Network analysis uncovers putative genes affecting resistance to tick infestation in Braford cattle skin.

BACKGROUND: Genetic resistance in cattle is considered a suitable way to control tick burden and its consequent losses for livestock production. Exploring tick-resistant (R) and tick-susceptible (S) hosts, we investigated the genetic mechanisms underlying the variation of Braford resistance to tick infestation. Skin biopsies from four-times-artificially infested R (n = 20) and S (n = 19) hosts, obtained before the first and 24 h after the fourth tick infestation were submitted to RNA-Sequencing. Differential gene expression, functional enrichment, and network analysis were performed to identify genetic pathways and transcription factors (TFs) affecting host resistance. RESULTS: Intergroup comparisons of hosts before (Rpre vs. Spre) and after (Rpost vs. Spost) tick infestation found 51 differentially expressed genes (DEGs), of which almost all presented high variation (TopDEGs), and 38 were redundant genes. Gene expression was consistently different between R and S hosts, suggesting the existence of specific anti-tick mechanisms. In the intragroup comparisons, Rpost vs. Rpre and Spost vs. Spre, we found more than two thousand DEGs in response to tick infestation in both resistance groups. Redundant and non-redundant TopDEGs with potential anti-tick functions suggested a role in the development of different levels of resistance within the same breed. Leukocyte chemotaxis was over-represented in both hosts, whereas skin degradation and remodeling were only found in TopDEGs from R hosts. Also, these genes indicated the participation of cytokines, such as IL6 and IL22, and the activation of Wingless (WNT)-signaling pathway. A central gene of this pathway, WNT7A, was consistently modulated when hosts were compared. Moreover, the findings based on a genome-wide association study (GWAS) corroborate the prediction of the WNT-signaling pathway as a candidate mechanism of resistance. The regulation of immune response was the most relevant pathway predicted for S hosts. Members of Ap1 and NF-kB families were the most relevant TFs predicted for R and S, respectively. CONCLUSION: This work provides indications of genetic mechanisms presented by Braford cattle with different levels of resistance in response to tick infestation, contributing to the search of candidate genes for tick resistance in bovine.

Linkage disequilibrium, persistence of phase and effective population size estimates in Hereford and Braford cattle.

BACKGROUND: The existence of moderate to high levels of linkage disequilibrium (LD) between genetic markers and quantitative trait loci (QTL) affecting traits of interest is fundamental for the success of genome-wide association (GWAS) and genomic selection (GS) studies. Knowledge about the extent and the pattern of LD in livestock populations is essential to determine the density of single nucleotide polymorphisms (SNP) required for accurate GWAS and GS. Moreover, observed LD is related to historical effective population sizes (Ne), and can provide insights into the genetic diversity history of populations. Estimates of the consistency of linkage phase across breeds (R H,B ) can be used to determine if there is sufficient relationship to use pooled reference populations in multi-breed GS programs. The objective of this study was to estimate LD levels, persistence of phase and effective population size in Hereford and Braford cattle populations sampled in Brazil. RESULTS: Mean LD estimates, measured using the squared correlation of alleles at two loci (r (2)), obtained between adjacent SNP across all chromosomes were 0.21 ± 0.27 for Herefords (391 samples with 41,241 SNP) and 0.16 ± 0.22 for Brafords (2044 samples and 41,207 SNP). Estimated r(2) was > 0.2 and 0.3, respectively, for 34 and 25% of adjacent markers in Herefords, and 26 and 17% in Brafords. Estimated N e for Brafords and Herefords at the current generation was 220 and 153 individuals, respectively. The two breeds demonstrated moderate to strong persistence of phase at all distances (R H,B = 0.53 to 0.97). The largest phase correlations were found in the 0 to 50 Kb bins (R H,B = 0.92 to 0.97). Estimated LD decreased rapidly with increasing distance between SNP, however, useful linkage for GWAS and GS (r(2) > 0.2) was found spanning to ~50 Kb. CONCLUSIONS: Panels containing about 50,000 and 150,000 SNP markers are necessary to detect minimal levels of LD between adjacent markers that would be useful for GWAS and GS studies to Hereford and Braford breeds, respectively. Markers are expected to be linked to the same QTL alleles in distances < 50 Kb in both populations due to observed high persistence of phase levels.

Longevity of musca domestica, diptera muscidae, parasitized by habronema muscae carter nematoda habronematidae

Este trabajo buscó evidenciar la influencia del parásito habronema muscae sobre la longevidad de musca domestica. Larvas de los muscóides de segunda generación, con cerca de 30 h, fueron sometidas a la infección en dieta artificial en la cual se inocularon huevos de H. muscae recuperados de las hembras de los helmintos. Los muscídeos fueron mantenidos en cajas con paredes de tela, manteniendose a 27ºC, 60 ñ 10 por ciento de HR y 14 h de fotofase hasta la formación de las pupas. Los números de muscídeos muertos fueron conferidos diariamente. Posteriormente, estos fueron disecados para ratificación de las larvas infectantes de los nemátodos. La intensidad media de infección fue de 3,11 larvas infectantes por muscídeo (rango: 0-14) en el grupo infectado. Este último grupo mostró reducción significativa de la longevidad cuando se comparó al grupo no expuesto a la infección (25,0 y 32,5 días, respectivamente). No fue evidenciado diferencia entre las longevidades de los muscóides machos y hembras