Feeding level is associated with altered liver transcriptome and follicle selection in the hen

Genetic selection for particular traits in domestic animals may have altered the optimal feedback regulation among systems regulating appetite, growth, and reproduction. Broiler breeder chickens have been selected for fast and efficient growth and, unless feed restricted, consume excessively resulting in poor reproductive efficiency. We examined the effect of dietary treatment in full fed (FF) and restricted fed (RF) broiler breeder hens on ovarian responses and on liver morphology and transcriptome associated with reproductive function. Although FF broiler breeder hens had lower egg production (p < 0.01), the total number of ovarian follicles >8 mm (p < 0.01), 6-8 mm (p < 0.03), and 3-5 mm (p < 0.04) were greater in FF hens compared to RF hens. There was a large amount of lipid accumulation in the liver of FF hens and differential gene analysis yielded 120 genes that were differentially expressed >2-fold in response to feeding level (p < 0.01; FDR < 0.05). Elevated T3 may indicate that general metabolism was affected by diet and GHR (p < 0.01) and IGF1 (p < 0.04) mRNA expression were both greater in the liver of FF hens as compared to RF hens. It is likely that selection for increased growth, associated with enhanced activity of the IGF1 system, has altered nutritional coupling of feed intake to follicle development.

Ad Libitum Feeding in Broiler Breeder Hens Alters the Transcriptome of Granulosa Cells of Pre-Hierarchal Follicles

Intense selective breeding of chickens has resulted in suboptimal egg production in broiler breeder hens. This reproductive phenotype is exacerbated by ad libitum feeding, which leads to excessive and disorganized follicular growth. One strategy used to improve broiler breeder hens' reproductive efficiency is restricted feeding. In this study, we sought to identify transcriptional changes, which translate the level of dietary intake into increased follicle selection. Broiler breeder hens (n = 16 per group) were raised according to commercial guidelines until 28 weeks of age and then randomly assigned to an ad libitum diet (FF) or continued on a restricted diet (RF) for 6 weeks. Following dietary treatment, FF hens (n = 2) with excessive follicle selection and RF hens (n = 3) with normal follicle selection were selected for RNA-sequencing. Transcriptomes of granulosa cells from 6-8-mm follicles were sequenced to identify transcriptional differences in the follicle population from which selection was made for the preovulatory stage. Differential expression analysis identified several genes known to play a role in follicle development (CYP11A1, STAR, INHA, and INHBB) that are upregulated in FF hens. These changes in gene expression suggest earlier granulosa cell differentiation and steroidogenic competency in the granulosa layer from FF hens.

The Autophagy Gene Atg16L1 is Necessary for Endometrial Decidualization

Uterine receptivity is critical for establishing and maintaining pregnancy. For the endometrium to become receptive, stromal cells must differentiate into decidual cells capable of secreting factors necessary for embryo survival and placental development. Although there are multiple reports of autophagy induction correlated with endometrial stromal cell (ESC) decidualization, the role of autophagy in decidualization has remained elusive. To determine the role of autophagy in decidualization, we utilized 2 genetic models carrying mutations to the autophagy gene Atg16L1. Although the hypomorphic Atg16L1 mouse was fertile and displayed proper decidualization, conditional knockout in the reproductive tract of female mice reduced fertility by decreasing the implantation rate. In the absence of Atg16L1, ESCs failed to properly decidualize and fewer blastocysts were able to implant. Additionally, small interfering RNA knock down of Atg16L1 was detrimental to the decidualization response of human ESCs. We conclude that Atg16L1 is necessary for decidualization, implantation, and overall fertility in mice. Furthermore, considering its requirement for human endometrial decidualization, these data suggest Atg16L1 may be a potential mediator of implantation success in women.

Anti-Müllerian hormone type II receptor in avian follicle development

Anti-Müllerian hormone (AMH) helps maintain the ovarian reserve by regulating primordial follicle activation and follicular selection in mammals, although its role within the avian ovary is unknown. In mammals, AMH is primarily produced in granulosa cells of preantral and early antral follicles. Similarly, in the hen, the granulosa cells of smaller follicles are the predominant source of AMH. The importance of AMH in mammalian ovarian dynamics suggests the protein and its specific Type II receptor, AMHRII, may have conserved functions in the hen. AMHRII mRNA expression is highest (P < 0.01) in small follicles of the hen and decreases as follicle size increases. Similarly, expression of AMHRII and AMH is highest in granulosa cells from small follicles as compared to larger follicles. Dissection of 3-5 mm follicles into ooplasm and granulosa components shows that AMHRII mRNA levels are greater in ooplasm than granulosa cells. Furthermore, immunohistochemistry also revealed AMHRII staining in the oocyte and granulosa cells. AMH expression in mammals is elevated during periods of reproductive dormancy, possibly protecting the ovarian reserve. AMHRII and AMH mRNA were significantly higher (P < 0.05) in nonlaying ovaries of broiler hens. In molting layer hens, AMHRII mRNA was significantly greater (P < 0.05) compared to nonmolting hen ovaries. These results suggest that AMH may have a direct effect on the oocyte and, thereby, contribute to bidirectional communication between oocyte and granulosa cells. Enhanced expression of AMHRII and AMH during reproductive quiescence supports a potential role of AMH in protecting the ovarian reserve in hens.

