Mitochondrial DNA origin of indigenous malagasy chicken.

We report the mitochondrial DNA (mtDNA) characterization of 77 indigenous chickens (fighting and meat birds) from Madagascar, using DNA sequences of the first hypervariable segment of the D-loop. Comparison with reference samples from the African continent and Asia revealed two mtDNA haplogroups, suggesting a dual geographic and genetic origin for the indigenous Malagasy chickens. The most common haplogroup was present in 65 individuals of the two types; it is likely of Indonesian origin. The second haplogroup was observed in 12 fighting birds and meat chickens; it could be of African continental origin and/or the result of recent introgression with commercial lines. We further studied a G/A single nucleotide polymorphism at nucleotide position 1892 bp of the coding sequence of the Mx gene that is reported to be one of the candidate susceptible/resistant genes to viral infection in chicken. Our results indicate the "susceptible" allele G is the most common with frequencies of 65% and 70% in Malagasy fighting and meat chickens, respectively. However, the allelic frequency difference between the two types of chickens is not significant (P > 0.05). These results are discussed in light of our current linguistic and archaeological knowledge on the origin of indigenous Malagasy chickens.

Renitelo cattle dermatophilosis and PCR-RFLP analysis of MHC gene.

Renitelo breed is a cattle breed created at Kianjasoa station (Madagascar) by a triple crossing Malagasy Zebu x Limousine x Afrikander. This breed besides many valuable advantages, such as rapid growth and drought power, presents a huge disadvantage which is sensitivity to skin disease, dermatophilosis, previously known as streptotrichosis. This disease caused by Dermatophilus congolensis is one of the major threats for the population of Renitelo cattle. An allele of MHC gene has been shown to be dramatically associated to hypersensitivity to the disease in other cattle breed. To bring further information to tick borne disease clinical survey, mainly dermatophilosis, we wanted to verify if such allele could be found in this breed. Renitelo cattle included in this study were chosen for the presence of dermatophilosis lesions in more or less severe form (N = 17). These animals were blood sampled and a genetic analysis on the MHC gene BoLA-DRB3 was performed, by PCR amplification using BOD 31 & BOD 32 primers. Amplified products were analyzed by RFLP using enzymes. Restriction band profiles were characterized according to previously defined patterns. Three cows out of the 17 cattle analyzed for MHC gene presented the hypersensitive allele FDA. Two out of the three hypersensitive cows were pure breed while one was half breed. All the cows presented dermatophilosis lesions at least during rainy season but one of them particularly suffered from severe lesions covering all its body and died of the illness. This study shows that hypersensitivity allele found in other bovine breeds can be found in Renitelo breed. This result seemed to suggest that this characterization could be utilized in breeding program for this breed.

Selection assisted by a BoLA-DR/DQ haplotype against susceptibility to bovine dermatophilosis.

Bovine dermatophilosis is a severe skin infection of tropical ruminants inducing a severe loss in productivity and a 15% mortality rate. This disease is caused by the actinomycete bacterium Dermatophilus congolensis associated with the tick Amblyomma variegatum. Currently there are no prospects for a vaccine, and acaricide or antibiotic control is hampered by the development of chemoresistance. Animal breeders have observed that dermatophilosis susceptibility seems to be determined genetically, and we previously identified a BoLA-DRB3-DQB class II haplotype marker for high (R2= 0.96) susceptibility to the disease. With this marker, we developed a successful eugenic selection procedure for zebu Brahman cattle in Martinique (FWI). Over a period of five years, a marked reduction in disease prevalence, from 0.76 to 0.02 was achieved, and this low level has been maintained over the last two years. The selection procedure, based on a genetic marker system targeting the highly polymorphic BoLA locus, eliminates only those individuals which are at the highest risk of contracting the disease. In the present work, we discuss the properties of this system, including the "heterozygote advantage" and the "frequency dependence" theories, and examine their involvement in the biological mechanisms at the host/pathogen interface. We speculate on the exact role of the MHC molecules in the control of the disease, how the natural selection pressure imposed by the pathogens selectively maintains MHC diversity, and how our results can be practically applied for integrated control of dermatophilosis in developing countries.

Molecular immunogenetics in susceptibility to bovine dermatophilosis: a candidate gene approach and a concrete field application.

To identify molecular genetic markers of resistance or susceptibility to dermatophilosis in cattle, we used a functional candidate gene approach to analyze the DNA polymorphisms of targeted genes encoding molecules implicated in known mechanisms of both nonspecific and specific immune responses existing in the pathogen/host interface mechanisms. The most significant results were obtained within the Major Histocompatibility Complex (MHC) where the BoLA-DRB3 and DQB genes encode molecules involved in the antigen presentation to T cell receptors. A unique BoLA class II haplotype, made up of one DRB3 exon 2 allele and one DQB allele, highly correlates with the susceptibility character (P < 0.001). This haplotype marker of susceptibility was also found and validated in other bovine populations. A eugenic marker-assisted selection was developed in the field by eliminating only the animals having this haplotype. The disease prevalence was thereby reduced from 0.76 to 0.02 over 5 years. A crossbreeding plan is in progress to study the genetic transmission of the genotypic and phenotypic characters of susceptibility to dermatophilosis. In conclusion, we discuss several hypotheses at the molecular and cellular levels to better define the exact role of the MHC molecules in disease control and to answer the question: How is MHC diversity selectively maintained by natural selection imposed by pathogens?

Interspecific nucleotide sequence differences in the cytochrome B gene of indriidae (Primates, Strepsirhini).

The comparison of partial sequence of the mitochondrial cytochrome b gene nucleotides for different Indriidae allowed us to confirm the species status ofAvahi laniger, A. occidentalis, and Propithecus tattersalli. The nucleotide sequence allowed also to propose a phylogenetic tree which is discussed taking into account morphological, cytogenetic and former molecular biology data.