Dpysl2 (CRMP2) is required for the migration of facial branchiomotor neurons in the developing zebrafish embryo.

Dihydropyrimidinase-like family proteins (Dpysls) are relevant in several processes during nervous system development; among others, they are involved in axonal growth and cell migration. Dpysl2 (CRMP2) is the most studied member of this family; however, its role in vivo is still being investigated. Our previous studies in zebrafish showed the requirement of Dpysl2 for the proper positioning of caudal primary motor neurons and Rohon-Beard neurons in the spinal cord.In the present study, we show that Dpysl2 is necessary for the proper migration of facial branchiomotor neurons during early development in zebrafish. We generated a dpysl2 knock-out (KO) zebrafish mutant line and used different types of antisense morpholino oligonucleotides (AMO) to analyze the role of Dpysl2 in this process. Both dpysl2 KO mutants and morphants exhibited abnormalities in the migration of these neurons from rhombomers (r) 4 and 5 to 6 and 7. The facial branchiomotor neurons that were expected to be at r6 were still located at r4 and r5 hours after the migration process should have been completed. In addition, mutant phenotypes were rescued by injecting dpysl2 mRNA into the KO embryos. These results indicate that Dpysl2 is involved in the proper migration of facial branchiomotor neurons in developing zebrafish embryos.

Robo1 and 2 Repellent Receptors Cooperate to Guide Facial Neuron Cell Migration and Axon Projections in the Embryonic Mouse Hindbrain.

The facial nerve is necessary for our ability to eat, speak, and make facial expressions. Both the axons and cell bodies of the facial nerve undergo a complex embryonic developmental pattern involving migration of the cell bodies caudally and tangentially through rhombomeres, and simultaneously the axons projecting to exit the hindbrain to form the facial nerve. Our goal in this study was to test the functions of the chemorepulsive receptors Robo1 and Robo2 in facial neuron migration and axon projection by analyzing genetically marked motor neurons in double-mutant mouse embryos through the migration time course, E10.0-E13.5. In Robo1/2 double mutants, axon projection and cell body migration errors were more severe than in single mutants. Most axons did not make it to their motor exit point, and instead projected into and longitudinally within the floor plate. Surprisingly, some facial neurons had multiple axons exiting and projecting into the floor plate. At the same time, a subset of mutant facial cell bodies failed to migrate caudally, and instead either streamed dorsally toward the exit point or shifted into the floor plate. We conclude that Robo1 and Robo2 have redundant functions to guide multiple aspects of the complex cell migration of the facial nucleus, as well as regulating axon trajectories and suppressing formation of ectopic axons.

Fetal anatomy of the facial nerve trunk and its relationship with posterior auricular artery.

PURPOSE: The aims of the study are to define anatomy of the facial nerve (FN) and its main trunks as well as their relationship with the posterior auricular artery in fetal period to evaluate the data for regional surgery in newborns and young infants. METHODS: Formalin-fixed 34 fetuses from anatomy laboratory collection with a mean gestational age of 26.4 ± 4.6 (20-36) weeks were dissected. Parameters regarding the presence of major or minor trunks, width, length, branching pattern of FN were evaluated according to side, gender and trimester. The positional relationship of posterior auricular artery with the FN trunk was inspected. RESULTS: On all sides only the major trunk of the FN was detected. For length and width parameters, there was no statistically significant difference for side and gender except for trimester. Linear functions were found as 0.329 + 0.025 × weeks for width and 5.264 + 0.185 × weeks for length. There are statistically significant linear relationships between width and length of the FN trunk and week parameters as r = 0.507, p < 0.001 and r = 0.484, p < 0.001, respectively. Posterior auricular artery crossed FN trunk laterally in 42 of 53 sides, medially in 9 sides while it was puncturing it proximally in 2 sides. In all cases, it was in close contact to the FN trunk. FN trunk showed bifurcation in 82% and trifurcation in 18%. CONCLUSION: Dimensions of FN trunk, growth ratio and linear functions can be beneficial in understanding the fetal growth of FN trunk and its usage for grafts. Data about the relationship of the posterior auricular artery with FN trunk may be crucial in avoiding iatrogenic injuries during surgery in early ages.

Molecular specification of facial branchial motor neurons in vertebrates.

