Male Differentiation in the Marine Copepod

Copepods are among the most numerous animals, and they play an essential role in the marine trophic web and biogeochemical cycles. The genus Oithona is described as having the highest density of copepods. The Oithona male paradox describes the activity states of males, which are obliged to alternate between immobile and mobile phases for ambush feeding and mate searching, respectively, while the female is less mobile and feeds less. To characterize the molecular basis of this sexual dimorphism, we combined immunofluorescence, genomics, transcriptomics, and protein-protein interaction approaches and revealed the presence of a male-specific nervous ganglion. Transcriptomic analysis showed male-specific enrichment for nervous system development-related transcripts. Twenty-seven Lin12-Notch Repeat domain-containing protein coding genes (LDPGs) of the 75 LDPGs identified in the genome were specifically expressed in males. Furthermore, some LDPGs coded for proteins with predicted proteolytic activity, and proteases-associated transcripts showed a male-specific enrichment. Using yeast double-hybrid assays, we constructed a protein-protein interaction network involving two LDPs with proteases, extracellular matrix proteins, and neurogenesis-related proteins. We also hypothesized possible roles of the LDPGs in the development of the lateral ganglia through helping in extracellular matrix lysis, neurites growth guidance, and synapses genesis.