Identification and phylogenetic analysis of Drosophila melanogaster myosins

Myosins constitute a superfamily of motor proteins that convert energy from ATP hydrolysis into mechanical movement along the actin filaments. Phylogenetic analysis currently places myosins into 17 classes based on class-specific features of their conserved motor domain. Traditionally, the myosins have been divided into two classes depending on whether they form monomers or dimers. The conventional myosin of muscle and nonmuscle cells forms class II myosins. They are complex molecules of four light chains bound to two heavy chains that form bipolar filaments via interactions between their coiled-coil tails (type II). Class I myosins are smaller monomeric myosins referred to as unconventional myosins. Now, at least 15 other classes of unconventional myosins are known. How many myosins are needed to ensure the proper development and function of eukaryotic organisms? Thus far, three types of myosins were found in budding yeast, six in the nematode Caenorhabditis elegans, and at least 12 in human. Here, we report on the identification and classification of Drosophila melanogaster myosins. Analysis of the Drosophila genome sequence identified 13 myosin genes. Phylogenetic analysis based on the sequence comparison of the myosin motor domains, as well as the presence of the class-specific domains, suggests that Drosophila myosins can be divided into nine major classes. Myosins belonging to previously described classes I, II, III, V, VI, and VII are present. Molecular and phylogenetic analysis indicates that the fruitfly genome contains at least five new myosins. Three of them fall into previously described myosin classes I, VII, and XV. Another myosin is a homolog of the mouse and human PDZ-containing myosins, forming the recently defined class XVIII myosins. PDZ domains are named after the postsynaptic density, disc-large, ZO-1 proteins in which they were first described. The fifth myosin shows a unique domain composition and a low homology to any of the existing classes. We propose that this is classified when similar myosins are identified in other species.     

Megalencephalic leukoencephalopathy with subcortical cysts; a founder effect in Israeli patients and a higher than expected carrier rate among Libyan Jews

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive inherited neurological disorder characterized by macrocephaly, deterioration in motor functions and cerebellar ataxia. In Israel the disease is found in an increased frequency among Libyan Jews. The disease is caused by mutations in the MLC1 gene, which encodes a putative CNS membrane transporter. We describe three novel mutations (p.G59E, p.P92S, and 134_136insC) in seven MLC families. One of these mutations, p.G59E, was found in the vast majority of MLC patients in Israel. Screening of 200 normal Libyan Jewish individuals for the p.G59E mutation, revealed a carrier rate of 1/40 compared with an expected carrier rate of 1/81. Several explanations could account for this difference the most likely one is an admixture of the Libyan Jewish population.     

Tyrosinase maturation and oligomerization in the endoplasmic reticulum require a melanocyte-specific factor

Tyrosinase is a glycoprotein responsible for the synthesis of melanin in melanocytes. A large number of mutations have been identified in tyrosinase, with many leading to its misfolding, endoplasmic reticulum (ER) retention, and degradation. Here we describe the folding and maturation of human tyrosinase (TYR) using an in vitro translation system coupled with ER-derived microsomes or with semipermeabilized cells, as an intact ER source. TYR remained misfolded as determined by its sensitivity to trypsin digestion and its persistent interaction with the ER resident lectin chaperones calnexin and calreticulin when produced in ER-derived microsomes or nonmelanocytic semipermeabilized cells. However, when TYR was translocated into semipermeabilized melanocytes, chaperone interactions were transient, maturation progressed to a trypsin-resistant state, and a TYR homodimer was formed. The use of semipermeabilized mouse melanocytes defective for tyrosinase or other melanocyte-specific proteins as the ER source indicated that proper TYR maturation and oligomerization were greatly aided by the presence of wild type tyrosinase and tyrosinase-related protein 1. These findings suggested that oligomerization is a step in proper TYR maturation within the ER that requires melanocyte-specific factors.     

