My subjective picks for the top 10 developmental biology papers of the year, with the caveat that I’m not a developmental biologist by trade, just an avid follower of the field, with my main interest being evo devo and phylogenetic inferences from developmental biology. The master list contains 16 papers. [OA] indicates open access papers.
I summarised the development of the tracheal system in larval Drosophila in this post. This paper fills in the details of the connection between the branches of the tracheal system, at the branching point.
I gleefully support any research that doesn’t use model organisms. This one fulfils that criterion by using a brittlestar rather than sea urchins. The paper itself is a characterisation of its development and gene expression during gastrulation, and notes the similarities and differences to sea urchins.
This paper studies the expression of Lhx genes in Mnemiopsis leidyi, a ctenophore. Lhx genes are homeobox genes involved in the development of the nervous system – they’re responsible for patterning various types of neurons. There are four of them in this organism, and their expression is diagrammed above. As expected, the expression is concentrated where the most neurons and sensory cells are found. Combined with the phylogenetic analysis in this paper finding that ctenophores and sponges are rather close to each other, this suggests that Lhx first evolved as a way to specify sensory cells: sponges don’t have nerves, but their larvae do have photoreceptive cells that are specified by Lhx. So, in all, this is an important paper for giving us more data to work with when thinking of the original evolution of the nervous system.
Entoprocts (also called Kamptozoa) are a phylum of tiny benthic marine invertebrates, suggested by most to be the sister group to the molluscs (the Tetraneuralia hypothesis). This paper studies the development of Loxosomella, a solitary entoproct (species in other families are colonial). It exhibits spiral cleavage along with an apical cross; this confirms that entoprocts belong in the Spiralia. Further analyses in the paper also lend more support for the Tetraneuralia hypothesis.
This paper investigates the expression of several important head patterning genes in the millipede Glomeris marginata. The importance of the paper hinges on the two current leading hypotheses in arthropod phylogeny: the Pancrustacea hypothesis states that insects and crustaceans are sisters, or that insects are crustaceans; and the Atelocerata hypothesis that states that insects and myriapods (millipedes, centiupedes, and their ilk) are sisters. The findings in this paper come out in favour of the Atelocerata – there are several important developmental gene expressions shared between insects and myriapods, but not with crustaceans. Although these could also be explained by convergence.
Notch is one of the most important proteins in animal development. It’s a transmembrane receptor that controls cell-cell communication, and it also coordinates a signalling cascade found in all animals by regulating gene expression – such multitasking by a single protein is very rare. This paper studies Notch signalling in the early nervous system development of a model organism, the water flea Daphnia magna, showing that Notch is key for neuroblast formation (as in vertebrates, which the authors refer to as a case of convergent evolution) and for patterning the ventral neuroectoderm.
The neural crest has long been considered the key innovation that allowed vertebrates to achieve their evolutionary success. Some authors even go as far as treating it as a fourth germ layer. Basically, the neural crest is a dorsal fold of the neural tube from which a population of migratory multipotent cells is derived. These migrate along specific pathways to form, among other things: the skull and face, teeth, a lot of the heart and circulatory vessels, pigment cells, the spinal column and the peripheral nervous system, and the thyroid and adrenal glands. It’s also long been known that its evolution was not a spontaneous one, but that glimmers of it can be seen in other chordates. This paper is significant in that it identifies more than “glimmers”: it finds that all that’s needed to make a rudimentary neural crest in the tunicate Ciona intestinalis is a misexpression of the a protein called Twist in population of pigment cells in the embryonic head, granting that population migratory abilities identical to those of neural crest cells. This provides a clear scenario for the evolution of the full neural crest of the vertebrates.
The neoblasts of annelids should not be confused with neoblasts of planarians: many annelids have no neoblasts and can regenerate just fine, so this paper examines what the true function of annelidan neoblasts is by looking at two closely-related annelids, an asexual one with neoblasts and a sexual one without. It turns out that their role is geared towards making asexual reproduction effective: the sexual species has no neoblasts and has limited regeneration abilities only in the front of the body, whereas the asexual species can regenerate if cut anywhere.
This paper examines the expression of Hox genes in a harvestman, and compares them to the expression in spiders. The biggest differences are found to be in the opisthosome – the back half – of the animals, as seen in B above. It’s those differences that lead to the body plan variability in chelicerates, so this research exposes a new avenue of research for chelicerate evo devo.
The drastic form of today’s echinoderms’ body plan (they haven’t always been this screwed up, Recent echinoderms are just a fraction of their past diversity) has always been a stumbling block in the evo devo of deuterostomes. They’re so derived that homologising the structures of echinoderms with chordates is a pretty tentative affair. This paper attempts to do just that by examining the development of the sea urchin Holopneustes purpurescens. It finds that the hydrocoel could be homologous to the notochord, and the coelomic mesoderm homologous to chordate mesoderm, based on the positions of those tissues, as well as gene expression. By extension, this would lead to homologisation of the ambulacra with the chordate body axis. Of course, modern echinoderms have a pentameric body plan; this is explained by duplication. Overall, it’s an interesting and intriguing hypothesis, which is why I place it so high up here (I recommend reading the Discussion section of this paper for the full details). It’s not perfect (I can think of several critiques), but certainly worth considering.
A related paper, not from developmental biology, is Echinoderms Have Bilateral Tendencies: it investigates bilaterian-like behaviour in starfish.