Dorsal Body Wall Research Articles

A Tale of Three Oceans—Taxonomy of the Holothuria (Thymiosycia) arenicola Semper, 1868 complex (Echinodermata: Holoturoidea: Holothuriidae)

The ubiquitous sea cucumber Holothuria (Thymiosycia) arenicola Semper, 1868, externally characterized by a double row of dark blotches of various sizes on its dorsal body wall and a cryptic behaviour, is generally assumed to have a wide tropical distribution, although it has not been reported from the Eastern Atlantic. Careful morphological examination, with emphasis on the ossicle assemblage, of type and non-type H. arenicola specimens sampled in the Indian, Pacific and Atlantic Ocean, its subjective synonyms and species with a similar colouration and habit, revealed that H. arenicola is often confused with other species. This paper formally separates the different species in the H. arenicola complex, one of them being a species new to science: Holothuria (Thymiosycia) kerriensis sp. nov. Additionally, we describe two other species that are often confused with H. arenicola: Holothuria (Lessonothuria) gracilis Semper, 1868 and H. (Thymiosycia) strigosa Selenka, 1867. The H. arenicola complex per se is keyed-out, with the ossicle assemblage of the musculature being recognised as an important, previously largely neglected, guide. This contribution highlights the importance of building and curating well-maintaned natural history collections to understand biodiversity through time and space.

Alternative reproductive tactics in goby fishes of the Caspian Sea.

Here we report on the reproductive morphology and histology of three Gobiidae species (the Caspian monkey goby, Neogobius pallasi; the Caspian goby, Neogobius caspius; and the round goby, Neogobius melanostomus) from the Iranian coastline of the Caspian Sea. Based on ageing, reproductive histology, and internal and external morphological measures, it appears that all three of these goby species have two types of reproductive males, a large courting, territorial, male type and a small cuckolding parasitic male type, a phenomenon known as alternative reproductive tactics (ART). Although ARTs have been reported previously for one of these species, the round goby, all reports stem from its invasive range; ARTs have never been reported before in any fish species in the Caspian Sea. In all three goby species there was a large, older male type, with a wide head, dark body colouration, and a large investment in accessory glands (AG), an organ important for female attraction and parental care. But there was also a small, light, younger male type, with a narrow head, longer urogenital papilla, and little investment in AGs. The Caspian goby were the largest of the three species, and in this species the smaller, lighter, presumably cuckolding male morph was quite rare (only about 5% of the reproductive male population). In contrast, many of the round goby and monkey goby males were the small, lighter parasitic type, making up nearly half the population of reproductive males (48% and 40%, respectively). Round goby and Caspian goby males had a prominent mesorchial gland, a fibrous sheath of pheromone-releasing connective tissue that attaches the testes to the dorsal body wall, but all the monkey goby specimens examined lacked this structure. Although ARTs are well documented across fish species and appear to be particularly common in gobies, our study provides the first evidence for ARTs in goby fishes from the Caspian Sea.

Muscles of the sex organs of Panagrolaimus detritophagus (Chromodorea: Rhabditida: Panagrolaimidae)

Summary The sex organs are important for nematode systematics, but the associated muscles are rarely used as phylogenetic characters. This research aimed to study the musculature of Panagrolaimus detritophagus, using confocal microscopy. The ring-shaped anal sphincter is pierced by a biconical X-structure and connected by two pairs of processes to the subventral stomato-intestinal muscles and dorsal body wall. The female has two pairs of vaginal dilators that are connected to the proximally invaginated vaginal sphincter and subventral body wall. The anal depressor is a pair of dorsoventral muscles. The male has 7-8 pairs of caudal diagonal muscles located beneath the ventral body wall muscles, followed by five pairs of postcloacal oblique muscles. The paired posterior longitudinal muscles are connected to the cloacal opening and tail tip. The paired anterior retractors of the spicule connect the spicule capitula to the lateral body wall; a pair of spicule-gubernacular protractors runs from spicule capitula to the anterior part of gubernaculum, and paired ventral protractors run from spicule capitula to anterior cloacal lip. Two pairs of gubernaculum erectors are attached to the mid-gubernaculum, and the unpaired gubernaculum protractor extends ventrally to attach to the body wall at the posterior cloacal lip. The sex muscle pattern is of the Rhabditidae-Cephalobidae type with a 15-character code for phylogenetic reconstructions: 63313-22234-42243.

