Assessment of the Effects of Double-Stranded RNAs Corresponding to Multiple Vitellogenesis-Inhibiting Hormone Subtype I Peptides in Subadult Female Whiteleg Shrimp, Litopenaeus vannamei

Vitellogenesis-inhibiting hormone (VIH) negatively regulates reproduction in shrimp and other decapod crustaceans. In order to assess the effects of transcriptional silencing by multiple VIH subtype I sinus gland peptides (SGPs) on ovarian maturation in female whiteleg shrimp, Litopenaeus vannamei, we synthesized five dsRNAs targeting Liv-SGP-A, −B, −C, −F, and −G and injected them into subadults. The following treatments were employed: sgpG-dsRNA (targeting Liv-SGP-G), sgpC-dsRNA (targeting Liv-SGP-C), and mixed-dsRNA (targeting Liv-SGP-A, −B, and −F). The expression of Liv-SGP-G in eyestalks was significantly decreased at 10, 20, and 30 days after the injection of sgpG-dsRNA In addition, it was significantly decreased at 10 and 30 days after the injection of mixed-dsRNA. The expression of vitellogenin (Vg) gene expression in the ovaries, and concentrations of Vg protein in the hemolymph, were not changed by the administration of any dsRNA treatment (the ovaries remained immature in all treated individuals and contained mostly oogonia and previtellogenic oocytes). Although the administration of dsRNAs corresponding to multiple VIHs did not promote ovarian maturation, this is the first report of the co-transcriptional repression of Liv-SGP-G by the injection of dsRNA for homologous genes (Liv-SGP-A, −B, and −F). These results indicate that subadults can respond to the techniques of transcriptional silencing.

Fine structure of neurosecretory cells and sinus gland in the eyestalk of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae)

This study elucidated the fine structure of neurosecretory cells and sinus gland in the optic ganglia of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae). The eyestalk ganglion showed the presence of four well defined ganglia arranged below the ommatidium: lamina ganglionaris, medulla externa, medulla interna and medulla terminalis of which the lamina ganglionaris, was devoid of neurosecretory cells. Groups of neurosecretory cells seen distributed along the medulla externa, interna and terminalis regions constitute the X-organs. Electron microscopic observations of the eyestalk ganglia revealed ten types of neurosecretory cells, mostly apolar with a few unipolar and bipolar cells classified according to the size, shape and density of the cell and nucleus, cell organelles/inclusions, together with the arrangement and properties of chromatin. These cells were characterized by the presence of large nuclei with unusually condensed chromatin, inclusions like vacuoles and vesicles of varying size, shape and density and organelles like Golgi, endoplasmic reticulum, ribosomes and mitochondria and neurosecretory material. The sinus gland of T. schirnerae was positioned laterally between the externa and interna regions, composed of axonal endings of the neurosecretory cells of the optic ganglia with interspersed glial cells. The axon terminals were enclosed with several small to large membrane bound homogenously dense neurosecretory granules which also occur in the preterminal areas of the axons. Based on size, shape and density of granules and axoplasmic matrix, seven terminal types could be distinguished in the sinus gland of T. schirnerae. Mostly, the granules contained in a terminal were of the same type; rarely, the same terminal enclosed granules of varying size, shape and density. The neurosecretory cell types and axon terminal types represent the types of neurohormones they contained. A precise knowledge of the morphology and cytology of neurosecretory cells in the XO-SG complex of the eyestalk that secrete neurohormones controlling major physiological processes such as growth and reproduction is imperative for successful captive breeding of a species of aquaculture potential.

Identification of peptides from sinus gland extracts in the red swampcrayfish Procambarus clarkii by mass spectrometry

Crustacean sinus gland (SG) is a well-defined neuroendocrine organ that controls the secretion of various neuropeptides which regulate many physiological activities. The red swamp crayfish Procambarus clarkii is a decapod crustacean with both high economic and scientific importance in China. To facilitate physiological investigations of SG peptide/hormone function in this species, we have been employed tissue extract fractionation by HPLC to obtain a complete description of neuropeptidome and used Electrospray ionization-Fourier transform mass spectrometry (ESI-FTMS) to detect the peptidome present in its organ. In total, 48 peptide sequences belonging to several known neuropeptide families including crustacean cardioactive peptide, CHH precursor-related peptides (CPRPs), orcokinins and pigment dispersing hormones were identified. Among these 48 sequences, 26 are novel peptides and 22 are previously identified. Overall, the results give a stimulus for future physiological studies of SG neuropeptides in P. clarkii and other crustaceans.