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Open Access Highly Accessed Research article

Transcriptional analysis of an immune-responsive serine protease from Indian malarial vector, Anopheles culicifacies

Janneth Rodrigues14, Neema Agrawal1, Anil Sharma13, Pawan Malhotra12, Tridibes Adak13, Virander S Chauhan12 and Raj K Bhatnagar1*

  • * Corresponding author: Raj K Bhatnagar raj@icgeb.res.in

  • † Equal contributors

Author Affiliations

1 Insect Resistance Group, International Centre for Genetic Engineering and Biotechnology (ICGEB) PO Box 10504, Aruna Asaf Ali Marg, New Delhi 110067, India

2 Malaria Group, ICGEB, New Delhi 67, India

3 National Institute of Malaria Research 2, Nanak Enclave, (Radio Colony), Delhi 110009, India

4 Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, Maryland, USA

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BMC Molecular Biology 2007, 8:33  doi:10.1186/1471-2199-8-33

Published: 15 May 2007

Abstract

Background

The main vector for transmission of malaria in India is the Anopheles culicifacies mosquito species, a naturally selected subgroup of which is completely refractory (R) to transmission of the malaria parasite, Plasmodium vivax;

Results

Here, we report the molecular characterization of a serine protease (acsp30)-encoding gene from A. culicifacies, which was expressed in high abundance in the refractory strain compared to the susceptible (S) strain. The transcriptional upregulation of acsp30 upon Plasmodium challenge in the refractory strain coincided with ookinete invasion of mosquito midgut. Gene organization and primary sequence of acsp30 were identical in the R and S strains suggesting a divergent regulatory status of acsp30 in these strains. To examine this further, the upstream regulatory sequences of acsp30 were isolated, cloned and evaluated for the presence of promoter activity. The 702 bp upstream region of acsp30 from the two strains revealed sequence divergence. The promoter activity measured by luciferase-based reporter assay was shown to be 1.5-fold higher in the R strain than in the S. Gel shift experiments demonstrated a differential recruitment of nuclear proteins to upstream sequences of acsp30 as well as a difference in the composition of nuclear proteins in the two strains, both of which might contribute to the relative abundance of acsp30 in the R strain;

Conclusion

The specific upregulation of acsp30 in the R strain only in response to Plasmodium infection is suggestive of its role in contributing the refractory phenotype to the A. culicifacies mosquito population.