Gametic synapses, nanotubes and sperm RNAs – Redefining the origin of maternal determinants

The female germline cells, i.e., the oocytes/eggs, contain a subpopulation of unique organelles and molecules (RNA and proteins) collectively called "the maternal determinants" that are indispensable for the determination of cell fate in the developing embryo. Although it has been known for some time that somatic cells deliver low-molecular-weight molecules to the oocyte/egg, the paradigm has been that the larger molecules and organelles are synthesized by the female germline cells without input from the surrounding somatic cells. However, recent discoveries of novel types of intercellular connections such as gametic synapses and tunneling nanotubes, allowing the transfer of large, externally derived molecules to the oocyte/egg, may dismantle the paradigm of the transcriptional/translational self-containment of the female gamete and add novel and unexpected aspects to the origin and identity of maternal determinants. In addition, the discovery that sperm delivers various RNAs to the egg suggests that sperm may not only epigenetically modify the egg genome but also influence or modify information contained in the maternal determinants.