Lymphoid Tissue Ontogeny in the Mummichog, Fundulus heteroclitus

Abstract

Most studies that examine the ontogeny of lymphoid organ development in teleostean fishes use species of interest to aquaculture or genetic research and, to date, have focused strictly on marine or freshwater species. The mummichog, Fundulus heteroclitus, also known as the estuarine killifish, is a unique model for studies on developmental immunobiology, because it is euryhaline, has a high degree of thermal tolerance, and has a unique reproductive strategy. Embryonic and larval mummichogs were examined for the ontogeny of lymphoid tissue development. The first lymphoid organ to appear was the head kidney at 1 dph, followed by the spleen at 1 wph, and then the thymus at 3 wph. Rag-1 was partially cloned and sequenced and shown to be highly conserved among other vertebrate Rag-1 genes. Using QT-PCR to monitor the temporal expression of Rag-1, it was shown to reach a maximum intensity at 3 and 4 wph and then to drop to pre-2-wph levels. Overall, this study suggests that juvenile mummichogs do not possess the ability to mount T-or B-cell responses until some time after 5 wph. Even though the estuarine killifish tolerates a wide range of salinities, the developmental patterns of lymphoid tissues are similar to what has been reported for strictly marine (stenohaline) teleosts. Thus, the mummichog should be a convenient model for understanding the developmental immunobiology of most marine teleosts.

Histology and ultrastructure of the thymus during development in tilapia, Oreochromis niloticus

“…Previous studies have shown that recombination-activating genes are highly conserved in different types of fishes (Brinkmann et al 2004;Hunt & Rice, 2008) and are specifically expressed in the early stage of thymus development (Hunt & Rice, 2008;Iwanami et al 2008Iwanami et al , 2011. Therefore, in the present study, the position of the thymus in the early developmental stages was confirmed using the position of Rag1 in WISH of tilapia embryos.…”

“…Previous studies have shown that recombination‐activating genes are highly conserved in different types of fishes (Brinkmann et al. ; Hunt & Rice, ) and are specifically expressed in the early stage of thymus development (Hunt & Rice, ; Iwanami et al. , ).…”

Thymus development in the zebrafish (Danio rerio) from an ecoimmunology perspective

“…However, as shown by the present study and by Lam et al (2002), expansion and rapid growth of the thymus takes place only during the juvenile period of zebrafish. This thymus development pattern appears to be more generally realized in teleost fish, with the thymus being the first lymphoid organ to differentiate morphologically (Davidson & Zon, 2004; Rombout et al, 2005; Seemann et al, 2015; Zapata et al, 2006) and becoming only functional in the juvenile period (Falk‐Petersen, 2005; Hunt & Rice, 2008; Lam et al, 2004; Mulero et al, 2007; O'Neill, 1989; Parichy et al, 2009; Tatner & Manning, 1983). This late onset of thymus development and adaptive immune systems appears to be expressed in all teleost species that have been studied to date.…”

Role of maternally derived immunity in fish

“…The major lymphomyeloid organs of fishes are thymus, head kidney and spleen [20,21]. The ontogeny of the lymphomyeloid organs start developing within few hours post fertilization [22][23][24][25][26][27][28][29][30][31][32][33][34][35] (Table 1) but the sequence of development differs markedly among the freshwater, estuarine and marine species [25][26][27][28][29][30][36][37][38][39]. Thymus is the first organ to become lymphoid, followed by kidney and spleen [38].…”