Developmental Genetics on the Lactate Dehydrogenase (LDH) Isozyme During Early Embryogenesis in Salmonids

Lactate dehydrogenase (LDH) isozyme patterns were surveyed to obtain useful genetic markers in the developmental genetics among 5 species of salmonid fishes, masu salmoa (Oncorhynchus masou), chum salmon (0. ketal, coho salmon (0. kisutch) , whitespotted char (Salvelinus leucomaenis) and dolly varden char (S .. malma). There were electrophoretic differences in isozyme patterns of the LDH-B system between masu salmon and the other four species of salmonids. Developmental studies showed that only maternal LDH isozyme had appeared until the time of the tail bud stage characterized by the enclosure of blastopore and formation of the tail bud. Paternal isozyme subunit became detectable at this stage in the viable intergeneric hybrids, masu salmon !j1 X whitespotted char ~, masu salmon !j1 X dolly varden char ~ a.nd the interspecific hybrid, masu salmon !j1 X coho salmon ~. At about the same stage, changes in LDH isozyme pattern were also observed both in chum salmon and whitespotted char. The results obtained here suggest that the paternal gene activation on Ldh-B1 and -B. loci may start from the tail bud stage in the embryogenesis of salmonids. An effective approach in the developmental genetics is to hybridize animals each having phenotypically distinct isozymes. Analyses of the paternal gene activation by means of the zymogramic detection of paternal isozymic subunit during the embryogenesis of the resultant hybrid were carried out in some teleosts.1-7) The present authors in the previous workS) demonstrated that maternal isozyme pattern appeared during earlier stages of embryogenesis, and an additional isozyme containing paternal LDH-Bl isozymic subunit also appeared from the tail but stage in the interspecific hybrid masu salmon ~ X pink salmon 6. Although these results suggested that the activation of paternal Ldh-Bt gene occurred at the tail bud stage, we could not determine the activation time of paternal Ldh-B2 gene in that interspecific hybrid experiment because the position of LDH-B: was overlapped between masu salmon and pink salmon. As it has been proven in the present study that there is an allelic difference in Ldh-B2 gene locus between masu salmon and two species of Salvelinus; whitespotted char, dolly varden char, we aimed to study further the activation time of the paternal Ldh-B2 gene which originated from Salvelinus in the intergeneric hybrid masu salmon ~ X whitespotted char 6 and masu salmon ~ X dolly varden char * Oontribution No. 15 from the Nanae Fi8h Oulture Experimental Station ** Present address: School of Fisheries Sciences, Kitasato University, Sanriku-cho KesenGun. Iwate prefecture (~I:;.!I!*~ Jj(it~flII) *** Labolatory of Embryology and Genetics, Faculty of Fisheries Hokkaido University (~l:;tlUi*~ Jj(it~$ ~~~iI~~iIIt~)