Molecular characterization, developmental expression and immunolocalization of clathrin heavy chain in the ovary of the American cockroach, Periplaneta americana during oogenesis

Clathrin is the principal protein involved in receptor mediate endocytosis and the main component of the coated vesicles. It is composed of three identical clathrin heavy chains (CHC), each with an attached light chain. We characterized the deduced amino acid sequence of the partial cDNA clone of the American cockroach, Periplaneta americana (Pam) CHC. The analysis showed that this sequence is represented as multiple alpha helical repeats occurred in the arm region of the CHC and displayed a high level of identity and similarity to mosquitoes and Drosophila melanogaster CHCs. This is the first report on CHC from a hemimetabolous insect. The amplified CHC probe could hybridize two CHC transcripts in the current preparations, 6.3 kb and 7.3 kb. The Northern blot analysis confirmed that a 6.3 kb transcript is specifically expressed in ovarian tissues at high levels throughout the ovarian development, especially in previtellogenic ovaries (Days 1-4) but dropped during the vitellogenic period (days 5-7) and ultimately no transcript was detected in fully vitellogenic ovaries (days 9-13). Immunoblot analysis detected an ovary specific CHC protein of ~175 kDa that was present in previtellogenic ovaries on the day of female emergence and after initiation of vitellogenesis and onset of Vg uptake. Immunocytochemistry localized CHC protein to germ-line derived cells, oocytes, and revealed that CHC translation begins very early during oocyte differentiation in the germarium. The present work suggested a possible role for clathrin in the early fluid phase endocytosis (pinocytosis) in addition to its role in receptor-mediated endocytosis.