Slovenian Veterinary Research (Feb 2024)
VARIATION IN THE ASIP AND DUN GENES RESPONSIBLE FOR COAT COLOUR IN BOSNIAN MOUNTAIN HORSE
Abstract
Within the Bosnian Mountain Horse Registry (BMH), some specific coat colours are permitted. Accurate determination of coat colours can be challenging as there are variations in coat colour shades and several dun dilution variants occur. The previously found single nucleotide polymorphisms (SNPs) within two coat colour loci, T-box 3 (TBX3) and Agouti Signalling Protein (ASIP), were genotyped in 313 BMH individuals. The obtained genotypes were then compared to the predicted phenotypes by using the observed coat colour types from the International Association of Bosnian Mountain Horse Breeders (IABMHB) database. It was found that the dark bay and black coat colours were the most representative coat colours both phenotypically and genotypically. The frequency of the dominant Dun (D) dilution allele is (0.09), and this frequency is higher than the previously predicted frequency recorded in the available BMH registers, as also demonstrated. Among the identified alleles, there was a discrepancy or inconsistency between the predicted coat colour based on genotypes and the observed coat colour in 73 horses (23%). The most frequent error concerned the misclassification of horses with genotypes aa and Aa at the ASIP gene, non-dun1/non-dun1 (nd1/nd1) and non-dun2/non-dun1 (nd1/nd2) at the TBX3 gene, which can be associated with the occurrence of slight dilution phenotypes in these individuals. In contrast to the Konik and Hucul breeds, no homozygosity of the D allele was found in the BMH. The D allele can be easily overlooked or not recognised in different phenotypic groups, such as dark bay and black horses. Therefore, the hypothesis that Dun dilution effects itself is not as strongly epistatic in the BMH as described in other horse breeds. This could be the result of an additional genetic modifier suppressing the phenotypic effect of the D allele. It also suggests that there has been a persistent selection pressure in favour of dark base colours, which may have contributed to the observed differences in BMH. Finally, a significant proportion (35%) of BMH individuals with genetically black coat colour were officially classified as dark bay. We hypothesise that the difficulty in visually distinguishing these two phenotypes is due to an independent locus upstream of the ASIP gene. This locus was recently identified as a factor that darkens the typical pigmentation in dark bay horses. The results of the study confirm the importance of molecular testing in accurately determining the coat colour of horses. This would help to avoid errors in coat colour descriptions in official breeding records and provide valuable information for selective breeding programmes aimed at producing specific and desired coat colours. Variabilnost genov ASIP in DUN, odgovornih za barvo dlake pri bosanskem planinskem konju Določanje barv dlake pri bosanskem planinskem konju (BPK) je lahko izziv, ker obstajajo razlike v barvnih odtenkih dlake in več oblik redčenja barve dlake (plavci). Pri 313 konjih pasme BPK smo genotipizirali polimorfizme posameznih nukleotidov (SNP) znotraj dveh lokusov za barvo dlake T-box 3 (TBX3) in polimorfizma 11-bp indel znotraj Agouti signalnega proteina (ASIP). Posamezne genotipe smo nato primerjali z vpisanimi fenotipi barv dlake iz baze podatkov MZRBPK (Mednarodno združenje rejcev bosanskega planinskega konja). Ugotovljeno je bilo, da sta bili temna rjava in črna najbolj reprezentativni barvi dlake pri BPK. Pogostnost prevladujočega alela za redčenje Dun (D) v študiji je višja (0,09) od predhodno zabeležene v razpoložljivem registru BPK. Med ugotovljenimi aleli je prišlo do neskladja ali nedoslednosti med predvideno barvo dlake na podlagi genotipov in opazovano barvo dlake pri 73 konjih (23%). Najpogostejša napaka se je nanašala na napačno razvrstitev konjev z genotipoma aa in Aa v genu ASIP, non-dun1/non-dun1 (nd1/nd1) in non-dun1/non-dun2 (nd1/nd2) pri genu TBX3, kar je lahko povezano s pojavom redčenja barve dlake pri teh fenotipih.V nasprotju s pasmami Konik in Hucul pri BPK ni bila ugotovljena homozigotnost alela D. Alel D je mogoče zlahka spregledati ali ga ne prepoznati v različnih fenotipskih skupinah, kot so temni rjavci in vranci. Zato hipoteza, da učinki redčenja Dun (plavci) pri BPK sami po sebi niso tako močno epistatični, kot je to opisano pri drugih pasmah konj. Rezultati študije potrjujejo pomen molekularnega testiranja pri natančnem določanju barve dlake konj. To bi pripomoglo k preprečevanju napak pri opisih barve dlak v uradnih rejskih evidencah in pomembna informacija pri selekciji na posebne in želene barve dlake pri konjih. Ključne besede: barva dlake konj; dun redčenje barve dlake; polimorfizem DNK; frekvenca alelov; frekvenca genotipa; bosanski planinski konj
Keywords
