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PubMed1995

Both basic fibroblast growth factor and ciliary neurotrophic factor promote the retention of polyneuronal innervation of developing skeletal muscle fibers.

At birth, nearly all rat muscle fibers receive synaptic inputs from more than one motoneuron at a single end-plate site. By the end of the third postnatal week all but one of these inputs has been eliminated. During this loss of polyneuronal innervation, developing neuromuscular synapses compete with one another. Although the nature of this competition is not known, it is commonly assumed that it is mediated through differential activity of the competing inputs. One means by which such differential activity might be translated into a biological signal would be if the synapses compete in an activity-dependent manner for a scarce supply of neurotrophic molecules. A prediction of this hypothesis is that excess quantities of such trophic molecules will reduce competition and thereby slow down or abolish the normal loss of polyneuronal innervation. In newborn rats, the effects of injection of either basic fibroblast growth factor (bFGF) or ciliary neurotrophic factor (CNTF) on the outcome of neuromuscular synapse elimination were investigated. Daily injections of either bFGF or CNTF were made for 1 week into the lateral gastrocnemius muscle beginning at the postnatal age of 2 days. The amount of polyneuronal innervation of fibers in trophic molecule-injected muscles and saline-injected contralateral muscles was assayed using intracellular recording methods. For both bFGF- and CNTF-injected muscles, an increase in the percentage of polyneuronally innervated fibers relative to saline-injected muscles was noted. For bFGF-injected muscles, the amount of polyneuronal innervation remained at nearly 60% as late as the postnatal age of 14 days (P14). This is the amount of polyneuronal innervation found at age 6 days in normal animals. Nearly 40% of the fibers of CNTF-injected muscles remained polyneuronally innervated at age P14, the amount expected at age 9 days. These results indicate that both bFGF and CNTF exert powerful and long-lasting effects on developing neuromuscular synapses.

Animals↗

PubMed1995

Sympathetic innervation modulates the expression of angiotensin II receptors in embryonic rat heart grafted in oculo.

Angiotensin II acts as a cardiac growth factor, and causes both inotropic and chronotropic changes within the heart. In the present study, we used an in oculo model system to examine the effects of sympathetic innervation on the density of cardiac angiotensin II receptors. Quantitative autoradiography was used to determine the density of angiotensin II receptors in embryonic rat hearts grafted into either sympathetically innervated or sympathetically denervated eye chambers of adult host rats. The density of specific binding to angiotensin II receptors was nearly three-fold higher in sympathetically non-innervated compared to sympathetically innervated heart grafts (30.8 +/- 4.2 v 11.5 +/- 3.2 fmol/mg protein). Specific binding to angiotensin II receptors in heart grafts was displaced by addition of the AT1 receptor antagonist losartan, but not by addition of the AT2 receptor competitor PD 123177. Thus, only AT1 receptors were present in sympathetically innervated and sympathetically non-innervated embryonic rat hearts grafted in oculo. We conclude that changes in sympathetic innervation caused changes in the density of cardiac angiotensin II receptors in the present study. Our results may have implications for growth and function not only during cardiac development, but also during cardiac disease.

Age Factors↗

PubMed1998

Neuronal innervation, intracellular signal transduction and intercellular coupling: a model for syncytial tissue responses in the steady state.

A model tissue is proposed in which chemically responsive cells are interconnected by gap junctions and innervated by the autonomic nervous system. The model is explicitly dependent on the following physiologically relevant assumptions: (1) a fraction of the cells are directly innervated, and these cells respond to a periodic neuronal stimulus (i.e. the release of neurotransmitter) by production of an intracellular substance (i.e. second messenger molecule); (2) production of second messenger molecules modulates the amplitude of a cellular response, such as contraction or secretion; (3) intracellular formation of second messenger molecules in innervated cells is proportional to the periodicity of the neuronal stimulus, while the intracellular concentration in non-innervated cells is governed by the half-life of the second messenger molecule and the extent of cell-to-cell coupling; (4) the amplitude of the graded response of the individual cell is related to the intracellular second messenger concentration by a Michaelis-Menten function; (5) the amplitude of the graded tissue response is a function of the innervation density, the frequency of stimulation, and the extent of intercellular coupling. Thus, a stimulus-response relationship was developed, where the magnitude of the tissue response was described as a function of the total tissue stimulus. The predicted stimulus-response curve was encapsulated by two parameters: (1) the Hill-exponent, which reflects the steepness of the stimulus-response curve; and (2) the location of the stimulus-response curve, or the half-maximally effective stimulus. Both random and uniform neuronal innervation patterns were considered in model tissues with various effective dimensions. The simulations were also applied to a realistic model of vascular tissue. The shape of the stimulus-response curve is critically dependent on the geometry of innervation. For physiologically relevant (10-90% over 2-3 orders of magnitude) dose-response curves, the model yields an implicit relationship between three different dimensionless parameters. If, in a system, two of these parameters are known, the model can be used to bracket the possible range of the third parameter.

