Connectin: a homophilic cell adhesion molecule expressed on a subset of muscles and the motoneurons that innervate them in Drosophila.

Each abdominal hemisegment in the Drosophila embryo contains a stereotyped array of 30 muscles, each specifically innervated by one or a few motoneurons. We screened 11,000 enhancer trap lines, isolated several expressing beta-galactosidase in small subsets of muscle fibers prior to innervation, and identified two of these as inserts in connectin and Toll, members of the leucine-rich repeat gene family. Connectin contains a signal sequence, ten leucine-rich repeats, and a putative phosphatidylinositol membrane linkage; in S2 cells, connectin can mediate homophilic cell adhesion. Connectin is expressed on the surface of eight muscles, the motoneurons that innervate them, and several glial cells along the pathways leading to them. During synapse formation, the protein localizes to synaptic sites; afterward, it largely disappears. Thus, connectin is a novel cell adhesion molecule whose expression suggests a role in target recognition.     

The development of the trigeminal jaw adductor musculature in the grass snake Natrix natrix

The ontogenetic development of the jaw adductor musculature in Natrix natrix (L.) is described in detail and related to patterns of ossification in the skull. A comparison with the development of the jaw adductors in the lizard Podarcis sicula reveals some interesting differences of dynamics in the developing head. The problem of the establishment of topological relations of similarity (homology) in developing systems is discussed.
The homologies of the external jaw adductor compartments in lizards and snakes are revised. Early ontogenetic divergence explains the reversal of fibre direction in the anterior portion of the external adductor of snakes, and renders the homologization of that fibre bundle with part of the external adductor in lizards impossible.     

The development of the trigeminal jaw adductor musculature and associated skull elements in the lizard Podarcis sicula

The ontogenetic development of the jaw adductor musculature in Podarcis sicula (Raftnesque) is described in detail and related to patterns of ossification in associated skull elements. It was found that the coronoid bone ossifies in continuity with the developing bodenaponeurosis, whereas the elements of the upper temporal arcade ossify prior to (and seemingly independently of) the realization of an attachment of the developing jaw adductors.
Various aspects of the development of the jaw adductors are discussed in the light of theoretical claims concerning conflicting models of ontogeny, as is the role of ontogenetic studies in the determination of character polarity. It is concluded that the present study supports the model of epigenetic development, and that ontogeny alone is insufficient for the assessment of character polarity. Instead, ontogeny must be interpreted in the context of phylogenetic hypotheses.     

Characterization of an ethylene-inducible, calcium-dependent nuclease that is differentially expressed in cucumber flower development

? Production of unisexual flowers is an important mechanism that promotes cross-pollination in angiosperms. We previously identified primordial anther-specific DNA damage and organ-specific ethylene perception responsible for the arrest of stamen development in female flowers, but little is known about how the two processes are linked. ? To identify potential links between the two processes, we performed suppression subtractive hybridization (SSH) on cucumber (Cucumis sativus L.) stamens of male and female flowers at stage 6, with stamens at stage 5 of bisexual flowers as a control. ? Among the differentially expressed genes, we identified an expressed sequence tag (EST) encoding a cucumber homolog to an Arabidopsis calcium-dependent nuclease (CAN), designated CsCaN. Full-length CsCaN cDNA and the respective genomic DNA sequence were cloned and characterized. The CsCaN protein exhibited calcium-dependent nuclease activity. CsCaN showed ubiquitous expression; however, increased gene expression was detected in the stamens of stage 6 female flowers compared with male flowers. As expected, CsCaN expression was ethylene inducible. It was of great interest that CsCaN was post-translationally modified. ? This study demonstrated that CsCaN is a novel cucumber nuclease gene, whose DNase activity is regulated at multiple levels, and which could be involved in the primordial anther-specific DNA damage of developing female cucumber flowers.     