Rehabilitation of two deep-sea holothurian species in genus Pannychia from the northwest Pacific Ocean

Genus Pannychia Théel, 1882 is one of the dominant sea cucumber genus in the bathyal zone of the North Pacific Ocean. Previously seven species/subspecies were described in Pannychia and another closest genus Laetmophasma Ludwig, 1894 from all over the Pacific Ocean, but all of them were synonymized into Pannychia moseleyi Théel, 1882, which is currently single valid species in the Pacific Ocean. In this study, we rehabilitate Pannychia henrici Ludwig, 1894 and Pannychia virgulifera Ohshima, 1915 as separate species from the northwest Pacific Ocean, which were originally established as geographical variation/subspecies of P. moseleyi. This study includes molecular phylogenetic analysis based on specimens collected from broad part of the northwest Pacific Ocean, and morphological comparison including re-examination of both subspecies type specimens. Genetically these two northwest Pacific taxa and P. moseleyi are clearly distinguished from each other, which corresponded to different characteristics of dorsal papillae arrangement, the body coloration, and the ossicle density in dorsal body wall. As a result of rehabilitation of P. henrici and P. virgulifera, the genus Pannychia was reorganized to 4 valid species, but P. moseleyi still include large morphological variations, and it is necessary to a further taxonomic revision. Additionally, P. henrici and P. virgulifera particularly represent an example of importance of body coloration in taxonomy of the deep-sea Holothuroidea.

Limb Morphology in the Macaroni Penguin (Eudyptes chrysolophus) Exhibits Adaptations for Both Sub‐aqueous Flying and Locomotion on Land

Requiring both wing‐propelled swimming and rugged overland locomotion, Macaroni penguins possess highly specialized morphology in both limbs. We dissected both the wing and hindlimb of one female and one male macaroni penguin. The distal wing exhibits very reduced musculature, and only retains very small brachialis and dorsal ulno‐metacarpal muscles. The elbow and metacarpal joints exhibit significantly decreased mobility compared to other birds. Proximal extrinsic wing muscles extend long tendons into the distal wing to control the dorso‐ventrally flattened flipper. Two sesamoid bones at the elbow joint provide a main attachment point for the proximal musculature, and probably contribute to the stiffening of the wing during underwater propulsion. The enlarged and extended sternum houses an extensive pectoralis muscle, responsible for the downstroke, which comprises nearly the entire ventral body wall. Supracoracoideus, found anatomically deep to pectoralis major and responsible for the upstroke, weighed about half of the pectoralis muscle, unlike most birds, where supracoracoideus weighs only about one‐fifth. An enlarged supracoracoideus increases the strength of the upstroke against viscous water. The tendons of latissimus dorsi cranialis and caudalis pass through a fibrous trochlea extending from the triceps complex to attach to the humerus, and possibly increases wing forces when moving the wing caudally. Unlike the sparse wing musculature, extensive leg musculature comprises about half of the dorsal body wall. The sartorius muscle, the most cranial hindlimb muscle, lies cranial to the caudal edge of the scapula, and cranial to the caudal margin of the sternum. Despite this, penguins exhibit restricted mobility during locomotion on land including apparent reduced range of motion in the knee joint, which contributes to their signature waddle. In addition, both Macaroni penguin specimens possess a unique muscle we have named the adductor tibialis. This muscle extends from the tibia of one hindlimb, across the midline where it slightly connects to the sternum, and attaches to the tibia of the contralateral limb, effectively tying the hindlimbs together. This permanent adduction probably helps create a streamlined figure while swimming to create faster speeds. In contrast to the knee, the penguin can greatly extend and flex the tarsus during locomotion. The considerable extensor system in the tarsus helps the penguin cross different terrains while walking, as well as give them the ability to jump.

Tergal and pleural wing-related tissues in the German cockroach and their implication to the evolutionary origin of insect wings.