Animals↗

PubMed1999

Poly- and mononeuronal innervation in a model for the development of neuromuscular connections.

In the normal development of connections between motor neurons and muscle fibres, an initial stage of polyneuronal innervation is followed by withdrawal of connections until each muscle fibre is innervated by a single axon. However, polyneuronal innervation has been found to persist after prolonged nerve conduction block, in spite of the resumption of normal neuromuscular activity. Here we analyse in detail a model proposed for the withdrawal of nerve connections in developing muscle, based on competition between nerve terminals. The model combines competition for a pre-synaptic resource with competition for a post-synaptic resource. Using bifurcation and phase space analysis, we show that polyneuronal innervation, as well as mononeuronal innervation, can be stable. The model accounts for the development of mononeuronal innervation and for persistent polyneuronal innervation after prolonged nerve conduction block, which appears as a consequence of the general competitive interactions operating during normal development.

Animals↗

PubMed1984

Ultrastructure and innervation of the swimbladder of Tetractenos glaber (Tetraodontidae).

The general structure, ultrastructure and innervation of the swimbladder of the smooth toadfish, Tetractenos glaber, were examined with light-microscopic, fluorescence-histochemical, and transmission electron-microscopic techniques. The structure of the swimbladder is similar to that of other euphysoclists. Fluorescence histochemistry showed adrenergic fibres in both the secretory and resorptive areas of the swimbladder. Transmission electron microscopy revealed two morphologically distinct axon profiles: type-I profiles containing many small, flattened vesicles; type-II profiles containing both large, granular vesicles and rounded, small clear vesicles in varying proportions. The gas-gland cells and surrounding muscularis mucosae are innervated by both type-I and type-II fibres. Type-I fibres also innervate pre-rete arteries. The rete- and gas-gland capillaries do not appear to be innervated. Arteries running to the resorptive area are innervated by type-I fibres. Both type-I and type-II profiles make contact with the muscularis mucosae in the resorptive area. Only type-I fibres innervate the radial dilator muscle in the oval sphincter region, whereas only type II fibres innervate the circular muscle of the oval sphincter. Type-I fibres took up alpha-methyl-noradrenaline, and could not be found after pre-treatment with 6-hydroxydopamine. They are, therefore, assumed to be adrenergic. Type-II fibres were tentatively identified, by exclusion, as cholinergic.

Air Sacs↗

PubMed1978

The pattern of innervation of a polyneural muscle: axolotl iliotibialis.

The pattern of innervation on individual iliotibialis muscle fibres from axolotl (Ambystoma mexicanum) has been investigated histologically and electrophysiologically. These polyneural fibres were found to be innervated on average at five end plate sites. The sites were distributed irregularly along each fibre. Average end plate length was found to be approximately 70 micrometer. Most end plates were separated by less than 1000 micrometer; 26% by less than 150 micrometer; the average separation was 516 micrometer. Advantage was taken of the dual innervation of the muscle to investigate the separation between synaptic terminals from different axons. Some individual fibres were found to be innervated by axons from two different spinal nerves. End plate sites on dually innervated fibres were located by ACh iontophoresis. 30% of such sites were found to be innervated by more than one axon terminal. The average separation of such sites was found to be 9 micrometer. Four different axons were found to innervate some individual muscle fibres. It is suggested that the unusual ability of axolotl muscle fibres to accept synaptic terminals from different axons at closely adjacent sites may be a major factor underlying selective reinnervation in this animal.

Ambystoma↗

PubMed1982

Histochemical properties and innervation pattern of fast and slow-tonic fibre types of the anterior latissimus dorsi muscle of the chick.