Metamorphosis of wing motor system in the silk moth,Bombyx mori L. (Lepidoptera: Bombycidae): Anatomy of the sensory and motor neurons that innervate larval mesothoracic dorsal musculature,stretch receptors,and epidermis

Anatomy of dorsal mesothoracic structures, such as muscles, sensory organs, and innervation, was studied in the silkworm, Bombyx mori L. (Lepidoptera : Bombycidae), and compared with the adult wing motor system. Musculature and nerve innervation were investigated by dissection and electron micrograph; and central projection of sensory fibers and morphology of somata and dendrites of motor neurons by cobalt back-filling, followed by silver intensification. There are 23 muscle bundles (DLM) and 2 stretch receptors (SR). The DLMs, SRs, and epidermis are innervated by a branch of the dorsal nerve trunk emerging from the mesothoracic ganglion (MSG). The branch bifurcates into a dorsal sensory branch of about 300 sensory fibers and a dorsal motor branch of 14 fibers. The sensory fibers project mainly to a longitudinal portion near the mid line in the ventral neuropil of MSG and the metathoracic ganglion. Several fibers extend into the prothoracic ganglion (PG) and a few into the subesophageal and 1st abdominal ganglia. At least 13 (probably 14) motor neurons send axons to DLMs: 9 (probably 10) in PG, and 4 in MSG. Their dendrites are located mostly on the dorsoipsilateral side of the neuropil, but several branches cross the mid line and give rise to many fine branches on the contralateral side. Comparison between the larval (present study) and adult motor system shows a significant similarity in the musculature, peripheral nerve pattern, and motor neurons with some peculiarities.     

nanos1: a mouse nanos gene expressed in the central nervous system is dispensable for normal development

A mouse nanos (nanos1) gene was cloned and its function was examined by generating a gene-knockout mouse. The nanos1 gene encodes an RNA-binding protein, which contains a putative zinc-finger motif that exhibits similarity with other nanos-class genes in vertebrates and invertebrates. Although nanos1 is not detected in primordial germ cells, it is observed in seminiferous tubules of mature testis. Interestingly, maternally expressed nanos1 is observed in substantial amounts in oocytes, but the amount of maternal RNA is rapidly reduced after fertilization, and the transient zygotic nanos1 expression is observed in eight-cell embryos. At 12.5 days postcoitum, nanos1 is re-expressed in the central nervous system and the expression continues in the adult brain, in which the hippocampal formation is the predominant region. The nanos1 -deficient mice develop to term without any detectable abnormality and they are fertile. No significant neural defect is observed in terms of their behavior to date.     

Amygdaloid-induced jaw opening and facilitation or inhibition of the trigeminal motoneurons in the rat

1. Repetitive stimulation of the rat'se central amygdaloid (CAm) nucleus induced rhythmic masticatory jaw movements or continuous jaw opening. Both types of jaw movements were accompanied by coincidental activities of the mylohyoid (Myl) nerve. 2. The effects of CAm stimulation were examined on activities of bilateral Myl and masseteric (Mass) nerves or their motoneurons (Myl-Dig and Mass, respectively). 3. CAm stimulation induced contralaterally dominant facilitation of the Myl nerve activity as well as Myl-Dig motoneurons. These facilitatory effects were caused by EPSPs seen in Myl-Dig motoneurons. 4. One third of the Mass motoneurons were inhibited or hyperpolarized by contralateral CAm stimulation, while a few were facilitated and the majority unaffected.     

Conduction in ulnar nerve bundles that innervate the proximal and distal muscles: a clinical trial

Background  

This study aims to investigate and compare the conduction parameters of nerve bundles in the ulnar nerve that innervates the forearm muscles and hand muscles; routine electromyography study merely evaluates the nerve segment of distal (hand) muscles.     

Crystal structure and biochemical characterization of human kallikrein 6 reveals that a trypsin-like kallikrein is expressed in the central nervous system

The human kallikreins are a large multigene family of closely related serine-type proteases. In this regard, they are similar to the multigene kallikrein families characterized in mice and rats. There is a much more extensive body of knowledge regarding the function of mouse and rat kallikreins in comparison with the human kallikreins. Human kallikrein 6 has been proposed as the homologue to rat myelencephalon-specific protease, an arginine-specific degradative-type protease abundantly expressed in the central nervous system and implicated in demyelinating disease. We present the x-ray crystal structure of mature, active recombinant human kallikrein 6 at 1.75-A resolution. This high resolution model provides the first three-dimensional view of one of the human kallikreins and one of only a few structures of serine proteases predominantly expressed in the central nervous system. Enzymatic data are presented that support the identification of human kallikrein 6 as the functional homologue of rat myelencephalon-specific protease and are corroborated by a molecular phylogenetic analysis. Furthermore, the x-ray data provide support for the characterization of human kallikrein 6 as a degradative protease with structural features more similar to trypsin than the regulatory kallikreins.     

