Rollins-Smith Louise A, Woodhams Douglas C, Reinert Laura K, Vredenburg Vance T, Briggs Cheryl J, Nielsen Per F, Conlon J Michael
Department of Microbiology and Immunology, Vanderbilt University, A-5301 Medical Center North, Nashville, TN 37232, USA.
Dev Comp Immunol. 2006;30(9):831-42. doi: 10.1016/j.dci.2005.10.005. Epub 2005 Nov 9.
The mountain yellow-legged frog (Rana muscosa) inhabits high elevation lakes in California that are largely undisturbed by human activities. In spite of this habitation in remote sites, populations continue to decline. Although predation by non-native fish is one cause for declines, some isolated populations in fishless lakes are suffering new declines. One possible cause of the current wave of declines is the introduction of the pathogenic chytrid fungus (Batrachochytrium dendrobatidis) which invades the adult skin to cause chytridiomycosis. In many amphibian species, the skin is protected by antimicrobial peptides secreted into the mucous. Here we show that R. muscosa produces three previously unknown antimicrobial peptides belonging to the ranatuerin-2 and temporin-1 families of antimicrobial peptides. These three peptides, along with bradykinin, are the most abundant peptides in the skin secretions detected by mass spectrometry. Natural mixtures of peptides and individual purified peptides strongly inhibit chytrid growth. The concentration of total peptides recovered from the skin of frogs following a mild norepinephrine induction is sufficient to inhibit chytrid growth in vitro. A comparison of the species susceptibility to chytridiomycosis and the antichytrid activity of peptides between R. muscosa and R. pipiens suggest that although R. muscosa produces more total skin peptides, it appears to be more vulnerable to B. dendrobatidis in nature. Possible differences in the antimicrobial peptide repertoires and life history traits of the two species that may account for differences in susceptibility are discussed.
加州山黄腿蛙（Rana muscosa）栖息于加利福尼亚州高海拔湖泊中，这些湖泊基本未受人类活动干扰。尽管栖息在偏远地区，但该蛙种群数量仍在持续下降。虽然非本地鱼类的捕食是数量下降的一个原因，但一些无鱼湖泊中的孤立种群也在遭受新的数量减少。当前这波数量下降的一个可能原因是致病性壶菌（Batrachochytrium dendrobatidis）的引入，这种真菌会侵入成年蛙的皮肤，引发壶菌病。在许多两栖动物物种中，皮肤受到分泌到黏液中的抗菌肽的保护。在此我们表明，加州山黄腿蛙会产生三种先前未知的抗菌肽，它们属于抗菌肽的蛙皮素 -2 和爪蟾抗菌肽 -1 家族。这三种肽与缓激肽一起，是通过质谱检测到的皮肤分泌物中含量最丰富的肽。肽的天然混合物和单个纯化肽都能强烈抑制壶菌生长。轻度去甲肾上腺素诱导后从蛙皮肤中回收的总肽浓度足以在体外抑制壶菌生长。对加州山黄腿蛙和豹蛙对壶菌病的易感性以及肽的抗壶菌活性进行比较表明，尽管加州山黄腿蛙产生的皮肤总肽更多，但在自然环境中它似乎更容易受到蛙壶菌的侵害。我们还讨论了这两个物种在抗菌肽库和生活史特征方面可能存在的差异，这些差异或许可以解释它们易感性的不同。