The anterior latissimus dorsi muscle of the chick is largely composed of slow-tonic fibres but contains a few fast fibres defined by their acid-labile, alkali-stable myofibrillar ATPase activity. These fibres are referred to as alpha fibres. Differing from the slow-tonic (alpha' and beta') fibres which are multiply innervated with en grappe endings, the alpha (fast) fibres are innervated by typical en plaque endings. The innervation of thirty-two alpha fibres were studied closely and it was concluded that about a half of the alpha fibres were focally innervated whereas a half were innervated in two distinct loci by en plaque endings. In only one case, a fast fibre with three widely spaced en plaque endings was observed. The mean intersynaptic length was significantly larger on alpha fibres than on alpha' and beta' fibres. No variation in the histochemical properties of myofibrillar ATPase was observed either along the entire length of singly and dually innervated alpha fibres, or along alpha' and beta' fibres. It is concluded that the three extrafusal fibre types of the anterior latissimus dorsi muscle maintain uniform histochemical characteristics along their length in spite of a possible innervation by several motoneurons.

Acetylcholinesterase↗

PubMed1988

Electrophysiological and morphological study of polyneuronal innervation in the cutaneous pectoris muscle of adult frog (Rana esculenta).

The incidence of polyneuronal innervation in the cutaneous pectoris muscle of the adult frog, Rana esculenta, was determined quantitatively using electrophysiological and morphological techniques. The mean percentages of multiple innervated endplates obtained with both techniques from a series of 19 muscles examined at all times of the year were in very good correlation: 30.7% (196/639 endplates) by electrophysiology and 30.5% (478/1569 endplates) by morphology. In nine muscles examined during the period from December to March the mean percentages, 36.8% (110/299) by electrophysiology and 38.6% (281/727) by morphology, were significantly higher than those obtained for 10 muscles investigated during the period from May to November, 25.3% (86/340) and 23.4% (197/842) with both techniques respectively. The higher incidence of collateral sprouted branches detected at polyinnervated endplate sites in muscles of winter frogs might be related to these seasonal variations. Most of the 1688 fibres from 26 muscles examined throughout the year exhibited one centrally located endplate. However, around 11% of them were found to be innervated at two separate endplate sites. Muscle fibres exhibiting this type of innervation were invariably the largest fibres in each muscle tested, having an apparent diameter greater than 48 micron. The distance between the endplates of these fibres represented between 10 and 30% of their total length. No significant seasonal variations were observed in the incidence of these dually innervated fibres. In conclusion, both electrophysiological and morphological results show that the normal incidence of polyneuronal innervation in the cutaneous pectoris muscle of adult Rana esculenta is affected by seasonal related factors which influence the nodal sprouting activity. Moreover, they show that a dual pattern of innervation is a common feature in large fibres of this muscle.

Animals↗

PubMed1991

Patterns of hair cell survival and innervation in the cochlea of the bronx waltzer mouse.

A massive loss of inner hair cells typifies the cochleae of Bronx waltzer mutant mice. We have characterized the surviving inner hair cells and their modified innervation by immunocytochemistry using antibodies against neuron-specific enolase, with additional stains for neural cell adhesion molecule and neurofilaments, and by electron microscopy. The surviving inner hair cells vary in size, neuron-specific enolase content and innervation. All neuron-specific enolase-positive cells are innervated by neuron-specific enolase-positive endings. There is apparent correspondence between the neuron-specific enolase immunoreactivity of sensory cells and their innervation. Well-stained cells are richly innervated (and large) while lightly stained cells received fewer nerve endings. Neuron-specific enolase-negative inner hair cells innervated either by neuron-specific enolase-positive or -negative nerve endings are very rare. Ultrastructurally, the surviving inner hair cells vary from those of a normal morphological appearance to underdeveloped or vacuolated. Most of the apparently normal inner hair cells are associated with few nerve endings; instead nerve growth cones are abundant in the adjacent inner spiral sulcus epithelium. Cells forming ribbon synapses with afferent endings are rare. The contingent of efferent endings in the inner spiral bundle depends on the presence of afferent endings. The absence of inner hair cells and the uneven distribution of nerve endings on the surviving cells results in the disruption of normal innervation patterns, especially in the thinning out or discontinuation of the inner spiral bundle and an uneven distribution of tunnel fibres. We infer that the sprouting of nerve endings and their convergence on a selected population of the surviving inner hair cells represents a compensatory regenerative phenomenon in response to the loss and the genetic defect of the remaining inner hair cells.

Animals↗

PubMedDate not supplied

Neuronal pathways from low-threshold muscle and cutaneous afferents innervating tail to trunk muscle motoneurons in the cat.

