EXPRESSION OF ENGRAILED IN AN ARRAY OF IDENTIFIED SENSORY NEURONS - COMPARISON WITH POSITION, AXONAL ARBORIZATION, AND SYNAPTIC CONNECTIVITY

engrailed (en) is expressed in the posterior region of embryonic segme nts and appendages of the cockroach, Periplaneta americana. By 23% of embryogenesis En immunoreactivity is apparent in the dorsal half of th e cercus, appendages of segment All, By 40% of development, En stainin g is present in the dorsomedial half of the cercus, The nucleus of the medial filiform hair sensory neuron (M), born in this region, express es en strongly. Staining is never seen in the lateral neuron (L). En i s 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, E n immunoreactivity is only seen in the medial neurons, In second-insta r and adult cerci err expression is also seen in medially located neur ons. We compared the levels of En staining in the array of 25 second i nstar neurons with their position, axonal arbor type, and synaptic con nections, Staining intensity correlates with distance from the cereal midline, suggesting that en is regulated by other circumferential posi tional determinants, The expression of en does not correlate with the formation of an M-type arbor. Although 10 of 12 sensory neurons that e xpress en form synapses with giant interneuron 5, the correlation is n ot precise. These results suggest that, if En does form part of a comb inatorial system of positional information in the cercus, its actions are modulated by other gene products. (C) 1995 John Wiley & Sons, Inc.