Acknowledgements Part of this work was supported by grants from the Department of Biotechnology (DBT), Government of India. We gratefully acknowledge SAIF-DST (Sophisticated Analytical Instrumentation FacilityDepartment of Science and Technology, Department of Anatomy–AIIMS) for providing the transmission electron microscopy facility. O.P. and K.K. acknowledge CSIR-UGC (Government of India) for research fellowships. We would like to thank J. P. Euze´by for etymological advice and J. S. Bhatti for critical reading of the manuscript.