The imprinted H19 gene produces a non-coding RNA of unknown function. Mice lacking H19 show an overgrowth phenotype, due to a cis effect of the H19 locus on the adjacent Igf2 gene. To explore the function of the RNA itself, we produced transgenic mice overexpressing H19. We observed postnatal growth reduction in two independent transgenic lines and detected a decrease of Igf2expression in embryos. An extensive analysis of several other genes from the newly described imprinted gene network (IGN) was performed in both loss- and gain-of-function animals. We found that H19 deletion leads to the upregulation of several genes of the IGN. This overexpression is restored to the wild-type level by transgenic expression of H19. We therefore propose that the H19 gene participates as a trans regulator in the fine-tuning of this IGN in the mouse embryo. This is the first in vivo evidence of a functional role for the H19 RNA. Our results also bring further experimental evidence for the existence of the IGN and open new perspectives in the comprehension of the role of genomic imprinting in embryonic growth and in human imprinting pathologies.

Glycylation regulates axonemal dyneins: Physiological functions of the microtubule cytoskeleton are expected to be regulated by a variety of posttranslational tubulin modifications. For instance, tubulin glycylation is almost exclusively found in cilia and flagella, but its role in the function of these organelles remains unclear. Gadadhar et al. now demonstrate in mice that glycylation, although nonessential for the formation of cilia and flagella, coordinates the beat waveform of sperm flagella. This activity is a prerequisite for progressive sperm swimming and thus for male fertility. At the ultrastructural level, lack of glycylation perturbed the distribution of axonemal dynein conformations, which may explain the observed defects in flagellar beat. Science , this issue p. eabd4914

The process of gamete fusion has been largely studied in the mouse and has revealed the crucial role of the tetraspanin CD9. By contrast, human gamete fusion remains largely unknown. We now show that an anti-α6 integrin mAb (GoH3) strongly inhibited human sperm-egg fusion in human zona-free eggs. Furthermore, a mAb directed against CD151, a tetraspanin known to associate with α6β1, partially inhibited sperm-egg fusion. By contrast, the addition of an anti-CD9 mAb to zona free eggs had no effect. The integrin α6β1, CD151 and CD9 tetraspanins were evenly distributed on human zona-intact oocytes. On zona-free eggs, the integrin α6β1 and tetraspanin CD151 patched and co-localized but the tetraspanin CD9 remained unchanged. CD9 mAb prevented α6β1 integrin clustering and gamete fusion when added prior to, but not after, zona removal. Antibody-mediated aggregation of integrin α6β1 yielded patches that were bigger and more heterogeneous in mouse oocytes lacking CD9. Moreover, a strong labelling of α6β1 could be observed at the sperm entry point. Altogether, these data show that CD9 controls the redistribution of some membrane proteins including the α6β1 integrin into clusters that may be necessary for gamete fusion.

CD9 tetraspanin is the only egg membrane protein known to be essential for fertilization. To investigate its role, we have measured, on a unique acrosome reacted sperm brought in contact with an egg, the adhesion probability and strength with a sensitivity of a single molecule attachment. Probing the binding events at different locations of wild-type egg we described different modes of interaction. Here, we show that more gamete adhesion events occur on Cd9 null eggs but that the strongest interaction mode disappears. We propose that sperm–egg fusion is a direct consequence of CD9 controlled sperm–egg adhesion properties. CD9 generates adhesion sites responsible for the strongest of the observed gamete interaction. These strong adhesion sites impose, during the whole interaction lifetime, a tight proximity of the gamete membranes, which is a requirement for fusion to take place. The CD9-induced adhesion sites would be the actual location where fusion occurs.