Homeotic genes influence the axonal pathway of a Drosophila embryonic sensory neuron

Each abdominal hemisegment of the Drosophila embryo has two sensory neurons intimately associated with a tracheal branch. During embryogenesis, the axons of these sensory neurons, termed the v'td2 neurons, enter the CNS and grow toward the brain with a distinctive pathway change in the third thoracic neuromere. We show that the axons use guidance cues that are under control of the bithorax gene complex (BX-C). Pathway defects in mutants suggest that a drop in Ultrabithorax expression permits the pathway change in the T3 neuromere, while combined Ultrabithorax and abdominal-A expression represses it in the abdominal neuromeres. We propose that the axons do not respond to a particular segmental identity in forming the pathway change; rather they respond to pathfinding cues that come about as a result of a drop in BX-C expression along the antero-posterior axis of the CNS.

The distribution and morphological characteristics of cholinergic cells in the brain of monotremes as revealed by ChAT immunohistochemistry

The present study employs choline acetyltransferase (ChAT) immunohistochemistry to identify the cholinergic neuronal population in the central nervous system of the monotremes. Two of the three extant species of monotreme were studied: the platypus (Omithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus). The distribution of cholinergic cells in the brain of these two species was virtually identical. Distinct groups of cholinergic cells were observed in the striatum, basal forebrain, habenula, pontomesencephalon, cranial nerve motor nuclei, and spinal cord. In contrast to other tetrapods studied with this technique, we failed to find evidence for cholinergic cells in the hypothalamus, the parabigeminal nucleus (or nucleus isthmus), or the cerebral cortex. The lack of hypothalamic cholinergic neurons creates a hiatus in the continuous antero-posterior aggregation of cholinergic neurons seen in other tetrapods. This hiatus might be functionally related to the phenomenology of monotreme sleep and to the ontogeny of sleep in mammals, as juvenile placental mammals exhibit a similar combination of sleep elements to that found in adult monotremes. Copyright (C) 2002 S. Karger AG, Basel.

New species of Opechona Looss, 1907 and Cephalolepidapedon Yamaguti, 1970 (Digenea: Lepocreadiidae) from fishes off northern Tasmania

Two new species of lepocreadiid trematodes are described from teleost fishes from off the coast of northern Tasmania. Opechona kahawai sp. nov. from Arripis sp. (Arripidae) differs from congeners by a combination of a longer prepharynx, longer excretory vesicle and the genital pore antero-sinistral to the ventral sucker. Cephalolepidapedon warehou sp. nov. from Seriolella punctata (Centrolophidae) differs from its only congener in the vitellarium reaching into the posterior forebody, a heavy concentration of eye-spot pigment in the forebody, a relatively narrower and more elongate body, a longer prepharynx and a more distinct oesophagus.

Description of Paeon asymboli n. sp. (Copepoda : Sphyriidae), parasitic on Asymbolus spp. (catsharks) and a new host record for P-australis Kabata, 1993.

Paeon asymboli n. sp. ( Copepoda: Sphyriidae) is described and illustrated from two female specimens taken from the gills of a grey spotted catshark Asymbolus analis ( Ogilby) and an orange spotted catshark A. rubiginosus ( Last, Gomon & Gledhill) ( Scyliorhinidae) from off southeastern Queensland, Australia. The key features for identification are: a pear- shaped trunk, longer than it is wide, along with a cephalothorax characterised by two large ventral papillae, projecting laterally and supporting a number of secondary lobes; a single mid- line, subconical papilla located antero- dorsal to the ventral papillae; an anterior surface bearing two prominent stalked papillae; and an absence of posterolateral lobular processes. P. australis Kabata, 1993 is recorded for the first time from the eastern shovelnose ray Aptychotrema rostrata ( Shaw & Nodder) ( Rhinobatidae).