The mechanisms underlying sex determination are astonishingly plastic. Particularly the triggers for the molecular machinery, which recalls either the male or female developmental program, are highly variable and have evolved independently and repeatedly. Fish show a huge variety of sex determination systems, including both genetic and environmental triggers. The advent of sex chromosomes is assumed to stabilize genetic sex determination. However, because sex chromosomes are notoriously cluttered with repetitive DNA and pseudogenes, the study of their evolution is hampered. Here we reconstruct the birth of a Y chromosome present in the Atlantic herring. The region is tiny (230 kb) and contains only three intact genes. The candidate male-determining gene BMPR1BBY encodes a truncated form of a BMP1B receptor, which originated by gene duplication and translocation and underwent rapid protein evolution. BMPR1BBY phosphorylates SMADs in the absence of ligand and thus has the potential to induce testis formation. The Y region also contains two genes encoding subunits of the sperm-specific Ca2+ channel CatSper required for male fertility. The herring Y chromosome conforms with a characteristic feature of many sex chromosomes, namely, suppressed recombination between a sex-determining factor and genes that are beneficial for the given sex. However, the herring Y differs from other sex chromosomes in that suppression of recombination is restricted to an ∼500-kb region harboring the male-specific and sex-associated regions. As a consequence, any degeneration on the herring Y chromosome is restricted to those genes located in the small region affected by suppressed recombination.

Herein we report the first synthesis of a monopyrrolotetrathiafulvalene (MPTTF) with two alkyl substituents, performed using a triphenylphosphine-mediated coupling reaction. An Ullmanntype N-arylation reaction was used to prepare a calixarene-based bis-MPTTF receptor, as well as an arylated mono-MPTTF derivative.Complexation studies with electron-deficient compounds showed strongly enhanced affinity of the alkyl-substituted MPTTF derivatives in comparison with the non-substituted MPTTF analogues.

An approach for the lower rim modification of the calix [4]arenebased molecular tweezes with monopyrrolo-tetrathiafulvalene (MPTTF) arms attached to the upper rim of calixarenes is described. First, calixarene-MPTTF conjugates with free hydroxyl on the lower rim are synthesized using the Ullmann reaction, then hydroxyl groups are substituted by propargyl groups, which can be used for further modification by the click reaction.The new calixarene-TTF derivatives displayed reversible redox processes, as well as demonstrated binding affinity for electrondeficient molecular guests such as tetracyanoquinodimethane. The described synthetic approach will be used for the modular synthesis of molecular receptors tailored for specific applications.