Orofacial muscles are critical for life-sustaining behaviors, such as feeding and breathing. Centuries of work by neuroanatomists and surgeons resulted in the mapping of bulbar motor neurons in the brainstem and the course of the cranial nerves that carry their axons. Despite the sophisticated understanding of the anatomy of the region, the molecular mechanisms that dictate the development and maturation of facial motor neurons remain poorly understood. This fundamental problem has been recently revisited by physiologists with novel techniques of studying the rhythmic contraction of orofacial muscles in relationship to breathing. The molecular understanding of facial motor neuron development will not only lead to the comprehension of the neural basis of facial expression but may also unlock new avenues to generate stem cell-derived replacements. This review summarizes the current understanding of molecular programs involved in facial motor neuron generation, migration, and maturation, including neural circuit assembly.

Relations of Facial Nerve With Retromandibular Vein in Human Fetuses.

The relationship of facial nerve (FN) and its branches with the retromandibular vein (RMV) has been described in adults, whereas there is no data in the literature regarding this relationship in fetuses. The study was conducted to evaluate the anatomic relationships of these structures on 61 hemi-faces of fetuses with a mean age of 26.5 ±â€Š4.9 weeks with no visible facial abnormalities. The FN trunk was identified at its emergence at the stylomastoid foramen. It was traced till its ramification within the parotid gland. In 46 sides, FN trunk ramified before crossing RMV and ran lateral to it, while in 8 sides FN trunk ramified on the lateral aspect of the RMV. In 3 sides, FN trunk ramified after crossing the RMV at its medial aspect. In only 1 side, FN trunk trifurcated as superior, middle, and inferior divisions and RMV lied anterior to FN trunk, lateral to superior division, medial to middle and inferior divisions. In 2 sides, FN trunk bifurcated as superior and inferior divisions. Retromandibular vein was located anterior to FN trunk, medial to superior division, lateral to inferior division in both of them. In 1 side, RMV ran medial to almost all branches, except the cervical branch of FN. Variability in the relationship of FN and RMV in fetuses as presented in this study is thought to be crucial in surgical procedures particularly in early childhood.

Fetal facial nerve course in the ear region revisited.

PURPOSE: The aim of this study was to re-examine the structures that determine course of the facial nerve (FN) in the fetal ear region. MATERIALS AND METHODS: We used sagittal or horizontal sections of 28 human fetuses at 7-8, 12-16, and 25-37 weeks. RESULTS: The FN and the chorda tympani nerve ran almost parallel until 7 weeks. The greater petrosal nerve (GPN) ran vertical to the distal FN course due to the trigeminal nerve ganglion being medial to the geniculate ganglion at 7 weeks. Afterwards, due to the radical growth of the former ganglion, the GPN became an anterior continuation of the FN. The lesser petrosal nerve ran straight, parallel to the FN at 7 weeks, but later, it started to wind along the otic capsule, possibly due to the upward invasion of the tympanic cavity epithelium. Notably, the chorda tympanic nerve origin from the FN, and the crossing between the vagus nerve branch and the FN, was located outside of the temporal bone even at 37 weeks. The second knee of the FN was not evident, in contrast to the acute anterior turn below the chorda tympanic nerve origin. In all examined fetuses, the apex of the cochlea did not face the middle cranial fossa, but the tympanic cavity. CONCLUSION: Topographical relation among the FN and related nerves in the ear region seemed not to be established in the fetal age but after birth depending on growth of the cranial fossa.

The atypical cadherin Celsr1 functions non-cell autonomously to block rostral migration of facial branchiomotor neurons in mice.

The caudal migration of facial branchiomotor (FBM) neurons from rhombomere (r) 4 to r6 in the hindbrain is an excellent model to study neuronal migration mechanisms. Although several Wnt/Planar Cell Polarity (PCP) components are required for FBM neuron migration, only Celsr1, an atypical cadherin, regulates the direction of migration in mice. In Celsr1 mutants, a subset of FBM neurons migrates rostrally instead of caudally. Interestingly, Celsr1 is not expressed in the migrating FBM neurons, but rather in the adjacent floor plate and adjoining ventricular zone. To evaluate the contribution of different expression domains to neuronal migration, we conditionally inactivated Celsr1 in specific cell types. Intriguingly, inactivation of Celsr1 in the ventricular zone of r3-r5, but not in the floor plate, leads to rostral migration of FBM neurons, greatly resembling the migration defect of Celsr1 mutants. Dye fill experiments indicate that the rostrally-migrated FBM neurons in Celsr1 mutants originate from the anterior margin of r4. These data suggest strongly that Celsr1 ensures that FBM neurons migrate caudally by suppressing molecular cues in the rostral hindbrain that can attract FBM neurons.

