Todd S M, Sonenshine D E, Hynes W L
Department of Biological Sciences, Old Dominion University, Norfolk, Virginia 23529, USA.
Med Vet Entomol. 2007 Jun;21(2):141-7. doi: 10.1111/j.1365-2915.2007.00682.x.
The transcript sequence of the Amblyomma americanum Linnaeus (Acari: Ixodidae) defensin, termed amercin (amn), was ascertained and a 219-bp amn coding region identified. The gene encodes a 72-amino acid prepropeptide with a putative 37-amino acid mature peptide. This gene shows little similarity to either of the defensins from Amblyomma hebraeum Koch, the only other Amblyomma species for which a defensin has been described. Sequence comparisons with other tick defensins reveal amn to be shorter (6 bp or 2 amino acids) than the Ixodes scapularis Linnaeus (Acari: Ixodidae) and Dermacentor variabilis (Say) (Acari: Ixodidae) defensin sequences. The amercin prepropeptide has 60.8% and 59.5% similarity with the I. scapularis and D. variabilis prepropeptides, respectively, whereas the mature amercin peptide has 73.7% and 71.1% similarity with the mature peptides of these ticks. Similarity with other tick defensins ranges from 42% to 71%. In A. americanum, defensin transcript was found in the midgut, fat body and salivary gland tissues, as well as in the haemocytes. Defensin transcript was also present in early-stage eggs (less than 48 h old), late-stage eggs (approximately 2 weeks old), larvae and nymphs of A. americanum and I. scapularis, both of which are vector-competent for Borrelia spirochetes.
美洲钝眼蜱（蜱螨亚纲：硬蜱科）防御素的转录本序列已确定，其被命名为美洲钝眼蜱防御素（amn），并鉴定出一个219 bp的amn编码区。该基因编码一个含72个氨基酸的前原肽，其中有一个推测的含37个氨基酸的成熟肽。该基因与希伯来钝眼蜱科赫防御素的相似性均较低，希伯来钝眼蜱是唯一一种已被描述有防御素的其他钝眼蜱物种。与其他蜱防御素的序列比较显示，amn比肩突硬蜱（蜱螨亚纲：硬蜱科）和变异革蜱（赛伊）（蜱螨亚纲：硬蜱科）的防御素序列短（6 bp或2个氨基酸）。美洲钝眼蜱防御素前原肽与肩突硬蜱和变异革蜱前原肽的相似性分别为60.8%和59.5%，而成熟的美洲钝眼蜱防御素肽与这些蜱的成熟肽的相似性分别为73.7%和71.1%。与其他蜱防御素的相似性范围为42%至71%。在美洲钝眼蜱中，防御素转录本存在于中肠、脂肪体、唾液腺组织以及血细胞中。防御素转录本也存在于美洲钝眼蜱和肩突硬蜱的早期卵（小于48小时龄）、晚期卵（约2周龄）、幼虫和若虫中，这两种蜱均具有传播疏螺旋体的能力。
