Abstract
BackgroundAvian eggs have a proteinaceous cuticle. The quantity of cuticle varies and the deposition of a good cuticle in the uterus (Shell-gland) prevents transmission of bacteria to the egg contents.ResultsTo understand cuticle deposition, uterus transcriptomes were compared between hens with i) naturally good and poor cuticle and, ii) where manipulation of the hypothalamo-pituitary-gonadal-oviduct axis produced eggs with or without cuticle. The highest expressed genes encoded eggshell matrix and cuticle proteins, e.g. MEPE (OC-116), BPIFB3 (OVX-36), RARRES1 (OVX-32), WAP (OVX-25), and genes for mitochondrial oxidative phosphorylation, active transport and energy metabolism. Expression of a number of these genes differed between hens laying eggs with or without cuticle. There was also a high expression of clock genes. PER2, CRY2, CRY1, CLOCK and BMAL1 were differentially expressed when cuticle deposition was prevented, and they also changed throughout the egg formation cycle. This suggests an endogenous clock in the uterus may be a component of cuticle deposition control. Cuticle proteins are glycosylated and glycosaminoglycan binding genes had a lower expression when cuticle proteins were deposited on the egg. The immediate early genes, JUN and FOS, were expressed less when the cuticle had not been deposited and changed over the egg formation cycle, suggesting they are important in oviposition and cuticle deposition. The uterus transcriptome of hens with good and poor cuticle deposition did not differ.ConclusionsWe have gained insights into the factors that can affect the production of the cuticle especially clock genes and immediate early genes. We have demonstrated that these genes change their expression over the period of eggshell formation supporting their importance. The lack of differences in expression between the uterus of hens laying eggs with the best and worse cuticle suggest the genetic basis of the trait may lie outside the oviduct.
Highlights
IntroductionCuticle deposition is not an extension of shell organic matrix production but is a specific event that occurs in the uterus, often referred to as the shell gland pouch, very close to the time of oviposition [6]
Experiment 2: manipulation of cuticle deposition by endocrinological intervention At post mortem, there was no difference in body weight between the hens used for RNA sequencing transcriptome analysis that received arginine vasotocin (AVT) or Gonadotropin-releasing hormone 1 (GNRH1) (1812 ± 138 g v 1732 ± 189 g; n = 8; F1,14 0.35)
We found no evidence for the AVT prostaglandin system that is thought to mediate the brain to ovary signalling of oviposition timing being involved in cuticle deposition [6]
Summary
Cuticle deposition is not an extension of shell organic matrix production but is a specific event that occurs in the uterus, often referred to as the shell gland pouch, very close to the time of oviposition [6]. This was elucidated by utilizing precise temporal manipulation of the hypothalamo-pituitarygonadal-oviduct axis to manipulate the daily laying cycle and obtain eggs at the same time in the daily cycle which had cuticle deposition or did not have cuticle deposition [6]. The question of what precise pathways are responsible for the secretion of the cuticle remains unresolved
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