Proteins foretelling head or abdomen development in the embryo of Smittia spec. (Chironomidae, Diptera)

Two chromosome-level genomes of Smittia aterrima and Smittia pratorum (Diptera, Chironomidae)

Chironomids are one of the most abundant aquatic insects and are widely distributed in various biological communities. However, the lack of high-quality genomes has hindered our ability to study the evolution and ecology of this group. Here, we used Nanopore long reads and Hi-C data to produce two chromosome-level genomes from mixed genomic data. The genomes of Smittia aterrima (SateA) and Smittia pratorum (SateB) were assembled into three chromosomes, with sizes of 78.45 Mb and 71.56 Mb, scaffold N50 lengths of 25.73 and 23.53 Mb, and BUSCO completeness of 98.5% and 97.8% (n = 1,367), 5.68 Mb (7.24%) and 1.94 Mb (2.72%) of repetitive elements, and predicted 12,330 (97.70% BUSCO completeness) and 11,250 (97.40%) protein-coding genes, respectively. These high-quality genomes will serve as valuable resources for comprehending the evolution and environmental adaptation of chironomids.

From egg to pole cells: ultrastructural aspects of early cleavage and germ cell determination in insects

Insect eggs are giant and very complex cells covered by an extremely resistant shell. Both the egg cell and surrounding eggshell express anteroposterior and ventrodorsal polarity. The molecular and cytoplasmic organization of both axes originates during oogenesis and leads to the production of an ooplasmic system which consists of euplasm and deutoplasm (yolk) and contains a nucleus as well as extranuclear determinants of maternal origin. Both are part of the store of information for early embryogenesis. In addition, the deutoplasm serves as raw material and early nutrient supply for building the embryo. The insect egg cell, which is arrested in the first maturation division when released from the ovary during oviposition, will be activated by different stimuli among different species to complete meiosis and start embryogenesis. The zygote nucleus undergoes a number of synchronous mitotic divisions leading to cleavage energids which initially form a syncytial blastoderm and subsequently the cellular blastoderm. In many insects, prior to blastoderm formation, polar granules (or oosome material) are incorporated in a single cell or a small number of cells which bud off at the posterior pole. These so called pole cells give rise to the primordial germ cells. Therefore, polar granules or the oosome material mark the germ line, and while structural counterparts of determinants of body pattern formation have so far not been found, the polar granules or oosome serve as an autonomous ooplasmic determinant for the pole or germ cells. Anteroposterior body polarity can arise independent of the germ plasm.