We studied neuronal pathways from low-threshold muscle (group I, II) and cutaneous afferents (group A(alpha)beta) innervating the tail to motoneurons innervating trunk muscles (m. iliocostalis lumborum and m. obliquus externus abdominus) in 18 spinalized cats. Stimulation of group I muscle afferents produced excitatory postsynaptic potentials or excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials in all motoneurons innervating the m. iliocostalis lumborum which showed effects (32%), and predominantly inhibitory postsynaptic potentials in motoneurons innervating the m. obliquus externus abdominus (47%). Stimulation of group I+II afferents produced significant increases of the incidence of motoneurons showing postsynaptic potentials (the notoneurons innervating the m. iliocostalis lumborum, 87%; the motoneurons innervating the m. obliquus externus abdominus, 82%). The effects of low threshold cutaneous afferents were bilateral, predominantly producing inhibitory postsynaptic potentials in motoneurons innervating both muscles. These results suggest that neuronal pathways from muscle afferents to back muscle motoneurons mainly increase the stiffness of the trunk to maintain its stability, while those to abdominal muscles help to extend the dorsal column by decreasing their activities. The results also indicate that neuronal pathways from cutaneous afferents to trunk motoneurons functionallY disconnect the tail from the trunk.

Action Potentials↗

PubMed2001

How heterogeneous is the cardiac autonomic innervation?

The rich autonomic innervation of the heart plays an important role in modifying cardiovascular function. Recently developed in vivo scintigraphic imaging techniques allow for visualization of the autonomic innervation of the heart. Studies using the modalities have shown heterogeneity of sympathetic innervation in various kinds of pathological conditions as well as normal human heart. The inferioposterior region shows typically less sympathetic innervation than the anterior region. In addition, neuropathic processes appear to commence in inferior-apical regions extending towards the base of the heart. Arrhythmogeneity has been related to the heterogeneous innervation of the heart and heterogeneous uptake of radiolabeled catecholamine analogues, such as I-123 metaiodobenzylguanidine, can be found in patients with arrhythmia. In dilated cardiomyopathy, reduced uptake indicates a poor prognosis which allows risk stratification for patients with heart failure. Heterogeneity of the reinnervation process following heart transplantation has also been investigated. Evidence was found of reinnervation primarily in the basal anterioseptal region and to a lesser degree in the inferioposterior and apical regions. Tracer approaches are uniquely suited to identify regionally altered innervation and provide tools for linking information on cardiac autonomic innervation with other clinical aspects.

Arrhythmias, Cardiac↗

PubMed2005

Enteric co-innervation of motor endplates in the esophagus: state of the art ten years after.

The existence of a distinct ganglionated myenteric plexus between the two layers of the striated tunica muscularis of the mammalian esophagus represented an enigma for quite a while. Although an enteric co-innervation of vagally innervated motor endplates in the esophagus has been repeatedly suggested, it was not possible until recently to demonstrate this dual innervation. Ten years ago, we were able to demonstrate that motor endplates in the rat esophagus receive a dual innervation from both vagal nerve fibers originating in the brain stem and from varicose enteric nerve fibers originating in the myenteric plexus. Since then, a considerable amount of data could be raised on enteric co-innervation and its occurrence in a variety of species, including humans, its neurochemistry, spatial relationships on motor endplates, ontogeny, and possible roles during esophageal peristalsis. These data underline the significance of this newly discovered innervation component, although its function is still largely unknown. The aim of this review is to summarize current knowledge about enteric co-innervation of esophageal striated muscle and to provide some hints as to its functional significance.

Animals↗

PubMed2000

Nitrergic and peptidergic innervation in the developing rat heart.

The phenotypic expression and anatomic distribution of nitrergic and peptidergic innervation in the developing rat heart was localized by reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and immunohistochemistry using antibodies against neuronal isoform of nitric oxide synthase (nNOS), neuropeptide Y (NPY) and calcitoningene-related peptide (CGRP). NPY-immunoreactive nerve fibers showed the earliest expression by 16 days of gestation, with preferential innervation of the nodal and perinodal areas, followed by the innervation of the valves and ventricles by postnatal day 7. NPY immunoreactivity was also localized to a large proportion of the intrinsic cardiac ganglia from 16 days of gestation onwards with a progressive increase in the number of neuronal cell bodies per ganglia with age. CGRP-positive nerve fibers appeared by 19 days of gestation and were less dense during the gestational and early postnatal periods, and showed a quantitative increase in density by 7 days, followed by a decrease by 3 weeks postnatal. None of the intrinsic ganglia were stained positive for CGRP, indicating the extrinsic sensory origin of these stained fibers. Nitrergic innervation paralleled the sensory innervation, with the cardiac ganglia and nerve fibers showing a positive labeling from 19 days of gestation onwards. NADPH-d and nNOS were partially co-localized. Double-label immunohistochemistry showed that a considerable proportion of sensory CGRP-immunopositive fibers were also immunoreactive for NOS. The results of the present study show that neuropeptides and nitric oxide are expressed by the late gestational period and that autonomic efferent innervation precedes sensory and nitrergic innervation in the developing heart.

