Hox Gene Expression Leads to Differential Hind Leg Development between Honeybee Castes

Abstract

Beyond the physiological and behavioural, differences in appendage morphology between the workers and queens of Apis mellifera are pre-eminent. The hind legs of workers, which are highly specialized pollinators, deserve special attention. The hind tibia of worker has an expanded bristle-free region used for carrying pollen and propolis, the corbicula. In queens this structure is absent. Although the morphological differences are well characterized, the genetic inputs driving the development of this alternative morphology remain unknown. Leg phenotype determination takes place between the fourth and fifth larval instar and herein we show that the morphogenesis is completed at brown-eyed pupa. Using results from the hybridization of whole genome-based oligonucleotide arrays with RNA samples from hind leg imaginal discs of pre-pupal honeybees of both castes we present a list of 200 differentially expressed genes. Notably, there are castes preferentially expressed cuticular protein genes and members of the P450 family. We also provide results of qPCR analyses determining the developmental transcription profiles of eight selected genes, including abdominal-A, distal-less and ultrabithorax (Ubx), whose roles in leg development have been previously demonstrated in other insect models. Ubx expression in workers hind leg is approximately 25 times higher than in queens. Finally, immunohistochemistry assays show that Ubx localization during hind leg development resembles the bristles localization in the tibia/basitarsus of the adult legs in both castes. Our data strongly indicate that the development of the hind legs diphenism characteristic of this corbiculate species is driven by a set of caste-preferentially expressed genes, such as those encoding cuticular protein genes, P450 and Hox proteins, in response to the naturally different diets offered to honeybees during the larval period.

Hormonal control and target genes of ftz‐f1 expression in the honeybee Apis mellifera: a positive loop linking juvenile hormone, ftz‐f1, and vitellogenin

“…The honeybee CPR genes responsive to Ftz‐F1 encode RR‐1 ( CPR14 , CPR25 , CPR28 , SgAbd‐2 ) and RR‐2 ( CPR1 , CPR4 , pro‐resilin‐like CPR , pro‐resilin CPR23 , CPR5 ) Consensus‐type proteins, and five of these genes ( CPR14 , CPR25 , CPR28 , CPR4 and CPR23 ) were previously validated in the thoracic integument of A. mellifera through microarray hybridizations and qPCR (Soares et al ., ). Interestingly, the putative gene coding for the cuticle protein CPR4 (GB15203), found in our experiments to be repressed by Ftz‐f1, is a member of the group of genes exhibiting a caste‐specific transcription pattern favouring the development of the worker hind leg phenotype in honeybees (Bomtorin et al ., ).…”

The ontogenetic saga of a social brain

“…The molecular underpinnings of another morphogenetic field, that of the hind leg structures, have recently been revealed. Bomtorin et al (2012) showed that the development of the Bshaved tibia^used by workers to carry pollen (pollen basket) depends upon ultrabithorax expression during prepupal and early pupal phases. This finding was then confirmed by Medved et al (2014) using gene expression interference by RNAi.…”

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…This is a rare example in which the genomic locus of phenotypic evolution has been identifi ed. In honeybees, workers and queens differ in leg bristle patterns, which are controlled by differences in the timing and expression levels of Ubx (Bomtorin et al 2012 ;Medved et al 2014 ). These caste differences are phenotypically plastic, but it is not yet known how the environmental signal is translated into a difference in Ubx expression.…”