Starch gel electrophoresis of the multiple haemo-globins of small and large larval Chironomus— a developmental haemoglobin sequence in an invertebrate

Abstract

ABSTRACT Small larvae (1-4 mg each) of Chironomus plumosus, whether surveyed in pooled samples or individually, have eight different haemoglobins in the haemolymph. Large larvae (8-11 mg each) of this species have ten different haemoglobins. Seven of the haemoglobins are unchanged throughout larval development. However, small larvae lack two of the major and one of the minor haemoglobins found in all large larvae; furthermore, a unique major haemo-globin of small larvae occurs only in traces in large larvae. The heterogeneity and the ontogenetic differences in Chironomus haemo-globin persist whether the haemoglobin is studied as oxyhaemoglobin, carbon-monoxyhaemoglobin, methaemoglobin or methaemoglobin cyanide, although the electrophoretic mobilities of some of the haemoglobin components are shifted by combination with different ligands and, especially, by oxidation to methaemoglobin. The heterogeneity and the ontogenetic differences are not altered by treatment of the haemoglobin with —SH and —S—S— reagents, nor by conversion of haemoglobin to globin by splitting off the haem with acid-acetone. Electrophoresis of globins prepared from each of the isolated major and minor Chironomus haemoglobins suggests that, in contrast to typical vertebrate haemoglobins, there is only a single polypeptide chain type in each of the multiple Chironomus haemoglobins. However, each of the multiple haemo-globins probably has a unique haemoglobin chain type, suggesting that each Chironomus haemoglobin component is coded from a different gene. Thus the insect Chironomus resembles the human in possessing an onto-genetic haemoglobin sequence involving both constant expression of some haemoglobin genes and modulation of the activity of others. As, in contrast to the human, Chironomus possesses giant chromosomes in many of its tissues, this discovery of an ontogenetic sequence to the major soluble protein present in larval Chironomus presents an attractive system for studying the interrelations between protein phenotype and the nuclear genotype during development.