Limits...
Comparative venom gland transcriptomics of Naja kaouthia (monocled cobra) from Malaysia and Thailand: elucidating geographical venom variation and insights into sequence novelty

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Background: The monocled cobra (Naja kaouthia) is a medically important venomous snake in Southeast Asia. Its venom has been shown to vary geographically in relation to venom composition and neurotoxic activity, indicating vast diversity of the toxin genes within the species. To investigate the polygenic trait of the venom and its locale-specific variation, we profiled and compared the venom gland transcriptomes of N. kaouthia from Malaysia (NK-M) and Thailand (NK-T) applying next-generation sequencing (NGS) technology.

Methods: The transcriptomes were sequenced on the Illumina HiSeq platform, assembled and followed by transcript clustering and annotations for gene expression and function. Pairwise or multiple sequence alignments were conducted on the toxin genes expressed. Substitution rates were studied for the major toxins co-expressed in NK-M and NK-T.

Results and discussion: The toxin transcripts showed high redundancy (41–82% of the total mRNA expression) and comprised 23 gene families expressed in NK-M and NK-T, respectively (22 gene families were co-expressed). Among the venom genes, three-finger toxins (3FTxs) predominated in the expression, with multiple sequences noted. Comparative analysis and selection study revealed that 3FTxs are genetically conserved between the geographical specimens whilst demonstrating distinct differential expression patterns, implying gene up-regulation for selected principal toxins, or alternatively, enhanced transcript degradation or lack of transcription of certain traits. One of the striking features that elucidates the inter-geographical venom variation is the up-regulation of α-neurotoxins (constitutes ∼80.0% of toxin’s fragments per kilobase of exon model per million mapped reads (FPKM)), particularly the long-chain α-elapitoxin-Nk2a (48.3%) in NK-T but only 1.7% was noted in NK-M. Instead, short neurotoxin isoforms were up-regulated in NK-M (46.4%). Another distinct transcriptional pattern observed is the exclusively and abundantly expressed cytotoxin CTX-3 in NK-T. The findings suggested correlation with the geographical variation in proteome and toxicity of the venom, and support the call for optimising antivenom production and use in the region. Besides, the current study uncovered full and partial sequences of numerous toxin genes from N. kaouthia which have not been reported hitherto; these include N. kaouthia-specific l-amino acid oxidase (LAAO), snake venom serine protease (SVSP), cystatin, acetylcholinesterase (AChE), hyaluronidase (HYA), waprin, phospholipase B (PLB), aminopeptidase (AP), neprilysin, etc. Taken together, the findings further enrich the snake toxin database and provide deeper insights into the genetic diversity of cobra venom toxins.

No MeSH data available.


Pairwise sequence alignment of hyaluronidase transcript from the venom gland transcriptome of NK-T in comparison to the annotated hyaluronidase sequence.Green, consensus sequence; red, sequence diversification; black, mismatched sequences.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5384570&req=5

fig-10: Pairwise sequence alignment of hyaluronidase transcript from the venom gland transcriptome of NK-T in comparison to the annotated hyaluronidase sequence.Green, consensus sequence; red, sequence diversification; black, mismatched sequences.

Mentions: Acetylcholinesterase (Ahmed et al., 2009) and HYA (Tu & Hendon, 1983) are two well-investigated snake venom enzymes, yet their content in snake venom is usually very low and often undetectable in venom proteome, although the enzymatic activities have been detected in various cobra venoms (Tan & Tan, 1988). In the present study, transcripts of the two enzymes were reported from N. kaouthia venom glands, supporting the expression of the proteins in N. kaouthia venom. Importantly, the full sequences of AChE were unveiled in the venom gland transcriptomes of NK-M (NKM_ACE01) and NK-T (NKT_ACE01), with identical sequences observed (Data S3). This is also the first report of N. kaouthia AChE sequence (as well as the complete sequence in Naja species), which are homologous to the AChE (UniProtKB: Q92035) reported from B. fasciatus (Data S3). On the other hand, HYA gene expression was detected in NK-T venom gland, with full-length protein-encoding transcript (NKT_HYA01) obtained. The HYA transcript (NKT_HYA01) representing the first reported sequences of HYA of N. kaouthia as well as in Naja species and share 84% homology with HYA from Echis ocellatus (UniProtKB: A3QVN2) (Fig. 10). HYA gene, a relatively less investigated venom enzyme family, is likely well-conserved across many lineages of Elapidae and Viperidae as a result of purifying selection.


