Cloning of cDNA and prediction of peptide structure of Plzf expressed in the spermatogonial cells of Labeo rohita

The promyelocytic leukemia zinc finger (Plzf) gene containing an evolutionary conserved BTB (bric-a-brac/tramtrack/broad complex) domain plays a key role in self-renewal of mammalian spermatogonial stem cells (SSCs) via recruiting transcriptional co-repressors. Little is known about the function of Plzf in vertebrate, especially in fish species. To gain better understanding of its role in fishes, we have cloned Plzf from the testis of Labeo rohita (rohu), a commercially important freshwater carp. The full-length cDNA contains an open reading frame (ORF) of 2004 bp translatable to 667 amino acids (aa) containing a conserved N-terminal BTB domain and C-terminal C2H2-zinc finger motifs. L. rohita Plzf, which is phylogenetically related to Danio rerio counterpart, abundantly expressed in spermatogonial stem cells (SSCs). A three-dimensional (3D) model of BTB domain of Plzf protein was constructed by homology modeling approach. Molecular docking on this 3D structure established a homo-dimer between two BTB domains creating a charged pocket containing conserved aa residues: L33, C34, D35 and R49. Thus, Plzf of SSC is structurally and possibly functionally conserved. The conserved aa residues in the cleft resulting from Plzf BTB self-association are likely to be the binding platform for interaction with recruited co-repressor peptides. The identified Plzf could be the first step towards exploring its role in rohu SSC behavior.