Shox2 is required for the proper development of the facial motor nucleus and the establishment of the facial nerves.

BACKGROUND: Axons from the visceral motor neurons (vMNs) project from nuclei in the hindbrain to innervate autonomic ganglia and branchial arch-derived muscles. Although much is known about the events that govern specification of somatic motor neurons, the genetic pathways responsible for the development of vMNs are less well characterized. We know that vMNs, like all motor neurons, depend on sonic hedgehog signaling for their generation. Similarly, the paired-like homeobox 2b (Phox2b) gene, which is expressed in both proliferating progenitors and post-mitotic motor neurons, is essential for the development of vMNs. Given that our previous study identified a novel role for the short stature homeobox 2 (Shox2) gene in the hindbrain, and since SHOX2 has been shown to regulate transcription of islet 1 (Isl1), an important regulator of vMN development, we sought to determine whether Shox2 is required for the proper development of the facial motor nucleus. RESULTS: Using a Nestin-Cre driver, we show that elimination of Shox2 throughout the brain results in elevated cell death in the facial motor nucleus at embryonic day 12.5 (E12.5) and E14.5, which correlates with impaired axonal projection properties of vMNs. We also observed changes in the spatial expression of the vMN cell fate factors Isl1 and Phox2b, and concomitant defects in Shh and Ptch1 expression in Shox2 mutants. Furthermore, we demonstrate that elimination of Shox2 results in the loss of dorsomedial and ventromedial subnuclei by postnatal day 0 (P0), which may explain the changes in physical activity and impaired feeding/nursing behavior in Shox2 mutants. CONCLUSIONS: Combined, our data show that Shox2 is required for development of the facial motor nucleus and its associated facial (VII) nerves, and serves as a new molecular tool to probe the genetic programs of this understudied hindbrain region.

Cranial nerve development requires co-ordinated Shh and canonical Wnt signaling.

Cranial nerves govern sensory and motor information exchange between the brain and tissues of the head and neck. The cranial nerves are derived from two specialized populations of cells, cranial neural crest cells and ectodermal placode cells. Defects in either cell type can result in cranial nerve developmental defects. Although several signaling pathways are known to regulate cranial nerve formation our understanding of how intercellular signaling between neural crest cells and placode cells is coordinated during cranial ganglia morphogenesis is poorly understood. Sonic Hedgehog (Shh) signaling is one key pathway that regulates multiple aspects of craniofacial development, but whether it co-ordinates cranial neural crest cell and placodal cell interactions during cranial ganglia formation remains unclear. In this study we examined a new Patched1 (Ptch1) loss-of-function mouse mutant and characterized the role of Ptch1 in regulating Shh signaling during cranial ganglia development. Ptch1(Wig/ Wig) mutants exhibit elevated Shh signaling in concert with disorganization of the trigeminal and facial nerves. Importantly, we discovered that enhanced Shh signaling suppressed canonical Wnt signaling in the cranial nerve region. This critically affected the survival and migration of cranial neural crest cells and the development of placodal cells as well as the integration between neural crest and placodes. Collectively, our findings highlight a novel and critical role for Shh signaling in cranial nerve development via the cross regulation of canonical Wnt signaling.

The morphology and morphometry of the fetal fallopian canal: a microtomographic study.

BACKGROUND: The canal for facial nerve (the fallopian canal, FC) is a bony structure passing through the petrous part of the temporal bone. The anatomy of this demanding and important for oto- and neurosurgeons structure is well described in literature. Among several studies on radiological anatomy of this region, still little papers focus on the developmental measurements in prenatal period. AIM: Assessment of a microtomographic appearance of FC and dimensions based on available landmarks. METHOD: The study was performed on 22 fetal temporal bones aged 16-27 Hbd. Specimens were scanned in micro-CT scanner. Length (FC1, FC2) and width (FC1W, FC2W) of the labyrinthine and tympanic portions of FC, angle of the first curve of FC (A1-2), length of the internal acoustic meatus (IAM), distance from FC to the basal cochlear turn (BCT) and to the lateral semicircular canal (LSC) were measured. RESULTS: The paper discusses problems and a value of micro-CT in neuroanatomical studies. FC was found in 20/22 cases. Average value of all distances measured was: FC1 1.38 ± 0.35 mm; FC2 6.68 ± 1.34 mm; FC1W 1.07 ± 0.1 mm; FC2W 1.25 ± 0.13 mm; A1-2 87.24 ± 4.05°; IAM 4.89 ± 0.60 mm; BCT 0.35 ± 0.05 mm; LSC 0.55 ± 0.05 mm. CONCLUSIONS: Labyrinthine portion starts to ossify between 16th and 18th weeks of gestation and tympanic portion is fully ossified only after 20th week. Labyrinthine and tympanic portion of FC and the IAM elongate with age, whereas the angle of the first curve of FC and the distances to the BCT and the LSC remain stable and present no correlation with age.

