Distinct regulatory networks control toxin gene expression in elapid and viperid snakes.

BACKGROUND: Venom systems are ideal models to study genetic regulatory mechanisms that underpin evolutionary novelty. Snake venom glands are thought to share a common origin, but there are major distinctions between venom toxins from the medically significant snake families Elapidae and Viperidae, and toxin gene regulatory investigations in elapid snakes have been limited. Here, we used high-throughput RNA-sequencing to profile gene expression and microRNAs between active (milked) and resting (unmilked) venom glands in an elapid (Eastern Brown Snake, Pseudonaja textilis), in addition to comparative genomics, to identify cis- and trans-acting regulation of venom production in an elapid in comparison to viperids (Crotalus viridis and C. tigris). RESULTS: Although there is conservation in high-level mechanistic pathways regulating venom production (unfolded protein response, Notch signaling and cholesterol homeostasis), there are differences in the regulation of histone methylation enzymes, transcription factors, and microRNAs in venom glands from these two snake families. Histone methyltransferases and transcription factor (TF) specificity protein 1 (Sp1) were highly upregulated in the milked elapid venom gland in comparison to the viperids, whereas nuclear factor I (NFI) TFs were upregulated after viperid venom milking. Sp1 and NFI cis-regulatory elements were common to toxin gene promoter regions, but many unique elements were also present between elapid and viperid toxins. The presence of Sp1 binding sites across multiple elapid toxin gene promoter regions that have been experimentally determined to regulate expression, in addition to upregulation of Sp1 after venom milking, suggests this transcription factor is involved in elapid toxin expression. microRNA profiles were distinctive between milked and unmilked venom glands for both snake families, and microRNAs were predicted to target a diversity of toxin transcripts in the elapid P. textilis venom gland, but only snake venom metalloproteinase transcripts in the viperid C. viridis venom gland. These results suggest differences in toxin gene posttranscriptional regulation between the elapid P. textilis and viperid C. viridis. CONCLUSIONS: Our comparative transcriptomic and genomic analyses between toxin genes and isoforms in elapid and viperid snakes suggests independent toxin regulation between these two snake families, demonstrating multiple different regulatory mechanisms underpin a venomous phenotype.

Comparative morphology of oral glands in snakes of the family Homalopsidae reveals substantial variation and additional independent origins of salt glands within Serpentes.

Using diffusible iodine-based contrast-enhanced computed tomography (diceCT), we examined the morphology of the oral glands of 12 species of the family Homalopsidae. Snakes of this family exhibit substantial interspecific morphological variation in their oral glands. Particular variables are the venom glands, ranging from large (e.g., Subsessor bocourti) to small (e.g., Erpeton tentaculatum). The supra- and infralabial glands are more uniform in morphology, being the second most developed in almost all the sampled species. Premaxillary glands distinct from the supralabial glands were observed in five species (Myron richardsonii, Bitia hydroides, Cantoria violacea, Fordonia leucobalia, and Gerarda prevostiana), in addition to Cerberus rynchops, the only species in which this condition was previously documented associated with the excretion of salt. In the three species of the saltwater group of homalopsids (C. violacea, F. leucobalia, and G. prevostiana), the premaxillary glands also extend posteriorly, occupying a large area above the supralabial gland, a condition not observed in any other species of snake studied thus far. Character evolution analyses indicate that premaxillary glands differentiated from the supralabial gland and evolved independently three or four times in the family, always in lineages that invaded marine habitats. Our results suggest that the differentiated premaxillary glands are likely salt glands, as is the case in C. rynchops. If corroborated, this increases to six or seven the number of independent evolutionary origins of salt glands in snakes that have undergone an evolutionary transition to marine life.

Comparing morphological and secretory aspects of cephalic glands among the New World coral snakes brings novel insights on their biological roles.