Animals↗

PubMed1979

Development of the noradrenergic innervation of neocortex.

The development of the noradrenaline (NA)-neuron innervation of rat neocortex was studied by fluorescence histochemistry, high affinity uptake of [3H-]NA, and biochemical assay of regional NA content. Fluorescence histochemistry indicates that NA axons enter areas of developing neocortex prenatally and the innervation matures rapidly during early postnatal life. Frontal and lateral neocortical areas are the first to be innervated followed by occipital and parietal areas. All cortical layers receive innervation. The distribution and density of neocortical NA innervation achieves the adult pattern by the end of the first postnatal week. High affinity uptake studies confirm the observations from fluorescence histochemistry and show a very rapid maturation of the NA axon innervation with adult levels of uptake occurring by postnatal day 9. Following birth, there is a brief rise in NA content from PO to P2 in all neocortical areas. NA content then drops to low levels in all areas by P4. This is followed by a gradual increase in NA content in all areas occuring over several months. This pattern of development of NA axon innervation of neocortex demonstrates that the density and distribution of NA axons in developing neocortex matures much earlier than shown in previous studies whereas the NA content of the developing axonal plexus achieves adult levels later in postnatal life.

Adrenergic Fibers↗

PubMed1986

Correspondences between afferent innervation patterns and response dynamics in the bullfrog utricle and lagena.

Otoconial afferents in the bullfrog were characterized as gravity or vibratory sensitive by their resting activity and their responses to head tilt and vibration. The responses of gravity afferents to head tilt were tonic, phasic-tonic, or phasic. A few afferents, termed vibratory/gravity afferents, had gravity as well as vibratory sensitivity. Functionally identified otoconial afferents were injected with Lucifer Yellow and subsequently traced to their peripheral arborizations. Morphological maps, previously constructed with the scanning electron microscope, were used to identify microstructural features of the sensory maculae associated with the peripheral arborizations of dye-filled afferents. The utricular and lagenar macula each is composed of a specialized central band surrounded by a peripheral field. The central bands are composed of densely packed medial rows and more sparsely packed lateral rows of hair cells. Hair cells exhibit a variety of surface topographies which correspond with their macular location. The response dynamics of afferents in the utricle and lagena correspond with the macular locations of their peripheral arborizations. Tonic afferents were traced to hair cells in the peripheral field. Phasic-tonic and phasic afferents innervated hair cells in the lateral rows of the central band, the former innervating hair cells at the edges of the central band and the latter innervating hair cells located more medially. Afferents with vibratory sensitivity were traced to hair cells in the medial rows of the lagenar central band. The response dynamics of afferents corresponded with the surface topography of their innervated hair cells. Tonic and phasic-tonic gravity afferents innervated hair cells with stereociliary arrays markedly shorter than their kinocilium (Lewis and Li types B and C) while phasic gravity and vibratory afferents innervated hair cells with stereociliary arrays nearly equal to their kinocilium (Lewis and Li types E and F). Vibratory sensitivity was uniquely associated with hair cells possessing bulbed kinocilium (Lewis and Li type E) while afferents sensitive to both gravity and vibration innervated hair cells from both of the above groups. We argue that afferent response dynamics are determined, at least in part, at the level of the sensory hair bundle and that morphological variations of the kinocilium and the otoconial membrane are dictated by specialization of sensitivity. We propose that morphological variations of the kinocilium reflect variations in its viscoelastic properties and that these properties determine the nature of the mechanical couple between the stereociliary array and the otoconial membrane.

Acoustic Maculae↗

PubMed1992

Anatomical evidence for genetic differences in the innervation of the rat spinal cord by noradrenergic locus coeruleus neurons.

