Temporal data series and logistic models reveal the dynamics of SARS-CoV-2 spike protein D614G variant in the COVID-19 pandemic

The COVID-19 pandemic is caused by the worldwide spread of the RNA virus SARS-CoV-2. Because of its mutational rate, wide geographical distribution, and host response variance this coronavirus is currently evolving into an array of strains with increasing genetic diversity. Most variants apparently have neutral effects for disease spread and symptom severity. However, in the viral spike protein, which is responsible for host cell attachment and invasion, the D614G variant, containing the amino acid substitution D to G in position 614, was suggested to increase viral infection capability. Here we propose a novel method to test the epidemiological impact of emergence of a new variant, by a combination of epidemiological curves (for new cases) and the temporal variation of relative frequencies of the variants through a logistic regression model. We applied our method to temporal distributions of SARS-CoV-2 D614 or G614, in two geographic areas: USA (East Coast versus West Coast) and Europe-Asia (East Countries versus West Countries). Our analysis shows that the D614G prevalence and the growth rates of COVID-19 epidemic data curves are correlated at the early stages and not correlated at the late stages, in both the USA and Europe-Asia scenarios. These results show that logistic models can reveal the potential selective advantage of D614G, which can explain, at least in part, the impact of this variant on COVID-19 epidemiology.

Spermiogenesis and sperm ultrastructure in Cichla intermedia with some considerations about Labroidei spermatozoa (Teleostei, Perciformes, Cichlidae).

Spermiogenesis and spermatozoal structure were studied in Cichla intermedia, a primitive species of Neotropical Cichlids. The analysis shows that spermiogenesis is characterized by chromatin compaction, flagellum development, nuclear rotation, nuclear fossa formation and residual cytoplasm elimination. In the spermatozoa, the head is round, the nucleus contains highly condensed filamentous clusters of chromatin and an acrosome is absent. The nuclear fossa is slightly eccentric and shows a projection that penetrates into the nuclear outline. The proximal centriole is located in the initial segment of the nuclear fossa. The midpiece and the cytoplasmic channel are long. The mitochondria, about 10 in number, are round or slightly elongated, disposed in two layers around the initial segment of the flagellum. The flagellum has a classical 9+2 axoneme and two lateral fins. The data available show that no characteristics of spermiogenesis or spermatozoa are exclusively found in members of the suborder Labroidei. However, three characteristics seem to be exclusively observed in Cichlidae: (1) compact filamentous clusters of chromatin; (2) slightly eccentric nuclear fossa; and, (3) number of mitochondria.