Developmental expression of glucose and triose phosphate isomerase genes in teleost fishes (brachydanio)

Abstract

The ontogeny of glucosephosphate isomerase (GPI; E.C. 5.3.1.9) and triosephosphate isomerase (TPI; E.C. 5.3.1.1) isozymes in Brachydanio rerio, (zebra danio), B. albolineatus (pearl danio) and hybrids formed by their reciprocal crosses were examined by electrophoretic and spectrophotometric methods. The two species showed virtually identical adult, tissue-specific distributions and developmental progressions for both GPI and TPI isozymes. The Gpi-A and Tpi-B loci were expressed in all tissues studied. The Gpi-B locus was predominantly expressed in skeletal muscle and the Tpi-A locus in eye, brain and ovary. The GPI-A2, TPI-A2, TPI-AB and TPI-B2 isozymes were continuously expressed from fertilization through 5 days postfertilization. The GPI-B2 isozyme initially appeared at 35 hours postfertilization, temporally correlating with the early differentiation of trunk somite myoblasts. Spectrophotometric analysis of total GPI showed fluctuations in activity through 48 hours, followed by a steady increase through 4 days postfertilization. Total TPI showed increased activity by the end of gastrulation and a sharp rise in activity beginning at 25 hours postfertilization. Embryos of reciprocal hybrids between B. rerio and B. albolineatus showed that isozymes derived from the activation of the paternal Tpi-B, Gpi-A and Tpi-A alleles were initially detected at 20, 25, and 48 hours following fertilization, respectively. The maternal and paternal isozymes of the Gpi-B locus were synchronously expressed at 35 hours postfertilization. The pattern of GPI-B2 expression in hybrids followed a pattern similar to that in intraspecific crosses. Exposure of B. rerio embryos to pulses of actinomycin D at various stages prior to 35 hours postfertilization showed that messenger RNA encoding the GPI-B2 isozyme was first transcribed over a 14-hour interval initiated during mid-gastrulation. Translation of the GPI-B2 message occurred during a 13-hour period immediately preceding the embryonic expression of the GPI-B2 isozyme. Our studies with Brachydanio indicate that several gene loci are activated at gastrulation and transcribe messenger RNA molecules coding for histospecific isozymes associated with later stages of organogenesis.