The acquisition of wings has facilitated the massive evolutionary success of pterygotes (winged insects), which now make up nearly three-quarters of described metazoans. However, our understanding of how this crucial structure has evolved remains quite elusive. Historically, two ideas have dominated in the wing origin debate, one placing the origin in the dorsal body wall (tergum) and the other in the lateral pleural plates and the branching structures associated with these plates. Through studying wing-related tissues in the wingless segments (such as wing serial homologs) of the beetle, Tribolium castaneum, we obtained several crucial pieces of evidence that support a third idea, the dual origin hypothesis, which proposes that wings evolved from a combination of tergal and pleural tissues. Here, we extended our analysis outside of the beetle lineage and sought to identify wing-related tissues from the wingless segments of the cockroach, Blattella germanica. Through detailed functional and expression analyses for a critical wing gene, vestigial (vg), along with re-evaluating the homeotic transformation of a wingless segment induced by an improved RNA interference protocol, we demonstrate that B. germanica possesses two distinct tissues in their wingless segments, one with tergal and one with pleural nature, that might be evolutionarily related to wings. This outcome appears to parallel the reports from other insects, which may further support a dual origin of insect wings. However, we also identified a vg-independent tissue that contributes to wing formation upon homeotic transformation, as well as vg-dependent tissues that do not appear to participate in wing formation, in B. germanica, indicating a more complex evolutionary history of the tissues that contributed to the emergence of insect wings.

Synergy between mechanical injury and toxins triggers the urticating system of marine fireworms

Marine fireworms (Annelida, Amphinomidae) are notorious for their stinging dorsal bristles (notochaetae). In the large-size species Hermodice carunculata, characterized by invasive potential and great predatory ability, notochaetae deter consumers and damage prey. The origin of fireworm defensive and offensive capacities, the mechanism of action of the stinging chaetae, and whether other chemical defenses occur are still uncertain. In the present study, we tested if the urticating system of fireworms is the result of a synergy between mechanical injury, due to notochaetae penetration, and the release of toxins vehiculated. To determine whether and where chemical or structural deterrents were present, different body parts of H. carunculata involved in inter-specific interactions were assayed (i.e. dorsal body wall, gills, dorsal and ventral parapodia). Feeding bioassays were performed to assess palatability against a fish (generalist consumer) and deterrent action on contact with two sea anemones (fireworm prey). In all the assays, only the offers bearing the dorsal chaetae (notochaetae) strongly deterred consumers and induced paralysis in prey. The notochaetae treated with organic solvents lost their deterrence against fish. Besides, the notopodia were palatable to fish and anemones after the removal of the notochaetae. These findings support a powerful synergy between chemical deterrence and physical structure. To date, the only acute inflammation inducer isolated from an amphinomid is “complanine”, a trimethylammonium compound. High-resolution LC-MS/MS and preliminary NMR analyses suggested the presence of complanine-related compounds in the notochaetae. The present results suggest that the release of compounds and their strong deterrent effect should be mediated by mechanical injury. The sharp, fragile and hollow structure of the notochaetae combined with inflammatory substances could support the success of fireworms in marine benthic environments. Further research is required to ascertain the nature and localization of these chemicals in H. carunculata, broadening knowledge on the chemical ecology of amphinomids.

<i>Elpidia soyoae</i>, a New Species of Deep-sea Holothurian (Echinodermata) from the Japan Trench Area

A new species of holothurian, Elpidia soyoae sp. nov., is described from the Japan Trench area, at depths of 3570–4145 m. It is distinguished from its congeners in having: four or five paired papillae and unpaired papillae present along entire dorsal radii (four to seven papillae on each radius), with wide separation between second and third paired papillae; maximum length of Elpidia-type ossicles in dorsal body wall exceeds 1000 µm; axis diameter of dorsal Elpidia-type ossicles less than 40 µm; tentacle Elpidia-type ossicles with arched axis and shortened, occasionally completely reduced arms and apophyses. Purple pigmentation spots composed of small purple particles on both dorsal and ventral body wall. This is the second species of Elpidia Théel, 1876 from Japanese abyssal depths. The diagnosis of the genus Elpidia is modified to distinguish from all other elpidiid genera. A morphological comparison of the species of the slender axis group of genus Elpidia, and partial mitochondrial cytochrome c oxidase subunit I (COI) gene sequences of type specimens are provided.

Nociceptive neurons respond to multimodal stimuli in Manduca sexta.

The caterpillar Manduca sexta produces a highly stereotyped strike behavior in response to noxious thermal or mechanical stimuli to the abdomen. This rapid movement is targeted to the site of the stimulus, but the identity of the nociceptive sensory neurons are currently unknown. It is also not known whether both mechanical and thermal stimuli are detected by the same neurons. Here, we show that the likelihood of a strike increases with the strength of the stimulus and that activity in nerves innervating the body wall increases rapidly in response to noxious stimuli. Mechanical and thermal stimuli to the dorsal body wall activate the same sensory unit, suggesting it represents a multimodal neuron. This is further supported by the effects of rapidly repeated thermal or mechanical stimuli, which cause a depression of neuronal responsiveness that is generalized across modalities. Mapping the receptive fields of neurons responding to strong thermal stimuli indicates that these multimodal, nociceptive units are produced by class γ multidendritic neurons in the body wall.

