Anatomical Society of Great Britain and Ireland

Future meetings

24–26 July 2000. Department of Anatomy, University of Cambridge; this will be a tripartite meeting with the Anatomische Gesellschaft and the Nederlandse Anatomen Vereniging. This will include symposia on ‘The neuroanatomical basis of the emergence of behaviour’, and ‘Anatomy: the challenges for the 21st century.’

4 September 2000. University of York. One day symposium (part of the International Congress of Histochemistry and Cytochemistry, 3–8 September 2000) on ‘Digital image capture, processing and analysis’.

During insect development, morphological differences between segments are controlled by the Hox gene family of transcription factors. Recent evidence also suggests that variation in the regulatory elements of these genes and their downstream targets underlies the evolution of several segment-specific morphological traits. This review introduces a new model system, the larval oenocyte, for studying the evolution of fate specification by Hox genes at single-cell resolution. Oenocytes are found in a wide range of insects, including species using both the short and the long germ modes of development. Recent progress in our understanding of the genetics and cell biology of oenocyte development in the fruitfly Drosophila melanogaster is discussed. In the D. melanogaster embryo, the formation of this cell type is restricted to the first 7 abdominal segments and is under Hox gene control. Oenocytes delaminate from the dorsal ectoderm of A1-A7 in response to an induction that involves the epidermal growth factor receptor (EGFR) signalling pathway. Although the receptor itself is required in the presumptive oenocytes, its ligand Spitz (Spi) is secreted by a neighbouring chordotonal organ precursor (COP). Thus, in dorsal regions, local signalling from this component of the developing peripheral nervous system induces the formation of oenocytes. In contrast, in lateral regions of the ectoderm, Spi signal from a different COP induces the formation of secondary COPs in a homeogenetic manner. This dorsoventral difference in the fate induced by Spi ligand is controlled by a prepattern in the responding ectoderm that requires the Spalt (Sal) transcription factor. Sal protein is expressed in the dorsal but not lateral ectoderm and acts as a competence modifier to bias the response to Spi ligand in favour of the oenocyte fate. We discuss a recently proposed model that integrates the roles of Sal and the EGFR pathway in oenocyte/chordotonal organ induction. This model should provide a useful starting point for future comparative studies of these ectodermal derivatives in other insects.

Anatomical Society of Great Britain and Ireland

15–17 July 1997. Medical School, University of Edinburgh.

6–8 January 1998. University of Newcastle upon Tyne.

24–2 July 2000. University of Cambridge.

We recently reported the results of applying immunohistochemical methods to examine the distribution of neuropeptides and neurotransmitter synthesising enzymes in the autonomic nerve fibres of specimens of human vas deferens obtained at vasectomy (Jen et al. 1999). As anticipated from previous neurohistochemical and electron microscopic studies (Baumgarten et al. 1971), the majority of nerves supplying the muscle coat are noradrenergic in type as demonstrated by the presence of tyrosine hydroxylase (TH) and dopamine beta hydroxylase (DbH) (Dixon et al. 1998), both of which are enzymes involved in the synthesis of noradrenaline.

In addition to the profuse intramuscular plexus of nerves, a second nerve plexus occurs at the base of the epithelium lining the vas deferens. These subepithelial nerves are immunopositive for vesicular acetylcholine transporter (VAChT) and therefore cholinergic in type, presumably serving a secretomotor function (Jen et al. 1999). Our immunohistochemical studies have also shown the presence of neuropeptide Y (NPY) in most of these subepithelial nerves in the human vas deferens with minor populations containing vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS), an enzyme involved in the formation of nitric oxide.