retain mobility within the coacervate droplets, as demonstrated by rapid recovery from photobleaching. Coacervation is reversible with changes in solution temperature due to changes in the polyU structure that impact its interactions with polyamines. We further demonstrate that lipid vesicles assemble at the droplet interface without impeding RNA entry/egress. These vesicles remain intact at the interface and can be released upon temperature-induced droplet dissolution.

This article evaluates the “Frames, then Content” hypothesis for speech acquisition, which states that much of the patterning of babbling is a direct result of production of syllabic “Frames” by means of rhythmic mandibular oscillation, with relatively little of the intrasyllabic and intersyllabic “Content” of the syllable-like cycles under mandible-independent control. Analysis was based on a phonetically transcribed corpus of 6,659 utterances of 6 normally developing infants obtained from one-hour weekly audio-recordings over a 4–6 month period. Intrasyllabic predictions were that front vowels would preferentially co-occur with front (alveolar) consonants, back vowels with back (velar) consonants, and central vowels with labial consonants, with the latter effect presumably resulting from mandibular oscillation alone. Intersyllabic predictions were for more variegation in tongue height for vowels than in front-back tongue movement, and for consonant manner changes to predominate over place changes (related primarily to mandibular oscillation). All 30 individual predictions from both hypotheses were confirmed, leading to a conception of the articulatory basis of babbling as “Frame Dominance.”

MHC I1 from lysosomes but also by regulating the exit of MHC I from the ER. In addition, CIIVs are probably not the only factor responsible for the increase in surface MHC I1 transport upon DC maturation. For example, DCs regulate the post-Golgi transport of newly synthesized MHC I1 molecules to lysosomes versus the plasma membrane by controlling both cathepsin S-mediated proteolysis of Ii chain and endocytosis of MHC I1 ap dimers from the cell surface (6, 20).CIIVs appear to permit the recovery of MHC I1 synthesized before maturation and thus delivered to lysosomes.DCs are perhaps the most potent of all APCs, being unsurpassed in their ability to stimulate immunologically naive T cells (8). The features described here may contribute to their efficiency in several ways. First, the coupling of CIIV formation with the onset of DC maturation might explain how DCs sequester antigen in peripheral tissues for display to lyrnphoid organs, often days later. This strategy would enhance immune surveillance and maintenance of T cell memory. Second, the ability of MHC I1 and B7 molecules to cluster on the plasma membrane suggests that they are organized in a polyvalent configuration that may help to activate a quiescent T cell. In contrast, the recently described ability of T cells to mediate clustering of MHC and costimulatory molecules (20, 21) may serve to sustain rather than initiate an immune response.

Exposure to English and Spanish may result in a higher English error rate in typically developing bilinguals, including the application of Spanish phonological properties to English. Slightly higher error rates are likely typical for bilingual preschool-aged children. Change over time at these time points for all 3 groups was similar, suggesting that all will reach an adult-like system in English with exposure and practice.

Comparison was made between performance-based and competence-based approaches to the understanding of first word production. The performance-related frame/content approach is representative of the biological/functional perspective of phonetics in seeking explanations based on motor, perceptual and cognitive aspects of speech actions. From this perspective, intrasyllabic consonant-vowel (CV) co-occurrence patterns and intersyllabic sequence patterns are viewed as reflective of biomechanical constraints emerging from mandibular oscillation cycles. A labial-coronal sequence effect involved, in addition, the problem of interfacing the lexicon with the motor system, as well as the additional problem of initiation of movement complexes. Competence-based approaches to acquisition are within the generative phonological tradition; involving an initial assumption of innate, speech-specific mental structures. While various current phonological approaches to acquisition involve consideration of sequence effects and intrasyllabic patterns, they do not adequately establish the proposed mental entities in infants of this age, and are nonexplanatory in the sense of not considering the causes of the structures and constraints that they posit.