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In this study, one of Doublesex genes from the common freshwater cladoceran Daphnia carinata, designated DapcaDsx1, was cloned using primers based on homologous sequences and rapid amplification of cDNA ends (RACE). qPCR was employed to quantify differences in DapcaDsx1 expression between the different sexual phases, with expression levels being higher in sexual females. The role of DapcaDsx1 in the reproductive transformation was further investigated in parthenogenetic-phase females and sexual-phase females using whole-mount in situ hybridization. This cellular localization study showed specific expression of DapcaDsx1 in the thoracic segments, second antenna and part of the ventral carapace. Higher expression levels were exhibited in sexual females compared to parthenogenetic females. This suggests that the DapcaDsx1 gene plays significant roles in switching modes of reproduction and during sexual differentiation., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The cladoceran Daphnia carinata undergoes an unusual transition from asexual to sexual reproduction in response to environmental stimuli. Previously, a D. carinata cuticular protein (CP) was identified in an EST library. In this study, the full-length CP cDNA was cloned and sequenced (GenBank accession number: KF551931), and the expression levels in different reproductive states were assessed. Parthenogenetic and sexual female D. carinata were isolated, and CP expression was investigated using semiquantitative reverse transcription polymerase chain reaction (RT-PCR). CP was expressed during both reproductive stages, but expression was higher in sexual females. Cellular localization was also investigated using digoxin-labeled RNA probes in RNA whole-mount in situ hybridization assays, and CP was mainly expressed in the first pair of thoracic appendages, the surface of the head, shell spines, and other parts of the epidermis in parthenogenetic organisms. In contrast, CP expression was restricted to the thoracic appendages in sexual females.

Daphnia (water fleas) are small crustaceans that undergo an unusual switch from asexual to sexual reproduction that is dependent on environmental conditions. In this study, a senescence-associated protein (SAP) from the common freshwater species Daphnia pulex was cloned using primers based on homologous sequences and rapid amplification of cDNA ends (RACE). Real-time PCR was employed to quantify the expression of D. pulex SAP (DpSAP) in individual organisms. The role of DpSAP in the reproductive transformation was further investigated in both parthenogenetic and sexual females by using digoxin-labeled SAP RNA probes and RNA whole-mount in situ hybridization. DpSAP was more highly expressed in sexual females, indicating a role in growth and reproduction. Cellular localization studies using RNA whole-mount in situ hybridization showed specific expression in the second tentacle joints. These expression patterns suggest an important role for DpSAP in the reproductive transformation of D. pulex., (Copyright © 2013 Elsevier B.V. All rights reserved.)