Sex differences in Caenorhabditis elegans in body composition, lipid storage and gene expression under ad libitum and dietary restriction conditions

The nematode Caenorhabditis elegans (C. elegans) contains two sexes, males and hermaphrodites, which are highly dimorphic in anatomy, nervous system and behavior. However, the physiology of males in comparison to hermaphrodites under normal feeding conditions and in the context of dietary restriction (DR) is largely unexplored. Here, body proportions and composition, certain aspects of carbohydrate metabolism, fat storage and gene expression of males and hermaphrodites were analyzed under ad libitum and DR conditions. Furthermore, males were used to determine the influence of different paternal DR regimes on F1 progeny fat content. In this study male-enriched mutant stains were used, one with a sex-specific GFP signal, led to a large number of males being separated from hermaphrodites by flow-cytometry. Analysis of sex differences under ad libitum conditions unraveled that the fat-to-fat-free mass as well as the body volume adjusted fat mass was similar between the sexes, although the body size was over 50 % lower in adult males than in age-matched hermaphrodites. In contrast, males had an about 2-fold lower volume adjusted total RNA content than hermaphrodites. Biochemical and NMR-based analyses revealed higher trehalose and much lower glucose levels in males than in hermaphrodites, resulting in a 5.4-fold higher trehalose to glucose ratio. These sex differences were reflected by gene expression data since genes encoding key enzymes of the glycolysis and trehalose synthesis pathway were higher expressed in males than in hermaphrodites. Notably, the phosphofructokinase gene (C50F4.2) showed a 29-fold higher expression level in males. Comparative analysis of gene expression data identified 285 male-specific and 160 hermaphrodite-specific genes including transcription factors and many C-type lectin genes. More than 35 % of all C-type lectin genes were higher expressed in males and many of them had a more than 100-fold higher expression level. As response to DR both sexes increased their fat-to-fat-free mass ratio and enlarged their lipid droplets to a similar extent. However, the reduction of body size, protein content and total RNA content was more pronounced in hermaphrodites under DR than in males. Functional enrichment analysis of gene expression data showed a DR-induced down-regulation of several embryogenesis-associated genes in hermaphrodites. Moreover, DR promoted an ongoing expression of sperm-associated genes from young adulthood to adulthood in hermaphrodites but not in males. In order to examine the influence of paternal diet on the next generation, fog-2 mutant strain was used. fog-2 hermaphrodites do not produce sperm and are therefore termed as females, while fog-2 males are unaffected. Males undergoing several DR regimes were crossed with ad libitum fed females. The corresponding progeny were analyzed according to their fat content with BODIPYTM 493/503 staining. An inverted U-shaped relationship between the extent of paternal DR and the level of progeny fat content was found. The relationship was evident in both progeny sexes, while body proportions did not change. In conclusion, these findings extend the knowledge of sex differences in C. elegans under ad libitum and DR conditions. The data identified sex differences in carbohydrate metabolism, which are linked to gene expression under ad libitum condition. DR increases the fat stores of both sexes in form of large lipid droplets and prolongs the reproductive program of hermaphrodites. Furthermore, these results establish a connection between paternal food consumption and adaptive developmental plasticity.