Biochemical and Biophysical Research Communications
Integrative omics analysis reveals differentially distributed proteins in dimorphic euspermatozoa of the squid, Loligo bleekeri
Introduction
In essence, most cells can respond and adapt to their environments by means of transcriptional, post-transcriptional and post-translational events [1]. In particular, a specific set of gene expression facilitates a cell’s optimal reactions in favorable or unfavorable conditions. Spermatozoa are highly specialized, differentiated haploid cells that largely lack transcriptional and translational activities, although some exceptional cases have been reported [2]. Basically, sperm design and their behavioral traits are endowed during spermatogenesis and spermiogenesis. Therefore, in the same species, each sperm cell is expected to behave equally in response to the same environmental cue. In this context, the squid Loligo bleekeri offers a very unique feature regarding two separate sperm traits in two separate male types; (1) large males called “consort” produce small spermatozoa and small “sneaker” males produce ∼50% much larger sperm [3], (2) for the sneakers only, spermatozoa form a cluster in response to carbon dioxide [4], [5]. Such sperm dimorphism is tightly linked to male mating behaviors. Large males have an advantage in copulation, placing sperm inside the oviduct. Small males, however, avoid male-male competition and undertake “sneaky copulation” placing their spermatozoa on the buccal membrane of the female [6], [3], [7]. Fitness consequences of these different sperm phenotypes remain unknown. Moreover, the mode of inheritance as well as the ontogenetic question of how this male dimorphism arose remains unanswered.
Apart from trying to gather some insight into these intriguing evolutionary questions, we attempted to understand the developmental processes that drive spermatogenesis into different types of sperm cells. Because sperm are in general translationally silent, the differences should be evident at the levels of transcription and/or translation in the testis. Using this assumption, we used a comparative “omics” approach to identify differentially expressed transcripts and proteins that can potentially contribute to consort- or sneaker-specific traits.
Section snippets
Handling of animals and spermatozoa
Mature L. bleekeri were collected at Miura (Sagami-bay, Kanagawa) or Matsumae (southeast Hokkaido Island), Japan, and transported in chilled containers (4 °C) to the laboratory within two days. Adult males produce spermatophores, which are cylindrical capsules containing mature sperm. Consort males and sneaker males were distinguished by spermatophore lengths and spermatangium morphology [6], [3]. Spermatozoa were released from spermatophores by mechanically stimulating the spermatophoric
Results and discussion
The lifespan of L. bleekeri is estimated to be ∼1 year [16] and during the last few months (Dec–Apr) of their lifetime individuals conduct the mass spawning in shallow water. Sneaker and consort males were collected simultaneously at the same place to obtain comparative gene/protein expression profiles (Fig. 1). We undertook this in the middle of the spawning season (Feb in Sagami-bay) and relatively smaller mature individuals for both male types were chosen to collect testicular mRNAs, because
Acknowledgments
The authors thank NIG Cell Innovation program (http://cell-innovation.nig.ac.jp/g). Supported by MEXT (NH), Yamada Science Foundation (NH), and NRF (WHHS).
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These authors equally contributed to this work.