PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: A proteome-based model for sperm mobility phenotype1,2

Abstract

Sperm mobility is defined as sperm movement against resistance at body temperature. Although all mobile sperm are motile, not all motile sperm are mobile. Sperm mobility is a primary determinant of male fertility in the chicken. Previous work explained phenotypic variation at the level of the sperm cell and the mitochondrion. The present work was conducted to determine if phenotypic variation could be explained at the level of the proteome using semen donors from lines of chickens selected for low or high sperm mobility. We began by testing the hypothesis that premature mitochondrial failure, and hence sperm immobility, arose from Ca(2+) overloading. The hypothesis was rejected because staining with a cell permeant Ca(2+)-specific dye was not enhanced in the case of low mobility sperm. The likelihood that sperm require little energy before ejaculation and the realization that the mitochondrial permeability transition can be induced by oxidative stress arising from inadequate NADH led to the hypothesis that glycolytic enzymes might differ between lines. This possibility was confirmed by 2-dimensional electrophoresis for aldolase and phosphoglycerate kinase 1. This outcome warranted evaluation of the whole cell proteome by differential detergent fractionation and mass spectrometry. Bioinformatics evaluation of proteins with different expression levels confirmed the likelihood that ATP metabolism and glycolysis differ between lines. This experimental outcome corroborated differences observed between lines in previous work, which include mitochondrial ultrastructure, sperm cell oxygen consumption, and straight line velocity. Although glycolytic proteins were more abundant within highly mobile sperm, quantitative PCR of representative testis RNA, which included mRNA for phosphoglycerate kinase 1, found no difference between lines. In summary, we propose a proteome-based model for sperm mobility phenotype in which a genetic predisposition puts sperm cells at risk of premature mitochondrial failure as they pass through the excurrent ducts of the testis. In other words, we attribute mitochondrial failure to sperm cell and reproductive tract attributes that interact to affect sperm in a stochastic manner before ejaculation. In conclusion, our work provides a starting point for understanding chicken semen quality in terms of gene networks.

Artificial Insemination in Poultry

“…The observations that receptors for estrogen and progesterone exist in the SSTs has led to the suggestion that these compounds may trigger release of resident sperm, possibly in response to hormonal cues over the course of the ovulatory cycle [50][51][52]. However, an alternate theory suggests the inherent mobility of the sperm plays a larger role than hormonal induction in egress of sperm from SSTs [9]. Resident sperm exhibit a slow, synchronized oscillatory movement in the lumen of SSTs, suggesting the presence of a fluid current through the SST lumen [23][24].…”

“…This selection occurs initially in the vagina: only highly mobile (defined as progressive movement in a viscous medium at 40 o C) sperm traverse the vagina [9]. While sperm mobility is a major factor in sperm selection in the vagina, sperm selection is also dependent upon the glycoprotein composition of the sperm plasma membrane.…”

“…Alternatively, about 7-10 days before their first ovulation, hens mate, sperm ascend the vagina and then enter the SSTs. At the onset of egg production, individual sperm are slowly released from the SSTs, transported to the anterior end of the oviduct, and interact with the surface of the ovum (see [9][10] for recent reviews). Whether fertilized or not, over the next 24-26 hr the ovum is transported though the oviduct, accruing the outer perivitelline layer (PL) in the infundibulum, the albumen in the magnum, the shell membrane in the isthmus, and the hard shell in the uterus (also referred to as the shell gland) before oviposition.…”

“…Following deposition in the oviduct, sperm are transported to UVJ by a combination of their intrinsic motility and cilia beat activity [9][10][22][23]. Within the SST lumen, sperm are either widely spaced or oriented parallel with their heads toward the distal end of the SST ( Figure 4).…”

“…Such motilityenhancing factors may include changes in environmental pH and neuroendocrine factors such as serotonin [58][59][60][61][62]. Further oxidation of sperm fatty acids, possibly sequestered from the surround milieu, generates the energy required for sperm to respond to such motilityenhancing factors and transcend the oviduct [9,22,55,63].…”