Chauvigne, F. | Search bioRxiv

bioRxiv2021

Protamine lacking piscine spermatozoa are transcriptionally active

Transcriptional quiescence of post-meiotic spermatozoa associated with protamine-mediated chromatin condensation is widely recognized in animals. How sperm acquire the extratesticular maturational competence to move and fertilize the egg is therefore thought to occur via non-transcriptional mechanisms. Here, using transcriptional profiling during spermatozoon differentiation in a fish that does not condense chromatin with protamines, we uncover spatially distinct roles of the GnRH receptor and PDGF signaling pathways between the somatic epithelia of the extratesticular ducts and the maturing spermatozoa. In vitro induction and inhibition experiments demonstrate that the endocrine signaling pathways are conserved in different lineages of fish and activate de novo transcription of spermatozoon genes required for the acquisition of full motility. These experiments further confirmed that mitochondrial translation is important for sperm maturation in anamniotes as in amniotes, but that transcriptional quiescence of post-meiotic spermatozoa is not a pan vertebrate phenomenon. On the contrary, the data show that the identified signal transduction pathways between the soma and the sperm upregulate effector genes essential for maturational competence and male fertility.

cell biology↗

bioRxiv2020

Providing recombinant gonadotropin-based therapies that induce complete gametogenesis and produce viable larvae from an immature teleost, flathead grey mullet (Mugil cephalus)

Under intensive captive conditions, wild-caught flathead grey mullet (Mugil cephalus) females remained arrested at early gonad development and no sperm could be obtained from males. With the aim to induce and complete oogenesis, induce the release of sperm and obtain fertilized eggs, adult female and male grey mullet were treated with M. cephalus single-chain recombinant gonadotropins (rGths), follicle-stimulating (rFsh) and luteinizing (rLh) hormones. In Experiment 1, fish were treated with a weekly dose of rFsh (15 g kg-1), which in females significantly (P < 0.001) increased plasma concentration of 17{beta}-estradiol and induced vitellogenic oocyte growth up to a maximum mean diameter of 425 {+/-} 19 m after 9 weeks of treatment. In Experiment 2, fish were treated with weekly injections of both rFsh and rLh at different doses (from 2.5 to 12 g kg-1). Oocyte diameter reached 609 {+/-} 5 m, from which final oocyte maturation and ovulation was induced with 30 g kg-1 of rLh and 40 mg kg-1 of progesterone. Good quality sperm (> 75% motile spermatozoa) was obtained from males in both experiments, and in Exp. 2 the addition of rLh induced the production of higher quantities of sperm that were used to fertilise the eggs. Although fertilisation was low (0.4 %), these fertilized eggs with embryo development produced viable larvae (71% hatching rate). This is the first report in a teleost species, to obtain larvae from eggs that were from immature females induced through to maturation with rGths. In comparison, control females remained arrested as immature fish and control males did not produce sperm. The study demonstrated that both rGths are effective to induce the entire process of oogenesis in sexually immature female grey mullet and to obtain flowing sperm from males, adding more data to confirm the roles of the Gths in teleost gametogenesis. This advance provides the bases of a therapy for the use in the aquaculture of teleost of commercial interest or the conservation of endangered species.

physiology↗