HIGH EXPRESSION OF HMOX1 IN BLUE-SHELLED CHICKENS IS ASSOCIATED WITH A TG HAPLOTYPE

Z Wang,R Liu,Ai Wang,X Deng

doi:10.1590/1516-635x1703267-274

Abstract

HMOX1 is an important gene in biosynthesis of the eggshell pigment of blue eggs. Previous studies found that HMOX1 is highly expressed in the shell gland of hens laying blue eggs (BlueH) compared with hens laying brown eggs (BrownH); however, the reasons for the differential expression are unclear. In this study five single nucleotide polymorphism (SNP) in HMOX1 were genotyped in 111 BlueH and 115 BrownH. The association of haplotypes of these SNP with the blue egg phenotype was tested. Haplotype-specific expression of HMOX1 was detected in the shell gland. The interaction of sequence variants and transcription factors was analyzed using electrophoretic mobility shift assay (EMSA). A TG haplotype covering upstream 1.4 kb region of HMOX1 was significantly associated with blue eggs (p<0.05). Furthermore, the birds (n=12) with the haplotype expressed 3.8 fold more transcripts than those (n=12) without the haplotype (p<0.05). After re-sequencing a 2.2 kb region harboring the TG haplotype, a total of 26 SNP were found, of which a SNP was predicted to create a binding site of Nrf2, a transcription factor initiating HMOX1 expression. However, subsequent EMSA failed to confirm the Nrf2-DNA interaction. Taken together, the data suggested that the TG haplotype is not directly involved in regulation of HMOX1 expression; a regulatory mutation located near the haplotype and linked with the haplotype may exist and be responsible for the differential expression ofHMOX1.

Highlights

Birds are the only class of vertebrates that have evolved eggshell pigmentation (Cassey et al, 2010)
Five major haplotypes were observed in BlueH and BrownH, of which only the GAGTG haplotype showed a significant association with blue eggs (p
As the “sliding window” size was reduced, three haplotypes (TGGT, TGG, and TG) showed increasing association with blue egg, with the TG haplotype showing the strongest association with blue eggs (Table 3)

Summary

Introduction

Birds are the only class of vertebrates that have evolved eggshell pigmentation (Cassey et al, 2010). Appearance of eggshell colors represents an important event of bird evolution. Blue-green coloration is a common eggshell color among birds. It is present in wild birds, and in domestic fowls (i.e., several indigenous chicken breeds, such as Chilean Araucano, Chinese Dongxiang, and Lushi chickens) (Kennedy & Verves, 1973; Wang et al, 2013). The blue-green coloration is believed to function as a signal of female health to attract males involved in the supervision of the offspring (Morales et al, 2010)

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