The expression of anterior nervous system markers in the chaetognath Spadella cephaloptera


Saghar Sadraei

MSc Student
Advisors: Tim Wollesen

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna


During the development of different bilaterian and cnidarian taxa an apical organ appears in the larval stage of some of their representatives which is restricted to this stage and consists of a ciliary tuft and receptor cells. This special organ is connected to the nervous system through a network of neurites. The apical organ is mostly located in the anterior region of the larvae and as a sensory organ, it is hypothesized to play a role in settlement, movement and metamorphosis.

Chaetognaths are spiralian protostomes belonging to the Gnathifera which is the sister group to the Lophotrochozoa. The benthic chaetognath Spadella cephaloptera is direct developer without a larval stage and apical organ.

In my Master thesis, I will study the expression patterns of genes that are expressed in the apical organ of various bilaterians and cnidarians. My study will reveal where these genetic markers are expressed in S. cephaloptera. Studied candidate genes encode transcription factors and include fezf, foxj, pax2/5/8, syt, otp, hb9, foxg, and nk2.1.

So far, only gene expression patterns for the gene fezf have been obtained. These indicate that fezf is expressed in the ventral nerve center which is involved among others in locomotion. In addition, fezF is expressed in triangle-shaped form in the brain region of S. cephaloptera.

According to previous analyses, expression of fezf is restricted to the anterior forebrain of vertebrates indicating that it plays an important role in vertebrate brain patterning. As a preliminary summary, we can conclude that fezf is an evolutionary conserved homeobox gene expressed in the anterior nervous system of various bilaterians including the enigmatic chaetognaths.