Immune and sex-biased gene expression in the threatened Mojave desert tortoise, Gopherus agassizii

Abstract

The immune system of ectotherms, particularly non-avian reptiles, remains poorly characterized regarding the genes involved in immune function, and their function in wild populations. We used RNA-Seq to explore the systemic response of Mojave desert tortoise (Gopherus agassizii) gene expression to three levels of Mycoplasma infection to better understand the host response to this bacterial pathogen. We found over an order of magnitude more genes differentially expressed between male and female tortoises (1,037 genes) than differentially expressed among immune groups (40 genes). There were 8 genes differentially expressed among both variables that can be considered sex-biased immune genes in this tortoise. Among experimental immune groups we find enriched GO biological processes for cysteine catabolism, regulation of type 1 interferon production, and regulation of cytokine production involved in immune response. Sex-biased transcription involves iron ion transport, iron ion homeostasis, and regulation of interferon-beta production to be enriched. More detailed work is needed to assess the seasonal response of the candidate genes found here. How seasonal fluctuation of testosterone and corticosterone modulate the immunosuppression of males and their susceptibility to Mycoplasma infection also warrants further investigation, as well as the importance of iron in the immune function and sexbiased differences of this species. Finally, future transcriptional studies should avoid drawing blood from tortoises via subcarapacial venipuncture as the variable aspiration of lymphatic fluid will confound the differential expression of genes.

Iron dyshomeostasis and time-course changes in iron-uptake systems and ferritin level in relation to pro-inflammatory microglia polarization in sepsis-induced encephalopathy

“…Furthermore, the sex differences in immune responses depend on sex-biased gene expression, mainly of genes associated with iron-uptake systems. Immune cells sequester iron to deprive the pathogens from iron, thus limiting their proliferation (Xu et al, 2020;Kezele and Ćurko-Cofek, 2020;Sharawy et al, 2011).…”

Immunity in Sea Turtles: Review of a Host-Pathogen Arms Race Millions of Years in the Running

“…The dramatic increase in FP prevalence since the 1980s is attributed to a virus, and an unknown environmental factor thought to be anthropogenic in nature [68][69][70]. Results from genomic [71], proteomic [72][73][74] and transcriptomic studies [70,75,76] have consistently identified immune genes as dysregulated between healthy and diseased turtles or by levels of exposure to marine contaminants [73]. Additionally, sea turtles are possible reservoirs for zoonotic viruses, as C. mydas, along with snakes and pangolins, have been suggested as potential intermediate hosts of SARS-CoV-2 [77].…”