Heat Shock Protein 40 (HSP40) in Pacific White Shrimp (Litopenaeus vannamei): Molecular Cloning, Tissue Distribution and Ontogeny, Response to Temperature, Acidity/Alkalinity and Salinity Stresses, and Potential Role in Ovarian Development

Abstract

Heat shock proteins (HSPs), a family of conserved proteins that are produced by cells in response to stresses, are known as molecular chaperones with a range of housekeeping and cellular protective functions. The 40 kD heat shock protein (HSP40) is a co-chaperone for HSP70 in the regulation of ATP hydrolysis. Unlike its well-documented cofactor HSP70, little is currently known regarding the biological functions of HSP40 in crustacean species such as penaeid shrimp. In the present study, the cDNA encoding HSP40 (<i>Lv</i>-HSP40) was identified from the Pacific white shrimp <i>Litopenaeus vannamei</i>, a highly significant commercial culture species. The structural organization indicates that Lv-HSP40 belongs to the type-I HSP40s. The muscle, gill, and hepatopancreas are the main sites of <i>Lv-HSP40</i> transcript expression. Within these tissues, <i>Lv-HSP40</i> mRNA were predominantly exhibited in the myocytes, epithelial cells and hepatopancreatic cells, respectively. Under acute thermal stress in the culture environment, <i>Lv-HSP40</i> transcript levels are significantly induced in these three tissues, while low pH stress only upregulates <i>Lv-HSP40</i> mRNA in the hepatopancreas and gill. During ontogenesis, <i>Lv-HSP40</i> transcript levels are high at early embryonic stages and drop sharply at late embryonic and early larval stages. The ovary is another major organ of <i>Lv-HSP40</i> mRNA expression in female shrimp, and <i>Lv-HSP40</i> transcripts were mainly presented in the follicle cells but only weekly detected in the oocytes. Ovarian <i>Lv-HSP40</i> mRNA levels increase continuously during gonadal development. Silencing of the <i>Lv-HSP40</i> gene by RNA interference may effectively delay ovarian maturation after unilateral eyestalk ablation. The roles of Lv-HSP40 in ovarian development are speculated to be independent of its cofactor HSP70, and the vitellogenesis factor vitellogenin (<i>Vg</i>) and vitellogenin receptor (<i>VgR</i>). Our study, as a whole, provides new insights into the roles of HSP40 in multiple physiological processes in <i>L. vannamei</i>: (1) HSP40 is a responding factor during stressful conditions; and (2) HSP40 participates in embryonic and ovarian development.