Steffen Harzsch's studies of neurogenesis in lobsters (Harzsch et al., 1998; 1999a; 1999b) brought the Beltz lab into a new era. Initially we examined neurogenesis during embryonic and larval development (Harzsch et al., 1999a; Benton and Beltz, 2002) but gradually began to focus on life-long neurogenesis. Steffen Harzsch had shown that even adult lobsters continue to make new neurons, and so our interests gradually concentrated on regulation of neuronal birth in post-larval lobsters. We showed that serotonin is a powerful regulator of neurogenesis in clusters 9 and 10 in the brain (Beltz et al., 2001; Benton and Beltz, 2001). We then discovered that neurogenesis is under circadian control (Goergen et al., 2002), with the peak rate of neuronal production at dusk when these nocturnal animals are most active. A review of neurogenesis in crustaceans was published in 2003 (Beltz and Sandeman, Arthropod Structure and Development 32:39-60), and this article includes an overview of these early studies.

Yet another phase in our story emerged when Jeremy Sullivan began to examine neurogenesis in crayfish and crabs. His work in crayfish definitively showed that the newborn cells differentiate as neurons (Sullivan and Beltz, 2005b). In the crab Libinia emarginata, which undergoes a terminal molt, he demonstrated that although the peripheral sensory neurons cease to turn over when molting stops at maturity, the central neurons continue to proliferate (Sullivan and Beltz, 2005c). This study suggests that the turnover of the sensory neurons in the antennules is not the primary force driving central neurogenesis, as had been proposed for a variety of organisms where olfactory interneurons continue to be born throughout life.

The most recent chapter in our understanding of neurogenesis was Jeremy Sullivan's discovery of a neurogenic niche in crayfish and lobsters (Sullivan, Benton, Sandeman and Beltz, Journal of Comparative Neurology, epub November, 2006).  While Jeremy characterized the glial nature of the precursor cells that generate the lineage resulting in the birth of adult neurons, Jeannie Benton and David Sandeman did experiments that defined the migratory stream.  Jeannie and David demonstrated that daughter cells migrate from the neurogenic niche to the medial (MPZ) and lateral (LPZ) proliferation zones in cell clusters 9 and 10, where these precursors divide one more time before differentiating into neurons.  These studies allow us to work with the entire system generating the adult-born neurons, from the precursor (stem?) cells, through the intermediate precursors (transit amplifying cells?), to the differentiating neurons.

Confocal image: The neurogenic niche, migratory streams and proliferation zones in Procambarus clarkii.
Sullivan, Benton, Sandeman and Beltz (2007) Journal of Comparitive Neurology 500:3 In press.