Mouse hindbrain ex vivo culture to study facial branchiomotor neuron migration.

Embryonic neurons are born in the ventricular zone of the brain, but subsequently migrate to new destinations to reach appropriate targets. Deciphering the molecular signals that cooperatively guide neuronal migration in the embryonic brain is therefore important to understand how the complex neural networks form which later support postnatal life. Facial branchiomotor (FBM) neurons in the mouse embryo hindbrain migrate from rhombomere (r) 4 caudally to form the paired facial nuclei in the r6-derived region of the hindbrain. Here we provide a detailed protocol for wholemount ex vivo culture of mouse embryo hindbrains suitable to investigate the signaling pathways that regulate FBM migration. In this method, hindbrains of E11.5 mouse embryos are dissected and cultured in an open book preparation on cell culture inserts for 24 hr. During this time, FBM neurons migrate caudally towards r6 and can be exposed to function-blocking antibodies and small molecules in the culture media or heparin beads loaded with recombinant proteins to examine roles for signaling pathways implicated in guiding neuronal migration.

Anastomoses between lower cranial and upper cervical nerves: a comprehensive review with potential significance during skull base and neck operations, part I: trigeminal, facial, and vestibulocochlear nerves.

Descriptions of the anatomy of the neural communications among the cranial nerves and their branches is lacking in the literature. Knowledge of the possible neural interconnections found among these nerves may prove useful to surgeons who operate in these regions to avoid inadvertent traction or transection. We review the literature regarding the anatomy, function, and clinical implications of the complex neural networks formed by interconnections among the lower cranial and upper cervical nerves. A review of germane anatomic and clinical literature was performed. The review is organized in two parts. Part I concerns the anastomoses between the trigeminal, facial, and vestibulocochlear nerves or their branches with any other nerve trunk or branch in the vicinity. Part II concerns the anastomoses among the glossopharyngeal, vagus, accessory and hypoglossal nerves and their branches or among these nerves and the first four cervical spinal nerves; the contribution of the autonomic nervous system to these neural plexuses is also briefly reviewed. Part I is presented in this article. An extensive anastomotic network exists among the lower cranial nerves. Knowledge of such neural intercommunications is important in diagnosing and treating patients with pathology of the skull base.

The fallopian canal: a comprehensive review and proposal of a new classification.

INTRODUCTION: The facial nerve follows a complex course through the skull base. Understanding its anatomy is crucial during standard skull base approaches and resection of certain skull base tumors closely related to the nerve, especially, tumors at the cerebellopontine angle. METHODS: Herein, we review the fallopian canal and its implications in surgical approaches to the skull base. Furthermore, we suggest a new classification. CONCLUSIONS: Based on the anatomy and literature, we propose that the meatal segment of the facial nerve be included as a component of the fallopian canal. A comprehensive knowledge of the course of the facial nerve is important to those who treat patients with pathology of or near this cranial nerve.

An anatomical study on the facial nerve trunk in fetus cadavers.

BACKGROUND/AIM: Facial nerve paralysis is the most worrying parotid surgery complication. Little attention has been paid to the facial nerve trunk, especially in children. Pathological variations, tumors, and anatomic variations of the facial nerve may cause parotid and facial nerve surgery difficulties. This study describes the facial nerve trunk. MATERIALS AND METHODS: We measured the facial nerve trunk from 8 female and 8 male fetus cadavers aged 21.0 to 35.5 gestational weeks. The locations and positions of the trunks were described. The length of the facial nerve trunk (K) was measured and bifurcation and trifurcation of the trunk was examined. Values were analyzed separately for right and left sides and for male and female fetuses. RESULTS: The most common facial nerve trunk type was bifurcation (81.25%), followed by trifurcation (18.75%). K was 11.59 + 2.80 mm in the total fetuses. There was no significant difference between K measurements. CONCLUSION: Facial nerve injury during parotid surgery is a main cause of pediatric facial paralysis. There are few previous descriptions of the facial trunk in children. K must be accurately known in any surgical procedure planned for the area. The main furcation of the facial nerve should also receive special attention.

