The Engrailed-expressing secondary head spots in the embryonic crayfish brain: examples for a group of homologous neurons in Crustacea and Hexapoda?

Abstract

Hexapoda have been traditionally seen as the closest relatives of the Myriapoda (Tracheata hypothesis) but molecular studies have challenged this hypothesis and rather have suggested a close relationship of hexapods and crustaceans (Tetraconata hypothesis). In this new debate, data on the structure and development of the arthropod nervous system contribute important new data ("neurophylogeny"). Neurophylogenetic studies have already provided several examples for individually identifiably neurons in the ventral nerve cord that are homologous between insects and crustaceans. In the present report, we have analysed the emergence of Engrailed-expressing cells in the embryonic brain of a parthenogenetic crayfish, the marbled crayfish (Marmorkrebs), and have compared our findings to the pattern previously reported from insects. Our data suggest that a group of six Engrailed-expressing neurons in the optic anlagen, the so-called secondary head spot cells can be homologised between crayfish and the grasshopper. In the grasshopper, these cells are supposed to be involved in establishing the primary axon scaffold of the brain. Our data provide the first example for a cluster of brain neurons that can be homologised between insects and crustaceans and show that even at the level of certain cell groups, brain structures are evolutionary conserved in these two groups.

Different functions for homologous serotonergic interneurons and serotonin in species-specific rhythmic behaviours

“…Homologous neurons can be identified across species, allowing their behavioural functions to be assessed (Sakharov 1976;Weiss & Kupfermann 1976;Pentreath et al 1982;Croll 1987;Paul 1991;Katz & Tazaki 1992;Bulloch & Ridgway 1995;Katz et al 2001;Murphy 2001;Sintoni et al 2007). In this study, we examined the functions of homologous neurons in two nudibranch species within the suborder Dendronotoidea that exhibit different swimming behaviours: Tritonia diomedea and Melibe leonina.…”

“Crustacea”: Decapoda – Astacida

“…4.5G , I and 4.6C ; Alwes and Scholtz 2006 ;Vilpoux et al 2006 ;Sintoni et al 2007 ;FabritiusVilpoux et al 2008 ). The entire cell row a begins to express the Engrailed protein (En) as well as some cells in row b (Patel et al 1989 ;Alwes and Scholtz 2006 ).…”

The expression of wingless and Engrailed in developing embryos of the mayfly Ephoron leukon (Ephemeroptera: Polymitarcyidae)

“…The absence of labral En expression is typical of all insects examined except Drosophila (e.g., Patel et al 1989;Peterson et al 1998;Rogers and Kaufman 1996). Similarly, clusters of En-expressing cells in the ventral region have been documented in a host of arthropods including several crustaceans (Procambarus clarkii, Porcellio scaber; Abzhanov and Kaufman 2000), Marmokrebs (Sintoni et al 2007), and insects (Thermobia domestica: Peterson et al 1998;Schistocerca: Boyan and Williams 2002;Siegler et al 2001;Tribolium: Patel et al 1989;Drosophila: DiNardo et al 1985). Mutational analyses in D. melanogaster suggest that En functions in neural specification during embryogenesis (Brower 1986;DiNardo et al 1985).…”