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 (Lv-HSP40) was identified from the Pacific white shrimp Litopenaeus vannamei, 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 Lv-HSP40 transcript expression. Within these tissues, Lv-HSP40 mRNA were predominantly exhibited in the myocytes, epithelial cells and hepatopancreatic cells, respectively. Under acute thermal stress in the culture environment, Lv-HSP40 transcript levels are significantly induced in these three tissues, while low pH stress only upregulates Lv-HSP40 mRNA in the hepatopancreas and gill. During ontogenesis, Lv-HSP40 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 Lv-HSP40 mRNA expression in female shrimp, and Lv-HSP40 transcripts were mainly presented in the follicle cells but only weekly detected in the oocytes. Ovarian Lv-HSP40 mRNA levels increase continuously during gonadal development. Silencing of the Lv-HSP40 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 (Vg) and vitellogenin receptor (VgR). Our study, as a whole, provides new insights into the roles of HSP40 in multiple physiological processes in L. vannamei: (1) HSP40 is a responding factor during stressful conditions; and (2) HSP40 participates in embryonic and ovarian development.
Highlights
Heat shock proteins (HSPs), known as heat stress proteins, are a family of proteins that are produced by cells in response to various stressful conditions (Zhu et al, 1996; Johnston et al, 2018)
By prediction using the SMART and ScanProsite programs, a DnaJ domain, a glycine/phenylalanine-rich (G/F) domain, a Zn2+-binding CR domain and a CT domain were found in the deduced Lv-HSP40 protein sequence (Figures 1, 2A)
A 3-D model of the Lv-HSP40 dimer showed that the J domains were located in the exterior part, and the CT domains were located in the inner part (Figure 2B)
Summary
Heat shock proteins (HSPs), known as heat stress proteins, are a family of proteins that are produced by cells in response to various stressful conditions (Zhu et al, 1996; Johnston et al, 2018). HSPs were first identified in fruit flies that were exposed to a severely heat-shocked environment (Ritossa, 1962) and were subsequently demonstrated to be ubiquitously and evolutionarily conserved molecular chaperones that are present in all living organisms (Srivastava, 2002). According to their molecular weights, HSPs can be categorized into different families, including the HSP100, HSP90, HSP70, HSP60, HSP40 families and several small HSP families (Feder and Hofmann, 1999). HSPs participate in cellular processes such as protein folding and transport, cell cycle regulation and apoptosis (Mallouk et al, 1999; Johnston et al, 2018), as well as in physiological processes such as embryonic development, gonadal development and spermatogenesis (Allen et al, 1996; Binder, 2014; Chan et al, 2014)
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