Morphology of the facial motor nuclei in a rat model of autism during early development.

The development of facial nuclei in animal models of disease is poorly understood, but autism is sometimes associated with facial palsy. In the present study, to investigate migration of facial neurons and initial facial nucleus formation in an animal model of autism, rat embryos were treated with valproic acid (VPA) in utero at embryonic day (E) 9.5 and their facial nuclei were analyzed by in situ hybridization at E13.5, E14.5 and E15.5. Signals for Tbx20, which is expressed in early motor neurons, appeared near the floor plate at the level of the vestibular ganglion and extended caudolaterally, where they became ovoid in shape. This pattern of development was similar between control and VPA-exposed embryos. However, measurements of the migratory pathway and the size of the facial nuclei revealed that exposure to VPA hindered the caudal migration of neurons to the facial nuclei. Signals for cadherin 8, which is expressed in mature facial nuclei, revealed that exposure to VPA caused a significant reduction in the size of the facial nuclei. Our findings provide the first quantitative description of tangential migration and nucleus formation in the developing hindbrain in a rat model of autism.

Planar cell polarity and the developmental control of cell behavior in vertebrate embryos.

Planar cell polarity (PCP), the orientation and alignment of cells within a sheet, is a ubiquitous cellular property that is commonly governed by the conserved set of proteins encoded by so-called PCP genes. The PCP proteins coordinate developmental signaling cues with individual cell behaviors in a wildly diverse array of tissues. Consequently, disruptions of PCP protein functions are linked to defects in axis elongation, inner ear patterning, neural tube closure, directed ciliary beating, and left/right patterning, to name only a few. This review attempts to synthesize what is known about PCP and the PCP proteins in vertebrate animals, with a particular focus on the mechanisms by which individual cells respond to PCP cues in order to execute specific cellular behaviors.

A different type of branchial fistula as part of a branchiootorenal syndrome.

We describe an extremely rare case of a complete fistula, a combination of the first 2 branchial arches as a component of branchiootorenal syndrome. A 13-year-old girl presented with the complaint of intermittent drainage from bilateral preauricular and right lower neck external openings. A contrast fistulogram revealed a complete fistula. Diagnostic features and surgical techniques are discussed in detail.

Marginal mandibular branch of the facial nerve in human fetuses.

OBJECTIVE: To observe the course of the marginal mandibular branch (MMB) and its relation to the inferior border of the mandible and facial vessels. METHODS: This study was conducted in the Department of Anatomy, Gulhane Military Medical Academy, Etlik, Ankara, Turkey from February 2009 to April 2010. The 44 hemi-face specimens of 22 fetuses were selected for this study, and dissected under a stereomicroscope. The MMB relationship was evaluated between adjacent structures (like vessels and muscles) and the lower border of the mandible. RESULTS: We found a number of one to 4 branches of the MMB. The MMB ran laterally to the facial vein in 42 (95.5%) of the 44 specimens. All the branches of the MMB ran laterally to the facial artery in 30 (68.2%) of the 44 specimens. In 2 specimens, it ran medially to the facial artery. In 10 specimens, the facial artery ran between 2 branches of the MMB. In 2 specimens, the 2 branches of the MMB ran between facial artery and vein. There were no statistical differences between the left and right sides, and in both genders. CONCLUSION: The inferior border of the mandible may be an important landmark to avoid injury to the MMB of the facial nerve. It is for this reason, that surgeons who are willing to operate on this area should have a true knowledge and accurate judgement regarding the anatomy of this branch.

Differentiation of the facio-vestibulocochlear ganglionic complex in human embryos of developmental stages 13-15.

A study was made on 18 embryos of developmental stages 13-15 (5(th) week). Serial sections made in horizontal, frontal, and sagittal planes were stained with routine histological methods and some of them were treated with silver. In embryos of stage 13, the otic vesicle is at the rhombomere 5, and close to the vesicle is the facial-vestibulocochlear ganglionic complex in which the geniculate, vestibular, and cochlear ganglion may be discerned. These ganglia are well demarcated in embryos of stage 14. In the last investigated stage (15(th)) the nerve fibres of the ganglia reach the common afferent tract.