Oral and other cephalic glands have been surveyed by several studies with distinct purposes. Despite the wide diversity and medical relevance of the New World coral snakes, studies focusing on understanding the biological roles of the glands within this group are still scarce. Specifically, the venom glands of some coral snakes were previously investigated but all other cephalic glands remain uncharacterized. In this sense, performing morphological and molecular analysis of these glands may help better understand their biological role. Here, we studied the morphology of the venom, infralabial, rictal, and harderian glands of thirteen species of Micrurus and Micruroides euryxanthus. We also performed a molecular characterization of these glands from selected species of Micrurus using transcriptomic and proteomic approaches. We described substantial morphological variation in the cephalic glands of New World coral snakes and structural evidence for protein-secreting cells in the inferior rictal glands. Our molecular analysis revealed that the venom glands, as expected, are majorly devoted to toxin production, however, the infralabial and inferior rictal glands also expressed some toxin genes at low to medium levels, despite the marked morphological differences. On the other hand, the harderian glands were dominated by the expression of lipocalins, but do not produce toxins. Our integrative analysis, including the prediction of biological processes and pathways, helped decipher some important traits of cephalic glands and better understand their biology.

Comparing morphological and secretory aspects of cephalic glands among the New World coral snakes brings novel insights on their biological roles

Oral and other cephalic glands have been surveyed by several studies with distinct purposes. Despite the wide diversity and medical relevance of the New World coral snakes, studies focusing on understanding the biological roles of the glands within this group are still scarce. Specifically, the venom glands of some coral snakes were previously investigated but all other cephalic glands remain uncharacterized. In this sense, performing morphological and molecular analysis of these glands may help better understand their biological role. Here, we studied the morphology of the venom, infralabial, rictal, and harderian glands of thirteen species of Micrurus and Micruroides euryxanthus. We also performed a molecular characterization of these glands from selected species of Micrurus using transcriptomic and proteomic approaches. We described substantial morphological variation in the cephalic glands of New World coral snakes and structural evidence for protein-secreting cells in the inferior rictal glands. Our molecular analysis revealed that the venom glands, as expected, are majorly devoted to toxin production, however, the infralabial and inferior rictal glands also expressed some toxin genes at low to medium levels, despite the marked morphological differences. On the other hand, the harderian glands were dominated by the expression of lipocalins, but do not produce toxins. Our integrative analysis, including the prediction of biological processes and pathways, helped decipher some important traits of cephalic glands and better understand their biology.

Phylogenetic and morphological evidence reveals the association between diet and the evolution of the venom delivery system in Neotropical goo-eating snakes

Advanced endoglyptodont snakes share a complex but homologous venom delivery system associated with the upperjaw and its dentition. Recently, a remarkable novel lower jaw venom delivery system was described for the Neotropicaldipsadine radiation of goo-eating snakes. While most dipsadines are opistoglyphous and exhibit large, mainly serousvenom glands associated with the upper jaw and supralabial glands, goo-eating dipsadine snakes are aglyphous and lackserous upper labial venom glands. Here, we provide new morphological and histological information on the oral glandsand maxillary dentition of representatives of the major lineages of dipsadines that help trace the evolutionary steps thatshaped the venom delivery system of dipsadines. We performed a maximum likelihood analysis on a molecular datasetthat includes 443 terminals and seven loci. Our results show that goo-eating dipsadines form a monophyletic assemblagethat includes the genusAdelphicosfor the first time, along withGeophis,Atractus,Ninia,Chersodromus,Tropidodipsas,Sibon, andDipsas. We also provide the first evidence of a complete shift from an upper jaw to a lower jaw venomdelivery system associated with their specialized feeding behaviour. Unlike other dipsadines who exhibit typicalendoglyptodont anteroposteriorly ridged posterior maxillary teeth, goo-eating dipsadines have uniform lateromediallyridged teeth throughout their maxilla. Our results indicate that the loss of the endoglyptodont venom delivery systemoccurred in the most recent common ancestor of goo-eating dipsadines, probably resulting from the loss of theembryonic posterior maxillary lamina responsible for the development of the venom delivery system.

A bite by the emerald snake, Hapsidophrys smaragdinus Schlegel, 1837 (Colubridae, Colubrinae) causing atopic eczema with comments on the formal documentation of non-front-fanged snakebites.

