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Transcript levels of the soluble sperm factor protein phospholipase C zeta 1 (PLCζ1) increase through induced spermatogenesis in European eel

M. Morini, D.S. Peñaranda, M.C. Vílchez, V. Gallego, R. Nourizadeh-Lillabadi, J.F. Asturiano, F.-A. Weltzien, L. Pérez

Activation at fertilization of the vertebrate egg is triggered by Ca²⁺ waves. Recent studies suggest the phospholipase C zeta (PLCζ), a sperm-specific protein, triggers egg activation by an IP3-mediated Ca²⁺ release and allow Ca²⁺ waves at fertilization.

In the present study we cloned, characterized, and phylogenetically positioned the European eel PLCζ (PLCζ1). It is 1521bp long, with 10 exons encoding an open reading frame of 506 amino acids. The amino acid sequence contains an EF-hand domain, X and Y catalytic domains, and a carboxy-terminal C2 domain, all typical of other PLCζ orthologous. The sequence is truncated not only at the N-terminus of the EF-hand domain, as in all teleost PLCζ, but also in the C-terminal region of the X-domain and in a large part of the N-terminal X/Y linker region.

The tissue distribution was studied, and the gene expression was determined in testis during induced sexual maturation at three different thermal regimes. Also, brain and pituitary expression were studied through sex maturation at constant temperature. plcζ1 was expressed in brain of male and female, in testis but not in ovaries. By first time in vertebrates, it is reported plcζ1 expression in the pituitary gland. Testis plcζ1 expression increased through spermatogenesis under all the thermal regimes, but being significantly elevated at lower temperatures. It was very low when testis contained only spermatogonia or spermatocytes, while maximum expression was found during spermiogenesis. These results support the hypothesis for an eel sperm-specific PLCζ1 inducing egg activation, similarly to mammals and some teleosts, but different from some other teleost species, which express this protein in ovaries, but not in testes.