Roth, Z. | Search bioRxiv

bioRxiv2023

Egg MVBs elicit an antimicrobial pathway to degrade paternal mitochondria after fertilization

Mitochondria are maternally inherited, but the mechanisms underlying paternal mitochondrial elimination (PME) after fertilization are far less clear. Using Drosophila, we show that special egg-derived multivesicular bodies (MVBs) promote PME by activating LC3-associated phagocytosis (LAP), a cellular defense pathway commonly employed against invading microbes. Upon fertilization, the egg MVBs engage and densely coat the sperm flagellum, forming extended flagellum vesicular sheaths (FVSs), within which the paternal mitochondria degrade. Inactivation of multiple LAP pathway components, such as Rubicon, a LAP-specific class III PI(3)K complex protein, significantly attenuates PME. Furthermore, recruitment of Atg8/LC3 to the FVS requires both Rubicon and the Atg8/LC3 conjugation machinery. Other LAP pathway events, such as production of the phospholipid PtdIns(3)P and reactive oxygen species (ROS), also unfold during PME. Finally, we provide evidence that a similar pathway might also mediate PME in mammals, highlighting the notion that eggs may regard paternal mitochondria as potentially dangerous trespassers.

developmental biology↗

bioRxiv2021

Examining the quality and fertilization competence of bovine ejaculate with low progressive motility, should we give it a chance?

Spermatozoa progressive motility is positively correlated with fertilization competence. Bulls ejaculates with progressive motility lower than 50% are routinely rejected through the process of straw preparation, designated for artificial insemination of dairy cows. We examined the quality and fertility competence of ejaculates with relative low progressive motility (55-60%, n = 5; control) with those of very low progressive motility i.e. below the lower threshold, (20-45%, n = 5; rejected). Analysis revealed a lower volume for the control vs. rejected samples. Dip-Quick staining revealed a higher proportion of spermatozoa with abnormal morphology in the rejected group, in particular those with detached heads. Activation of spermatozoa with calcium ionophore, resulted by a lower proportion of activated spermatozoa in the rejected group. In addition, a higher proportion of spermatozoa with DNA damage were recorded in the rejected vs. the control samples. Following in-vitro fertilization, the proportion of oocytes that developed to the 2- and 4-cell stage embryos did not differ between groups. However, the proportion of embryos that further developed to blastocysts, was higher in the control group. Transcript abundance of selected genes in the blastocysts and the apoptotic index did not differ between groups, suggesting that the forming blastocysts were of the same quality. It is suggested that in specific cases, for example genetically superior bulls, ejaculates with very low progressive motility can be used for in vitro production of embryo. Further in vivo examinations, i.e. artificial insemination or transferring of embryos derived from these inferior ejaculates, might clarified this point.

physiology↗