The mixed quality evidence about non-front-fanged snake bites has included unsupported speculation and presumption; the possible role of atopy and/or primary hypersensitivity have often been prematurely discounted. Described is a medically insignificant bite by a captive African emerald snake, Hapsidophrys smaragdinus Schlegel, 1837 (Colubridae, Colubrinae) that caused the development of moderate Type IV hypersensitivity; the 44-year-old male victim experienced persistent pruritis and an erythematous bite site maculopapular dermatitis that slowly resolved and required 6 days for full resolution. The victim had received several previous medically insignificant bites from non-front-fanged snakes. Brief comparison is made with a previously reported case consistent with a mixed clinical picture of local mild envenoming and hypersensitivity from a bite by another colubrine, the coin snake (Hemmorhois nummifer). This case highlights slowly accumulating evidence supporting the risk of acquired and primary hypersensitivity to some snakebites in susceptible individuals. In order to provide accurate medical risk profiles for less-known snake species it is essential that the case of any patient developing acute or delayed effects from bites by these species is formally documented. The need for further attention to atopic risks, especially in private collectors, is emphasised with consideration of venom/other ophidian product-induced anaphylaxis.

The first reported snakebite by an African snake-eater, Polemon spp. (Atractaspididae, Aparallactinae); Local envenoming by Reinhardt's snake-eater, Polemon acanthias (Reinhardt, 1860).

The first reported snakebite by an African snake-eater, Polemon spp. (Atractaspididae, Aparallactinae); Local envenoming by Reinhardt's snake-eater, Polemon acanthias (Reinhardt, 1860). Toxicon XX, xxx. A 51-yr-old male herpetologist was bitten on the left index finger by a captive male Polemon acanthias while manually removing fragments of incompletely shed skin from the specimen. The snake sustained its bite for approximately 2 mins, advancing its jaws several times. The victim rapidly developed moderate pain, erythema, progressive edema that ultimately extended to the left wrist; a blister later developed in the wound site, as well as joint stiffness in the bitten and adjacent two fingers that limited flexion and extension. These effects regressed during the week following the bite, but recurred thereafter and were similar to the effects that developed immediately post-envenoming. There were no systemic signs or symptoms. The victim sought medical advice and was treated with broad-spectrum antibiotics, antihistamines and wound care; no laboratory investigations were conducted. He improved during the subsequent month with complete resolution in 5 and one-half weeks. This is the first documented bite by a Polemon spp. and the victim's clinical course suggests the development of local effects from venom components. The phylogenetic relationship of Polemon spp. with the burrowing asps (Atractaspis spp.) and the similarity of some of the features of this local envenoming by P. acanthias with mild/moderate envenoming by some Atractaspis spp., suggests that none of these snakes should be handled; they should be considered capable of inflicting potentially serious envenoming.

The Harderian gland transcriptomes of Caraiba andreae, Cubophis cantherigerus and Tretanorhinus variabilis, three colubroid snakes from Cuba.

The Harderian gland is a cephalic structure, widely distributed among vertebrates. In snakes, the Harderian gland is anatomically connected to the vomeronasal organ via the nasolacrimal duct, and in some species can be larger than the eyes. The function of the Harderian gland remains elusive, but it has been proposed to play a role in the production of saliva, pheromones, thermoregulatory lipids and growth factors, among others. Here, we have profiled the transcriptomes of the Harderian glands of three non-front-fanged colubroid snakes from Cuba: Caraiba andreae (Cuban Lesser Racer); Cubophis cantherigerus (Cuban Racer); and Tretanorhinus variabilis (Caribbean Water Snake), using Illumina HiSeq2000 100 bp paired-end. In addition to ribosomal and non-characterized proteins, the most abundant transcripts encode putative transport/binding, lipocalin/lipocalin-like, and bactericidal/permeability-increasing-like proteins. Transcripts coding for putative canonical toxins described in venomous snakes were also identified. This transcriptional profile suggests a more complex function than previously recognized for this enigmatic organ.