Co-option of wing-patterning genes underlies the evolution of the treehopper helmet.

Understanding the origin of novelty is a key question in evolutionary developmental biology. In arthropods, the body wall has served as a repeated source of morphological novelty. In treehoppers, an ancestrally flat part of the dorsal body wall (the pronotum) was transformed into a three-dimensional structure (the helmet), which was subsequently moulded by natural selection into diverse shapes. Here, we test three hypotheses for the developmental origin of the helmet by comparing body-region transcriptomes in a treehopper and a leafhopper that retains more ancestral morphology. In leafhoppers, pronotal gene expression is most similar to that of its serial homologue, the mesonotum. By contrast, in treehoppers, helmet gene expression is most similar to that of wings, supporting the wing-patterning network co-option hypothesis for the origin of the helmet. These results suggest that serial homologues may diverge evolutionarily through replacement of, rather than tinkering with, their ancestrally shared patterning network.

Holothuria (Mertensiothuria) viridiaurantia sp. nov. (Holothuriida, Holothuriidae), a new sea cucumber from the Eastern Pacific Ocean revealed by morphology and DNA barcoding.

Holothuria (Mertensiothuria) viridiaurantiasp. nov. is described based on specimens from rocky reefs of northern Chocó in the Colombian Pacific Ocean; however, it also occurs along the Eastern Pacific Ocean from Mexico and Panama. Although specimens from Mexico and Panama were previously identified as Holothuria (Mertensiothuria) hilla Lesson, 1830 the new species is easily distinguished morphologically and via mtDNA. In terms of morphology, the species can be identified by its olive-green background and white-orange papillae and tentacles, larger tentacles with deep indentations and also by larger buttons on the dorsal and ventral body wall, papillae and tube feet; large, thick and rough tentacle rods, and the absence of ossicles in the longitudinal muscles. The new species is included in the subgenus Mertensiothuria considering molecular evidence.

First report of Paelopatides (Synallactida, Synallactidae) for the SW Atlantic, with description of a new species from the deep-sea off Argentina

The present study describes a new species, Paelopatides shumel n. sp., from Argentinian deep-sea waters. This is the first report of the order Synallactida for Argentina, the fifth for southern hemisphere and the deepest report for the Argentinian holothuroid fauna (almost 3000 m). The species has up to 330 mm length, light brown color and around 19 pairs of dorsal appendages. The ventral side has one ventral ambulacra, with two rows of tube feet. Ossicles are present in dorsal appendages, tube feet, tentacles and body wall near the anus, and are mainly crosses, tables and rods-shaped. The depth at which P. shumel n. sp. has been found is occupied by the North Atlantic Deep Water current. This association with North Atlantic waters could be related with the occurrence of members of Paelopatides in the North Atlantic.

Detailed analysis of the prothoracic tissues transforming into wings in the Cephalothorax mutants of the Tribolium beetle

Despite the immense importance of the wing in the evolution and successful radiation of the insect lineages, the origin of this critical structure remains a hotly-debated mystery. Two possible tissues have been identified as an evolutionary origin of wings; the lateral expansion of the dorsal body wall (tergal edge) and structures related to an ancestral proximal leg segment (pleural tissues). Through studying wing-related tissues in the red flour beetle, Tribolium castaneum, we have previously presented evidence in support of a dual origin of insect wings, a third hypothesis proposing that wings evolved from a combination of both tergal and pleural tissues. One key finding came from the investigation of a Cephalothorax (Cx) mutant, in which the ectopic wing characteristic to this mutant was found to be formed from both tergal and pleural contributions. However, the degree of contribution of the two tissues to the wing remains elusive. Here, we took advantage of multiple Cx alleles available in Tribolium, and produced a variety of degrees and types of ectopic wing tissues in their prothoracic segments. Through detailed phenotypic scoring of the Cx phenotypes based on nine categories of mutant traits, along with comprehensive morphological analysis of the ectopic wing tissues, we found that (i) ectopic wing tissues can be formed at various locations in the prothorax, even internally, (ii) the lateral external ectopic wing tissues have tergal origin, while the internal and posterior external ectopic wing tissues appear to be of pleural origin, and (iii) the ectopic wing tissues of both tergal and pleural origin are capable of transforming into wing surface tissues. Collectively, these outcomes suggest that the evolutionary contribution of each tissue to a complete wing may be more complex than the simple binary view that is typically invoked by a dual origin model (i.e. the wing blade from the tergal contribution + musculature and articulation from the pleural contribution).