Occludin expression and regulation in small follicles of the layer and broiler breeder hen

Synchronized yolk accumulation and follicle development are essential for egg production in oviparous species. In birds, yolk is incorporated into the oocyte by an avian specific yolk receptor (LR8), and it has been suggested that occludin (OCLN), a tight junction protein, mediates transfer of yolk material to the oocyte surface. OCLN may be a key regulator of yolk accumulation and follicle growth, however, the expression and regulation of OCLN in granulosa cells during various stages of follicle development is unknown. In the first experiment, we found that LR8 and OCLN mRNA were highest in small follicles within the ovary. In addition, OCLN decreased with increasing follicle size. OCLN mRNA was more abundant in the germinal disc region of the granulosa cell layer than the non-germinal disc region. In addition, we found epidermal growth factor (EGF) and activin B, decreased OCLN mRNA, while activin A increased OCLN. In the second experiment, restricted fed (RF) broiler breeder hens were randomly divided into two groups and one group remained on RF and the other was fed ad libitum (FF). OCLN expression in granulosa cells of 3-5mm follicles of FF hens was lower compared to RF hens and yolk weights were higher in the FF group, however, LR8 mRNA in small whole follicles (<3mm) did not differ between groups. In conclusion, the level of feed intake is related to or may directly regulate OCLN mRNA expression or may have an indirect effect through paracrine or autocrine factors in the ovary.

Bone morphogenetic protein 15 may promote follicle selection in the hen

In the hen, optimal ovulation rate depends on selection of a single follicle into the pre-ovulatory hierarchy. Follicle selection is associated with increased oocyte growth and changes in gene expression in granulosa cells surrounding the oocyte, in preparation for ovulation. This study investigated the expression, function and regulation of bone morphogenetic protein-15 (BMP15) during follicle development in the hen. BMP15 mRNA expression was analyzed in the ooplasm and granulosa cells of 3mm follicles and was confirmed to be primarily in the ooplasm. BMP15 was detected by immunoblotting in 6 and 8mm follicles near the time of follicle selection. Expression of mRNA for BMP15 receptors (BMPR1B and BMPR2) in granulosa cells increased with follicle size, indicating that BMP15 may play an important role around follicle selection. The function of BMP15 was examined by culturing granulosa cells from 3-5mm and 6-8mm follicles with recombinant human BMP15 (rhBMP15). BMP15 increased expression of follicle stimulating hormone receptor (FSHR) mRNA and decreased anti-Müllerian hormone (AMH) mRNA and occludin (OCLN), factors associated with follicle maturation and growth in the hen. Hormonal regulation of BMP15 was assessed by whole follicle culture with estradiol (E2) which increased BMP15 mRNA expression. The distinct expression pattern of BMP15 and its receptors, coupled with the effects of BMP15 to increase FSHR mRNA and decrease AMH mRNA and OCLN mRNA and protein expression suggest that the oocyte may have a role in follicle selection in the chicken.

The domestic chicken: Causes and consequences of an egg a day

The domestic laying chicken has been intensely selected to be a persistent ovulator. That is, the tendency for broodiness has been nearly eliminated and, given the appropriate lighting and nutrition, many strains of laying hens produce an egg on almost every day. The regulatory mechanisms involved in coordination of neuroendocrine and ovarian events have been well studied and described. In spite of this, there has been little attention focused on the oocyte itself. Recent findings in mammals have indicated that the oocyte produces several oocyte-specific factors, including growth differentiation factor 9 (GDF9) and bone morphogenetic factor 15 (BMP15), which influence the surrounding cells and follicular development. Our studies indicate that GDF9 is present in the hen oocyte and influences granulosa cell proliferation. Additionally, Bmp15 mRNA is most abundant in oocytes of small follicles and stimulates an increase in follicle stimulating hormone (FSH) receptor mRNA in granulosa cells. BMP15 also enhances yolk uptake in growing follicles by decreasing tight junctions between granulosa cells. These studies indicate that the oocyte likely contributes to follicle development. Commercial laying hens also spontaneously develop ovarian cancer at a high rate, and susceptibility to this disease has been associated with ovulatory events in women. Studies have shown that ovulation, or events associated with ovulation, increase the prevalence of ovarian cancer in hens. Inhibition of ovulation in hens through a hormonal strategy mimicking oral contraceptives results in a decrease of ovarian cancer incidence. Recent studies in women have suggested that some ovarian tumors may arise from the distal oviduct. Gene expression profiles in very early stage tumors from hens show a high expression of oviduct-related genes, supporting the possibility of oviduct origin for some ovarian tumors. Genetic selection for high productivity in commercial laying hens has generated an efficient and valuable food source as well as an important animal model for human ovarian cancer.