Pontospinal noradrenergic neurons located in the A5, A6 (locus coeruleus, LC), and A7 cell groups are the major source of the noradrenergic innervation of the spinal cord. We have recently examined the specific terminations of these three cell groups in the spinal cord and found that the LC provides the major noradrenergic innervation of the ventral horn, while the A7 and A5 cell groups innervate the dorsal horn and intermediate zone, respectively. However, the results of similar experiments from another laboratory have shown that noradrenergic neurons in the locus coeruleus primarily innervate the dorsal horn, while the A5 and A7 innervate the intermediate zone and the ventral horn. These conflicting results may be due to fundamental genetic differences between the rats used in our experiments (Sasco Sprague-Dawley) and those used by the other laboratory (Harlan Sprague-Dawley). This possibility was examined by determining the projections of coeruleospinal neurons in these two rat substrains using the anterograde tracer Phaseolus vulgaris leucoagglutinin. The results indicate that in Sasco rats the LC neurons project through the ipsilateral ventromedial funiculus and terminate almost exclusively in the medial part of laminae VII and VIII, the motoneuron pool of lamina IX, and lamina X. In contrast, LC neurons in Harlan rats project bilaterally through the superficial dorsal horn and the dorsolateral funiculus and terminate most heavily in dorsal horn laminae I-IV. In addition, the LC neurons of Sasco rats innervate cervical spinal cord segments more densely than lumbar spinal cord segments, while in Harlan rats the lumbar spinal cord is more densely innervated than the cervical spinal cord. These results indicate that the projections of coeruleospinal neurons in Sasco rats are fundamentally different from those in Harlan rats and suggest that noradrenergic LC neurons may have different physiological functions in these two rat substrains.

Animals↗

PubMed1991

Difference in central projection of primary afferents innervating facial and intraoral structures in the rat.

Transganglionic transport of horseradish peroxidase-wheat germ agglutinin conjugate was used to study the central projection of primary afferent neurons innervating facial and intraoral structures. The examined primary neurons innervating the facial structures were those comprising the frontal and zygomaticofacial nerves and those innervating the cornea, while the primary neurons innervating the intraoral structures included those innervating the mandibular incisor and molar tooth pulps and those comprising the palatine nerve. The primary afferents innervating the facial structures project to the lateral or ventral parts of the trigeminal principal, oral and interpolar subnuclei, and to the rostral cervical spinal dorsal horn across laminae I through V, with a greater proportion being directed to the spinal dorsal horn. The primary afferents innervating the intraoral structures terminate in the dorsomedial subdivisions of the trigeminal principal, oral and interpolar subnuclei, and in laminae I, II, and V of the medial medullary dorsal horn, with a much denser projection being distributed to the rostral subnuclei. In addition to the above brain stem trigeminal sensory nuclear complex, they project to the supratrigeminal nucleus, caudal solitary tract nucleus, and paratrigeminal nucleus. These observations agree with previously reported data that the central projection of trigeminal nerve is organized in different manners for the facial and intraoral structures. Furthermore, the present findings in conjunction with our previous studies clarify that the central projection of primary afferents from the facial skin is organized in a clear somatotopic fashion and that the terminal fields of primary afferents from the intraoral structures extensively overlap in the brain stem trigeminal nuclear complex particularly in its rostral subdivisions. The central mechanism of trigeminal nociception is discussed with particular respect to its difference between the facial and intraoral structures.

Afferent Pathways↗

PubMed1992

The paired box gene pox neuro: a determinant of poly-innervated sense organs in Drosophila.

This study describes the structure and function of pox neuro (poxn), a gene previously isolated by virtue of a conserved domain, the paired box, which it shares with the segmentation genes paired and gooseberry. Its expression pattern has been analyzed, particularly during development of the PNS. We propose that poxn is a "neuroblast identity" gene acting in both the PNS and the CNS on the basis of the following evidence. Its expression is restricted to four neuronal precursors in each hemisegment: two neuronal stem cells (neuroblasts) in the CNS, and two sensory mother cells (SMCs) in the PNS. The SMCs that express poxn produce the poly-innervated external sense organs of the larva. In poxn- embryos, poly-innervated sense organs are transformed into mono-innervated. Conversely, ectopic expression of poxn in embryos transformed with a heat-inducible poxn gene can switch mono-innervated to poly-innervated sense organs. Expression of poxn in the wing disc is restricted to the SMCs of the poly-innervated sense organs, suggesting that poxn also determines the lineage of poly-innervated adult sense organs.

Amino Acid Sequence↗