Neurexins and Neuroligins: Recent Insights from Invertebrates

During brain development, each neuron must find and synapse with the correct pre- and postsynaptic partners. The complexity of these connections and the relatively large distances some neurons must send their axons to find the correct partners makes studying brain development one of the most challenging, and yet fascinating disciplines in biology. Furthermore, once the initial connections have been made, the neurons constantly remodel their dendritic and axonal arbours in response to changing demands. Neurexin and neuroligin are two cell adhesion molecules identified as important regulators of this process. The importance of these genes in the development and modulation of synaptic connectivity is emphasised by the observation that mutations in these genes in humans have been associated with cognitive disorders such as Autism spectrum disorders, Tourette syndrome and Schizophrenia. The present review will discuss recent advances in our understanding of the role of these genes in synaptic development and modulation, and in particular, we will focus on recent work in invertebrate models, and how these results relate to studies in mammals

The Macronuclear Genome of Stentor coeruleus\textit{Stentor coeruleus} Reveals Tiny Introns in a Giant Cell

The giant, single-celled organism $\textit{Stentor coeruleus}$ has a long history as a model system for studying pattern formation and regeneration in single cells. $\textit{Stentor coeruleus}$ [1, 2] is a heterotrichous ciliate distantly related to familiar ciliate models, such as Tetrahymena or Paramecium. The primary distinguishing feature of $\textit{Stentor}$ is its incredible size: a single cell is 1 mm long. Early developmental biologists, including T.H. Morgan [3], were attracted to the system because of its regenerative abilities-if large portions of a cell are surgically removed, the remnant reorganizes into a normal-looking but smaller cell with correct proportionality [2, 3]. These biologists were also drawn to $\textit{Stentor}$ because it exhibits a rich repertoire of behaviors, including light avoidance, mechanosensitive contraction, food selection, and even the ability to habituate to touch, a simple form of learning usually seen in higher organisms [4]. While early microsurgical approaches demonstrated a startling array of regenerative and morphogenetic processes in this single-celled organism, $\textit{Stentor}$ was never developed as a molecular model system. We report the sequencing of the $\textit{Stentor coeruleus}$ macronuclear genome and reveal key features of the genome. First, we find that $\textit{Stentor}$ uses the standard genetic code, suggesting that ciliate-specific genetic codes arose after $\textit{Stentor}$ branched from other ciliates. We also discover that ploidy correlates with $\textit{Stentor}$'s cell size. Finally, in the $\textit{Stentor}$ genome, we discover the smallest spliceosomal introns reported for any species. The sequenced genome opens the door to molecular analysis of single-cell regeneration in $\textit{Stentor}$.This work was supported by an ARCS Graduate Fellowship (M.M.S.), an American Cancer Society postdoctoral fellowship (P.S.), the Herbert Boyer Junior Faculty Endowed Chair (W.F.M.), a UCSF Resource Allocation Program New Directions grant (W.F.M.), and by NIH grants R01 GM090305 (W.F.M.) and R01 GM113602 (W.F.M.)