Evidence that the Pgp-1 glycoprotein is expressed on thymus-homing progenitor cells of the thymus

The Pgp-1 glycoprotein is found on the bone marrow prothymocyte; however, only a few percent of cells within the normal thymus express significant quantities of Pgp-1 glycoprotein. One hypothesis is that some or all of these Pgp-1+ thymocytes represent thymocyte progenitors or the immediate descendents of the bone marrow-derived prothymocyte. A cell present in the thymus which is able to home back to the thymus and to transiently repopulate it represents one class of thymocyte progenitor. Thymocyte populations enriched in this thymus-homing progenitor are enriched in Pgp-1+ cells. Treatment of these enriched populations with anti-Pgp-1 antibody inhibits activity of the thymus-homing progenitor. These results are consistent with the hypothesis that the thymus-homing progenitor bears Pgp-1 on its surface.     

Cerebroglycan: an integral membrane heparan sulfate proteoglycan that is unique to the developing nervous system and expressed specifically during neuronal differentiation

Heparan sulfate proteoglycans (HSPGs) are found on the surface of all adherent cells and participate in the binding of growth factors, extracellular matrix glycoproteins, cell adhesion molecules, and proteases and antiproteases. We report here the cloning and pattern of expression of cerebroglycan, a glycosylphosphatidylinositol (GPI)- anchored HSPG that is found in the developing rat brain (previously referred to as HSPG M13; Herndon, M. E., and A. D. Lander. 1990. Neuron. 4:949-961). The cerebroglycan core protein has a predicted molecular mass of 58.6 kD and five potential heparan sulfate attachment sites. Together with glypican (David, G., V. Lories, B. Decock, P. Marynen, J.-J. Cassiman, and H. Van den Berghe. 1990. J. Cell Biol. 111:3165-3176), it defines a family of integral membrane HSPGs characterized by GPI linkage and conserved structural motifs, including a pattern of 14 cysteine residues that is absolutely conserved. Unlike other known integral membrane HSPGs, including glypican and members of the syndecan family of transmembrane proteoglycans, cerebroglycan is expressed in only one tissue: the nervous system. In situ hybridization experiments at several developmental stages strongly suggest that cerebroglycan message is widely and transiently expressed by immature neurons, appearing around the time of final mitosis and disappearing after cell migration and axon outgrowth have been completed. These results suggest that cerebroglycan may fulfill a function related to the motile behaviors of developing neurons.     

Hormone signaling in evolution and development: a non-model system approach

Cooption and modularity are informative concepts in evolutionary developmental biology. Genes function within complex networks that act as modules in development. These modules can then be coopted in various functional and evolutionary contexts. Hormonal signaling, the main focus of this review, has a modular character. By regulating the activities of genes, proteins and other cellular molecules, a hormonal signal can have major effects on physiological and ontogenetic processes within and across tissues over a wide spatial and temporal scale. Because of this property, we argue that hormones are frequently involved in the coordination of life history transitions (LHTs) and their evolution (LHE). Finally, we promote the usefulness of a comparative, non-model system approach towards understanding how hormones function and guide development and evolution, highlighting thyroid hormone function in echinoids as an example.     

Intercellular junctions during development of the definitive kidney in lampreys: freeze fracture and morphometric analyses

The changing morphology of intercellular junctions in renal morphogenesis during lamprey metamorphosis was followed using freeze-fracture replicas and morphometry. Gap junctions and particle aggregates among strands of occluding junctions are conspicuous in the differentiating podocytes of the renal corpuscle and in the early ciliated neck and proximal segments but not in the distal segment. The cells of the segmented nephron arise from alpha nephrogenic cells which have a focal aggregate (macula occludens) of 4.8 junctional strands. Upon the initiation of metamorphosis the number of strands increases to 8 in undifferentiated cells with either maculae or zonulae occludentes. Differentiation of both neck and proximal segments is accompanied by gradual transformation of a 7-strand zonula occludens to a 4-strand junction but it becomes more shallow in the latter segment. Two types of undifferentiated cell are recognized through five of the seven metamorphic stages. Cells of two types of distal segments begin differentiation at the midpoint of transformation and immediately show zonula occludens of different morphology. Distal segment I (pars recta) has 5 strands and a 0.250 mum depth whereas segment II has 8-9 strands with twice the apical-basal depth. The larval archinephric duct undergoes a moderate transformation in junctional morphology with the addition of 2 strands and no increase in apical-basal depth in zonulae occludentes during metamorphosis. Changes and development of types of intercellular junctions along the nephron in lampreys are discussed with reference to known regional functional specialization in this organism and with the morphology of renal tubular intercellular junctions in other vertebrates.