Abrogation of TGF-beta signalling in TAGLN expressing cells recapitulates Pentalogy of Cantrell in the mouse

Pentalogy of Cantrell (PC) is a rare multi-organ congenital anomaly that impedes ventral body wall closure and results in diaphragmatic hernia, intra- and pericardial defects. The underlying cellular and molecular changes that lead to these severe developmental defects have remained unknown largely due to the lack of representative animal models. Here we provide in depth characterization of a mouse model with conditional ablation of TGFβRII in Transgelin (Tagln) expressing cells. We show that Tagln is transiently expressed in a variety of cells that participate in the embryonic development and patterning of ventral structures. Genetic ablation of TGFβRII in these cells leads to ventral midline closure defect, diaphragmatic hernia, dilated cardiac outflow tract and aberrant cardiac septation, providing a reliable model to study the morphological changes leading to PC. We show that myogenisis in the diaphragm is independent of TGFβ and the diaphragmatic hernia arises from fibroblast-specific migration defect. In the dorsal body wall Tagln expression is initiated after the closure process, revealing a remarkable difference between ventral and dorsal body walls development. Our study demonstrates the use of micro-CT scanning to obtain a 3-dimensional high-resolution overview of embryonic anomalies and provides the first mechanistic insight into the development of PC.

A taxonomic revision of the genus Apostichopus (Holothuroidea: Stichopodidae) from Japan.

Complete redescriptions of sea cucumbers in the genus Apostichopus Liao, 1980 are provided using the type specimens and specimens deposited in the National Museum of Nature and Science, Tsukuba, Japan. The genus consists of A. armatus (Selenka, 1867) and A. japonicus (Selenka, 1867), which can be distinguished by some spicules in the dorsal body wall; the rim of reduced table spicules in A. armatus is spinous, while that in A. japonicus is smooth. Spicules from the tentacles, papillae, tube feet, and cloaca are similar for both species.

Regulation of dorso-ventral polarity by the nerve cord during annelid regeneration: A review of experimental evidence.

An important goal for understanding regeneration is determining how polarity is conferred to the regenerate. Here we review findings in two groups of polychaete annelids that implicate the ventral nerve cord in assigning dorso‐ventral polarity, and specifically ventral identity, to the regenerate. In nereids, surgical manipulations indicate that parapodia develop where dorsal and ventral body wall territories contact. Without a nerve cord at the wound site, the regenerate differentiates no evident polarity (with no parapodia) and only dorsal identity, while with two nerve cords the regenerate develops a twinned dorso‐ventral axis (with four parapodia per segment instead of the normal two). In sabellids, a striking natural dorso‐ventral inversion in parapodial morphology occurs along the body axis and this inversion is morphologically correlated with the position of the nerve cord. Parapodial inversion also occurs in segments in which the nerve cord has been removed, even without any segment amputation. Together, these data strongly support a role for the nerve cord in annelid dorso‐ventral pattern regulation, with the nerve cord conferring ventral identity.

Diaphragmatic hernia in an adult cadaver: a case report

Abstract Introduction: The diaphragm is a musculofibrous structure that separates the thoracic cavity from the abdominal cavity. Although it is a continuous sheet, developmental^ it is derived from four different sources: the septum transversum, pleuroperitoneal membranes, lateral and dorsal body wall and the mesentery of oesophagus. Methodology: During routine dissection for undergraduate students in the department of Anatomy, Kasturba Medical College, Manipal a rare variation was encountered in a 65 year old female cadaver. Results: We observed a large defect in the left anterolateral aspect of the diaphragm with associated left pulmonary hypoplasia. The muscular contribution to the diaphragm from the left lateral and dorsal body wall was absent leading to the herniation of abdominal contents into the left thoracic cavity which included the stomach, intestinal loops, left colic flexure and the spleen. Conclusion: Diaphragmatic hernias presenting in adult life are rare and most commonly associated with a history of trauma. Congenital diaphragmatic hernia may remain asymptomatic as in the present case which is extremely rare and could be a chance finding during a routine chest x-ray. Knowledge of this anatomic defect in the diaphragm presenting in adult life would help prevent further complications leading to gastrointestinal or pulmonary distress.

