Identification and characterization of a hunchback orthologue, Lzf2, and its expression during leech embryogenesis.

Lzf1 and Lzf2 are leech zinc finger (Lzf) genes that are shown to be orthologues to the Drosophila gap gene hunchback (hb). Neither in situ hybridization nor RT-PCR detected Lzf1 transcripts in leech embryos or adults. Lzf2 expression was examined in leech embryos at various stages by in situ hybridization. Lzf2 is expressed continually throughout the early embryonic cleavage divisions, including the period during which the embryo forms stem cells that will give rise to the segmented tissues of the adult. At the time of segmental pattern formation, Lzf2 RNA is expressed uniformly along the length of the segmented trunk in both the ectodermal and mesodermal tissues. This is in contrast to the anteriorly restricted gradient of hb RNA shown to be critical to the normal anteroposterior (AP) patterning of the insect embryo. Thus, this leech orthologue of hb does not appear to play a comparable role in the patterning of the AP axis. In addition, Lzf2 is expressed during organogenesis in segmentally restricted patterns in the central nervous system, the gut, and epidermally derived structures. Lzf2 is the first hb orthologue to be characterized in detail outside of insects and its expression pattern suggests that hb may have acquired a gap gene function in arthropods or insects after their phyletic separation from the annelids.