Expression of engrailed in an array of identified sensory neurons: Comparison with position, axonal arborization, and synaptic connectivity

Abstract

engrailed (en) is expressed in the posterior region of embryonic segments and appendages of the cockroach, Periplaneta americana. By 23% of embryogenesis En immunoreactivity is apparent in the dorsal half of the cercus, appendages of segment A11. By 40% of development, En staining is present in the dorsomedial half of the cercus. The nucleus of the medial filiform hair sensory neuron (M), born in this region, expresses en strongly. Staining is never seen in the lateral neuron (L). En is expressed in M as the sensory axons enter the terminal ganglion and begin to form their different arborizations and synaptic connections. This pattern of expression persists through development to the second instar. In mutant animals with supernumerary filiform hair sensilla, En immunoreactivity is only seen in the medial neurons. In second-instar and adult cerci en expression is also seen in medially located neurons. We compared the levels of En staining in the array of 25 second instar neurons with their position, axonal arbor type, and synaptic connections. Staining intensity correlates with distance from the cercal midline, suggesting that en is regulated by other circumferential positional determinants. The expression of en does not correlate with the formation of an M-type arbor. Although 10 to 12 sensory neurons that express en form synapses with giant interneuron 5, the correlation is not precise. These results suggest that, if En does form part of a combinatorial system of positional information in the cercus, its actions are modulated by other gene products.

Engrailed expression in subsets of adult Drosophila sensory neurons: an enhancer-trap study

“…We have seen that en -driven membranous GFP persists in neurons of 1 week old adults, and a quantitative study of en-lacZ expression in the adult antenna determined that levels of expression fall only to about 60% of their initial levels over the entire lifetime of the animal (Rogina and Helfand, 1997). In other, more long-lived, insects it has been shown that En protein is persistently expressed in the adult CNS and sensory neurons (Blagburn et al, 1995, Siegler et al, 2001). What is the role of the persistent En expression seen in adult sensory neurons?…”

“…At a gross anatomical level, it is known that En expression in body segments and appendages of Drosophila persists into adulthood (Hama et al, 1990, Rogina and Helfand, 1997) and it has been observed in some sensory and central neurons of adult cockroaches and grasshoppers (Blagburn et al, 1995, Siegler et al, 2001). However, the extent and functions of this adult neuronal En expression are not known.…”

Neural Circuit Recording from an Intact Cockroach Nervous System

“…One of the reasons for exhibiting techniques for this classical preparation is that the cerci system has been and still is an active area of research in addressing questions of the development of neural circuitry as well as questions regarding synaptic repair and regeneration [26][27][28][29][30][31] . Either method of evoking activity in the cockroach ventral nerve cord can be used to examine the effects of pharmacological agents or insecticides on nervous system function.…”

Co-factors and co-repressors of Engrailed: expression in the central nervous system and cerci of the cockroach, Periplaneta americana

“…The results show that it is not. For technical reasons, the colocalization of Exd and En has not been possible, but visual comparison of the patterns of neuronal staining in the CNS (see Blagburn et al 1995) suggest that, although some neurons (such as the dorsal unpaired median neurons) express both, many others express only Exd or only En.…”

“…En in cercal neurons might utilize this "widespread binding" mechanism and act alone, without co-factors to increase its selectivity. Of note, a gradient of En protein expression has been observed in cockroach cercal sensory neurons (Blagburn et al 1995;Marie et al 2000); if En indeed binds widely to multiple low affinity sites, the amount of this protein in a sensory neuron might affect its phenotype in a quantitatively graded manner.…”