Department of Biochemistry, Biotechnology Research Institute, Kenya Agricultural and Livestock Research Organization, P.O. Box 362, Kikuyu, Kenya.
Department of Biochemistry and Molecular Biology, Egerton University, P.O. Box 536, Njoro, Kenya.
Parasit Vectors. 2017 Dec 19;10(1):614. doi: 10.1186/s13071-017-2569-7.
Tsetse flies (Glossina spp.) are the prominent vector of African trypanosome parasites (Trypanosoma spp.) in sub-Saharan Africa, and Glossina pallidipes is the most widely distributed species in Kenya. This species displays strong resistance to infection by parasites, which are typically eliminated in the midgut shortly after acquisition from the mammalian host. Although extensive molecular information on immunity for the related species Glossina morsitans morsitans exists, similar information is scarce for G. pallidipes.
To determine temporal transcriptional responses of G. pallidipes to Trypanosoma brucei brucei challenge, we conducted Illumina based RNA-seq on midgut organ and carcass from teneral females G. pallidipes at 24 and 48 h post-challenge (hpc) with T. b. brucei relative to their respective controls that received normal blood meals (without the parasite). We used a suite of bioinformatics tools to determine differentially expressed and enriched transcripts between and among tissues, and to identify expanded transcripts in G. pallidipes relative to their orthologs G. m. morsitans.
Midgut transcripts induced at 24 hpc encoded proteins were associated with lipid remodelling, proteolysis, collagen metabolism, apoptosis, and cell growth. Midgut transcripts induced at 48 hpc encoded proteins linked to embryonic growth and development, serine endopeptidases and proteosomal degradation of the target protein, mRNA translation and neuronal development. Temporal expression of immune responsive transcripts at 48 relative to 24 hpc was pronounced, indicative of a gradual induction of host immune responses the following challenge. We also searched for G. m. morsitans orthologous groups that may have experienced expansions in the G. pallidipes genome. We identified ten expanded groups in G. pallidipes with putative immunity-related functions, which may play a role in the higher refractoriness exhibited by this species.
There appears to be a lack of strong immune responses elicited by gut epithelia of teneral adults. This in combination with a compromised peritrophic matrix at this stage during the initial phase of T. b. brucei challenge may facilitate the increased parasite infection establishment noted in teneral flies relative to older adults. Although teneral flies are more susceptible than older adults, the majority of tenerals are still able to eliminate parasite infections. Hence, robust responses elicited at a later time point, such as 72 hpc, may clear parasite infections from the majority of flies. The expanded G. m. morsitans orthologous groups in G. pallidipes may also be functionally associated with the enhanced refractoriness to trypanosome infections reported in G. pallidipes relative to G. m. morsitans.
采采蝇（ Glossina spp.）是撒哈拉以南非洲地区非洲锥虫寄生虫（ Trypanosoma spp.）的主要传播媒介，而 G. pallidipes 是肯尼亚分布最广的物种。这种物种对寄生虫感染具有很强的抵抗力，寄生虫通常在从哺乳动物宿主获得后不久就在中肠中被消灭。尽管有关相关物种 Glossina morsitans morsitans 的免疫的广泛分子信息是可用的，但关于 G. pallidipes 的类似信息却很少。
为了确定 G. pallidipes 对布氏锥虫布鲁斯菌株（ Trypanosoma brucei brucei ）挑战的时间转录反应，我们对接受正常血液餐（无寄生虫）的 24 和 48 小时后（ hpc ）的 G. pallidipes 雌性幼虫的中肠器官和尸体进行了基于 Illumina 的 RNA-seq。我们使用了一系列生物信息学工具来确定组织之间和组织之间差异表达和丰富的转录本，并确定 G. pallidipes 中相对于其同源物 G. m. morsitans 扩展的转录本。
在 24 hpc 诱导的中肠转录物编码的蛋白质与脂质重塑，蛋白水解，胶原蛋白代谢，细胞凋亡和细胞生长有关。在 48 hpc 诱导的中肠转录物编码的蛋白质与胚胎生长和发育，丝氨酸内肽酶和靶蛋白的蛋白酶体降解，mRNA 翻译和神经元发育有关。在 48 小时相对于 24 小时表达的免疫反应转录本明显，表明宿主免疫反应逐渐诱导。我们还搜索了 Glossina m. morsitans 同源物组，这些同源物组可能在 G. pallidipes 基因组中发生了扩展。我们在 G. pallidipes 中鉴定了十个具有潜在免疫功能的扩展组，这可能在该物种表现出更高的抗药性中发挥作用。
似乎在接受初始阶段布鲁斯锥虫挑战时，年幼成虫的肠上皮细胞没有引起强烈的免疫反应。这与在此阶段受损的围食膜基质结合在一起，可能会促进在年幼成虫中观察到的寄生虫感染建立。尽管年幼的成虫比成年的成虫更容易受到感染，但大多数年幼的成虫仍能够消除寄生虫感染。因此，在稍后的时间点（例如 72 hpc）引发的强大反应可能会清除大多数成虫中的寄生虫感染。在 G. pallidipes 中扩展的 Glossina m. morsitans 同源物组也可能与 G. pallidipes 相对于 G. m. morsitans 报道的对锥虫感染的增强抗性在功能上相关。