Regulation of UNC-130/FOXD-mediated mesodermal patterning in C. elegans

Spatial polarity cues in animals are used repeatedly during development for many processes, including cell fate determination, cell migration, and axon guidance. In Caenorhabditis elegans, the body wall muscle extends the length of the animal in four distinct quadrants and generates an UNC-129/TGF-β-related signal that is much higher in the dorsal two muscle quadrants compared to their ventral counterparts. This pattern of unc-129 expression requires the activity of the proposed transcriptional repressor UNC-130/FOXD whose body wall muscle activity is restricted to the ventral two body wall muscle quadrants. To understand how these dorsal-ventral differences in UNC-130 activity are established and maintained, we have analyzed the regulation of unc-130 expression and the distribution of UNC-130 protein. We have identified widespread, cis-acting elements in the unc-130 promoter that function to positively regulate ventral body wall muscle expression and negatively regulate dorsal body wall muscle expression. We have defined the temporal distribution of UNC-130 protein in body wall muscle cells during embryogenesis, demonstrated that this pattern is required to establish the dorsal-ventral polarity of UNC-129/TGF-β, and shown that UNC-130 is not required post-embryonically to maintain the asymmetry of body wall muscle unc-129 expression. Finally, we have tested the impact of the depletion of a variety of transcription factors, repressors, and signaling molecules to identify additional regulators of body wall muscle UNC-130 polarity. Our results confirm and extend earlier studies to clarify the mechanisms by which UNC-130 is controlled and affects the pattern of unc-129 expression in body wall muscle. These results further our understanding of the transcriptional logic behind the generation of polarity cues involving this poorly understood subclass of Forkhead factors.

Development of the ventral body wall in the human embryo.

Migratory failure of somitic cells is the commonest explanation for ventral body wall defects. However, the embryo increases ~ 25-fold in volume in the period that the ventral body wall forms, so that differential growth may, instead, account for the observed changes in topography. Human embryos between 4 and 10 weeks of development were studied, using amira reconstruction and cinema 4D remodeling software for visualization. Initially, vertebrae and ribs had formed medially, and primordia of sternum and hypaxial flank muscle primordium laterally in the body wall at Carnegie Stage (CS)15 (5.5 weeks). The next week, ribs and muscle primordium expanded in ventrolateral direction only. At CS18 (6.5 weeks), separate intercostal and abdominal wall muscles differentiated, and ribs, sterna, and muscles began to expand ventromedially and caudally, with the bilateral sternal bars fusing in the midline after CS20 (7 weeks) and the rectus muscles reaching the umbilicus at CS23 (8 weeks). The near-constant absolute distance between both rectus muscles and approximately fivefold decline of this distance relative to body circumference between 6 and 10 weeks identified dorsoventral growth in the dorsal body wall as determinant of the 'closure' of the ventral body wall. Concomitant with the straightening of the embryonic body axis after the 6th week, the abdominal muscles expanded ventrally and caudally to form the infraumbilical body wall. Our data, therefore, show that the ventral body wall is formed by differential dorsoventral growth in the dorsal part of the body.

Exome Sequencing of Bilateral Testicular Germ Cell Tumors Suggests Independent Development Lineages

Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypothesized to arise during embryogenesis from developmentally arrested primordial germ cells (PGCs) or gonocytes. In early embryonal life, the PGCs migrate from the yolk sac to the dorsal body wall where the cell population separates before colonizing the genital ridges. However, whether the malignant transformation takes place before or after this separation is controversial. We have explored the somatic exome-wide mutational spectra of bilateral TGCT to provide novel insight into the in utero critical time frame of malignant transformation and TGCT pathogenesis. Exome sequencing was performed in five patients with bilateral TGCT (eight tumors), of these three patients in whom both tumors were available (six tumors) and two patients each with only one available tumor (two tumors). Selected loci were explored by Sanger sequencing in 71 patients with bilateral TGCT. From the exome-wide mutational spectra, no identical mutations in any of the three bilateral tumor pairs were identified. Exome sequencing of all eight tumors revealed 87 somatic non-synonymous mutations (median 10 per tumor; range 5-21), some in already known cancer genes such as CIITA, NEB, platelet-derived growth factor receptor α (PDGFRA), and WHSC1. SUPT6H was found recurrently mutated in two tumors. We suggest independent development lineages of bilateral TGCT. Thus, malignant transformation into intratubular germ cell neoplasia is likely to occur after the migration of PGCs. We reveal possible drivers of TGCT pathogenesis, such as mutated PDGFRA, potentially with therapeutic implications for TGCT patients.