Comparative venom gland transcriptomics of Naja kaouthia (monocled cobra) from Malaysia and Thailand: elucidating geographical venom variation and insights into sequence novelty
Pairwise sequence alignment of hyaluronidase transcript from the venom gland transcriptome of NK-T in comparison to the annotated hyaluronidase sequence.Green, consensus sequence; red, sequence diversification; black, mismatched sequences.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384570&req=5

fig-10: Pairwise sequence alignment of hyaluronidase transcript from the venom gland transcriptome of NK-T in comparison to the annotated hyaluronidase sequence.Green, consensus sequence; red, sequence diversification; black, mismatched sequences.
Mentions: Acetylcholinesterase (Ahmed et al., 2009) and HYA (Tu & Hendon, 1983) are two well-investigated snake venom enzymes, yet their content in snake venom is usually very low and often undetectable in venom proteome, although the enzymatic activities have been detected in various cobra venoms (Tan & Tan, 1988). In the present study, transcripts of the two enzymes were reported from N. kaouthia venom glands, supporting the expression of the proteins in N. kaouthia venom. Importantly, the full sequences of AChE were unveiled in the venom gland transcriptomes of NK-M (NKM_ACE01) and NK-T (NKT_ACE01), with identical sequences observed (Data S3). This is also the first report of N. kaouthia AChE sequence (as well as the complete sequence in Naja species), which are homologous to the AChE (UniProtKB: Q92035) reported from B. fasciatus (Data S3). On the other hand, HYA gene expression was detected in NK-T venom gland, with full-length protein-encoding transcript (NKT_HYA01) obtained. The HYA transcript (NKT_HYA01) representing the first reported sequences of HYA of N. kaouthia as well as in Naja species and share 84% homology with HYA from Echis ocellatus (UniProtKB: A3QVN2) (Fig. 10). HYA gene, a relatively less investigated venom enzyme family, is likely well-conserved across many lineages of Elapidae and Viperidae as a result of purifying selection.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Background: The monocled cobra (Naja kaouthia) is a medically important venomous snake in Southeast Asia. Its venom has been shown to vary geographically in relation to venom composition and neurotoxic activity, indicating vast diversity of the toxin genes within the species. To investigate the polygenic trait of the venom and its locale-specific variation, we profiled and compared the venom gland transcriptomes of N. kaouthia from Malaysia (NK-M) and Thailand (NK-T) applying next-generation sequencing (NGS) technology.

Methods: The transcriptomes were sequenced on the Illumina HiSeq platform, assembled and followed by transcript clustering and annotations for gene expression and function. Pairwise or multiple sequence alignments were conducted on the toxin genes expressed. Substitution rates were studied for the major toxins co-expressed in NK-M and NK-T.

Results and discussion: The toxin transcripts showed high redundancy (41–82% of the total mRNA expression) and comprised 23 gene families expressed in NK-M and NK-T, respectively (22 gene families were co-expressed). Among the venom genes, three-finger toxins (3FTxs) predominated in the expression, with multiple sequences noted. Comparative analysis and selection study revealed that 3FTxs are genetically conserved between the geographical specimens whilst demonstrating distinct differential expression patterns, implying gene up-regulation for selected principal toxins, or alternatively, enhanced transcript degradation or lack of transcription of certain traits. One of the striking features that elucidates the inter-geographical venom variation is the up-regulation of α-neurotoxins (constitutes ∼80.0% of toxin’s fragments per kilobase of exon model per million mapped reads (FPKM)), particularly the long-chain α-elapitoxin-Nk2a (48.3%) in NK-T but only 1.7% was noted in NK-M. Instead, short neurotoxin isoforms were up-regulated in NK-M (46.4%). Another distinct transcriptional pattern observed is the exclusively and abundantly expressed cytotoxin CTX-3 in NK-T. The findings suggested correlation with the geographical variation in proteome and toxicity of the venom, and support the call for optimising antivenom production and use in the region. Besides, the current study uncovered full and partial sequences of numerous toxin genes from N. kaouthia which have not been reported hitherto; these include N. kaouthia-specific l-amino acid oxidase (LAAO), snake venom serine protease (SVSP), cystatin, acetylcholinesterase (AChE), hyaluronidase (HYA), waprin, phospholipase B (PLB), aminopeptidase (AP), neprilysin, etc. Taken together, the findings further enrich the snake toxin database and provide deeper insights into the genetic diversity of cobra venom toxins.

No MeSH data available.