Alternative transcripts of Dclk1 and Dclk2 and their expression in doublecortin knockout mice

The doublecortin (DCX) gene, mutated in X-linked human lissencephaly, has 2 close paralogs, doublecortin-like kinase 1 and 2 (Dclk1 and 2). In this study we attempted to better understand the dramatic differences between human and mouse DCX/Dcx-deficient phenotypes, focusing on the Dclk genes which are likely to compensate for Dcx function in the mouse. Using sequence database screens, Northern blot analyses and in situ hybridization experiments, we characterized the developmental transcripts of Dclk1 and 2, questioning their conservation between mouse and human, and their similarity to Dcx. Like Dcx, Dcx-like transcripts of the Dclk1 gene are expressed in postmitotic neurons in the developing cortex. No changes of expression were observed at the RNA level for these transcripts in Dcx knockout mice. However, a minor change in expression at the protein level was detected. The Dclk2 gene is less well characterized than Dclk1 and we show here that it is expressed both in proliferating cells and postmitotic neurons, with a notably strong expression in the ventral telencephalon. No major differences in Dclk2 expression at the RNA and protein levels were identified comparing Dcx knockout and wild-type brains. We also analyzed Dclk1 and 2 expression in the hippocampal CA3 region which, unlike the neocortex, is abnormal in Dcx knockout mice. Interestingly, each transcript was expressed in CA3 neurons, including in the heterotopic pyramidal layer of Dcx knockout animals, but is presumably not able to compensate for a lack of Dcx. These results, in addition to characterizing the transcript diversity of an important family of genes, should facilitate further studies of compensation in Dcx-deficient mice.