Formation of microtubule-based traps controls the sorting and concentration of vesicles to restricted sites of regenerating neurons after axotomy

Transformation of a transected axonal tip into a growth cone (GC) is a critical step in the cascade leading to neuronal regeneration. Critical to the regrowth is the supply and concentration of vesicles at restricted sites along the cut axon. The mechanisms underlying these processes are largely unknown. Using online confocal imaging of transected, cultured Aplysia californica neurons, we report that axotomy leads to reorientation of the microtubule (MT) polarities and formation of two distinct MT-based vesicle traps at the cut axonal end. Approximately 100 microm proximal to the cut end, a selective trap for anterogradely transported vesicles is formed, which is the plus end trap. Distally, a minus end trap is formed that exclusively captures retrogradely transported vesicles. The concentration of anterogradely transported vesicles in the former trap optimizes the formation of a GC after axotomy.     

Possible linkage between the ability to change the period (tau) of the prolactin and cortisol rhythms in women and breast cancer risk

The 24 h profiles of plasma hormone concentrations are rhythmic. The circadian period (τ) changes in development, with seasons, and in women with different stages of the menstrual cycle. It is known that the rhythms of prolactin and cortisol are sensitive to environmental time cues, such as changes in day length and phase; however, the importance of these changes is not yet understood. This study investigates whether there is a relation between the ability of a subject to respond to external cues that are associated with seasonal changes causing alteration of the rhythm's periods in cortisol and prolactin and the epidemiologically determined susceptibility to breast cancer. It is shown that the rhythmic output pattern of prolactin and cortisol in vivo is generated by more than one oscillator and structured by more than one rhythmic component. Each cohort of American women, classified on an epidemiologic basis as high risk (HR) or low risk (LR) to develop breast cancer, expresses different rhythmic output patterns of both variables, suggesting that the genetic background as defined by the risk state is related to differences in the circadian time structure, including the ability of the subject to change the rhythm's τ. The LR cohort exhibited a statistically significant change between seasons in the rhythm's τ of both the prolactin and cortisol patterns. In contrast, the HR cohort showed no change in the rhythm's τ between seasons for prolactin and cortisol patterns. These results show that in human beings, the presence of a circannual rhythm in the circadian time structure or the ability to adapt the circadian rhythmic pattern of these variables to external cues, such as seasons, is related to the partly genetically determined risk state to develop breast cancer and may be of importance for human health.     

Cranial neural crest cells regulate head muscle patterning and differentiation during vertebrate embryogenesis

In the vertebrate head, mesoderm cells fuse together to form a myofiber, which is attached to specific cranial neural crest (CNC)-derived skeletal elements in a highly coordinated manner. Although it has long been recognized that CNC plays a role in the formation of the head musculature, the precise molecular underpinnings of this process remain elusive. In the present study we explored the nature of the crosstalk between CNC and mesoderm cells during head muscle development, employing three models for genetic perturbations of CNC development in mice, as well as experimental ablation of CNC in chick embryos. We demonstrate that although early myogenesis is CNC-independent, the migration, patterning and differentiation of muscle precursors are regulated by CNC. In the absence of CNC cells, accumulated myoblasts are kept in a proliferative state, presumably because of an increase of Fgf8 in adjacent tissues, which leads to abnormalities in both differentiation and subsequent myofiber organization in the head. These results have uncovered a surprising degree of complexity and multiple distinct roles for CNC in the patterning and differentiation of muscles during craniofacial development. We suggest that CNC cells control craniofacial development by regulating positional interactions with mesoderm-derived muscle progenitors that together shape the cranial musculoskeletal architecture in vertebrate embryos.     

Coexistence research requires more interdisciplinary communication

Coexistence theories develop rapidly at the ecology forefront, outpacing their experimental testing. I discuss the reasons for this gap, call on interdisciplinary researchers to construct a road map for coexistence research, and recommend the actions that should be implemented therein.

Coexistence theories outpace their experimental testing. I argue that this imbalance results from a combination of interdisciplinary gaps, a disparity in research approaches, and the limited accessibility of the theory to experimentalists. I call on interdisciplinary researchers to construct a road map for coexistence research, recommend the actions that should be implemented therein, and illustrate how multiple mechanisms can be integrated under the same coexistence terms, thus constructing a research landscape that can create uniformity in their experimental designs.