Mitochondrial transcription factor A induces the declined mitochondrial biogenesis correlative with depigmentation of brown eggshell in aged laying hens

Abstract

Eggshell color is an important characteristic for poultry eggs. Eggs from aged hens usually have poor shell color that is unacceptable for the table egg market. The objective of this study was to examine effects of pigment synthesis and mitochondrial biogenesis on brown eggshell color of aged laying hens. In this trial, 8 hens laying eggs with darker shell color and 8 hens laying eggs with lighter shell color were selected from 300 62-week-old Hy-Line brown-egg laying hens. Results showed that egg weight ( P < 0.05), eggshell weight ( P < 0.01), protoporphyrin IX ( Pp IX ) content of the eggshell and the shell gland ( P < 0.001), and biliverdin content of the shell gland ( P < 0.001) were significantly declined in the light-shell group compared with the dark-shell group. Relative mRNA expression of δ-aminolevulinic acid synthase1 ( ALAS1 ) ( P < 0.05), coproporphyrinogen oxidase ( P < 0.01), ATP-binding cassette transporter ABCG2 ( P < 0.01), and mitochondrial transcription factor A ( P < 0.05) was reduced in hens laying lighter brown eggshell. Moreover relative mRNA expression of mitochondrial DNA copy number ( P < 0.01), mitochondrial NADH dehydrogenase subunit 4 ( P < 0.05), mitochondrial ATP synthase F0 subunit 8 ( P < 0.05), and mitochondrial cytochrome c oxidase 1 ( P < 0.01) was significantly decreased in the shell gland of the light-shell group. In addition, NAD + contents of the shell gland were increased in the dark-shell group ( P < 0.01). Brown eggshell depigmentation is a result of decreased Pp IX content in the eggshell and the shell gland. Decreased mitochondrial biogenesis may contribute to the depigmentation of brown eggshell by targeting ALAS1 and ALAS1-mediated Pp IX biosynthesis.

Identification of crucial genes and metabolites regulating the eggshell brownness in chicken

“…The subject of whether eggshell color affects eggshell quality has attracted the interest of researchers. In our study, there were no significant differences between LBS and DBS lines in terms of eggshell thickness and eggshell proportion, which is consistent with previous research findings [ 23 , 26 ]. However, the eggshell strength of DBS line eggs was significantly weaker than that of LBS line eggs, which may be attributed to the influence of eggshell pigment on the eggshell calcification process.…”

“…Numerous studies have shown that eggshell brownness is regulated by synthases and transporters in the Pp IX/heme synthesis pathway. ALAS1 is the target gene for the regulation of Pp IX concentration in eggshells [ 19 , 23 ]. ABCG2 has been shown to regulate ALA-mediated Pp IX levels by exporting Pp IX from the mitochondria to the cytoplasm [ 24 ].…”

Refine localizations of functional variants affecting eggshell color of Lueyang black-boned chicken in the SLCO1B3

“…ABCG2 is responsible for the export of protoporphyrin out of cells ( Ajioka et al, 2006 ), and identified as a causative gene for blue eggs in the duck ( Chen et al, 2020 ). These genes had higher expression levels in the dark brown-shell chickens than the light brown-shelled ones ( Li et al, 2013 ; Zheng et al, 2014 ; Lu et al, 2021a ). ALAS1 was confirmed to be the key gene reducing protoporphyrin biosynthesis in response to nicarbazin treatment ( Samiullah et al, 2017 ).…”

Transcriptome and histological analyses on the uterus of freckle egg laying hens

“…Freckles are more likely to appear on brown-shelled eggs than on eggshells of other colors. Brown eggs are mainly composed of pigments such as protoporphyrin IX [ 9 ]. Currently, there are two prevailing views on the manner in which the site of pigment synthesis occurs in brown eggs: one view is that the pigment is synthesized by red blood cells in the circulatory system [ 10 ]; the other view is that the pigment is synthesized by epithelial cells in the uterus [ 11 , 12 ].…”