## 1 Introduction  
Vitellogenesis is a hormally regulated process for synthesizing yolk proteins and an important step in the reproductive development of crustaceans [1]. Vitellogenin (VTG), a precursor molecule of vitellin, is stored in crustacean hepatopancreas tissue and transported by the hemolymph to the ovaries. The sites of VTG synthesis are in the hepatopancreas and ovary tissues in decapod crustaceans [2; 3; 4; 5]. VTG genes have shown specific levels of expressions that vary by tissue, sex, and development stage [6]. VTG inductions were observed in aquatic invertebrates by exposure to estrogenic compounds [7; 8]. After endosulfan exposure, VTG gene expression was downregulated in Pandalus shrimp (_Pandalopsis japonica_) [9]. The regulation of VTG gene may be affected by several pollutants [7; 8; 9].  
Environmental chemical pollution is globally one of the most critical ecological problems, owing to the high risks it poses to ecosystems and human life [10]. Bisphenol A (BPA), a common endocrine disrupting chemical (EDC), is a carbon-based synthetic compound and a xenoestrogen that interferes with estrogen receptor signaling [11]. BPA concentrations observed in U.S. river estuaries were approximately 4 \(\upmu\)g L\({}^{-1}\) to 21 \(\upmu\)g L\({}^{-1}\)[12; 13]. Exposure to BPA induced transcription responses of the heat shock protein 90 (HSP90) gene in the marine crab _Charybdis japonicus_[14]. Di-(2-ethylhexyl) phthalate (DEHP), a suspected EDC, is widely used as plasticizer and may induce reproductive and developmental toxicities in aquatic environments [15]. DEHP toxicity induced changes in the VTG levels in African sharptooth catfish (_Clarias gariepinus_) and the Chinese rare minnow (_Gobiocypris arrus_) [16; 17]. DEHP levels were 0.47 to 12 \(\upmu\)g L\({}^{-1}\) in the China river estuary [18]. Irgarol, which is used as an aligicide, has been found in coastal and estuarine environments because it is commonly used in antifouling systems [19; 20]. Irgarol exposure induced downregulation of HSP90 expression in hard coral (_Acropora tenuis_) [21]. Worldwide, the environmental concentrations of irgarol in antifouling systems range from 1 ng L\({}^{-1}\) to 1 mg L\({}^{-1}\)[22]. Irgarol's long half-life poses an ecological risk in estuarine ecosystems [20]. Although these pollutants are ubiquitously distributed in aquatic environments, there is not enough information about the effects of embryogenesis in crustaceans.  
Crabs make up one of the largest crustacean families. The accumulation and synthesis of VTG is vital for oocyte and embryo development in crabs [2; 6; 23]. A burrowing mud crab, _Macrophthalmus japonicus_ (Ocypoodoidea), inhabits estuarine intertidal mud flats throughout the Indo-Pacific regions of Japan and Korea [24; 25; 26; 27]. _M. japonicus_ is also a major bioturbator of tidal flats and plays a crucial role in purifying sediment [28]. The movement of _M. japonicus_ may affect the distribution of macro-infauna because of the accompanying disturbance in the physical and chemical properties of the sediment [25]. Previous studies have suggested that _M. japonicus_ may be a useful indicator for modeling the exposure effects of chemical toxicity in the sediment environment [26; 27; 29; 30].  
In this study, we assessed the effects of crustacean embryogenesis and endocrine process by environmental chemical pollutants such as BPA, DEHP, and irgarol using the intertidal mud crab. To accomplish this, we characterized the _M. japonicus_ VTG gene and analyzed phylogenetic relationships. The transcriptional responses of VTG and the tissue distribution of VTG mRNA expression were investigated from _M. japonicus_ ovaries and hepatopancreases, plus other tissues, following exposure to either BPA, DEHP, or irgarol.